Chedighaii barberi, Gaffney & Tong & Meylan, 2006

GAFFNEY, EUGENE S, TONG, HAIYAN & MEYLAN, PETER A, 2006, EVOLUTION OF THE SIDE-NECKED TURTLES: THE FAMILIES BOTHREMYDIDAE, EURAXEMYDIDAE, AND ARARIPEMYDIDAE, Bulletin of the American Museum of Natural History 300 (300), pp. 1-698 : 373-457

Chedighaii barberi

Two partial skulls and a skull endocast are the basis for the skull descriptions for this taxon. The species type specimen is a shell ( Schmidt, 1940). The two skulls have shell material associated with them that is the basis for the identification. However, considering the conservative nature of other bothremydid shells, it is possible that more than one species have similar shells and that the cranial material here identified as C. barberi represents more than one species. Furthermore, the skulls are not complete enough to be sure that there are not some differences that have been missed due to nonpreservation. Nonetheless, the two skulls agree in all the preserved areas. Another consideration is the wide geographic spread (fig. 18) of shells attributable to Chedighaii , consistent with more than one species. See Note Added in Proof.

The endocast (figs. 166, 167) is identified as C. barberi because it agrees closely with the two partial skulls. The endocast is not just the cavum cranii but almost the entire (negative) skull, including the fossa orbitalis and fossa nasalis. The fact that it lacks pits (although subtle) was missed by the original describer ( Gaffney, 1977a; hey, it was a long time ago). The endocast shows some interesting information about the skull (see below), and a mold of the endocast allows direct comparisons to be made with the other skull specimens.

In the collections of the North Carolina State Museum is a series of otic chambers from the Campanian Tar Heel Formation of North Carolina (Gaffney and Schneider, ms.). These chambers are indistinguishable from the Chedighaii barberi ear regions available from the Selma Formation skulls but are too incomplete to be identified with certainty as C. barberi . The quadrate of one of these is figured here (fig. 286D).

One of the partial skulls, FMNH PR 247, was described by Gaffney and Zangerl (1968), and the endocast, YPM PU 12951, was described by Gaffney (1977a).

PREFRONTAL (figs. 160, 165)

Preservation: Portions of both prefrontals are present in ALAB PV 2001.2, with the left prefrontal being the most complete among the three specimens. This bone has the prefrontal descending process, the anterior margin, and part of the orbital rim preserved. The right prefrontal has only the horizontal area next to the midline. Both prefrontals preserve the ventral surface. In FMNH PR 247 portions of the horizontal plates of both prefrontals are present, but the margins are eroded. In the endocast, there are small fragments of both prefrontals anteriorly, and part of the ventral surface is on the endocast.

Contacts: The visible contacts in all three Chedighaii barberi specimens show the prefrontal meeting the other prefrontal medially, the maxilla anteroventrolaterally, and the frontal posteriorly. The maxillary contact does not form a dorsal extension as in Bothremys cooki and B. maghrebiana . The palatine is not well preserved, so possible contacts or a close approximation of palatine and prefrontal as in C. hutchisoni is not determinable.

Stuctures: The dorsal plate of the prefrontal in Chedighaii barberi is very similar to that in C. hutchisoni . There is a midline projection that is nearly identical in extent and shape, and the shape of the apertura narium externa margin is the same. The dorsal margin of the orbital rim is not preserved in any specimen except the endocast, and this shows that the interorbital distance in C. barberi is relatively narrow, as in C. hutchisoni but in contrast to the wider distance in Bothremys .

FRONTAL (figs. 160, 165)

Preservation: Parts of both frontals are preserved in FMNH PR 247 and ALAB PV 2001.2, but neither has the lateral, orbital margin region preserved. The endocast has the ventral surface of both frontals visible.

Contacts: The frontal in Chedighaii barberi contacts the other frontal medially, the prefrontal anteriorly, the parietal posteriorly, and the postorbital (visible only in the endocast) posterolaterally, all as in other Bothremydini .

Structures: The orbital margin is seen only in the endocast, which shows that Chedighaii barberi has the orbits facing dorsally, as in Bothremys and C. hutchisoni , as well as relatively small orbital openings, also in these taxa. The sulcus olfactorius is relatively narrow, as in C. hutchisoni and Bothremys .

PARIETAL (figs. 160, 165)

Preservation: The medial parts of both parietals are present in ALAB PV 2001.2 and FMNH PR 247; part of the ventral surface is in YPM PU 12951.

Contacts of dorsal plate: The parietal in Chedighaii barberi contacts the frontal anteriorly, the other parietal medially, and the supraoccipital posteroventrally. The lateral contact with the postorbital is visible in the endocast.

Structures of dorsal plate: The limits of the temporal roof are not preserved in any of the Chedighaii barberi specimens. In the endocast, the parietal has a ventral process forming part of the posterior wall of the fossa orbitalis, lateral to the sulcus palatinopterygoideus, as in other Bothremydini .

Contacts of processus inferior parietalis: Only the dorsal part of the processus is preserved in FMNH PR 247 and ALAB PV 2001.2; no ventral contacts are preserved. In YPM PU 12951 most of the processus is preserved on both sides, but the ventral contacts are missing.

Structures of processus inferior parietalis: The foramen interorbitale of Chedighaii barberi is preserved only in the endocast, and it is very similar to that in C. hutchisoni . The foramen nervi trigemini is not preserved.

JUGAL (figs. 160, 165, 167)

Preservation: The jugal is preserved only on the right side of ALAB PV 2001.2 and in the endocast as an imprint. The portion preserved in ALAB PV 2001.2 is a thin layer of the medial process that lies posterior to the maxilla and forms the anterior wall of the temporal chamber. The endocast portion is the region of the jugal forming part of the fossa orbitalis.

Contacts of lateral plate: Not preserved.

Structures of lateral plate: Not preserved.

Contacts of medial process: In the floor of the fossa orbitalis, the jugal contacts the maxilla anteromedially and the palatine medially. In the septum orbitotemporale, the jugal contacts the postorbital dorsomedially. The portion of the medial process preserved in ALAB PV 2001.2 contacts the maxilla only.

Structures of medial process: The endocast and the partial skull, ALAB PV 2001.2, show that Chedighaii barberi did not have the jugal forming part of a pit on the triturating surfaces as in Bothremys . This is clear from ALAB PV 2001.2 alone, because it is the posterior part of the triturating surface on the maxilla that is actually preserved (figs. 164, 165). In YPM PU 12951 (figs. 166, 167) it is less obvious, but the jugal and maxilla form a deep rim below the orbital margin, as in C. hutchisoni , which is very different from the absent rim of Bothremys cooki . The pit itself would not be seen in the endocast, but the floor of the fossa orbitalis is clearly very similar in C. hutchisoni and C. barberi and distinct from the floor in Bothremys .

The pitted bothremydids all have at least some of the jugal significantly altered from the primitive condition to form part of the pit. Enough of the jugal (and maxilla) is preserved in C. barberi to show that a pit was absent and that the jugal has no exposure on the triturating surface. The jugal in C. barberi is exposed in the anterior wall of the fossa temporalis, as in C. hutchisoni .

QUADRATOJUGAL

Preservation: No fragment remains of the poor quadratojugal in any of the three Chedighaii barberi specimens.

SQUAMOSAL (figs. 160, 165)

Preservation: Most of both squamosals are present in ALAB PV 2001.2, but only a fragment remains in FMNH PR 247. The anterodorsal margin is missing on both sides of ALAB PV 2001.2. The endocast has nothing of this bone.

Contacts: The squamosal in Chedighaii barberi contacts the quadrate anteriorly and anteromedially and the opisthotic medially. The anterodorsal margin is missing; a quadratojugal contact cannot be determined.

Structures: The squamosal in Chedighaii barberi has the posterior triangular projection typical of the Bothremydini , with a ventral ridge and thin, dorsolateral shelf continuing the line of the temporal emargination. The antrum postoticum is a narrow canal, as in Bothremys and C. hutchisoni .

POSTORBITAL (fig. 167)

Preservation: The only postorbital information for Chedighaii barberi is on the endocast which shows the exposure of the bone in the posterior wall of the fossa orbitalis.

Contacts and structures of lateral plate: Not preserved.

Contacts of medial process: In the endocast the fossa orbitalis shows the postorbital contacting the frontal anteromedially, the parietal posteromedially, the jugal ventrolaterally, and the palatine ventrally.

Structures of medial process: Only the endocast provides information on this area,

and it shows the fossa orbitalis, that is, the anterior wall of the septum orbitotemporale. The fossa orbitalis of Chedighaii barberi has a large posterior/posteroventral chamber formed primarily by the postorbital, jugal, parietal, and palatine. This chamber is particularly apparent in the endocast when the anterior position of the orbital margin is compared with the rest of the fossa. This posteroventral chamber in C. barberi is very similar to the one in C. hutchisoni , but the chamber is present in nearly all bothremydids.

PREMAXILLA (figs. 160, 161, 165, 167)

Preservation: The left premaxilla, lacking its more medial portion, and a small part of the right oneare preserved in ALAB PV 2001.2. The endocast shows the dorsal surface of the premaxilla.

Contacts: The premaxilla contacts the maxilla posteriorly and the other premaxilla medially. A possible vomer contact is not preserved.

Structures on dorsal surface: The endocast shows a relatively large premaxilla forming the floor of a wide fossa nasalis. The fossa is also wide in Chedighaii hutchisoni , although its floor and the premaxillae are missing. The fossa in Bothremys seems to be relatively narrower. The foramen praepalatinum lies within the premaxilla. It seems unlikely that a dorsal process, as in Araiochelys and Bothremys , was present in C. barberi . The endocast shows a relatively flat floor anteriorly, although the actual margin of the apertura narium externa is not present.

The ventral margin of the apertura narium externa is preserved laterally in ALAB PV 2001.2, and it shows a protuberant premaxilla, distinct from Bothremys and other Bothremydini . The midline portion is missing, so its complete outline is unknown, but it clearly had an apertura that faced more dorsally than in the other Bothremydini . Unfortunately, the ventral part of the apertura is missing in Chedighaii hutchisoni .

Structures on ventral surface: The labial ridge in Chedighaii barberi is straight, in contrast to the pinched or curved one in other Bothremydini . The premaxilla edge continues the shape and line of the maxilla edge. The ridge is acute along the margin; its surface is curved convex laterally and flat medially. None of the medial plate is preserved.

MAXILLA (figs. 160, 161, 165, 167)

Preservation: Nearly all of the vertical plate is preserved on the left side of ALAB PV 2001.2 and much of it on the right. The endocast preserves the maxillary surface inside the fossa nasalis and fossa orbitalis.

Contacts of vertical plate: The right and left maxillae of ALAB PV 2001.2 show the anterior contact with the premaxilla. The left maxilla has the anterodorsal contact with the prefrontal. The prefrontal extends ventrally along the dorsal process of the maxilla, as in Chedighaii hutchisoni , and probably comes close to a palatine contact. The palatine is present on the left side of ALAB PV 2001.2, but it is broken in the area of possible prefrontal contact. The position of the jugal contact on the lateral surface of the maxilla is indeterminate. The possible contact of the maxilla with the quadrate and quadratojugal is also indeterminate.

Structures of vertical plate: The orbital margin is not preserved in ALAB PV 2001.2 or FMNH PR 247, but in ALAB PV 2001.2 much of the rim is present. This agrees with the endocast in showing that there was a high rim above the floor of the fossa orbitalis. The deep maxilla seen in Chedighaii barberi also occurs in C. hutchisoni and Bothremys . The maxilla forms the dorsolateral edge of the apertura narium externa (see also Premaxilla, Prefrontal). In C. barberi the apertura is strongly inclined so that it faces anterodorsally, probably as in C. hutchisoni but in contrast to other Bothremydini , which are not as strongly inclined. The fossa nasalis in C. barberi is relatively wide, as in C. hutchisoni and Bothremys . It leads into the choanal passages, seen in the endocast and in fragments in ALAB PV 2001.2.

Contacts of horizontal plate: The maxilla contacts the premaxilla anteriorly, but the medial plate here is missing. The posteromedial maxilla-palatine contact is preserved in part on the left side of ALAB PV 2001.2, as is the jugal contact posterolaterally (see Jugal). In the endocast, the floor of the fossa orbitalis shows the dorsal surface contacts: palatine posteromedially and the jugal posterolaterally.

Structures of horizontal plate: The triturating surface in Chedighaii barberi is preserved only to a limited extent. Anteriorly it is missing, but the posterior part can be determined accurately using the two maxillae preserved in ALAB PV 2001.2. The labial ridge on the maxilla is as described for the premaxilla: relatively thin, acute margin, outer surface convex laterally, inner surface flat. The labial ridge in ventral view is straight, in contrast to Bothremys and other Bothremydini . Although curved, only Araiochelys , in addition to C. barberi , has a fairly thin labial ridge. It is possible, of course, that C. hutchisoni also has a narrow labial ridge, but this area is not known in that species. In lateral view, the labial ridge of C. barberi is slightly curved, concave ventrally. This is also unique among Bothremydini .

The triturating surface of Chedighaii barberi is only preserved in a short section on the left side of ALAB PV 2001.2. Nonetheless, there is enough preserved to determine that pits are absent and that it is much narrower than in C. hutchisoni . The part of maxilla preserved in ALAB PV 2001.2 shows a broad curve from the sloped internal surface of the labial ridge to the horizontal medial plate of the maxilla. In the pitted bothremydids this area is clearly marked by the concavity for the pit. The jugal in ALAB PV 2001.2 is not exposed in the triturating surface, and less of the palatine is exposed. The broad curved surface of the triturating surface in ALAB PV 2001.2 is narrower than in C. hutchisoni , and the angle of inclination of the labial ridge is somewhat more acute in C. barberi , presumably correlated with the narrower surface. The anterior median concavity is not preserved in C. barberi , but the medial edge of the triturating surface allows a certain amount of restoration to be controlled. It seems unlikely that in C. barberi there would be room for a wide anterior median concavity as seen in C. hutchisoni . A more likely size would be that seen in Bothremys cooki and Araiochelys .

VOMER Preservation: Not preserved.

PALATINE (figs. 160, 161, 165, 167)

Preservation: Part of the palatine just medial to the maxilla is present on the left side of ALAB PV 2001.2. The right maxilla in ALAB PV 2001.2 also has a small piece of palatine in this area. The endocast shows most of the dorsal surface of the palatine, but its anteromedial part is missing. Part of both palatines remains just anterior to the pterygoid in FMNH PR 247.

Contacts: The palatine contacts the maxilla anterolaterally, the other palatine medially, the pterygoid posteriorly, and the parietal dorsally in the anterior surface of the septum orbitotemporale. A possible vomer contact is indeterminate. The floor of the fossa orbitalis shows the palatine contacting the jugal anterolaterally, the maxilla anteriorly, and the postorbital dorsally.

Structures on dorsal surface: The palatine forms the posterior floor and much of the posterior wall of the fossa orbitalis, as in Chedighaii hutchisoni . The fossa orbitalis in C. barberi has the posteroventral enlargement seen in C. hutchisoni , Bothremys , Araiochelys , and Rosasia . The endocast shows this structure particularly well.

Structures on ventral surface: The palatine section preserved in ALAB PV 2001.2 lies just medial to the maxilla and forms the medial edge of the triturating surface. There is a narrow ledge above the triturating surface that curves medially to form the choanal wall. There is no real lingual ridge in either Chedighaii species; the edge just turns dorsally at its margin. The angle of the medial edge of the triturating surface seems to preclude a wide anterior median concavity (see Maxilla) in C. barberi ; instead, a narrow one, as in Araiochelys and Bothremys cooki , seems more likely. The apertura narium interna is also probably much narrower in C. barberi than in C. hutchisoni , but the posterior entry of the choanal passage seems about the same width.

QUADRATE (figs. 160, 163, 165, 286D)

Preservation: Most of both quadrates are present in ALAB PV 2001.2, but they lack the contacts with cheek elements and are broken around the anterior margin of the cavum tympani. In FMNH PR 247 most of the right quadrate is present, but it also lacks sutural contacts around the cavum tympani margins. The endocast has no quadrate information. A number of otic chambers probably belonging to Chedighaii barberi are in the North Carolina State Museum and are being described by Gaffney and Schneider (ms). One of these chambers, NCSM 12766, is figured here (fig. 286D).

Contacts on lateral surface: The only lateral contacts preserved are with the squamosal, which the quadrate contacts posterodorsally.

Structures on lateral surface: The cavum tympani can be determined using both ALAB PV 2001.2 and FMNH PR 247, although FMNH PR 247 is the most complete. The cavum in Chedighaii barberi is similar to that in C. hutchisoni : fossa precolumellaris absent, incisura columellae auris fully enclosed by bone and widely separated from the sulcus eustachii, antrum postoticum relatively small and tubelike, and shelf below cavum tympani present. The antrum in C. barberi ,

however, is smaller than that in C. hutchisoni .

Contacts on dorsal and anterior surfaces: As in Chedighaii hutchisoni and other Bothremydini , the quadrate in C. barberi contacts the prootic anteromedially, the opisthotic posteromedially, the supraoccipital medially, and the squamosal posterolaterally.

Structures on dorsal and anterior surfaces: The foramen stapedio-temporale in C. barberi is best seen in FMNH PR 247 and is well anterior on the otic chamber, near the foramen nervi trigemini.

Contacts on ventral surface: The quadrate contacts the pterygoid anteromedially, the basisphenoid medially, and the basioccipital posteromedially.

Structures on ventral surface: There is no fossa pterygoidea in Chedighaii barberi or C. hutchisoni , however, the bone surface is slightly depressed (so am I) around the foramen posterius canalis carotici interni in both species. The foramen posterius canalis carotici interni is formed by the pterygoid anteriorly and the quadrate posteriorly, as in C. hutchisoni , B. cooki , B. maghrebiana , Araiochelys , and B. arabicus . The condylus mandibularis in C. barberi is slightly anterior to the condylus occipitalis, whereas in C. hutchisoni it is even with the condylus occipitalis.

Contacts on posterior surface: The quadrate contacts the squamosal dorsolaterally, the opisthotic dorsomedially, the exoccipital medially, and the basioccipital ventromedially.

Structures on the posterior surface: The occipital surface of the skull in ALAB PV 2001.2 and FMNH PR 247 is not well preserved, so all the features cannot be seen clearly. The fenestra postotica is completely separated into two foramina (right side of ALAB PV 2001.2): a smaller, dorsomedial one for the stapedial artery, and a larger, ventrolateral one for the infamous lateral head vein. These divisions are only low ridges in Chedighaii hutchisoni .

PTERYGOID (figs. 160, 161, 163, 165, 167)

Preservation: All three specimens of Chedighaii barberi have some part of the pterygoid preserved, but none is even partially complete. The two sides of ALAB PV 2001.2 have the best pterygoids, with both lacking the processus trochlearis pterygoidei, the lateral margins, and the thin bone near the foramen nervi trigemini. The posterior and medial part of the right pterygoid remains in FMNH PR 247, but the bone surface is eroded. The endocast shows the medial dorsal surface of the pterygoid and some of the sulcus palatinopterygoideus floor.

Contacts on ventral surface: The pterygoid contacts the palatine anteriorly (only a few fragments of bone in ALAB PV 2001.2 and a small part of the palatine in FMNH PR 247), the quadrate posterolaterally, the other pterygoid medially, and the basisphenoid posteromedially. The basisphenoid contact is straight in Chedighaii barberi and curved in C. hutchisoni .

Structures on ventral surface: The processus trochlearis pterygoidei and associated flange are missing. The fossa pterygoidea is absent, but there is a shallow depression around the foramen posterius canalis carotici interni, which is formed between the pterygoid and quadrate. The foramen palatinum posterius medial margin that is formed by the pterygoid is present on both sides of ALAB PV 2001.2. It is in about the same position as in Chedighaii hutchisoni .

Contacts on dorsal surface: Although much of the dorsal surface of the pterygoid is visible, the crista pterygoidea is broken off close to its base in both ALAB PV 2001.2 and FMNH PR 247 and it is obscured by matrix in YPM PU 12951.

Structures on dorsal surface: A portion of the damaged foramen nervi trigemini is preserved on the left side of ALAB PV 2001.2 and shows that the pterygoid entered the foramen. Part of the sulcus and canalis cavernosus is adjacent.

SUPRAOCCIPITAL (figs. 160, 163, 167)

Preservation: The anterior part of the supraoccipital, lacking all but the base of the crista supraoccipitalis, is present in FMNH PR 247. A small section of the cavum cranii in YPM PU 12951 shows a supraoccipital imprint. A small part of the anteroventral edge and the lateral processes are preserved in ALAB PV 2001.2.

Contacts: The supraoccipital contacts the parietals anterodorsally, the prootic anterolaterally, the quadrate laterally (this is incorrectly identified as opisthotic in Gaffney and Zangerl, 1968: fig. 18), and the exoccipitals posteroventrally.

Structures: The base of the crista supraoccipitalis is preserved and it agrees with that in Chedighaii hutchisoni .

EXOCCIPITAL (figs. 160, 163, 165)

Preservation: Most of the right exoccipital is present in FMNH PR 247, but it is eroded and not well preserved so that sutures and foramina are unclear. The better preserved ALAB PV 2001.2 has some of both exoccipitals present, but the condylus occipitalis and most of the dorsal portions are broken away.

Contacts: The exoccipital in Chedighaii barberi contacts the supraoccipital dorsally, the opisthotic laterally, the quadrate ventrolaterally, and the basioccipital ventrally.

Structures: The shape of the foramen magnum in Chedighaii barberi cannot be determined, although one was almost certainly present. The only part of the condylus occipitalis preserved is in FMNH PR 247, and it does not show sutures; most of the bone surface is eroded away. The foramen nervi hypoglossi are present, but their position relative to sutures is unclear. The foramen jugulare posterius is also not well preserved. The fenestra postotica is widely separated by bone from the foramen jugulare posterius, and the lateral margin of the foramen jugulare posterius is largely present, showing that it was closed.

BASIOCCIPITAL (figs. 160, 163, 165)

Preservation: Most of the basioccipital is present in ALAB PV 2001.2 and FMNH PR 247, but it is damaged and the condylus occipitalis is missing or badly preserved.

Contacts: The basioccipital in Chedighaii barberi contacts the basisphenoid anteriorly, the quadrate laterally, and the exoccipital posterodorsally, as in the other Bothremydini .

Structures: Whether the basioccipital in Chedighaii barberi contributes to the condylus occipitalis cannot be determined. Distinct but shallow tubercula basioccipitale are present in C. barberi , and they are very similar in shape and position to those in C. hutchisoni . There is a shallow median concavity in C. barberi that is also the same as in C. hutchisoni .

PROOTIC (figs. 160, 163)

Preservation: The best prootic is on the right side of FMNH PR 247, with only small portions of the prootic remaining in ALAB PV 2001.2.

Contacts: The prootic in Chedighaii barberi contacts the parietal dorsomedially, the quadrate laterally, and the supraoccipital posterodorsally. The dorsal opisthotic contact is prevented by the broad quadrate-supraoccipital contact, as in most Bothremydini . The ventral pterygoid contact is likely but not preserved.

Structures: Very little of the internal features of the prootic are visible, although the path of the foramen nervi facialis can be seen on the left side of ALAB PV 2001.2. The position of the foramen nervi trigemini can be made out in both ALAB PV 2001.2 and FMNH PR 247, but its margins are gone.

OPISTHOTIC (figs. 160, 163, 165)

Preservation: Both opisthotics are present in ALAB PV 2001.2, missing their posterior edges and thinner occipital processes. The same is true of FMNH PR 247, but it also suffers from erosion disease.

Contacts: The opisthotic in Chedighaii barberi contacts the supraoccipital anteromedially, the quadrate anterolaterally, the squamosal posterolaterally, and the exoccipital posteromedially.

Structures: The fenestra postotica in Chedighaii barberi (see Quadrate) is subdivided into two foramina; its medial limits are formed by the opisthotic. The foramen jugulare posterius (see Exoccipital) is enclosed by bone and widely separated from the fenestra postotica.

BASISPHENOID (figs. 160, 163, 165, 167)

Preservation: All three skulls of Chedighaii barberi preserve the basisphenoid. Dorsal and ventral surfaces are in ALAB PV 2001.2, but it is missing its posterodorsal part and has breakage dorsally. All of the bone is present in FMNH PR 247, but the bone surface is eroded. The endocast shows nearly all of the dorsal surface in high fidelity (see also Gaffney, 1977a: fig. 3).

Contacts on ventral surface: The basisphenoid in Chedighaii barberi contacts the pterygoid anterolaterally, the basioccipital in a straight suture posteriorly, and the quadrate in a very narrow suture posterolaterally.

Structures on ventral surface: The ventral surface in Chedighaii barberi is flat, as in C. hutchisoni .

Contacts on dorsal surface: The basisphenoid in Chedighaii barberi contacts the pterygoid anterolaterally, the prootic laterally (seen in endocast), and the basioccipital posteriorly.

Structures on dorsal surface: The rostrum basisphenoidale in Chedighaii barberi ( Gaffney, 1977a: fig. 3) is an elongate rod, seen in all three specimens, that is similar in length and width to that in Podocnemis ( Gaffney, 1979a: fig. 54) rather than to the rostrum in Pelusios (fig. 24), which is wider and shorter. The sella turcica is elongate and deep, also as in Podocnemis and in contrast to Pelusios . The dorsum sellae in C. barberi overhangs the sella turcica to a greater extent than usually seen in Pelusios or Podocnemis . The foramen anterius canalis carotici interni lie at the corners of the sella turcica as usual. The processus clinoideus is absent; the canalis nervi abducentis is a shallow groove. This condition also occurs in Bothremys cooki and B. maghrebiana .

TRIBE TAPHROSPHYINI SUBTRIBE TAPHROSPHYINA Taphrosphys sulcatus

This, the first described bothremydid ( Leidy, 1856, as Platemys sulcatus ), is still known only from three incomplete skulls, as well as from a great deal of partial shell material. One of three species making up the genus, Taphrosphys sulcatus , is weakly supported as the sister taxon to T. ippolitoi . Taphrosphys itself is the sister group to Rhothonemys , Phosphatochelys , and Ummulisani .

Taphrosphys ippolitoi has the most complete cranial material of the three species. The three species of Taphrosphys are described in three separate sections, but only one species has the primary description and comparisons, depending on which species has the best preserved bone being described. The reader will therefore need to look at all three sections even if only one species is of interest. The particular species that has the best bone description for that particular element is always indicated in all three species descriptions.

PREFRONTAL (figs. 168, 170)

Preservation: Both prefrontals are present in ANSP 15544 and are undistorted.

However, the ventral process on both sides is broken off.

Contacts: In ANSP 15544 the prefrontal only contacts the parietal posteriorly and the other prefrontal medially, as the maxilla is missing. As in the other two Taphrosphys species, the frontal underlies the prefrontal ventrally, forming a V-shaped suture with the apex on the median suture line.

Structures: The prefrontal dorsal plate in Taphrosphys sulcatus is very similar to that in T. congolensis and Azabbaremys . It is smooth and lacks the swelling seen in T. ippolitoi . As in T. ippolitoi and T. congolensis the prefrontal in T. sulcatus is relatively thick, particularly along the midline, in contrast to most other bothremydids (e.g., Galianemys ).

The ventral surface of the prefrontal is visible in Taphrosphys sulcatus . It is very similar to that area in T. congolensis . The ventral process of the prefrontal and the anterior orbital margin are missing in both prefrontals in ANSP 15544. However, the right prefrontal has the dorsal orbital margin preserved as in T. congolensis .

FRONTAL (figs. 168, 170)

Preservation: Both frontals are nearly complete in ANSP 15544 and are visible dorsally and ventrally with clear sutures.

Contacts: The frontal in Taphrosphys sulcatus , as preserved in ANSP 15544, only contacts the prefrontal anteriorly and the parietal posteriorly. However, on both sides the frontals and parietals show that a postorbital was present and contacted the posterolateral edge of the frontal. This contact, however, is much shorter in T. sulcatus and T. congolensis than in Azabbaremys .

Structures: The frontal forms most of the dorsal orbital margin in Taphrosphys sulcatus , as in T. ippolitoi and most other bothremydids. When the orbit of T. sulcatus is restored on the basis of the curvature seen in ANSP 15544, the size is consistent with what could be restored for T. ippolitoi and T. congolensis based on different combinations of preserved elements. However, there is no one skull of Taphrosphys that has the orbit completely preserved, and the size and shape could vary among the three species.

PARIETAL (figs. 168, 170, 172, 173)

Preservation: Both parietals in ANSP 15544, the best skull roof for Taphrosphys sulcatus , are present and complete with no distortions except for the lateralmost margins, which are missing, and nearly all of the processus inferior parietalis, which is also gone on both sides. A partial skull, YPM PU 18707, has part of the left parietal preserved but it is much less complete than ANSP 15544. Another more complete skull, NJSM 11362, has both parietals present. These are complete dorsally and have good contacts with the supraoccipital, but they also lack most of the processus inferior parietalis on both sides.

Contacts of dorsal plate: In Taphrosphys sulcatus only the anterior contact with the frontal and the posteroventral contact with the supraoccipital are preserved.

Structures of dorsal plate: The posterior edge of the parietal in Taphrosphys sulcatus that forms the edge of the temporal emargination is preserved in both ANSP 15544 and NJSM 11362, but it is more complete in the latter. The degree of emargination in T. sulcatus is consistent with T. ippolitoi and is very similar to that in T. congolensis . The emargination limits are not determinable in T. sulcatus , as they are in T. congolensis . However, the emargination seems to be slightly wider in T. congolensis than in T. sulcatus because the parietal dorsal plate is slightly wider in T. sulcatus than in T. congolensis . The parietal margin of the temporal emargination in T. sulcatus appears to be straight or slightly convex laterally. The parietal on the midline extends posteriorly to the supraoccipital, being exposed in dorsal view as a small triangular or oblong shape.

Contacts of processus inferior parietalis: In Taphrosphys sulcatus, NJSM 11362 has enough of the foramen nervi trigemini on the pterygoid and prootic preserved to show that the parietal contacted those bones on either side of the foramen and made up its anterodorsal margin. The processus inferior parietalis also contacted the crista pterygoidea, as seen in NJSM 11362 and YPM PU 18707.

Structures of processus inferior parietalis: In Taphrosphys sulcatus only the very dorsal portion of this wall can be seen in ANSP 15544 and NJSM 11362. It is nearly identical to that in T. congolensis .

JUGAL

Preservation: Among the specimens identifiable as Taphrosphys sulcatus , there is no jugal. Due to the absence of the other palatal elements, maxilla, palatine, as well as cheek elements, it is not possible to find an adjacent bone articulating with the jugal.

QUADRATOJUGAL

Preservation: The element is absent in all available specimens of Taphrosphys sulcatus .

SQUAMOSAL (figs. 168, 169, 176, 177)

Preservation: The nearly complete right squamosal is present in NJSM 11362. It lacks its anteriormost margin and a small section of the posterior margin. ANSP 15544 has a right squamosal that is complete except for its ventral margin and its anteriormost edge.

Contacts: The squamosal has the same contacts on all three Taphrosphys species: it lies on the quadrate, contacting it anteriorly and anteromedially, and it contacts the opisthotic medially and the quadratojugal anterodorsally.

Contacts and structures: The only information on the postorbital in Taphrosphys sulcatus relates to the sutured edges on the frontals and parietals in ANSP 15544. These are consistent with a postorbital that is the same size and shape as the ones in T. congolensis and T. ippolitoi .

Structures: The antrum postoticum in Taphrosphys sulcatus is particularly visible in ANSP 15544, which includes a disarticulated right quadrate and right squamosal (fig. 176). The antrum itself is described under Quadrate, but its posterior cap is formed by the squamosal and can be seen in this specimen. In most turtles the antrum postoticum is a large cavity surrounded by relatively thin walls. In many bothremydids the antrum is small or absent. In Taphrosphys it is much smaller than in pelomedusids and smaller than in Galianemys , but it is still distinct. The removable right squamosal of ANSP 15544 shows that even though the antrum is reduced almost to a canal, it still significantly affects the formation of the squamosal and forms a smooth, hemispherical pocket that surrounds the tubelike extension of the quadrate.

The squamosal of Taphrosphys sulcatus , seen in NJSM 11362 (fig. 177), has a distinct ventral flange developed to about the same extent as in T. congolensis , both of which are smaller than in T. ippolitoi . Although the posterior margins of all the T. sulcatus squamosals are broken, they are very thin, and a posterior extension of the sort seen in Labrostochelys was not present.

POSTORBITAL

Preservation: Although one was almost certainly present, there is no postorbital in any available specimen of Taphrosphys sulcatus .

PREMAXILLA (figs. 168, 169, 171)

Preservation: The available material of Taphrosphys sulcatus lacks all the bones of the palate except for a single premaxilla, the left one, in YPM PU 18707. This element lacks its posterior plate.

Contacts and structures: The premaxilla in YPM PU 18707 is very similar to the better preserved premaxilla in the other Taphrosphys species, except that the labial ridge is deeper in T. congolensis than in T. sulcatus and T. ippolitoi . See T. ippolitoi description for more information on the Taphrosphys premaxilla.

MAXILLA

Preservation: Although one was almost certainly present, there is no maxilla in any of the available Taphrosphys sulcatus .

VOMER Preservation: The vomer is missing.

PALATINE

Preservation: Although one was almost certainly present, it is not preserved in the available specimens of Taphrosphys sulcatus .

QUADRATE (figs. 168, 169, 172, 173, 176, 177)

Preservation: Partial left and right disarticulated quadrates of Taphrosphys sulcatus are present in ANSP 15544, and a nearly complete right quadrate is in NJSM 11362.

Contacts on lateral surface: All three Taphrosphys sulcatus quadrates completely lack the anterior part of the bone, and the only suture visible in lateral view is the posterior one with the squamosal, which is the same as in the other two Taphrosphys species.

Structures on lateral surface: The cavum tympani in Taphrosphys is distinctly oval or kidney bean-shaped, not circular as in Azabbaremys and Phosphatochelys . T. sulcatus shows this shape, as do the other two Taphrosphys species. In T. sulcatus the cavum is slightly deeper than in T. congolensis ,

particularly the anteroventral part of the concavity. The incisura columellae auris in all Taphrosphys and in all Taphrosphyini is a round canal well separated by bone from the eustachian tube groove. In T. sulcatus there is a barely discernable groove from the incisura to the eustachian groove; a similar groove is in T. congolensis . However, in T. ippolitoi the groove is well defined by two parallel ridges, similar to the condition in Galianemys .

The antrum postoticum in Taphrosphys sulcatus is smaller than in pelomedusids and is similar in size to that in Phosphatochelys . The antrum in T. ippolitoi is slightly smaller than in T. sulcatus ; the T. congolensis quadrates are crushed down to the level of the antrum so that neither is visible. In T. sulcatus the antrum postoticum is close to the lateral edge of the quadrate, as in Phosphatochelys , but in T. ippolitoi the antrum is placed more deeply in the cavum tympani, presumably because the cavum is deeper.

Although the anterior part of the cavum tympani is missing in all Taphrosphys sulcatus specimens, and the upper part of the cavum is crushed in T. congolensis , comparison can still be made with T. ippolitoi . In the former two species the cavum is about as deep as in Phosphatochelys and Galianemys , but in T. ippolitoi the cavum tympani is about double the depth. This affects the entire area of the cavum so that there is a large dorsal overhang and a large shelf ventrally.

The eustachian tube in bothremydids (except for Foxemys , Cearachelys , and Polysternon ) is separated by a solid bony wall from the stapes. A notch, the sulcus eustachii, carries the tube into the cavum tympani medial to the tympanic membrane. This notch is formed by the quadrate, and in Taphrosphys sulcatus and T. congolensis it opens directly ventral to the incisura columellae auris. In T. ippolitoi the notch opens posteroventrally at an angle to the incisura. The eustachian tube notch in T. sulcatus and T. congolensis is more open, but in Taphrosphys ippolitoi there is a flange of quadrate projecting posterodorsally from the lower edge of the notch that partially closes the notch.

Contacts on dorsal and anterior surfaces: The dorsal contacts of the quadrates are the same in all three Taphrosphys species and in the Taphrosphyini : prootic anteromedially, opisthotic posteromedially, and squamosal posterolaterally. There is no quadrate-supraoccipital contact.

Contacts on ventral surface: The quadrate in all three Taphrosphys species contacts the opisthotic posteromedially, the squamosal posterolaterally, the pterygoid anteromedially, the basisphenoid medially, and the basioccipital posteromedially. In T. ippolitoi and T. congolensis there is a posteromedial contact with the exoccipital just behind the basioccipital. In T. sulcatus, ANSP 15544, this part of the quadrate is broken off, but an exoccipital contact was likely based on the articulated basioccipital and exoccipitals of YPM PU 18707, which show a contact area for the quadrate on the exoccipital.

Structures on ventral surface: The quadrate structures in ventral view are also very similar in the three Taphrosphys species. The foramen posterius canalis carotici interni is formed at the junction of the quadrate, basisphenoid, and pterygoid. The foramen is clear in T. ippolitoi (fig. 277D) and T. sulcatus , but the margins are eroded in T. congolensis . Nonetheless, small edges of the foramen are visible and the canalis caroticus internus can be followed to this point. There is no pterygoideus muscle attachment scar (as seen in some other bothremydids like Arenila ) in any of the three Taphrosphys species. The condylus mandibularis is positioned well anterior to the condylus occipitalis.

Structures on posterior surface: The fenestra postotica (fig. 177) is intact and uncrushed on the right side of NJSM 11362 in Taphrosphys sulcatus , on the right side of AMNH 30042 in T. ippolitoi , and on the left side of T. congolensis . In T. sulcatus and T. congolensis the fenestra is figure eight-shaped, an oval pinched in the center to separate the more dorsal stapedial artery from the more ventral lateral head vein. In the right side of T. congolensis , broken bone fragments separate the two parts into foramina, but this seems to be due to partial crushing. In T. ippolitoi , however, the fenestra is subdivided by bone that appears to be uncrushed and in its original condition. The quadrate in Taphrosphys as in other turtles forms the ventral part of the fenestra postotica, with the opisthotic forming the dorsal part. In T. ippolitoi the quadrate forms the process dividing it into two foramina.

In the three species of Taphrosphys there is a variably developed ridge on the posterior surface of the processus articularis of the quadrate. This ridge extends from the ventral part of the processus dorsomedially to the base of the processus and may have formed a concavity for the depressor mandibulae attachment. The ridge is larger and more massive in T. ippolitoi but it is well developed in T. sulcatus , although incompletely preserved. Both have a shallow, ventrally facing trough formed by the ridge. In T. congolensis the ridge is much less prominent, possibly exaggerated by crushing of this part of the processus articularis. A similar ridge and trough is present in Labrostochelys ; a rudimentary one is in Phosphatochelys and Azabbaremys .

PTERYGOID (figs. 168, 169, 172, 174, 177)

Preservation: The right pterygoid in Taphrosphys sulcatus is preserved in NJSM

11362 and in YPM PU 18707. Both are uncrushed and free of matrix on all sides, but they lack the processus trochlearis pterygoidei.

Contacts on ventral surface: See Taphrosphys ippolitoi for description.

Structures on ventral surface: See Taphrosphys ippolitoi for description.

Contacts on dorsal surface: The areas of the anterior contacts of the processus trochlearis pterygoidei, the sulcus palatinopterygoideus, and the posterior wall of the fossa nasalis are either absent or badly damaged in all three Taphrosphys species. The parietal contacts the crista pterygoidea anteriorly. More posteriorly there is a quadrate contact behind the foramen nervi trigemini on the dorsal surface.

Structures on the dorsal surface: The area of the processus trochlearis pterygoidei and sulcus palatinopterygoideus in Taphrosphys is either missing ( T. sulcatus ) or badly damaged ( T. congolensis and T. ippolitoi ), but enough of the parietal is preserved to show that the septum orbitotemporale was absent, as in Azabbaremys and Phosphatochelys .

The disarticulated pterygoids (YPM PU 18707 and NJSM 11362) of Taphrosphys sulcatus allow description of the internal aspects of the dorsal pterygoid surface (fig. 174), some of which is also visible in T. congolensis . There is a prominent crista pterygoidea articulating with the processus inferior parietalis. This wall is relatively narrow, as in Azabbaremys and Phosphatochelys , not extending to the anterior portion of the pterygoid or involving the palatine. Lateral to the crista pterygoidea, near the palatine contact, is a small foramen, the foramen nervi vidiani, as in most other Pelomedusoides. Medial to the crista pterygoidea is the sulcus cavernosus, and medial to that, in the suture between pterygoid and basisphenoid, is the canalis caroticus internus leading to the foramen posterius canalis carotici interni.

In Phosphatochelys , four bones make up the foramen nervi trigemini: parietal, prootic, pterygoid, and quadrate. In Taphrosphys congolensis at least the prootic and pterygoid enter the margin (preserved only on the right side) with possibly the quadrate, with the parietal being uncertain. In T. sulcatus the pterygoid clearly makes up the ventral margin and the quadrate probably enters it, but the prootic and parietal contributions are not determinable. Although the foramen stapedio-temporale is very close to the foramen nervi trigemini in Taphrosphys , its exact margins are ambiguous, except in T. ippolitoi, AMNH 30500. In this specimen, the foramen nervi trigemini and foramen stapedio-temporale are joined by the same outer rim formed by the parietal, prootic, pterygoid, and quadrate. This is quite different from the situation in Phosphatochelys and Labrostochelys in which the two foramina are very close but not actually fused. A thin sheet of prootic separates the two foramina, but it lies posterior to the outer rim.

SUPRAOCCIPITAL (figs. 168, 170, 172)

Preservation: A complete supraoccipital in Taphrosphys sulcatus is preserved in NJSM 11362 and a nearly complete one is in ANSP 15544.

Contacts: All three Taphrosphys species have these contacts: parietals dorsally, prootic anterolaterally, opisthotic laterally, and exoccipital posteroventrally. There is no quadrate contact.

Structures: The crista supraoccipitalis is short in Taphrosphys sulcatus , as in Azabbaremys and Phosphatochelys . Although in T. congolensis the margin is broken, it is thin and unlikely to be more extensive than in T. sulcatus . In T. ippolitoi its length is indeterminate.

EXOCCIPITAL (figs. 168, 172, 175, 177)

Preservation: Both exoccipitals in Taphrosphys sulcatus are preserved in NJSM 11362 and are prepared on all surfaces and completely visible. However, both have a small portion of the ventrolateral process broken. YPM PU 18707 has both exoccipitals, which are complete and visible ventrally but lack the dorsal processes.

Contacts: The contacts are the same in all three Taphrosphys species: supraoccipital dorsally, opisthotic laterally, quadrate ventrolaterally, basioccipital ventrally, and the other exoccipital ventromedially.

Structures: In all three Taphrosphys species the exoccipitals meet on the midline to form the condylus occipitalis and its neck in ventral view. Dorsally, the contact extends farther anteriorly to exclude the basioccipital from the floor of the foramen magnum. This is similar to the Azabbaremys condition, but Phosphatochelys has the basioccipital separating the exoccipitals to a slightly greater degree.

All three species of Taphrosphys have two pairs of the foramen nervi hypoglossi that penetrate the exoccipital (figs. 175, 177), with the more medial foramen being slightly larger than the more lateral one. The foramen jugulare posterius is completely enclosed, formed medially by the exoccipital and laterally by the opisthotic in all three species. The more lateral foramen nervi hypoglossi actually opens in the medial wall of the foramen jugulare posterius in all three Taphrosphys species, as it does in Phosphatochelys .

BASIOCCIPITAL (figs. 168, 169, 175)

Preservation: The complete basioccipital in Taphrosphys sulcatus is present in YPM PU 18707 and NJSM 11362; both are visible dorsally and ventrally. In NJSM 11362 the posterolateral margins are eroded, but they are complete in YPM PU 18707.

Contacts: The contacts are the same in all three Taphrosphys species: basisphenoid anteriorly, quadrate laterally, and exoccipitals posteriorly.

Structures: The condylus occipitalis is discussed under Exoccipital. All three Taphrosphys species have a shallow median concavity that parallels the basisphenoid suture. It is developed to about the same extent in Taphrosphys as it is in Phosphatochelys . It is not as flat as in Azabbaremys . The basioccipital of Taphrosphys also resembles Phosphatochelys in having a curved anterior margin rather than the straighter margin seen in Azabbaremys .

The tuberculum basioccipitale in Taphrosphys ippolitoi is more distinct than in Azabbaremys , Phosphatochelys , or the other two Taphrosphys species. In T. ippolitoi the tuberculum, formed by basioccipital and exoccipital, extends posterolaterally to form a distinct shelf ventral to the foramen jugulare posterius. This is not developed in T. sulcatus or T. congolensis .

PROOTIC (fig. 174)

Preservation: In Taphrosphys sulcatus the right and left disarticulated and complete prootics are preserved in YPM PU 18707. The nearly complete right prootic is in NJSM 11362.

Contacts: In all three Taphrosphys species there are the following contacts: parietal medially, quadrate laterally, supraoccipital posterodorsally, pterygoid ventrally, and opisthotic posteriorly.

Structures: In Taphrosphys sulcatus , T. congolensis , and T. ippolitoi the prootic forms the lateral and dorsal part of the anterior-facing foramen stapedio-temporale. The more medial limits and the separation between the foramen stapedio-temporale from the foramen nervi trigemini, also roofed by the prootic, are not clear in T. sulcatus and T. congolensis . In T. ippolitoi these two foramina are fused into a common opening, in contrast to Phosphatochelys and Labrostochelys . The Taphrosphys sulcatus specimens show the internal features of the prootic, but they do not differ from other Pelomedusoides.

OPISTHOTIC (figs. 168, 172, 174, 177)

Preservation: In Taphrosphys sulcatus a nearly complete right opisthotic is present in NJSM 11362 and a nearly complete right opisthotic is present in YPM PU 18707.

Contacts: In all three Taphrosphys species the contacts are: supraoccipital anteromedially, prootic anteriorly, quadrate anterolaterally and ventrally, squamosal posterolaterally, and exoccipital posteromedially.

Structures: The dorsal surface is the same in all three Taphrosphys species and differs from Phosphatochelys and Azabbaremys only in having a more extended posterior process at the end of the opisthotic.

On the ventral surface the opisthotic forms the roof of the fenestra postotica and the lateral wall of the foramen jugulare posterius. In all three Taphrosphys species the foramen jugulare posterius is closed by a process of the opisthotic contacting the dorsal and ventral margins formed by the exoccipital. The fenestra postotica in T. sulcatus and T. congolensis are figure eight-shaped openings with the dorsal half for the stapedial artery and the lateral head vein in the ventral half. The opisthotic forms most of the dorsal half and the quadrate the ventral half. In T. ippolitoi the fenestra postotica is divided by bone into two foramina, with the process being formed equally by opisthotic and quadrate, although there is cracking in this area and the quadrate alone may form the process.

BASISPHENOID (figs. 168, 169, 174)

Preservation: There is a nearly complete basisphenoid for Taphrosphys sulcatus showing both dorsal and ventral surfaces in NJSM 11362.

Contacts: In all three Taphrosphys species the basisphenoid contacts are: pterygoid anterolaterally, quadrate laterally, and basioccipital posteriorly. The prootic should contact the basisphenoid laterally on its dorsal surface, and in T. congolensis crushed bone from the prootic does lie on the basisphenoid, but not in its original condition. In NJSM 11362 the ventromedial edge of the prootic has been lost, and no basisphenoid contact is present.

Structures: In ventral view the basisphenoid is very similar in all three Taphrosphys species. The basisphenoid is five-sided in all three species, in contrast to the more triangular shape of Phosphatochelys , Azabbaremys , and Labrostochelys and to the V-shaped outline of Arenila . The dorsal surface is visible in all three Taphrosphys species. Beginning anteriorly on the basisphenoid, the anteriormost feature is the rostrum basisphenoidale, the ossification of the anterior portion of the trabeculae. In T. congolensis the rostrum is a laterally compressed process with a dorsal midline ridge, rather than being a cylinder commonly seen in other Pelomedusoides like Pelusios (fig. 24). In T. ippolitoi and T. sulcatus the midline area of the basisphenoid is flat, with no indication of an elongated or ridged rostrum basisphenoidale, a condition unusual for turtles. Directly posterior to the rostrum in T. congolensis is a well-defined oval depression, the sella turcica. Its floor is below the base of the rostrum basisphenoidale; there are deep lateral ridges and a high posterior dorsum sellae completely defining the deep sella turcica. This condition is more pronounced than in most turtles. In T. sulcatus and T. ippolitoi the sella turcica is a barely defined feature; there is only a low pair of anteromedial ridges along the basisphenoid-pterygoid suture, and a very low, nearly absent, dorsum sellae. Such a low and undefined sella turcica is unusual for turtles. The dorsum sellae of T. congolensis is high and nearly vertical. In T. sulcatus and T. ippolitoi it is a low, barely defined swelling. At the dorsolateral margin of the dorsum sellae in T. congolensis is the paired, relatively large, processus clinoideus, unusually well developed for a pelomedusoid. There is no sign of a processus clinoideus in T. sulcatus ; however, some erosion has taken place here on both sides, and a pair could easily have been present, although not as large as in T. congolensis . In T. ippolitoi the processus is low on both sides. The foramen anterius canalis carotici interni in T. congolensis is closer to the midline than that foramen in T. sulcatus and T. ippolitoi . The foramen is also angled to face anteromedially in T. congolensis due to the narrow sella turcica, while in T. sulcatus and T. ippolitoi the foramen anterius canalis carotici interni faces anteriorly and is not contained in a narrow sella turcica.

Taphrosphys ippolitoi

This species of Taphrosphys is represented by a nearly complete skull (AMNH 30042) and a partial skull (AMNH 30500) that shows internal features of the braincase. Together, they make this species the most completely known of the genus.

PREFRONTAL (figs. 178, 181, 183)

Preservation: Both prefrontals of Taphrosphys ippolitoi are present in AMNH 30042 and AMNH 30500. In AMNH 30042 they are pushed ventrally away from their original position, almost completely collapsing the fossa nasalis. Their ventral surfaces cannot be seen. Sutural contacts are clear in both skulls. There is some distortion posterolaterally in AMNH 30500, and the ventral edges are broken in AMNH 30500.

Contacts: As in other bothremydids, the prefrontal in Taphrosphys ippolitoi contacts the other prefrontal medially, the frontal posteriorly, and the maxilla ventrolaterally. In AMNH 30042 both prefrontals are in roughly life position, but they have been separated from their original contacts.

Structures: The dorsal plate of the prefrontal in Taphrosphys ippolitoi has the typical morphology seen in other Taphrosphyini , such as Azabbaremys . In T. ippolitoi the anterior margin of the prefrontal, which forms the dorsal edge of the apertura narium externa, is more protuberant than in T. sulcatus , T. congolensis , or Azabbaremys . The prefrontal in all three Taphrosphys species is thick on the midline, as in Azabbaremys and in contrast to Galianemys . In T. ippolitoi , however, the bone thickens anteriorly so that the anterior projection has a swelling visible in dorsal view, being thickest on the midline. This is absent in T. sulcatus and T. congolensis , as well as in other bothremydids. The ventral surface of most of the prefrontal is visible in AMNH 30042 and shows the roof of the relatively large fossa nasalis characteristic of T. ippolitoi . The fossa is smaller in T. sulcatus and T. congolensis . The prefrontal in Taphrosphys ippolitoi forms the anterodorsal margin of the orbit, as in other Taphrosphys species.

FRONTAL (figs. 178, 181, 183)

Preservation: Both frontals of Taphrosphys ippolitoi are present in both specimens and are undistorted. There is some breakage posterolaterally. Although the frontals are in good shape in AMNH 30042, the palatines have been crushed dorsally and obscure the posteroventral morphology of the sulcus olfactorius of the frontals, but this is visible in AMNH 30500.

Contacts: The frontal in Taphrosphys ippolitoi has these common bothremydid contacts: frontal on midline, prefrontal anteriorly, and parietal posteriorly. AMNH 30500 lacks postorbitals. The usual postorbital contact posterolaterally is obscured in AMNH 30042 due to breakage of both frontal and parietal and the apparent absence of the postorbital due to breakage. Although the space between the jugal and parietal seems to require a postorbital in the orbital margin, whether it contacted the frontal is unclear. There is a postorbital-frontal contact in T. congolensis and T. sulcatus .

Structures: The frontal forms most of the dorsal orbital margin in Taphrosphys ippolitoi , as in T. sulcatus . The margin is slightly eroded on both sides, and the shape of the orbit is not completely determinable. However, it is consistent with the orbital edge preserved in T. sulcatus . In Azabbaremys the frontal forms much less of the margin than in Taphrosphys .

The ventral surface of the frontal in Taphrosphys ippolitoi shows a well-defined sulcus olfactorius formed by a deep parasagittal ridge that increases in height posteriorly to merge with the processus inferior parietalis. The sulcus olfactorius ridge in T. ippolitoi is somewhat deeper than that in Azabbaremys and much deeper than that in Galianemys . The ridge in T. ippolitoi is also deeper than that in T. sulcatus . The frontal is unknown in T. congolensis .

PARIETAL (figs. 178, 181, 183)

Preservation: Both parietals are present in AMNH 30042 but both are damaged by breakage, particularly distally. Both also show some dislocation. Significant distortion seems to be absent, the sutures are clear, and only the dorsal surface is visible. In AMNH 30500 both parietals are nearly complete and visible dorsally and ventrally.

Contacts of dorsal plate: In the available material of Taphrosphys ippolitoi , the parietal in AMNH 30042 contacts the frontal anteriorly, the other parietal medially, and the supraoccipital posteromedially and ventrally, all as in other bothremydids. As preserved, the right parietal is overlapped by the right jugal anterolaterally, and the left parietal is near the left jugal. However, we have concluded that this is a result of crushing and considerable loss of height of the skull. Conservative restoration (fig. 178) strongly supports the interpretation that another bone was anterolateral to the parietal, presumably the postorbital. The parietal in Taphrosphys ippolitoi contacts the thin quadratojugal laterally, as in T. congolensis .

Structures of dorsal plate: The dorsal plate of the parietal in Taphrosphys ippolitoi has a shape that is very similar to that in T. congolensis and T. sulcatus . A very small section of the parietal-supraoccipital suture remains at the posterior edge of the skull roof in AMNH 30042.

The surface of the parietal, frontal, and prefrontal of Taphrosphys ippolitoi in AMNH 30042 has a roughly corrugated texture, in contrast to the very smooth surface in T. sulcatus and T. congolensis . In AMNH 30500 the surface is slightly rugose, but not corrugated as in AMNH 30042. Scale sulci are not visible in any of the Taphrosphys skulls.

Contacts of processus inferior parietalis: In Taphrosphys ippolitoi, AMNH 30500 has most of the processus inferior parietalis preserved. There is no palatine contact, but the usual, wide pterygoid contact extends posteriorly to the foramen nervi trigemini where the prootic contacts the parietal posteroventrally. Posteriorly the supraoccipital contacts the parietal.

Structures of processus inferior parietalis: The processus inferior parietalis in Taphrosphys ippolitoi is wider than in Azabbaremys and Phosphatochelys . It forms the anterodorsal margin of the foramen nervi trigemini, which is nearly combined with the foramen stapedio-temporale. The combined foramina form the common margin of an oval opening, with a narrow sheet separating the two foramina, well posterior to the common margin.

JUGAL (figs. 178, 181)

Preservation: In Taphrosphys ippolitoi both jugals are present in AMNH 30042, and both are in roughly their original position. However, they have been slightly disarticulated and disturbed. The left one seems to be more complete and may not be missing anything but some edges. The right jugal is smaller and seems to have more broken edges and probably lacks larger areas. AMNH 30500 lacks jugals.

Contacts of lateral plate: In Taphrosphys ippolitoi the left jugal in AMNH 30042 is in articulation with the maxilla anteroventrally in a suture that extends from the lower margin of the orbit to the maxilla-quadrate contact. On the right side in AMNH 30042, the jugal is displaced medially but the sutural surface is clear on the maxilla. Posteroventrally, the jugal contacts the quadrate, but it is displaced on the left side with some matrix in the jugal-quadrate suture. On the right side the jugal is more displaced and missing its posteroventral edge so that the jugal-quadrate suture is actually a narrow space.

Structures of lateral plate: Posterodorsally the right jugal in Taphrosphys ippolitoi, AMNH 30042, contacts the parietal margin as preserved, but this is interpreted as due to postmortem crushing in which the postorbital and quadratojugal are either covered or missing. In the reconstruction the jugal only contacts the postorbital and quadratojugal along its dorsal margin. Unfortunately, neither the postorbital or quadratojugal is clearly preserved in the region of their contacts with the jugal. A postorbital-jugal contact is very likely because what seems to be that contact is preserved at least in part on both jugals. The jugal-quadratojugal contact, however, is more speculative because this area is not preserved in either skull. The jugal of Taphrosphys ippolitoi enters the posteroventral margin of the orbit, and this is preserved on both sides in AMNH 30042. As in T. congolensis , the quadrate-maxilla contact prevents a jugal exposure on the cheek.

Contacts and structures of medial process: A portion of the medial jugal process in Taphrosphys ippolitoi is present on both sides of AMNH 30042, but displacement and breakage prevent a detailed description.

QUADRATOJUGAL (figs. 178, 181, 183)

Preservation: In AMNH 30042 the quadratojugal is completely missing on the left side, and only its narrow posterior extension is present on the right. In AMNH 30500, most of both quadratojugals are present.

Contacts and structures: The quadratojugal in Taphrosphys ippolitoi contacts the quadrate ventrally in a wide suture and the squamosal posteriorly in a very narrow suture. It contacts the parietal medially and the jugal anteroventrally. The anterodorsal suture is very likely present but not clearly preserved.

The quadratojugal forms part of the anterolateral edge of the temporal emargination. The quadratojugal in T. ippolitoi agrees with that in T. congolensis .

SQUAMOSAL (figs. 178, 183, 184, 286E)

Preservation: In Taphrosphys ippolitoi both squamosals are present in both skulls and they are nearly complete. In AMNH 30042 the left one is damaged dorsally and lacks the parasagittal ridge. Both lack part of the posterior margin. In AMNH 30500 the left one is broken dorsally.

Contacts: As in Taphrosphys sulcatus .

Structures: The antrum postoticum in Taphrosphys ippolitoi is preserved completely and prepared on the right side of AMNH 30042 and of AMNH 30500. It is similar in size and shape to that in T. sulcatus , but the lateral wall formed of quadrate plus squamosal is thicker in T. ippolitoi than it is in T. sulcatus . The ventral flange of the squamosal in Taphrosphys ippolitoi is deeper than in both T. sulcatus and T. congolensis . Its ventral margin is also curved medially in T. ippolitoi , rather than straight, as in T. sulcatus and T. congolensis . Although the posterior margin of the squamosal is slightly thicker than in the other two species, it does not extend posteriorly to a greater degree.

POSTORBITAL (fig. 178)

Preservation: Although one was almost certainly present in Taphrosphys ippolitoi , few of the fragments in the area of the postorbital can be clearly identified as such and none has clear contacts.

Structures and contacts: In Taphrosphys ippolitoi both the jugal and parietal on the left side and to some extent on the right side of AMNH 30042 preserve contacts that are best interpreted as postorbital sutures. The reconstruction hypothesizes a postorbital very similar to that in T. congolensis with a narrow frontal contact, a long orbital margin exposure, and a long jugal contact. AMNH 30500 preserves what are probably the postorbital contact on the anterolateral margin of both parietals and the posterior contact with both quadratojugals, so the contacts and shape of the postorbital can be determined. There is no sign of a medial process of the postorbital in Taphrosphys ippolitoi ; the medial process of the postorbital seems to be absent in the other Taphrosphys species.

PREMAXILLA (figs. 178, 179, 181)

Preservation: Both premaxillae are present in AMNH 30042: the left one is complete, and the right one lacks a small portion of the posterior plate. Premaxillae are missing in AMNH 30500.

Contacts: In Taphrosphys ippolitoi the midline contact is completely preserved for the full length of the element, and there is a presumed contact edge for the vomer, which is missing. Posterolaterally the premaxilla contacts the maxilla in a suture that is comparable in height to that in T. congolensis (the contact in T. sulcatus is not completely preserved).

Structures on dorsal surface: The premaxilla forms the floor of the apertura narium externa, which can be entirely reconstructed in Taphrosphys ippolitoi and partially in the other two Taphrosphys species. The apertura in T. ippolitoi is significantly wider than in the other two species, withmuch of the width being formed by a broader premaxilla. The floor of the fossa nasalis is also broader and deeper in T. ippolitoi than in the other two species.

Structures on ventral surface: In ventral view the premaxilla of Taphrosphys ippolitoi forms the medial portion of the triturating surface. Due to its greater width, it forms more of this surface in T. ippolitoi than in the other Taphrosphys species. The labial ridge in T. ippolitoi is similar to that in T. sulcatus , both of which are shallower than in T. congolensis . The anterior part of the triturating surface in T. ippolitoi is wider than in the other two species. The medial edge of the triturating surface is a very low ridge separating the nutrient-rich surface from the smooth medial area. This medial area is a shallow concavity; the comparable area is missing in T. congolensis and T. sulcatus . Near the posterior edge is the foramen praepalatinum, completely formed by the premaxilla in T. ippolitoi .

MAXILLA (figs. 178, 179, 181)

Preservation: Both maxillae are preserved and are nearly complete and uncrushed in AMNH 30042, although they are slightly displaced from their original positions. Maxillae are missing in AMNH 30500.

Contacts of vertical plate: The maxilla of Taphrosphys ippolitoi contacts the premaxilla anteriorly and the prefrontal anterodorsally. Posterodorsally there is a clear contact with the jugal that seems to exclude any contact with the postorbital. Posteriorly, below the jugal contact there seems to be a quadrate contact, although it is not present on either side as preserved. On the left side there is obvious displacement, but the maxilla and quadrate are very close nonetheless. In the restoration it is difficult to bring the surrounding elements into position without a strong maxilla-quadrate contact. There is no quadratojugal contact.

Structures of the vertical plate: The apertura narium externa lateral margins are slightly flared laterally in Taphrosphys ippolitoi , in contrast to T. congolensis in which they lie in the plane of the rest of the maxilla. The entire anterior half of the maxilla in T. ippolitoi is expanded laterally so that the snout is flared, in contrast to the more acute snout of T. congolensis and, presumably, T. sulcatus . In T. sulcatus the small premaxilla suggests a narrower snout, more like T. congolensis than T. ippolitoi .

Contact of horizontal plate: Very little of the dorsal surface of the fossa orbitalis is visible in Taphrosphys ippolitoi , so the elements making up the floor of the fossa orbitalis are not determinable. See T. congolensis for other contacts.

Structures of horizontal plate: The triturating surface of the maxilla in Taphrosphys ippolitoi has an acute, relatively deep labial ridge with a broadly curved medial surface, similar to that in Labrostochelys . This is in contrast to the medial surface meeting the labial ridge at right angles, as in Azabbaremys . The maxillary triturating surfaces of T. ippolitoi and T. congolensis are very similar, with T. ippolitoi being slightly more expanded anteriorly.

VOMER

Preservation: The vomer is missing in both skulls of Taphrosphys ippolitoi , but a sutural margin on the posterior edge of the left premaxilla in AMNH 30042 suggests that one was present.

PALATINE (figs. 178, 179, 181)

Preservation: Both palatines are present and nearly complete in AMNH 30042, although both lack their anterior margins. Both are fractured and pushed dorsally above the level of the pterygoids. Palatines are missing in AMNH 30500.

Contacts: Both Taphrosphys ippolitoi and T. congolensis specimens show the palatine contacting the maxilla anterolaterally, the other palatine medially, and the pterygoid posteriorly. There is probably a lateral contact with the jugal, but it is either disarticulated ( T. ippolitoi ) or missing ( T. congolensis ). The possible vomer contact is not preserved in either specimen. The dorsal surface contacts are not visible in either T. ippolitoi or T. congolensis .

Structures: The palatines of Taphrosphys ippolitoi and T. congolensis are very similar in shape and size. The palatine in both species does not enter onto the triturating surface to a significant extent, in agreement with other Taphrosphyini . Both species also lack the strong dorsal arching of the palatine seen in Azabbaremys and Phosphatochelys .

QUADRATE (figs. 178, 183, 184, 286E)

Preservation: In AMNH 30042 both quadrates are present and nearly complete although fractured. There is some ventral displacement of the dorsal part, particularly in the left quadrate. Both quadrates lack the anterodorsal sutural edge. In AMNH 30050, both quadrates are uncrushed and complete, except for their anterior margins.

Lateral view contacts and structures: The maxilla-quadrate contact of

Taphrosphys ippolitoi is described under Maxilla, and the quadrate is described under T. sulcatus .

Dorsal view contacts and structures: See Taphrosphys sulcatus for description.

Ventral view contacts and structures: See Taphrosphys sulcatus for description.

PTERYGOID (figs. 178, 179, 181, 277D)

Preservation: Both pterygoids are present in AMNH 30042, but they are visible only in ventral view. Each pterygoid is also nearly complete except for some fractures and the broken processus trochlearis pterygoidei, which is on each side, although displaced. In AMNH 30500, both pterygoids are present but lack their anterior area and processus trochlearis pterygoidei. The dorsal surface is visible.

Contacts on ventral surface: In all three Taphrosphys species these contacts are the same: palatine anteriorly, other pterygoid anteromedially, basisphenoid posteromedially, and quadrate posterolaterally. The pterygoids in Taphrosphys are not as completely separated by the basisphenoid as in Azabbaremys and Phosphatochelys .

Structures on ventral surface: Although at least part of the processus trochlearis pterygoidei is present in Taphrosphys congolensis and T. ippolitoi (but not T. sulcatus ), the angle or relative size is not determinable. The quadrate ramus of the pterygoid is preserved in all three Taphrosphys species and is very similar to that in Azabbaremys and Phosphatochelys . There is no depression or attachment scar for the pterygoideus musculature as seen in Arenila . The foramen posterius canalis carotici interni is formed equally by the pterygoid, basisphenoid, and quadrate in all three Taphrosphys species (fig. 277D). The edges of this foramen are slightly eroded in T. congolensis and T. sulcatus , but it is well preserved on the left side of AMNH 30042, T. ippolitoi . In AMNH 30500, the foramen posterius canalis carotici interni is formed mostly by the basisphenoid and quadrate, with the pterygoid nearly squeezed out. The foramen in AMNH 30042 is at the bottom of a slight depression that angles dorsomedially. There is no evidence that the pterygoid in any Taphrosphys species forms part of the foramen palatinum posterius.

Contacts on dorsal surface: See Taphrosphys sulcatus for description.

Structures on dorsal surface: See Taphrosphys sulcatus for description.

SUPRAOCCIPITAL (figs. 178, 181)

Preservation: In Taphrosphys ippolitoi in AMNH 30042, the anterior portion of the supraoccipital is largely covered by matrix, but the right portion is visible. The crista supraoccipitalis is broken at the foramen magnum. In AMNH 30500 the supraoccipital is entirely visible with clear sutures, but it also is missing nearly all of the crista supraoccipitalis.

Contacts and structures: See Taphrosphys sulcatus for description.

EXOCCIPITAL (figs. 178, 183, 184)

Preservation: Both exoccipitals are preserved and nearly complete in both skulls of Taphrosphys ippolitoi .

Contacts and structures: See Taphrosphys sulcatus for description.

BASIOCCIPITAL (figs. 178, 179, 183, 184, 277D)

Preservation: The basioccipital is complete and visible in ventral view in both skulls of Taphrosphys ippolitoi .

Contacts and structures: See Taphrosphys sulcatus for description.

PROOTIC (fig. 183)

Preservation: Although both prootics are presumed to be present in Taphrosphys ippolitoi , they are completely covered in AMNH 30042. In AMNH 30500, both prootics are visible, well preserved, and have clear sutures.

Contacts and structures: See Taphrosphys sulcatus for description.

OPISTHOTIC (figs. 178, 183, 184)

Preservation: In Taphrosphys ippolitoi in AMNH 30042, both opisthotics are present and nearly complete. The right is missing its posterior margin. Both are fractured on their dorsal surfacebut are in their original positions. Ventrally the right opisthotic is better preserved in the fenestra postotica region. In AMNH 30500 both opisthotics are complete with clear sutures.

Contacts and structures: See Taphrosphys sulcatus for description.

BASISPHENOID (figs. 178, 179, 183, 277D)

Preservation: The basisphenoid is complete, in both AMNH 30500 and AMNH 30042 of Taphrosphys ippolitoi .

Contacts and structures: See Taphrosphys sulcatus for description.

Taphrosphys congolensis

The single skull representing this species is crushed dorsoventrally, but during preparation, some of the skull roofing elements were removed, giving access to the internal basicranium and allowing reconstruction of the skull roof. Taphrosphys congolensis is weakly supported as the sister taxon to the other two Taphrosphys species. The type of this species is a shell, and this skull was apparently not found associated with a shell of Taphrosphys congolensis , it was only found in the same unit.

PREFRONTAL (figs. 185, 188)

Preservation: Only the left prefrontal in Taphrosphys congolensis is preserved, but it seems to be nearly complete. Although it is disarticulated and not in its original position with regard to the neighboring bones, the element itself appears to be uncrushed and not distorted. All of the dorsal and most of the ventral surfaces are visible.

Contacts: The prefrontal of Taphrosphys congolensis as preserved lies on the internal surface of the maxilla and partially contacts the parietal posteriorly. These are not its original relations and are due to postmortem disarticulation and disturbance of this element. Sutural surfaces are clear for the usual bothremydid contacts: prefrontal medially, maxilla ventrolaterally, and frontal posteriorly.

Structures: The prefrontal in Taphrosphys congolensis is very similar to that bone in Azabbaremys , T. ippolitoi , and T. sulcatus , although it is incomplete in the latter. Its surface is smooth and lacks the swelling seen in T. ippolitoi . The ventral surface of the prefrontal is largely visible in this specimen and shows the roof of the fossa nasalis, smaller than in T. ippolitoi but the same as in T. sulcatus . The midline suture is also visible, showing the bone to be much thicker on the midline than more laterally. Taphrosphys congolensis has a completely preserved ventral process of the prefrontal. This process forms most of the anterior orbital margin and a portion of the dorsal margin, a degree of orbital exposure also found in Azabbaremys .

FRONTAL (fig. 185)

Both frontals are completely missing in Taphrosphys congolensis . However, the preservation of the surrounding bones (prefrontal, parietal, and postorbital) gives a good idea of the position and shape of the frontal in T. congolensis .

PARIETAL (figs. 185, 188)

Preservation: Both parietals are preserved in Taphrosphys congolensis and are complete except for some missing edges laterally. The ventral and dorsal surfaces are visible on the right parietal, which has been removed from the rest of the specimen. The ventral edge and the contact of the processus inferior parietalis on both sides are either broken off (right) or crushed ventrally (left) and not visible.

Contacts of dorsal plate: As preserved, the left parietal of Taphrosphys congolensis touches (but does not share a suture with) the left prefrontal. A frontal was originally between these two bones, and the present condition is due to postmortem disarticulation and disturbance. The right and left parietals overlie the respective postorbitals and quadratojugals, a condition that is interpreted as the result of postmortem disarticulation. However, the relative positions of these bones have not changed much from the life position, so that the parietal contacted the postorbital anterolaterally and the quadratojugal posterolaterally, as indicated in the restoration (fig. 185).

The dorsal plate of the right parietal is more complete than the left one. The lateral edges are broken, but they very nearly fit with the associated postorbital and quadratojugal. Restored from these elements, the parietal has an anterolateral postorbital contact and a lateral quadratojugal contact. The postorbital contact is longer than the quadratojugal one. The other two Taphrosphys species are not well preserved in this area, but what is preserved in both is consistent with the condition in Taphrosphys congolensis .

Structures of the dorsal plate: The dorsal plate of the parietal is nearly complete in Taphrosphys congolensis . The emargination extends about halfway anteriorly up the length of the parietal, in contrast to forms like Azabbaremys in which it extends for only about one-third the length. More of the otic chamber is also exposed, but the degree of emargination is less than in Galianemys and much less than in Kurmademys . The edge of the parietal forming the emargination in T. congolensis is nearly straight with a small bulge just anterior to the supraoccipital contact.

Contacts of processus inferior parietalis: Although it is clear that most of the parietal contacted the crista pterygoidea in Taphrosphys congolensis as in all other turtles, the position of the foramen nervi trigemini and the bones forming it cannot be seen.

Processus inferior parietalis: The dorsal parts of this wall are present on both sides, and the cavum cranii roof forming the cerebral expansions is visible. These are very similar in both Taphrosphys congolensis and T. sulcatus (indeterminate in T. ippolitoi ). The processus inferior parietalis in T. congolensis and T. sulcatus is clearly wider than in Azabbaremys , which has an unusually narrow one.

JUGAL (figs. 185, 188)

Preservation: On the left side, a portion of what appears to be the jugal is preserved in Taphrosphys congolensis . Adjacent articulating elements (maxilla, quadrate, postorbital, and squamosal) provide some information on the jugal shape and contacts on the cheek. The medial process, however, is largely missing. On the right side a small fragment of what seems to be jugal is present between quadrate and postorbital.

Contacts and structures of lateral plate: In Taphrosphys congolensis the jugal shape is based primarily on a reconstruction of the elements around it. There is some degree of guesswork involved in this reconstruction because few of the surrounding elements are themselves in their original positions.

The maxilla-quadrate contact prevents a cheek exposure of the jugal, and the lower edge of the jugal contacts these two bones. The dorsal edge of the jugal contacts the postorbital anteriorly and the quadratojugal posteriorly. Presumably the jugal enters the orbital margin because a postorbital-maxilla contact, which would prevent that, is unlikely. However, none of the fragments possibly identifiable as jugal seems to have a natural edge. As reconstructed, the jugal in Taphrosphys congolensis is relatively long anteroposteriorly and short in height, similar to that bone in T. ippolitoi . It is possible that the jugal was nearly the same in both species, given the uncertainty of its shape in T. congolensis .

QUADRATOJUGAL (figs. 185, 188)

Preservation: Both quadratojugals are present in Taphrosphys congolensis . The right one is well preserved and in articulation with the postorbital and quadrate. The left one is fractured but complete and only slightly displaced anteriorly. Both have been pushed ventrally into the upper part of the quadrate. The left quadratojugal is fractured and partially distorted, but the right one appears to be in its original shape.

Contacts: The quadratojugal in Taphrosphys congolensis has a long ventral suture with the quadrate and a shorter anterior suture with the postorbital. Dorsomedially there is a short contact, visible on the left side, with the parietal posterior to the postorbital. The quadratojugal in T. congolensis and T. ippolitoi does not extend ventrally along the anterior margin of the quadrate to reach the cheek margin due to a jugal-quadrate contact. However, there is not a complete dorsal restriction of the quadratojugal as seen in Phosphatochelys , which has a postorbital-quadrate contact, absent in Taphrosphys . The jugal-quadratojugal contact is not clearly preserved in T. congolensis , but there is a sutural margin preserved on the right quadratojugal that is best interpreted as this contact. The reconstruction is consistent with this interpretation (fig. 185). The posteriormost extension of the quadratojugal contacts the squamosal in a narrow suture above the quadrate.

Structures: The quadratojugal in Taphrosphys congolensis is curved to cover the lateral part of the skull roof and part of the cheek. The right quadratojugal shows a well-preserved temporal margin just lateral to the parietal contact. The temporal emargination is formed laterally by the quadratojugal and part of the squamosal.

SQUAMOSAL (figs. 185, 188, 189)

Preservation: Both squamosals in Taphrosphys congolensis are present, uncrushed, and lack only their posterior margins.

Contacts: As in Taphrosphys sulcatus .

Structures: The antrum postoticum on the quadrate in Taphrosphys congolensis is crushed on both sides, so the internal structure of the antrum in the squamosal is not visible. The size and shape of the squamosal in T. congolensis are very similar in T. sulcatus . The ventral flange on the squamosal is nearly complete on the left side and is nearly identical to that in T. sulcatus .

POSTORBITAL (figs. 185, 188)

Preservation: Both postorbitals in Taphrosphys congolensis are preserved in their entirety, but they have been displaced ventrally from their original positions. Both are in roughly their original relations to other skull roof elements, and the right one is still articulated with the quadratojugal, further aiding in the reconstruction.

Contacts: The postorbital of Taphrosphys congolensis contacts the quadratojugal posteriorly and the parietal medially. A short sutural margin anteromedially is interpreted as a frontal contact, and the ventral sutural margin is interpreted as the jugal contact.

Structures: The anterior margin of the postorbital in Taphrosphys congolensis forms the posterior margin of the orbit. There is no exposure on the cheek or temporal emargination.

An important feature of most pleurodire postorbitals is the medial process that forms much of the septum orbitotemporale. However, in Azabbaremys , Labrostochelys , and Phosphatochelys this process is absent and the wall is open. In Taphrosphys congolensis both postorbitals are dropped ventrally out of their original positions, but both are only fractured and not crushed or deformed. Some of their medial-ventral surface is also visible. Although the matrix has not been entirely removed, there is no sign of a medial process in either postorbital, and the condition is the same as in the other Taphrosphyini .

PREMAXILLA (figs. 185, 186, 188)

Preservation: The left premaxilla is present in Taphrosphys congolensis , uncrushed but lacking its posteromedial extension.

Contacts: As in other bothremydids, the premaxilla of Taphrosphys congolensis meets the other premaxilla medially on the midline and the maxilla posterolaterally. The vomer and its presumed contact are missing.

Structures: The labial ridge is preserved in all three Taphrosphys species. The ridge is relatively shallow in T. ippolitoi and T. sulcatus , both of which presumably had at least a slight notching or upswing to the labial ridge in anterior view. In contrast, T. congolensis has a deeper and more acute labial ridge that would not form a dorsal curve.

MAXILLA (figs. 185, 186, 188)

Preservation: Only the left maxilla is preserved; it is uncrushed but pushed medially out of its original position. Its dorsal margins are mostly broken.

Contacts of vertical plate: The anteromedial contact with the premaxilla is present and intact. As preserved, despite being pushed medially, there is still a maxilla-quadrate contact posteriorly, and this is interpreted as original. The jugal is not present, but a short part of the jugal suture is interpreted as present. The anterodorsal suture with the prefrontal is partially preserved.

Structures of vertical plate: The vertical plate forms the labial ridge in Taphrosphys congolensis and is similar to that in T. ippolitoi , but it curves anteromedially rather than flares laterally as in T. ippolitoi . The maxilla is missing in T. sulcatus .

Contacts of horizontal plate: In both Taphrosphys ippolitoi and T. congolensis the maxilla has the same contacts: premaxilla anteromedially and palatine posteromedially. In both species the jugal (or a fragment of it) is present but displaced, still indicating the usual pelomedusoid posterolateral contact. Although it is not completely certain, a medially meeting process of the maxilla is unlikely in both T. congolensis and T. ippolitoi . In T. congolensis the medial margin of the maxilla seems to be complete enough to show that a process is absent. In T. ippolitoi the maxilla has a medial process, but it stops short of the midline due to the large premaxilla.

Structures of horizontal plate: See Taphrosphys ippolitoi for description.

VOMER

Preservation: The vomer is missing in Taphrosphys congolensis .

PALATINE (figs. 185, 186, 188)

Preservation: In Taphrosphys congolensis the left palatine is nearly complete, lacking its anterior margin, but the right one is missing its anterior half. Both are slightly fractured but in their original positions.

Contacts: See Taphrosphys ippolitoi for description.

Structures: See Taphrosphys ippolitoi for description.

QUADRATE (figs. 185–189)

Preservation: Both quadrates are present in Taphrosphys congolensis with the ventral halves relatively well preserved, but both have the dorsal half of the cavum tympani and antrum postoticum crushed. The dorsomedial margins are mostly damaged or covered.

Lateral view contacts and structures: The maxilla-quadrate contact is described under Maxilla, and the quadrate is described under Taphrosphys sulcatus .

Dorsal view contacts and structures: See Taphrosphys sulcatus for description.

Ventral view contacts and structures: See Taphrosphys sulcatus for description.

PTERYGOID (figs. 185–189)

Preservation: Both pterygoids in Taphrosphys congolensis are preserved in articulation, visible at least in part in dorsal as well as ventral view. The pterygoids are complete except for the processus trochlearis pterygoidei, which is missing in the left pterygoid and broken off but present, not in its original position, on the right side.

Contacts on ventral surface: See Taphrosphys ippolitoi for description.

Contacts on dorsal surface: See Taphrosphys sulcatus for description.

Structures on dorsal surface: See Taphrosphys sulcatus for description.

SUPRAOCCIPITAL (figs. 185, 188, 189)

Preservation: The supraoccipital in Taphrosphys congolensis is crushed ventrally into the cavum cranii and is missing some of the edge of the crista supraoccipitalis, but the main body of the bone is relatively undistorted and well preserved although partially displaced from surrounding elements.

Contacts and structures: See Taphrosphys sulcatus for description.

EXOCCIPITAL (figs. 185, 188, 189)

Preservation: Both exoccipitals in Taphrosphys congolensis are preserved and nearly complete although the supraoccipital has been crushed ventrally.

Contacts and structures: See Taphrosphys sulcatus for description.

(figs. 185–189)

Preservation: The basioccipital in Taphrosphys congolensis is complete and visible in ventral view.

Contacts and structures: See Taphrosphys sulcatus for description.

PROOTIC

Preservation: Both prootics are present in Taphrosphys congolensis , but only the right one is visible dorsally and anteriorly. It is partially disarticulated from surrounding elements and pushed ventrally.

Contacts and structures: See Taphrosphys sulcatus for description.

OPISTHOTIC (figs. 185, 186, 188, 189)

Preservation: Both opisthotics are present and complete in Taphrosphys congolensis .

Contacts of structures: See Taphrosphys sulcatus for description.

BASISPHENOID (figs. 185, 186, 188)

Preservation: The basisphenoid in Taphrosphys congolensis is complete with both dorsal and ventral surfaces visible.

Contacts and structures: See Taphrosphys sulcatus for description.

Labrostochelys galkini

This unusual species is known from two skulls, one of which (AMNH 30043) is crushed but still well preserved and is the basis for most of the description and figures. Labrostochelys is the sister taxon to the remaining members of the subtribe Taphrosphyina .

PREFRONTAL (figs. 190, 193)

Preservation: Both prefrontals are present in AMNH 30043 and AMNH 29984, but they are more complete in the former. In both specimens the snout elements are displaced ventrally, and in AMNH 30043 they lie on the vomer. However, significant distortion does not seem to have taken place in either skull.

Contacts: The prefrontal of Labrostochelys has the three usual contacts: prefrontal on midline, maxilla anteroventrolaterally, and frontal posteriorly. Because of its great length, the prefrontal and maxilla contacts are longer than in any other pleurodire. It is possible that the prefrontal contacted the premaxilla originally via a small anteroventral process that is now lost.

The ventral process of the prefrontal is preserved on both sides of AMNH 30043. Despite some displacement of both bones, it is clear that although the prefrontal comes close to contacting the palatine as preserved, this was not the original condition. The palatine sutural edges match the maxilla sutural edges and the prefrontal seems to be completely excluded.

Structures: The prefrontal of Labrostochelys is extremely long and narrow, longer and narrower than in any other turtle. It begins anteriorly at the apertura narium externa and extends posteriorly to the midpoint of the orbit, as in other Pelomedusoides. What in most other Pelomedusoides is a relatively short contact with the maxilla, in Labrostochelys it stretches for almost the entire length of the snout.

At the anterior margin of the left prefrontal is a thin anterior process, broken anteriorly, that comes close to reaching a rugosity, possibly a suture, on a dorsal process of the premaxilla. It is possible that originally the prefrontal and premaxilla were in contact and divided the apertura narium externa on the midline. On the ventral surface, the posterior part of the prefrontal, which lies in the orbital margin, forms the anterior part of the sulcus olfactorius, much as in other Pelomedusoides such as Pelusios .

FRONTAL (figs. 190, 193)

Preservation: Both frontals are preserved in both specimens of Labrostochelys .

30043 holotype with additions from AMNH 29984. [F. Ippolito, del.]

Contacts: The frontal of Labrostochelys has the usual contacts: other frontal on midline, prefrontal anteriorly, postorbital posterolaterally, and parietal posteriorly.

Structures: The frontal is widely exposed in the dorsal orbital margin in Labrostochelys , much as in Taphrosphys and in contrast to the smaller exposure in Azabbaremys . In AMNH 30043 some of the ventral surface of the frontal is visible and shows the sulcus olfactorius to be wide with deep ventral walls.

PARIETAL (figs. 190, 193)

Preservation: The anterior third or so of both parietals is present in AMNH 30043, with AMNH 29984 preserving much more of the temporal area but still missing the posterior parietal margins.

Contacts of dorsal plate: As preserved, the parietal in Labrostochelys contacts the frontal anteriorly and the postorbital anterolaterally. Quadratojugal and squamosal contacts are indeterminable.

Structures of dorsal plate: None of the temporal margin is preserved in either skull of Labrostochelys . However, natural edges of the quadrate and squamosal on the left side of AMNH 30043 show that the parietal roof was not extensive and probably did not extend posteriorly past the middle of the otic chamber. The skull roof in Labrostochelys , although elongate like the rest of the skull, was probably similar in temporal extent to that in Taphrosphys .

Contacts of processus inferior parietalis: Much of the ventral process of the parietal is damaged in both skulls, but it can be seen that it has the usual long contact with the pterygoid and a posteroventral contact with the prootic and supraoccipital. A palatine contact at the anterior edge of the processus parietalis inferior is likely but not definite.

Processus inferior parietalis: The parietal forms the anterodorsal edge of the foramen nervi trigemini, along with the prootic and pterygoid. Above the foramen the parietal forms a horizontal ridge that overhangs the foramen nervi trigemini and has a distinct, lateral process anterior to the foramen nervi trigemini. The ridge and process do not appear in any other pelomedusoid.

JUGAL (figs. 190, 193)

Preservation: Both jugals are present in both Labrostochelys skulls , somewhat disarticulated but in roughly their original positions.

Contacts: The jugal in Labrostochelys contacts the maxilla anteroventrally, the quadratojugal posterodorsally, and the postorbital dorsally. These contacts are highly likely and only slightly disarticulated. As restored, the jugal contacts the quadrate and quadratojugal ventrally and does not enter the cheek margin. This is also likely because of a preserved maxilla-quadrate contact on the right side. The quadratojugal relations, however, are somewhat problematic, as the quadratojugal is preserved only as fragments in AMNH 30043. The quadratojugal probably does not reach the maxilla, but it is possible.

Structures: The jugal in Labrostochelys forms the posteroventral margin of the orbit, as in Taphrosphys ippolitoi . The medial process of the jugal forms part of the floor of the fossa orbitalis, but none of the septum orbitotemporale, which is absent in Labrostochelys .

QUADRATOJUGAL (figs. 190, 193)

Preservation: The quadratojugal is missing in AMNH 29984 and only partially preserved in AMNH 30043. A narrow strip above the quadrate on the right side is quadratojugal, and on the left side a larger piece is present between jugal and quadrate.

Contacts: As restored the quadratojugal of Labrostochelys contacts the postorbital anteromedially, the jugal anteroventrally, the squamosal posteriorly, and the quadrate ventrally. A parietal contact is possible but not determinable.

Structures: The quadratojugal forms the posterolateral part of the skull roof emargination. Its medial extent is not determinable. The cheek area is disturbed in both skulls. As restored, the quadratojugal does not enter the cheek emargination, which is virtually absent in Labrostochelys .

SQUAMOSAL (figs. 190, 191, 193, 287)

Preservation: Little of the squamosal remains in AMNH 29984, but AMNH 30043 has nearly all of both squamosals.

Contacts: The squamosal of Labrostochelys has the usual contacts: quadrate anteriorly, opisthotic medially, and quadratojugal anterodorsally. However, because of its unique shape, the squamosal contact with the quadrate is much longer than in other Taphrosphyini , resulting in a ventral quadrate process lying under the squamosal.

Structures: Instead of the usual cone-shaped squamosal, Labrostochelys has a long, narrow squamosal developed into a vertical sheet forming a hornlike process at the back of the skull. This elongate squamosal is also seen in some trionychids, such as Cycloderma and Chitra ( Gaffney, 1979a) . The elongation is apparently related to jaw muscle attachments ( Schumacher, 1973). The adductor mandibulae attaches on the medial and dorsal surfaces, with the depressor mandibulae attaching on the lateral and ventral surfaces. Interestingly, Labrostochelys also has a pocket on the posterior surface of the quadrate, another attachment site for the depressor mandibulae.

The squamosal in Labrostochelys forms a small, lateral projection on its lateral surface near the quadrate contact (fig. 287). This is at the anterior margin of a curved ridge that separates the lateral surface from the dorsal surface and would appear to reflect the division of two muscle attachment sites. The antrum postoticum in Labrostochelys does not seem to extend into the squamosal in AMNH 30043, but it may in AMNH 29984 (see Quadrate).

POSTORBITAL (figs. 190, 193)

Preservation: The postorbital is present on both sides of AMNH 30043; the left is more complete, but neither includes the posterior limits. The right postorbital of AMNH 29984 is partially preserved.

Contacts: The postorbital of Labrostochelys contacts the frontal anterodorsally, the parietal dorsomedially, the jugal anteroventrally, the pterygoid medially, and the quadratojugal posteroventrally. The extent of the posterior contacts is indeterminate.

Structures: The postorbital in Labrostochelys forms part of the posterior orbital margin with less exposure than in Taphrosphys , Phosphatochelys , and Azabbaremys . Whether the postorbital extends posteriorly far enough to reach the temporal margin is not determinable, but it seems unlikely based on its preserved shape and similarity to Taphrosphys . In contrast to Phosphatochelys and Azabbaremys , there is a medial process of the postorbital forming at least a partial septum orbitotemporale and entering the sulcus palatinopterygoideus. This is only visible on the right side of AMNH 30043, and it is not well preserved.

PREMAXILLA (figs. 190, 191, 193)

Preservation: Both premaxillae are missing in AMNH 29984, but both are present and well preserved in AMNH 30043.

Contacts: The premaxilla in Labrostochelys contacts the maxilla posterolaterally, the premaxilla medially, and the vomer posteromedially. The anterodorsomedial edge of the premaxilla in AMNH 30043 has a short dorsal process that may have contacted an anteroventral process of the prefrontal, producing a divided apertura narium externa. This condition is not found in other Taphrosphyini but is seen in some Bothremys .

Structures: The premaxilla forms the ventral margin of the apertura narium externa and floor of the fossa nasalis. The apertura of Labrostochelys differs from the other Taphrosphyini in being much smaller and completely, or almost completely, divided on the midline. The uniquely narrow snout of Labrostochelys ends anteriorly in premaxillae that come to a blunt point, bearing the apertura narium externa at its end. The foramen praepalatinum on both premaxillae is incomplete, but it seems to have been formed entirely within the premaxilla, close to the midline suture but clearly separated from the vomer.

On the ventral surface, Labrostochelys also differs from all other pleurodires in having a premaxilla that bears an elongation anterior to the labial ridge of the triturating surface. This triangular plate bears the floor of the fossa nasalis on its dorsal surface. Ventrally and around its edges are a large number of vascular foramina, indicating that it bore part of the horny beak like the rest of the triturating surface.

The labial ridge is not a distinct ridge, but it forms a line where the flat anterior surface curves sharply dorsally to join the triturating surface proper. The posterior surface of the premaxilla forms a triangular shelf supporting the triturating surface. About midway along the surface, the premaxilla forms a midline concavity that is part of the roof of the mouth and leads into the apertura narium interna. The blunt ridge defining this concavity roughly parallels the labial ridge and may be interpreted as the lingual ridge. Laterally it is continuous with a more defined ridge on the maxilla that is clearly the lingual ridge.

MAXILLA (figs. 190, 191, 193)

Preservation: Both maxillae are present and nearly complete in both specimens.

Contacts of vertical plate: In external view, the maxilla of Labrostochelys has the usual contacts: premaxilla anteromedially, prefrontal anterodorsally, and jugal posteroventrally, as in Taphrosphys and Azabbaremys . It is possible that there is a small quadratojugal contact between the jugal and quadrate. The length of the prefrontal-maxilla contact is unique in turtles.

Structures of vertical plate: The dorsal process of the maxilla in Labrostochelys lies between the orbit and the apertura narium externa and is relatively distinct in shortsnouted forms like Phosphatochelys . In Labrostochelys , however, the area of the process is extremely lengthened and almost the same height as the posterior part of the bone so that the process is barely recognizable compared with other pleurodires. The maxilla forms the ventral margin of the orbit. Although the area is broken in AMNH 30043 and missing in AMNH 29984, there does not seem to be a cheek emargination, even a low one as in Taphrosphys .

Contacts of horizontal plate: The usual contacts are present in Labrostochelys : premaxilla anteromedially, palatine posteromedially, and jugal posterolaterally. There is also a short vomer contact just behind the premaxilla anterior to the apertura narium interna. The jugal is slightly displaced on both sides of AMNH 30043 and AMNH 29984, but it seems to have only a short contact without the longer lateral contact usually seen in Pelomedusoides.

In Labrostochelys the maxilla sends a small process medially to contact the vomer. Among the other Taphrosphyini , the vomer is unknown in Taphrosphys and Phosphatochelys , which could have had a contact. There is a contact in Nigeremys and Arenila , but not in Azabbaremys . As in Taphrosphys , the palatine does not extend into the area of the triturating surface.

The dorsal surface of the maxilla is visible only to a limited degree in both Labrostochelys skulls , but it is clear that the maxilla does not contribute significantly to the floor of the fossa orbitalis. This is similar to the condition in Taphrosphys and Azabbaremys and in contrast to Phosphatochelys .

Structures of horizontal plate: The ventral surface forms the triturating surface, which in Labrostochelys is relatively narrow and parallel-sided, similar to that in Taphrosphys in width. It is longer than in any Pelomedusoides due to the elongate snout. The labial ridge is deep and thin and curves evenly into the more horizontal part of the surface, in contrast to Azabbaremys and Phosphatochelys , which have an angled meeting, but very similar to T. ippolitoi . In Taphrosphys and Labrostochelys the maxillary part of the triturating surface is an inverted trough, unlike the morphology in other Pelomedusoides. The lingual ridge in Labrostochelys is low but distinct; still, it is slightly higher than in T. ippolitoi . The medial edge of the maxilla in Labrostochelys forms the apertura narium interna and, despite some breakage, seems to define a smaller apertura than in Taphrosphys , Phosphatochelys , and Azabbaremys .

VOMER (figs. 190, 191, 193)

Preservation: The vomer is present in AMNH 30043, but it is slightly displaced from its sutural contacts and is split anteriorly. Only the ventral surface is visible. The vomer is missing in AMNH 29984.

Contacts: The vomer in Labrostochelys contacts the premaxilla anteriorly and the palatines posteriorly, as in all other Pelomedusoides in which it is known. Anterolaterally there is a short maxilla contact (see Maxilla).

Structures: The vomer in Labrostochelys is long and narrow, not thick and short as in Nigeremys and Arenila . There is an expansion at both ends. The vomer does not participate in the foramen praepalatinum. The vomer forms the medial margin of the apertura narium interna, which in Labrostochelys is relatively small, smaller than in Azabbaremys and Phosphatochelys . None of the Taphrosphys skulls has well-preserved aperturae, but they seem to be larger than in Labrostochelys based on what is preserved.

PALATINE (figs. 190, 191, 193)

Preservation: Both palatines are present in both Labrostochelys skulls , but they are better preserved in AMNH 30043.

Contacts: The palatine in Labrostochelys has the usual Pelomedusoides contacts: vomer anteromedially, maxilla anterolaterally, palatine medially, and pterygoid posteriorly. Although both the palatines and jugals are slightly disarticulated and displaced dorsally in both skulls, the usual dorsolateral contact with the jugal is present. A dorsal contact with the parietal is possible but not determinable.

Structures on dorsal surface: The palatine in Labrostochelys forms nearly all of the floor of the fossa orbitalis, as in Taphrosphys but in contrast to Phosphatochelys , which has a much greater maxillary contribution. The foramen orbitonasale is mostly collapsed in both skulls, so it is present but cannot be easily compared with other taxa. The palatine forms the anterolateral edge of the apertura narium interna. This edge is broken so its original position is unknown, but what is preserved shows the apertura to be relatively small (see Maxilla). A dorsal process was probably not present, but the area is collapsed dorsally and not visible. If a process were present, it would probably cause some breakage or displacement through the thin palatine. The sulcus palatinopterygoideus is not well preserved, probably due to the absence of a postorbital wall, allowing dorsoventral crushing and collapse of the area.

Structures on ventral surface: The palatine of Labrostochelys is similar to that bone in Taphrosphys , broadly curving dorsally into the apertura narium interna, but to a lesser degree than in Azabbaremys , Phosphatochelys , Nigeremys , and Arenila . There is no contribution of the palatine to the triturating surface. The foramen palatinum posterius is formed anteriorly by the palatine and posteriorly by the pterygoid. It is larger than in Phosphatochelys , Azabbaremys , and Taphrosphys and roughly similar to those in Nigeremys and Arenila .

QUADRATE (figs. 190, 191, 193, 195, 277F, 287)

Preservation: Both quadrates in AMNH 30043 are nearly complete. Both in AMNH 29984 are missing the anterior and dorsal areas.

Lateral view contacts: In Labrostochelys the quadrate contacts the quadratojugal dorsally and anterodorsally and the squamosal posterodorsally. The squamosal contact (see Squamosal) is unusual in that the quadrate sends a process ventrally beneath much of the squamosal forming the greatly elongated posterior process. There is a maxilla-quadrate contact (see Maxilla); it is short, as in Taphrosphys congolensis . It is possible that there is a short jugal contact, as is likely in T. congolensis (see Jugal).

Lateral view structures: The cavum tympani of Labrostochelys (fig. 287) agrees with other Taphrosphyini in being shallower than in the Pelomedusidae and generally agreeing with the Bothremydini . In Labrostochelys the depth of the cavum tympani varies between the two skulls, but in this case AMNH 29984 seems to be better preserved than AMNH 30043. The cavum tympani in AMNH 29984 is deeper than in AMNH 30043, about as deep as in Taphrosphys . The two skulls do differ in other features, so this may be individual variation rather than preservation. There is no fossa precolumellaris, and the cavum tympani is smoothly concave except for the antrum postoticum. The cavum tympani in Labrostochelys is slightly wider than high, agreeing with Taphrosphys (as restored, see Taphrosphys ippolitoi ) and in contrast to Azabbaremys and Phosphatochelys , in which it is circular or slightly higher than wide.

As in all other Taphrosphyini , Labrostochelys has a closed incisura columellae auris forming a bony canal for the stapes. There is a low groove extending posteroventrally from the incisura columellae auris to a notch on the edge of the quadrate for the eustachian tube, the sulcus eustachii. The sulcus in Labrostochelys has a short process extending ventrally (fig. 287), as in Phosphatochelys . There is no sign of a dorsal process as seen in Taphrosphys ippolitoi .

The antrum postoticum in Labrostochelys differs between the two skulls. In AMNH 30043 it is about half the size of that in AMNH 29984. This does not seem to be a preservation or postmortem difference. In AMNH 29984 the antrum is about the size of the antrum in Phosphatochelys and Taphrosphys ippolitoi . In AMNH 29984 the opening of the antrum is oval, while in Taphrosphys and Phosphatochelys it is round. The antrum opening faces anterolaterally in both Labrostochelys skulls and anteriorly in Taphrosphys and Phosphatochelys . The antrum postoticum is absent in Azabbaremys and Nigeremys .

The shelf formed along the ventrolateral margin of the cavum tympani that is un-

[A. Venjara and E.S. Gaffney, del.]

usually large and prominent in Taphrosphys ippolitoi is smaller in Labrostochelys as it is in Phosphatochelys .

Contacts in dorsal view: In Labrostochelys the quadrate contacts vary on each side in AMNH 30043. On the right side it contacts the prootic anteromedially, the opisthotic posteromedially, and the squamosal posteriorly. These are the usual contacts in Taphrosphyini . On the left side, the squamosal has an anteromedial extension contacting the prootic, preventing a quadrate-opisthotic contact. This squamosal-prootic contact is unusual, possibly unique in turtles, and is interpreted as an individual variation. In AMNH 29984 the quadrate on the right side shows sutures, but the squamosal sutures are indistinct, so a squamosal-prootic contact cannot be determined.

Dorsal view structures: As in the other Taphrosphyini , the foramen stapedio-temporale in Labrostochelys is at the anterior edge of the otic chamber, close to the foramen nervi trigemini.

Ventral view contacts: As in the other Taphrosphyini , the quadrate of Labrostochelys contacts the pterygoid anteromedially, the basisphenoid medially, the basioccipital posteromedially, the exoccipital posteromedially (behind the basioccipital), and the squamosal posterolaterally. The basisphenoid and basioccipital contacts in Labrostochelys are narrower than in Taphrosphys , but similar in extent to Azabbaremys . The squamosalquadrate contact (see Squamosal) is uniquely long in Labrostochelys due to the posteriorly extended squamosal and a ventral quadrate process forming its ventral edge.

Ventral view structures: The foramen posterius canalis carotici interni in Labrostochelys is formed within the quadrate, but the suture follows it posteriorly from the pterygoid suture, so it may be interpreted as being formed within the pterygoid-quadrate suture (fig. 277F). If interpreted this way it agrees with Azabbaremys and Phosphatochelys (indeterminate in Nigeremys ). In Arenila it is between the basisphenoid and pterygoid. In Taphrosphys it is in the quadrate-pterygoid-basisphenoid suture.

The fenestra postotica in Labrostochelys (fig. 195) is formed by the quadrate ventrolaterally and the opisthotic dorsomedially, as in Azabbaremys , Taphrosphys , and Phosphatochelys . The fenestra is elongate horizontally in Labrostochelys , rather than being elongate more vertically, as in Phosphatochelys and Azabbaremys . The stapedial artery portion lies directly lateral (rather than dorsal) to the lateral head vein portion. In Taphrosphys the fenestra is usually subdivided by bone, but the portions are more vertical than horizontal, as in Labrostochelys .

The foramen chorda tympani inferius is a small hole on the posterior surface of the processus articularis. The posterior surface of the processus articularis in Labrostochelys has a posteroventrally opening concavity, similar to one seen in Taphrosphys ippolitoi (see Taphrosphys ). This seems to be an attachment site for the depressor mandibulae (fig. 195). As in Taphrosphys , the condylus mandibularis in Labrostochelys is far anterior to the condylus occipitalis.

PTERYGOID (figs. 190, 191, 193, 277F)

Preservation: The pterygoids in AMNH 29984 are present but damaged anteriorly and laterally. In AMNH 30043, however, they are just superb! The pterygoid flange, a thin sheet often broken even in recent pleurodire skulls, and almost always damaged in fossils, is complete on both sides of AMNH 30043. The bones articulating anteriorly to the pterygoid have been dislocated and rudely shoved dorsally, but the posterior contacts are still intact.

Contacts on ventral surface: The pterygoid in Labrostochelys has the usual Taphrosphyini contacts: palatine anteriorly, pterygoid anteromedially, basisphenoid medially, and quadrate posterolaterally. The pterygoid-pterygoid contact is very short, the same as in Arenila , much shorter than in Taphrosphys , but shorter than in all the other Taphrosphyini , except for Arenila . The anterolateral contact with the jugal is visible in ventral view.

Structures on ventral surface: The processus trochlearis pterygoidei in Labrostochelys is very small and oriented posteriorly to an extent that it is not visible in ventral view. In the Taphrosphyini the processus is smaller than in many other pleurodires, but the condition seen in Labrostochelys is not even approached in other Pelomedusoides. In some chelids, such as Chelus and Chelodina ( Gaffney, 1979a) , the processus is also oriented posteriorly and relatively small, but in none is the processus as small as it is in Labrostochelys . The processus trochlearis pterygoidei in Labrostochelys parallels the edge of the pterygoid web or flange and trends slightly laterally rather than being completely parasagittal as in some chelids.

The tubelike channel found in Phosphatochelys extending anterodorsally from the processus articularis of the quadrate is absent in Labrostochelys . This channel is present in Taphrosphys and Azabbaremys . The pterygoid flange and quadrate ramus in Labrostochelys are very close, being similar to Pelomedusidae in this feature. There is no concavity for the pterygoideus muscle attachment, but there is a low ridge on AMNH 30043 extending from the processus articularis medially on the quadrate ramus of the pterygoid that may mark an attachment site edge. The ridge is absent in AMNH 29984. The foramen palatinum posterius in Labrostochelys is formed posteriorly by the pterygoid and anteriorly by the palatine (see Palatine).

Contacts on dorsal surface: Some of the dorsal surface of the pterygoid and crista pterygoidea are visible in both Labrostochelys skulls , but they are not well preserved and most contacts are unclear. In AMNH 30043, the crista pterygoidea meets the processus inferior parietalis of the parietal in a clear suture seen on both sides. The suture ends anteriorly in matrix, so its entire extent cannot be seen. Posterior to the foramen nervi trigemini the crista meets the prootic and posterolaterally the quadrate, although the entire extent of the latter is unclear. The processus trochlearis pterygoidei has anterior contacts with the jugal anterolaterally and with the postorbital anterodorsally. This area is preserved only on the right side of AMNH 30043 and is not well preserved.

Structures on dorsal surface: Only part of the pterygoid dorsal surface is visible in the two Labrostochelys specimens, but some information can be obtained from the CT scans of AMNH 30043.

The processus trochlearis pterygoidei (described above) forms the lateral margin of the sulcus palatinopterygoideus. In Labrostochelys this sulcus is not cleanly preserved, but what is preserved differs from other taxa. The sulcus is not preserved in a number of Taphrosphyini , which also makes it hard to interpret Labrostochelys . In Arenila the septum orbitotemporale and sulcus palatinopterygoideus are preserved and these are similar to the usual bothremydid condition. In Labrostochelys the postorbital-pterygoid suture is higher and the bones are much thinner. There is a lateral excavation just above the base of the processus trochlearis pterygoidei that considerably reduced the width and thickness of the septum orbitotemporale in Labrostochelys in comparison to Arenila and more generalized bothremydids like Galianemys . The medial edge of the base of the processus trochlearis pterygoidei is free rather than sutured to the postorbital or parietal. The result is a sulcus palatinopterygoideus that is much wider and more open in Labrostochelys than in Arenila and more generalized bothremydids. In Azabbaremys and Phosphatochelys there is no septum orbitotemporale and no lateral definition of the sulcus palatinopterygoideus. Taphrosphys sulcatus is not completely preserved in this area; T. ippolitoi is also unclear, but could be similar to Labrostochelys ; and in T. congolensis it looks as if the septum is absent, but it is also crushed and unclear. It is possible to interpret the Labrostochelys condition as intermediate between the generalized bothremydid condition, like Arenila , and the derived condition seen in Phosphatochelys and Azabbaremys . A medially free pterygoid edge could be a common character for Labrostochelys , Azabbaremys , and Phosphatochelys .

The crista pterygoidea in Labrostochelys can be seen in part in both skulls. Although its anterior margin, along with the processus inferior parietalis and whatever contribution the frontal and palatine may make, is not clearly defined, it is apparent that the crista in Labrostochelys , as in Taphrosphys , is much longer than the very narrow crista of Azabbaremys and Phosphatochelys . The foramen nervi trigemini in Labrostochelys has the usual elements: pterygoid ventrally, parietal anterodorsally, and prootic posterodorsally. The foramen in Labrostochelys is nearly circular, while in Phosphatochelys and Azabbaremys it is oval and more elongated.

SUPRAOCCIPITAL (figs. 190, 193)

Preservation: The supraoccipital is present in both Labrostochelys skulls , but all of the posterior portion is gone, as is some of the dorsal area.

Contacts: The supraoccipital in Labrostochelys has the usual Taphrosphyini contacts: parietal dorsally, prootic anterolaterally, opisthotic posterolaterally, and exoccipital posteroventrally.

Structures: The most prominent supraoccipital structure, the crista supraoccipitalis, is completely missing in AMNH 30043, and only the base is present in AMNH 29984. The crista is very short in other Taphrosphyini and pleurodires in general.

EXOCCIPITAL (figs. 190, 193, 195, 277F)

Preservation: In Labrostochelys both exoccipitals are present and complete in both skulls.

Contacts: As in other Taphrosphyini , contacts in Labrostochelys are: supraoccipital dorsally, opisthotic laterally, quadrate ventrolaterally, and basioccipital ventrally.

Structures: The foramen magnum in Labrostochelys is as in Taphrosphys , being slightly receded anteriorly in comparison to Phosphatochelys . The condylus occipitalis is formed entirely from the exoccipitals, and the basioccipital barely enters the neck of the condyle. The foramen nervi hypoglossi consists of a larger, more medial foramen and a smaller one in the medial wall of the foramen jugulare posterius, as in Phosphatochelys . This results in only one foramen nervi hypoglossi being visible in direct posterior view. In Taphrosphys the more lateral foramen is not placed so far into the foramen jugulare posterius. The foramen jugulare posterius is completely enclosed and widely separated from the fenestra postotica, as in other Taphrosphyini .

BASIOCCIPITAL (figs. 190, 191, 193, 277F)

Preservation: The basioccipital is present and complete in both skulls of Labrostochelys . Very little of its dorsal surface is visible except in the CT scans.

Contacts: As in other Taphrosphyini the basioccipital contacts in Labrostochelys are: basisphenoid anteriorly, quadrate laterally, and exoccipitals dorsally. The basioccipital-quadrate contact is shorter than in Taphrosphys and Phosphatochelys but similar to that in Azabbaremys . The basioccipital in Labrostochelys is more triangular than in the other Taphrosphyini . The straight transverse anterior margin, narrow quadrate contacts, and straight exoccipital contacts diverging from an apex make a uniquely shaped basioccipital.

Structures: The condylus occipitalis in Labrostochelys has no basioccipital contribution. The tuberculum basioccipitale is slightly larger in AMNH 29984 than in AMNH 30043, but both are smaller than in Taphrosphys . The tuberculum is formed by exoccipital and quadrate to a greater extent than by basioccipital. In Labrostochelys the median concavity often seen anterior to the condylus occipitalis is hardly developed. There is a shallow, irregular depression but not the clearly formed, semicircular concavity seen in Taphrosphys ippolitoi and Phosphatochelys .

PROOTIC (fig. 193)

Preservation: Both prootics are present in both specimens of Labrostochelys , but clear contacts are only seen in AMNH 30043.

Contacts: The prootic contacts in Labrostochelys are common in other Taphrosphyini : parietal medially, quadrate laterally, supraoccipital posterodorsally, pterygoid ventrally, and opisthotic posteriorly. Additionally, on the left side of AMNH 30043 there is a posterolateral contact with the squamosal (see Squamosal).

Structures: As in other Taphrosphyini , the prootic of Labrostochelys forms the dorsal portion of the foramen nervi trigemini along with the parietal and pterygoid. The prootic forms the dorsomedial part of the foramen stapedio-temporale, with the quadrate forming the ventrolateral part. As in other Taphrosphyini , the foramen nervi trigemini is very close to the foramen stapedio-temporale. The foramen stapedio-temporale in Labrostochelys opens into a shallow groove, similar to that seen in Bothremys (and probably many other Bothremydidae if well enough preserved) leading to the foramen nervi trigemini.

OPISTHOTIC (figs. 190, 193, 195)

Preservation: Both are preserved complete in AMNH 30043, but they lack their posterior edges in AMNH 29984.

Contacts: Labrostochelys has the usual Taphrosphyini contacts: supraoccipital anteromedially, prootic anteriorly, squamosal posterolaterally, and exoccipital posteromedially. On the right side of AMNH 30043 the opisthotic has the usual contact with the quadrate anterolaterally. On the left side, however, the squamosal-prootic contact prevents an opisthotic-quadrate contact (see Squamosal). This latter condition is interpreted as an individual variation.

Structures: The opisthotic forms the dorsomedial margin of the fenestra postotica, with the quadrate (see Quadrate) forming the rest. The posterolateral process of the opisthotic (fig. 287) in Labrostochelys forms part of a ventrally opening channel at the back of the skull, similar to one seen in Taphrosphys ippolitoi . This channel is absent in Phosphatochelys and Azabbaremys .

BASISPHENOID (figs. 190, 191, 193, 277F)

Preservation: The basisphenoid is complete in both skulls of Labrostochelys . Sutures are clearly defined in AMNH 30043, but not in AMNH 29984. The dorsal surface is not visible except in CT scans of AMNH 30043.

Contacts: The basisphenoid of Labrostochelys has the usual Taphrosphyini contacts: pterygoids anterolaterally, quadrate laterally, and basioccipital posteriorly. The basisphenoid in Labrostochelys is unusually elongate and triangular, quite distinct from the pentagonal shape seen in Taphrosphys , the shorter, wider shapes seen in Azabbaremys and Phosphatochelys , and the V-shape seen in Arenila and Nigeremys .

Structures: In ventral view, the basisphenoid in Labrostochelys is smooth, having no muscle attachment sites, no foramina, no nothing.

Phosphatochelys tedfordi

This species is based on two Eocene specimens, AMNH 30008 (holotype) and MDEt 26, which vary somewhat (table 18) and could be interpreted as separate species. We consider them as the same species and note the differences in the description. Phosphatochelys is the sister taxon to Ummulisani . The type skull was described by Gaffney and Tong (2003), and some of that description is used here.

PREFRONTAL (figs. 196, 199, 202)

Preservation: Both prefrontals in AMNH 30008 are present and nearly complete with clear sutures. A small amount of the ventral process seems to be broken on both sides. The left prefrontal is completely clear of matrix, but the right one has some matrix posteriorly on its ventral surface. In MDEt 26 the right prefrontal is missing, and the left one lacks its medial edge and is covered by matrix ventrally.

Contacts: The contacts of the prefrontal in Phosphatochelys are with the maxilla anterolaterally, the frontal posteromedially, the parietal posterolaterally, and the other prefrontal anteromedially. The parietal-prefrontal contact of Phosphatochelys and Ummulisani is unusual and in fact unique among pleurodires and cryptodires ( Gaffney, 1979a). It is not even approached by any other bothremydid, which generally have large prefrontals. Unlike most Pelomedusoides in which the prefrontals meet on the midline for their entire length, Phosphatochelys has a midline length much shorter than its maximum length. The suture with the frontal is strongly convex anteriorly, quite different from the straight suture in Azabbaremys and other bothremydids. The median prefrontal contact length is less than the total prefrontal length, as in chelids, Araripemys , and euraxemydids. This may be a primitive condition; however, its absence in Azabbaremys and other close relatives of Phosphatochelys makes this unlikely.

On the ventral surface the prefrontal in Phosphatochelys contacts the parietal. The frontal is not exposed on the ventral surface. The ventral process of the prefrontal contacts the dorsal process of the maxilla, as in other Pelomedusoides. This contact area is quite narrow in Phosphatochelys , in contrast to the broad contact in Azabbaremys . The entire anterior snout area of Phosphatochelys is telescoped in comparison to Azabbaremys , Labrostochelys , and Taphrosphys .

Structures: The prefrontal in Phosphatochelys agrees with that in Rhothonemys and Ummulisani in being a relatively large element, larger than in other Taphrosphyini and much larger than in pelomedusids and euraxemydids. The prefrontal in Phosphatochelys has a distinct, anterior projection slightly subdividing the apertura narium externa. It is larger than in Azabbaremys but smaller than in Taphrosphys and Labrostochelys .

FRONTAL (figs. 196, 199)

Preservation: Both frontals are present in AMNH 30008. In MDEt 26 the left frontal is present but lacks its medial margin; the right frontal is missing.

Contacts: On the dorsal surface the frontal in Phosphatochelys contacts the prefrontal anterolaterally, the parietal posterolaterally, and the other frontal medially. The frontal is not exposed on the ventral surface, in contrast to all other bothremydids except Ummulisani .

Structures: The frontal in Phosphatochelys is very unusual for pleurodires, except Ummulisani . It is small, widely separated from the orbital margin, and covered ventrally by a sheet of parietal that reaches the prefrontal.

PARIETAL (figs. 196, 199, 202)

Preservation: Both parietals in AMNH 30008 are nearly complete, but some of the ventral surface is damaged or covered by matrix. In MDEt 26, the right parietal has most of the processus inferior parietalis present but largely covered by matrix. The dorsal plate is gone except for a small posteromedial piece. The left parietal has all of the dorsal plate except posterolaterally, where it is broken off. The rest is covered by matrix.

Contacts of dorsal plate: The dorsal plate of the parietal is large, as in Azabbaremys , but it is nearly rectangular rather than being an irregular quadrangle. It contacts the frontal anteromedially and the prefrontal anterolaterally. As mentioned (see Prefrontal), the broad prefrontal contact in Phosphatochelys and Ummulisani is unique among pleurodires and cryptodires. Also unique among pleurodires is the exposure of the parietal in the margin of the orbit. This condition is not approached by any other pleurodire or cryptodire. Laterally the parietal contacts the postorbital anteriorly and the quadratojugal posteriorly. The quadratojugal-parietal contact only occurs in Phosphatochelys , Ummulisani , and Taphrosphys among the Bothremydidae . Although it also occurs in the Euraxemydidae and Podocnemididae (including Hamadachelys ), it seems to be an independent acquisition within the Taphrosphyini .

Structures of dorsal plate: The posterior margin of the parietal along with the quadratojugal form the posterior limits of the posterior temporal emargination. The temporal emargination in Phosphatochelys is not different in extent from Azabbaremys , but the margin in Phosphatochelys is transverse while in Azabbaremys it is also straight but trends anterolaterally from the midline. To the extent it is known, this transverse edge is unique in Taphrosphyini , but a number of taxa ( Rosasia , Arenila , Zolhafah ) are incompletely known in the skull roof. Taphrosphys is more emarginate than Phosphatochelys . In AMNH 30008 the parietal has a very narrow exposure on the orbital margin (see Postorbital), while in MDEt 26 the postorbital-prefrontal contact prevents this.

Contacts and structures of processus inferior parietalis: The processus inferior parietalis (fig. 202) in Phosphatochelys , exposed only on the left side of AMNH 30008, is very narrow, as in Azabbaremys , and enters the foramen nervi trigemini, also as in Azabbaremys . The processus inferior parietalis contacts the pterygoid ventrally from the foramen interorbitale anteriorly to the foramen nervi trigemini posteriorly. The parietal also sends a process ventrally on the lateral side of the sulcus palatinopterygoideus, which contacts the palatine anteriorly and the pterygoid posteriorly. This process as well as an enclosed sulcus palatinopterygoideus are absent in Azabbaremys . As in Azabbaremys , the foramen interorbitale of Phosphatochelys is relatively small compared with other Pelomedusoides. Posteriorly the parietal contacts the supraoccipital in a nearly vertical suture above the prootic contact.

JUGAL (figs. 196, 199)

Preservation: Both jugals are present in AMNH 30008, but neither is complete. The left one is missing only part of its posterior edge. In MDEt 26 the right jugal is missing. The left one may be lacking part of its posterior edge. Both are mostly covered by matrix on their internal surfaces.

Contacts of lateral plate: The jugal in Phosphatochelys contacts the postorbital dorsally and the maxilla ventrally, as in other bothremydids. Because there was probably a narrow cheek emargination, the jugal may have had only a small or no contact with the quadrate (see below). The best preserved cheeks, the right sides of AMNH 30008 and MDEt 26, show no jugal-quadrate contact, but this may be due to breakage.

Structures of lateral plate: The jugal of Phosphatochelys is widely exposed in the posteroventral margin of the fossa orbitalis, contacting the postorbital dorsally and the maxilla ventrally, all as in Azabbaremys . In both specimens of Phosphatochelys , however, there appears to be a free posterior edge along the margin of the left jugal indicating a cheek emargination. The right jugal in AMNH 30008 is damaged posteriorly in this area. On the right side the quadrate and maxilla meet. This may be due to postmortem distortion, and the rest of the skull also supports this interpretation. In MDEt 26 the left jugal has what also appears to be a free edge along its posteroventral margin, just as in the left jugal of AMNH 30008. It seems likely, then, that there was a narrow cheek emargination, as shown in the restored lateral view (fig. 196C) with part of the jugal exposed on the margin of the emargination. Nonetheless, the dorsal placement of the quadratojugal and the close approximation of quadrate and maxilla are similar to Azabbaremys and Taphrosphys .

Contacts and structures of medial process: The medial process of the jugal is best preserved on the right side of AMNH 30008. It is barely visible in ventral view and does not extend onto the triturating surface. Most of the septum orbitotemporale is absent, as in the other Taphrosphyina , so the jugal has only a ventromedial process that reaches the maxilla and palatine in the orbital floor.

QUADRATOJUGAL (figs. 196, 199)

Preservation: The quadratojugal in AMNH 30008 is present only on the right side; the left one is missing. The quadratojugal is complete except along its anterior margin where some of its edge has been eroded. In MDEt 26 only the left quadratojugal is present and it has broken edges on three sides.

Contacts: The quadratojugal in Phosphatochelys contacts the parietal medially, the postorbital anteriorly, the quadrate ventrolaterally, and the squamosal posteroventrally. The area of the postorbital contact is damaged, but the presence of the contact is not in doubt. A quadratojugal-parietal contact also occurs in the podocnemidids, Erymnochelys and Peltocephalus , but among bothremydids it is known only in Taphrosphys , Ummulisani , and Labrostochelys . In Taphrosphys the quadratojugal is more extensive ventrally, and a jugal-quadrate contact is present.

Structures: In most turtles the quadratojugal is a large C-shaped element lying along the anterior margin of the quadrate on the cheek. This is the case in bothremydids like Foxemys , but in the Taphrosphyini (unknown in Nigeremys and Arenila ) the quadratojugal lies well above the main body of the quadrate and there is a jugal-quadrate contact.

SQUAMOSAL (figs. 196, 199, 203, 286C)

Preservation: Both squamosals are present in AMNH 30008; the right one is complete and the left one lacks some of its anterior process. In MDEt 26, parts of both squamosals are present, the left one is nearly complete, but the right one is lacking most of its lateral area.

Contacts: The squamosal in AMNH 30008 is the usual cone-shaped element lying on the posterolateral corner of the quadrate. It contacts the opisthotic medially on the dorsal, medial, and ventral surfaces. A short process of the squamosal contacts the quadratojugal along the lateral edge of the temporal embayment, as in Azabbaremys .

Structures: The squamosal in Phosphatochelys has a ventral flange or deep ridge, oriented vertically anteroposteriorly (fig. 203, sqf). This also occurs in Taphrosphys , Labrostochelys , Ummulisani , and Rhothonemys . On its lateral surface, there is a small ridge or tubercle overlapping outside the sulcus eustachii (fig. 286C) that also occurs in Taphrosphys and Labrostochelys and in some Bothremys maghrebiana .

POSTORBITAL (figs. 196, 199)

Preservation: The postorbital in Phosphatochelys is present on both sides of AMNH 30008. The left one is nearly complete; only some of its posterior edge is damaged, but the right postorbital is damaged with its posterior margin missing. The internal surface is visible on the left side, but only partially on the right. In MDEt 26 the postorbital is present on the left side only, in a more posterior, disarticulated fragment that is not definitely in its original position, and in the orbital margin. No medial process is visible.

Contacts of lateral plate: The postorbital of Phosphatochelys is a roughly square element, contacting the parietal medially, the quadratojugal posteriorly, the quadrate posteroventrally, and the jugal anteroventrally. The absence of a frontal contact, due to the prefrontal-parietal contact, is unusual and only occurs elsewhere in Ummulisani . The short postorbital of Phosphatochelys is completely separated from the posterior temporal emargination by the parietal-quadratojugal contact, quite different from the long postorbital of Azabbaremys that reaches the temporal emargination. It is possible that a very narrow postorbital-prefrontal contact was present, but as preserved the right side is eroded and the left side is broken at this point. Thus, we have restored the postorbital with no prefrontal contact and a narrow orbital exposure of the parietal. We consider this to be equivocal, however. In MDEt 26, only the left side preserves the postorbital, and here a very small postorbital-prefrontal contact is present, preventing orbital exposure of the parietal.

Contacts of medial process: As in most other Taphrosphyini , Phosphatochelys has no jugal-postorbital or palatine-postorbital contact of the medial process. The postorbitalparietal contact is small and there is no pterygoid contact here as well.

Structures of medial process: In most bothremydids the postorbital has a medial process that contacts the jugal and palatine to form the septum orbitotemporale. In the subtribe Taphrosphyina , however, this wall is small or absent. In Phosphatochelys the medial surface of the postorbital has a vertical ridge continuous with one from the jugal, which represents the fossa orbitalis margin. A much lower ridge is present in Azabbaremys . The postorbital contribution to the floor of the fossa orbitalis is also absent.

PREMAXILLA (figs. 196, 197, 199)

Preservation: Both premaxillae are present in AMNH 30008, but the right one lacks the labial ridge. In MDEt 26 both premaxillae are also present and nearly complete.

Contacts: The premaxilla in Phosphatochelys contacts the maxilla laterally and the other premaxilla medially. The vomer is missing in both skulls.

Structures on dorsal surface: The premaxilla in Phosphatochelys forms a deep, acute labial ridge with a median notch, in contrast to the hook seen in Azabbaremys . In Azabbaremys and many Pelomedusoides the ventral rim of the apertura narium externa protrudes well anterior to the labial ridge. In Phosphatochelys , however, the lower rim of the apertura is distinctly recessed, unlike any other bothremydid, so that the labial ridge is the anteriormost part of the skull. In Azabbaremys there is a median ridge with low troughs on either side communicating with the apertura narium externa. In Phosphatochelys there is also a median ridge but it is acute, not blunt as in Azabbaremys , and there are no troughs. Phosphatochelys does have a low concavity on the premaxilla that produces the recessed shape of the lower rim of the apertura. Below the concavity on the anterior face in Phosphatochelys there is a distinct pattern of the nutrient foramina, presumably for the horny beak. These occur in a band along the ventral edge of the labial ridge, premaxilla and maxilla, and which is slightly raised above the more dorsal parts of these bones. In Azabbaremys , Taphrosphys , and other bothremydids, the nutrient foramina are not so prominent on the outer surface of premaxilla and maxilla. The horizontal plate of the premaxilla forms the floor of the fossa nasalis, and in Phosphatochelys these form an acute dorsal ridge on the midline that is absent in Azabbaremys .

The premaxilla in AMNH 30008 is shorter than the premaxilla in MDEt 26, and it is not as inclined. The median notch is slightly deeper in AMNH 30008 than in MDEt 26. In both specimens there is a distinct sulcus or groove along the ventral edge of the apertura narium externa (fig. 279A). This sulcus is parallel-sided and seems to be a continuation of a sulcus running along the ventrolateral corner of the fossa nasalis (see Maxilla).

Structures on ventral surface: On the ventral surface, the premaxilla in Phosphatochelys forms the anterior part of the very high and acute labial ridge, higher than in Azabbaremys or any other bothremydid. Also in contrast to Azabbaremys and other bothremydids, the horizontal part of the triturating surface in Phosphatochelys is very narrow, particularly on the premaxilla, although it is more horizontal in MDEt 26 than in AMNH 30008. The lingual ridge might be identified as the very low, rounded margin separating the triturating surface proper from the median concavity that leads into the apertura narium interna. This concavity is large in Phosphatochelys , being wider and more open posteriorly in comparison to Azabbaremys .

MAXILLA (figs. 196, 197, 199)

Preservation: Both maxillae are present in AMNH 30008 and both are slightly damaged. The left maxilla is nearly complete but has a horizontal break running through the main body; not much bone seems to be missing however. The right maxilla is missing its anteriormost edge and has a broken area below the orbit. Both have the internal portion preserved. In MDEt 26, both maxillae are preserved; the left one is nearly complete. The right one is missing a small part of its dorsal margin.

Contacts of vertical plate: The maxilla of Phosphatochelys contacts the premaxilla anteromedially, the prefrontal anterodorsally in an unusually narrow suture, and the jugal posterodorsally.

Structures of vertical plate: The vertical plate in Phosphatochelys is more curved, convex anterolaterally, than the very flat maxilla of Azabbaremys , and it has a relatively larger fossa orbitalis and apertura narium externa than in Azabbaremys . As preserved, the maxilla contacts the quadrate on the right side. Based on the apparent free edges of the maxilla and jugal on the left side and some distortion on the right side, we have restored Phosphatochelys with a narrow cheek emargination. The prefrontal-maxilla contact is best preserved on the left side. It is much narrower than in Azabbaremys .

Contacts of horizontal plate: In ventral view, the maxilla contacts the premaxilla anteromedially, the jugal posteriorly, and the palatine posteromedially. In AMNH 3008 the area around the premaxilla-maxilla suture is broken on both sides as the suture approaches the apertura narium interna. The vomer, presumably present, is missing in both specimens. It is possible that the maxilla contacted the vomer, and, if not, it probably came close. The jugal does not extend onto the triturating surface in Phosphatochelys . The palatine contact is also farther from the triturating surface than it is in Azabbaremys . In the floor of the fossa orbitalis the horizontal plate of the maxilla contacts the palatine posteromedially and the jugal posterolaterally.

Structures of horizontal plate: The medial parts of the maxilla form part of the fossa nasalis anteriorly and the fossa orbitalis posteriorly. The fossa nasalis is relatively large for a bothremydid and does not have the posterolateral pocket seen in Azabbaremys . Along the ventrolateral margin of the fossa nasalis is a deep groove beginning as a shallow groove or sulcus (see Premaxilla) on the premaxilla and running posterolaterally to the fossa orbitalis (fig. 279A). This groove has two large foramina in it that open ventrolaterally into the main body of the maxilla. In Podocnemis and Pelusios, Albrecht (1976) described the canalis infraorbitalis and canalis alveolaris superior system that connect a series of foramina and contain the supramaxillary and superior alveolar arteries. The groove and foramina in Phosphatochelys seem to be part of this system. Although we have not seen it developed to this extent in any other Pelomedusoides, other taxa do have foramina in the same place in the fossa nasalis that communicate with the alveolar canals.

The lower border of the orbital margin is relatively high above the floor of the fossa nasalis, resulting in a deep pocket, deeper than seen in Azabbaremys and much deeper than seen in Bothremys , Foxemys , Podocnemis , and pelomedusids, but similar in extent to the one in Rhothonemys .

The ventral portion of the maxilla bears the triturating surface and forms part of the palate. The labial ridge of Phosphatochelys is much deeper than in Azabbaremys or other bothremydids. The snout is unusually foreshortened, and the labial ridge is very deep, resulting in a deep, horseshoe-shaped space. The flat portion of the triturating surface width is very small and not distinctly separated from the labial ridge or the lingual edge. The lingual ridge barely exists: it is just the rounded margin for the apertura narium interna. The triturating surface has the usual nutrient foramina but it is smooth, not corrugated as in Azabbaremys .

VOMER

Preservation: There is no vomer present in either specimen, but that may be due to postmortem loss.

PALATINE (figs. 196, 197, 199)

Preservation: Both palatines in AMNH 30008 are present but both are missing some of the anterior margin, although the right one seems to be nearly complete. Most of the dorsal surfaces are visible except posteromedially. In MDEt 26, both palatines are complete but visible only in ventral view.

Contacts: The palatine in Phosphatochelys contacts the maxilla anterolaterally, the pterygoid posteriorly, and the other palatine medially. In the orbital floor the palatine has a broad anterolateral contact with the maxilla and a broad lateral contact with the jugal. The absence of a septum orbitotemporale is associated with the absence of a postorbital contact.

Structures on dorsal surface: The dorsal surface of the palatine is complex, as it is involved in the fossa orbitalis, the sulcus palatinopterygoideus, and the remnant of the septum orbitotemporale. In Phosphatochelys , as in Azabbaremys and Taphrosphys , the septum orbitotemporale, so prominent in other bothremydids, is mostly absent. In dorsal view the palatine of Phosphatochelys is similar to Azabbaremys in forming most of the floor of the orbit and in having a broad anterolateral maxilla contact and a broad lateral jugal contact. The surface of the orbital floor is deeply concave, even more than in Azabbaremys . In contrast to Azabbaremys , Phosphatochelys has a narrow but completely enclosed sulcus palatinopterygoideus (figs. 202, 279A). In Azabbaremys the lateral wall of the sulcus is gone; in Phosphatochelys it is narrow but complete.

Structures on ventral surface: In ventral view the palatine in Phosphatochelys is smaller than the unusually large palatine of Azabbaremys . The palatine-pterygoid suture is roughly transverse in Phosphatochelys , not concave anteriorly as in Azabbaremys . The edges of the apertura narium interna in Phosphatochelys are best preserved in MDEt 26. They are more circular rather than triangular as in Azabbaremys . As in Azabbaremys , only a small part of the palatine enters onto the triturating surface. The palatine forms the roof of the choanal opening into the mouth, the apertura narium interna. In Phosphatochelys , Azabbaremys , and Nigeremys this roof is highly arched dorsally, in contrast to the flatter surface of other bothremydids. The foramen palatinum posterius in Phosphatochelys is formed almost entirely by the palatine, but it is very close to the pterygoid suture, and a small spur of the pterygoid may enter the foramen. The foramen palatinum posterius of Phosphatochelys is in a comparable position to that seen in Azabbaremys , but it is much more medial and closer to the apertura narium interna in Phosphatochelys than in Azabbaremys or other bothremydids.

QUADRATE (figs. 196, 197, 199, 202, 203, 286C)

Preservation: Both quadrates in AMNH 30008 are present and nearly complete. The left one lacks its anterior edge and the right one has some breakage along the jugal-maxilla contact. In MDEt 26, both quadrates are present. The left one seems to be all there, but it is cracked in a number of places with some displacement of the pieces. The right quadrate is less deformed, but it is missing its dorsal margin.

Contacts on lateral surface: In lateral view the quadrate of Phosphatochelys contacts the jugal anteriorly, the postorbital anterodorsally, the quadratojugal dorsally, and the squamosal posterodorsally. As preserved, there is a maxilla contact anteroventrally on the right of AMNH 30008, but this is interpreted as a narrow cheek emargination (see Maxilla). Both quadrates in MDEt 26 preserve an anterior margin that looks like a free edge, not a sutural contact.

Structures on lateral surface: The cavum tympani in Phosphatochelys (fig. 286C) has a completely enclosed incisura columellae auris, as in Azabbaremys and most bothremydids. Also as in Azabbaremys , the cavum is hemispherical and lacks a fossa precolumellaris. However, Phosphatochelys has a well-developed antrum postoticum, larger than in Taphrosphys sulcatus , which is in strong contrast to Azabbaremys , which completely lacks an antrum postoticum. At the posterior margin of the cavum tympani in Phosphatochelys is a groove for the eustachian tube, as in Azabbaremys . In Azabbaremys this groove is open, but in Phosphatochelys there is a well-developed ventral process or overhang that partially encloses the eustachian tube. As in Azabbaremys , there is a shelf along the ventral margin of the cavum tympani. It is very similar in size and shape in both Phosphatochelys and Azabbaremys .

Contacts on dorsal and anterior surfaces: The quadrate in Phosphatochelys contacts the prootic medially, the opisthotic posteromedially, and the squamosal posterolaterally. As in Azabbaremys and Taphrosphys , there is no quadrate-supraoccipital contact that is seen in other bothremydids. The dorsally directed trough and associated ridge (see Pterygoid) formed by pterygoid and quadrate lie just anterior to these foramina.

Structures on dorsal and anterior surfaces: The quadrate forms the posteroventral margins of the foramen stapedio-temporale and the foramen nervi trigemini, as in other bothremydids. These formaina are verly close to each other in Phosphatochelys .

Contacts on ventral surface: In ventral view the quadrate of Phosphatochelys contacts the pterygoid anteromedially, the basisphenoid medially, and the basioccipital posteromedially, as in Azabbaremys and other bothremydids. As in Azabbaremys , there is a narrow contact with the basisphenoid between the broader basioccipital and pterygoid contacts. The quadrate contacts the quadrate ramus of the pterygoid in a suture extending from the basisphenoid along the processus articularis of the quadrate, as in Azabbaremys and other pleurodires.

Structures on ventral surface: The foramen posterius canalis carotici interni is formed in the pterygoid-quadrate suture, but more is formed by the quadrate than by the pterygoid. In contrast to Azabbaremys , there is no contribution from the basisphenoid. There is a distinct groove on the quadrate leading anteriorly into the foramen posterius canalis carotici interni.

The processus articularis of the quadrate in Phosphatochelys is longer than in Azabbaremys so that the condylus mandibularis is much farther from the plane of the palate in Phosphatochelys than it is in Azabbaremys . This is presumably related to the very deep labial ridge in Phosphatochelys , although a lower jaw will be needed to demonstrate this. The quadrate and the basioccipital form the tuberculum basioccipitale, which is higher and more prominent than in Azabbaremys .

Contacts on posterior surface: In posterior view the quadrate in Phosphatochelys contacts the squamosal dorsolaterally, the opisthotic dorsally, the exoccipital medially, and the basioccipital ventromedially (not quite visible in occipital view).

Structures on posterior surface: The quadrate and opisthotic combine to form a fully enclosed fenestra postotica (fig. 203) in Phosphatochelys , very similar to that in Azabbaremys . In the shelf leading into the fenestra, both dorsally and ventrally, are low spurs suggesting a division of stapedial artery and lateral head vein. However, distinct ridges as seen in Taphrosphys are absent. As in Azabbaremys , the fenestra postotica of Phosphatochelys is widely separated from the foramen jugulare posterius by a well-developed opisthotic-quadrate contact. In Phosphatochelys and Azabbaremys the quadrate contacts the exoccipital and basioccipital ventral to the foramen jugulare posterius. On the posterior surface of Phosphatochelys is a continuation of the sulcus eustachii from the cavum tympani. This groove is roughly horizontal and is well defined dorsally by a shelf that has a slight ventral ridge resulting in an overhang partially enclosing the groove. Medially the groove flattens out and disappears.

PTERYGOID (figs. 196, 197, 199, 202)

Preservation: Both pterygoids in AMNH 30008 are present and nearly complete. The processus trochlearis pterygoidei is displaced on the right side but intact on the left. Both pterygoids are present and nearly complete in MDEt 26 as well. Only the ventral surfaces are visible due to matrix. On both sides the thin flange below and behind the processus trochlearis pterygoidei is divided into two narrow flanges. However, close examination reveals this to be an artifact of overpreparation; the flange was originally one piece, as in other pleurodires.

Contacts on ventral surface: In ventral view the pterygoid contacts in Phosphatochelys are as in other bothremydids: palatine anteriorly, quadrate posterolaterally, basisphenoid posteromedially, the other pterygoid medially. The midline pterygoid contact is slightly longer than in Azabbaremys .

Structures on ventral surface: The foramen posterius canalis carotici interni (see Quadrate) lies in the pterygoid-quadrate suture midway between the basisphenoid and lateral edge of the quadrate. Nonetheless, the foramen is in a similar position in Azabbaremys despite the fact that the basisphenoid enters the foramen in Azabbaremys . The basisphenoid is much wider in Azabbaremys than in Phosphatochelys , and that may be a factor.

The pterygoideus muscle scar is weakly developed in Azabbaremys , but it is absent in Phosphatochelys . There is no indication at all of its presence. However, there is a dorsally directed trough formed by pterygoid and quadrate in Phosphatochelys that may have held an insertion for the M. pterygoideus (fig. 203, in the area labeled ‘‘pt’’). This trough has a sharp ridge on the quadrate as its lateral margin and the crista pterygoidea and processus inferior parietalis as its medial limits. It trends posteroventrally from the parietal down to the condylus mandibularis and is open anteriorly. As it reaches the ventral edge of the pterygoid its posterior wall ends, and only the lateral ridge reaches the condylus mandibularis. Thus, in ventral view (fig. 197), the end of the trough lies behind the processus trochlearis pterygoidei just lateral to the thin web of bone behind the processus. This structure, developed to the extent seen in Phosphatochelys , and also in Ummulisani , is unique among pleurodires. It is possible that this trough contains a division of the M. pterygoideus ( Schumacher, 1973), probably either the pars ventrolateralis or possibly the pars ventroposterior (seen in Podocnemis ).

The processus trochlearis pterygoidei of Phosphatochelys is relatively well preserved on both sides. In many pleurodire fossils it is damaged due to the thin bone. In Azabbaremys only part of one is preserved, but it is similar to that in Phosphatochelys . The processus in both genera extends posteriorly at an angle of roughly 30 ° from the midline. There is a low ridge along the ventrolateral margin of the processus in Phosphatochelys , also as in Azabbaremys but absent in pelomedusids. The base of the processus trochlearis pterygoidei contacts the parietal anterodorsally and the palatine anteroventrally. The foramen palatinum posterius (see Palatine) is formed almost entirely by the palatine with a very narrow contribution from the pterygoid.

Contacts on dorsal surface: The pterygoid at the base of the processus trochlearis pterygoidei contacts the parietal anterodorsally and the palatine anterolaterally. The crista pterygoidea is very short in Phosphatochelys ; the pterygoid contacts the parietal dorsally and the prootic behind the foramen nervi trigemini.

Structures on dorsal surface: The crista pterygoidea in Phosphatochelys is completely covered with matrix on the right side and only partially exposed on the left in AMNH 30008. However, the left side does show the anterior margin and the foramen nervi trigemini clearly. The crista pterygoidea in Phosphatochelys is narrow in comparison to Bothremydini , but it is not as narrow as in Azabbaremys . In Azabbaremys both the processus inferior parietalis and the crista pterygoidea are roughly half the width of these walls in Phosphatochelys . The posterior edge of the crista pterygoidea forms the anteroventral margin of the foramen nervi trigemini in Phosphatochelys , as in Azabbaremys . In Phosphatochelys in contrast to Azabbaremys , there is a high, thin ridge along the anterior margin of the foramen nervi trigemini separating it from the more anterior part of the crista pterygoidea.

SUPRAOCCIPITAL (figs. 196, 199, 203)

Preservation: The supraoccipital in AMNH 30008 is nearly complete and well preserved, with all sides in it being visible. In MDEt 26 the supraoccipital is missing most of the crista supraoccipitalis, but it is otherwise complete.

Contacts: The laterally projecting otic portion of the supraoccipital in Phosphatochelys contacts the prootic anterolaterally, the opisthotic laterally, and the exoccipital posterolaterally. It does not contact the quadrate, although in MDEt 26 the opisthotic-prootic contact is much narrower than in AMNH 30008.

Structures: The supraoccipital of Phosphatochelys underlies the two parietals on the midline but not to the extent seen in Azabbaremys . This is presumably related to the shorter parietals in Phosphatochelys , because the supraoccipitals in both Phosphatochelys and Azabbaremys are quite similar. The crista supraoccipitalis is complete in Phosphatochelys and short as in Azabbaremys , extending only slightly past the level of the condylus occipitalis. Phosphatochelys has a slightly shorter crista than in Azabbaremys . The blade of the crista is deeper in Azabbaremys than in Phosphatochelys , but this seems to be related to the larger foramen magnum of Phosphatochelys , being in turn presumably related to its smaller size.

EXOCCIPITAL (figs. 196, 199, 203)

Preservation: Both exoccipitals are preserved in AMNH 30008 and in MDEt 26; they are complete, free of matrix, and have clear sutures.

Contacts: The exoccipital in Phosphatochelys contacts the supraoccipital dorsally, the opisthotic laterally, the quadrate ventrolaterally, and the basioccipital ventrally, as in Azabbaremys and other bothremydids.

Structures: The exoccipital in Phosphatochelys forms all of the condylus mandibularis, and the basioccipital enters the neck of the condyle and almost reaches the articulation surface, in contrast to the condyle in Azabbaremys where the basioccipital is more anterior. The exoccipitals are slightly eroded on the midline or perhaps they were not fully ossified, giving the occipital condyle a bilobed appearance as in BMNH R 16370, the type specimen of Azabbaremys moragjonesi . The foramen jugulare posterius is formed mostly by the exoccipital, with between a third and a half being formed by the opisthotic, in contrast to Azabbaremys in which only a very narrow process of the opisthotic enters the foramen margin. The foramen jugulare posterius is entirely enclosed by bone, as in Taphrosphys , Arenila , and Bothremys but in contrast to the open condition of Foxemys and Polysternon .

Between the foramen jugulare posterius and the condylus occipitalis are the two foramina nervi hypoglossi entirely formed by the exoccipital. Their positions differ significantly in Phosphatochelys and Azabbaremys . In Phosphatochelys the more medial foramen lies on the roughly flat posterior surface of the exoccipital and opens posterolaterally and is clearly visible in posterior view. The more lateral foramen lies within the entry to the foramen jugulare posterius and is so far within the margin that it is completely concealed in posterior view on the right side and only barely visible on the left. The more medial foramen nervi hypoglossi in Phosphatochelys is larger in diameter than the more lateral one. In Azabbaremys both foramina are very close to one another, they are the same size, and neither is close to the foramen jugulare posterius.

BASIOCCIPITAL (figs. 196, 197, 199, 203)

Preservation: The basioccipitals in AMNH 30008 and MDEt 26 are complete and clearly defined.

Contacts: The basioccipital in Phosphatochelys contacts the basisphenoid anteriorly, the quadrates laterally, and the exoccipitals posteriorly, as in Azabbaremys . Phosphatochelys has a broadly curved anterior margin rather than the straight suture seen in Azabbaremys . The basisphenoid contact is smaller and the quadrate contact more extensive in Phosphatochelys .

Structures: The basioccipital in Phosphatochelys makes up the medial half of the very low tuberculum basioccipitale. Between the paired tubercula is a median concavity that is deeper and more clearly defined than in Azabbaremys . The concavity in Phosphatochelys is almost exactly coincident with the basioccipital.

PROOTIC (figs. 196, 199, 202)

Preservation: Both prootics are present and complete in both skulls. In AMNH 30008 the left one is free of matrix, but the right one is covered anteromedially. Both have clear sutures. In MDEt 26 the prootics appear complete but are covered by matrix anteriorly.

Contacts: The prootic in Phosphatochelys contacts the supraoccipital posteromedially, the parietal medially, the pterygoid ventrally (internal to the foramen nervi trigemini), the quadrate laterally, and the opisthotic posterolaterally. The opisthotic contact is broader in AMNH 30008 and narrower in MDEt 26.

Structures: The prootic forms the dorsomedial margin of the foramen nervi trigemini, the parietal forms its anterodorsal margin, the pterygoid forms its anteroventral margin, and the quadrate forms its posteroventral margin. The foramen nervi trigemini is visible and complete on the left side of AMNH 30008 as well as the foramen stapedio-temporale, which lies entirely on the anterior face of the otic chamber and is not visible in dorsal view. This is the same condition in nearly all bothremydids. The quadrate forms the lower half of the foramen stapedio-temporale (see Quadrate). Both foramina are very close to each other.

OPISTHOTIC (figs. 196, 197, 199, 203)

Preservation: Both opisthotics are complete and well preserved with clear sutures in MDEt 26 and AMNH 30008.

Contacts: The opisthotic in Phosphatochelys has the usual bothremydid contacts: supraoccipital dorsomedially, prootic anteromedially, quadrate anterolaterally, squamosal posterolaterally, quadrate (again) ventrolaterally, and exoccipital posteromedially.

Structures: The opisthotic forms the roof of the fenestra postotica, with the ventral and greater portion being formed by the quadrate. The fenestra in Phosphatochelys is oblong with small ridges distally presumably indicating the positions of the stapedial artery and lateral head vein (see Quadrate). The processus interfenestralis of the opisthotic forms the wall between the fenestra postotica and foramen jugulare posterius, contacting the quadrate ventrally. This wall is quite thick in Phosphatochelys as it is in Azabbaremys and most Taphrosphyini and Bothremydini .

BASISPHENOID (figs. 196, 197, 199)

Preservation: The basisphenoid is complete and clearly defined in MDEt 26 and AMNH 30008, but its dorsal surface is covered with matrix.

Contacts: The basisphenoid of Phosphatochelys is roughly triangular in ventral view. It has a straight posterior contact with the basioccipital, posterolateral contacts with the quadrates, and anterolateral contacts with the pterygoids.

Structures: The basisphenoid in Phosphatochelys is about as wide as long, in contrast to the very short and wide basisphenoid in Azabbaremys .

Ummulisani rutgersensis

At present, three skulls of this taxon are known, but because two of them were discovered very late in the development of this project, it was only possible to describe in detail and figure one without incurring significant delays. The other two will be described soon (Gaffney and Tong, in prep.). Unfortunately, the figured skull, AMNH 30563 , is the least complete of the three ; although not ideal, it is complete enough to serve as the type. One of the new skulls, AMNH 30562 , is associated with a plastron that we were able to describe and figure (figs. 268, 269), even though the skull is still being prepared. The third skull, AMNH 30569 , is nearly complete. Some information from all three skulls is included in the description below .

Ummulisani is the sister taxon to Phosphatochelys within the subtribe Taphrosphyina .

PREFRONTAL (figs. 204, 207)

Preservation: Both prefrontals are complete in AMNH 30563 except for a small part of the maxilla contact. The posteromedial edge of the ventral process could have had a palatine contact; if so, this is also missing.

Contacts: There is a long medial contact with the other prefrontal and a very narrow anterolateral contact with the maxilla. The maxilla contact in Ummulisani is about the same size and position as in Phosphatochelys . It is narrower than in Taphrosphys and Azabbaremys . The posterior contact in the type specimen of Ummulisani is a straight transverse suture with the parietal. In the two other specimens of Ummulisani , the small frontals lie in the medial part of this suture. The only other pleurodire or turtle to have a prefrontal-parietal contact is Phosphatochelys . Phosphatochelys also has small frontals that are separated from the orbital margin by the prefrontal-parietal contact. Many other turtles have small frontals, but none combine that with large prefrontals to produce a prefrontal-parietal contact.

Structures: The prefrontal in Ummulisani has the midline projection seen in other Taphrosphyini . It is about the same size and shape as in Phosphatochelys .

Ummulisani is unique in having a hornlike process on the anterolateral margin of each prefrontal, developed to about the same extent in all three skulls. This process is cone-shaped and lies at the anterodorsal margin of the orbit. There is nothing similar in any other turtle. Phosphatochelys and other Taphrosphyini do not even have swellings or thickened bone in this area. Clearly, these horns were part of the complex rutting rituals in which males bashed what few brains they had out of each other, resulting in their extinction.

The ventral surface is visible in AMNH 30563. The prefrontal forms almost all of the roof of the fossa nasalis and the major part of the sulcus olfactorius.

FRONTAL

The frontal is absent in AMNH 30563, but a small frontal is present in the two other Ummulisani specimens, not yet described (Gaffney and Tong, in prep.). The absence of the frontal is presumably individual variation, not of particular systematic significance.

PARIETAL (figs. 204, 207)

Preservation: Both parietals are present in AMNH 30563. The dorsal plate of the right one is complete except on its posterior edge. The left one has a broken lateral and posterior margin. The processus inferior parietalis of both is present but slightly damaged by dorsoventral crushing that has obscured its ventral contacts. The anterior margin of the processus is broken on both sides.

Contacts of dorsal plate: The large parietal of Ummulisani contacts the other parietal medially, the prefrontal anteriorly (see Prefrontal), the postorbital anterolaterally, the quadratojugal posterolaterally, and a small dorsal plate of the supraoccipital posteromedially. Except for the absence of a frontal contact in the type specimen, AMNH 30563, these are similar to ones found in Phosphatochelys .

Structures of dorsal plate: The posterior temporal emargination in AMNH 30563 is represented by a broken edge on both sides, but, as preserved, the skull roof is nearly as extensive as in Phosphatochelys . The two new skulls show a similarly extensive skull roof. On the ventral surface, Ummulisani lacks the septum orbitotemporale and has a transverse ridge instead, marking the posterior limits of the fossa orbitalis. This shows that the fossa orbitalis was expanded, as in Phosphatochelys .

Contacts of processus inferior parietalis: The anterior margin of the processus inferior parietalis is mostly a broken edge; only a small part is present on the right side, and the palatines are missing as well. The possible palatine contact, as in Phosphatochelys , cannot be determined. The pterygoid contact is much wider in Ummulisani than in Phosphatochelys . The prootic contact above the foramen nervi trigemini is unclear posteriorly.

Structures of processus inferior parietalis: The foramen interorbitale is too poorly preserved in AMNH 30563 to characterize, but it is possible to say that the remaining portion of the processus inferior parietalis is much wider than in Phosphatochelys . In

Phosphatochelys the parietal has a ventral process that meets the pterygoid lateral to the sulcus palatinopterygoideus. In Ummulisani , the pterygoid area defining the sulcus is gone, but a small parietal process is present, although it does not seem to have been long enough to reach the pterygoid when the pterygoid was there.

JUGAL (figs. 204, 207)

Preservation: Only part of the right jugal is probably present in AMNH 30563, and that seems to have been displaced during an earlier bout of preparation. A bone below the orbit has a broken medial process that seems to be identifiable as a jugal, but it overlaps part of the quadrate behind it. The orbital margin and possible sutures, however, suggest that the bone may be the jugal and may only be displaced from its original position. The absence of a medial process and clear sutures preclude any further description.

QUADRATOJUGAL (figs. 204, 207)

Preservation: At least the anterior part of the right quadratojugal is present.

Contacts: The quadratojugal in Ummulisani contacts the parietal medially, the postorbital anteriorly, and the quadrate ventrolaterally.

Structures: The quadratojugal in Ummulisani is a small element placed well dorsal to the cheek margin. It is rectangular and not Cshaped. In these features it agrees with the quadratojugal in Phosphatochelys and Azabbaremys .

SQUAMOSAL (figs. 204, 207)

Preservation: The vicissitudes of death have dealt harshly with the squamosals of AMNH 30563. Only a few fragments of the right one remain, and the left one is badly broken and hanging on only by my imagination.

Contacts: The only contact remaining is with the quadrate, somewhat anteromedially.

Structures: The antrum postoticum is absent in Ummulisani , and the squamosal has no sign of a remnant canal or space. The left squamosal in Ummulisani has enough preserved to show that the ventral flange is large and similar to that structure in Taphrosphys , Rhothonemys , Phosphatochelys , and Labrostochelys . The lateral tubercle area is not preserved well enough to determine in AMNH 30563.

POSTORBITAL (figs. 204, 207)

Preservation: Only the right postorbital is present in AMNH 30563.

Contacts of lateral plate: The postorbital in Ummulisani contacts the parietal dorsomedially, the quadrate posteroventrally, the quadratojugal posteriorly, and the jugal ventrally. The jugal contact, however, is unclear, as the jugal is not definitely identified. The contacts are as in Phosphatochelys .

Structures of lateral plate: The postorbital in Ummulisani forms the posterior margin of the orbit and does not enter the temporal margin due to its relatively small size, in comparison to a form like Azabbaremys .

Contacts of medial process: The medial process only contacts the parietal medially in Ummulisani , as the septum orbitotemporale is nearly absent.

Structures of medial process: As in Phosphatochelys , the fossa orbitalis in Ummulisani is open posteriorly and the septum orbitotemporale is nearly absent. The postorbital and parietal form a transverse ridge on the ventral surface of the skull roof. This ridge is the remnant of the septum orbitotemporale and forms the posterior margin of the fossa orbitalis. The sulcus palatinopterygoideus is not preserved in AMNH 30563, so its degree of formation is not determinable.

PREMAXILLA (figs. 204–207)

Preservation: Both premaxillae are present and nearly complete in AMNH 30563, but their contacts with the maxillae are broken and filled with glue.

Contacts: The premaxilla in Ummulisani contacts the other premaxilla medially and the maxilla posterolaterally. The vomer and the vomer contact are not preserved.

Structures on dorsal surface: The premaxilla forms the floor of the fossa nasalis, which in Ummulisani is relatively large. The apertura narium externa is separated from the anterior skull surface only by a low ridge and a slight change in slope in Ummulisani , rather than by a sharp change in slope, as in Phosphatochelys and other Taphrosphyini . There is a midline ridge or carina that runs from the anterior margin of the premaxilla, the labial ridge, posteriorly through the apertura narium externa and into the fossa nasalis. In Phosphatochelys , the ridge is only within the fossa nasalis. In Ummulisani , the premaxilla is protuberant on the midline, forming an acute point, rather than the curved snout margin seen in Phosphatochelys , Taphrosphys , and Nigeremys . Rhothonemys has a slight protuberance, but not to the extent seen in Ummulisani . Labrostochelys has an extensive premaxillary process, but it ends in a blunt edge different from that in Ummulisani .

The floor of the fossa nasalis is a broad, curved trough separated by the midline carina. There is a groove along the inner margin of the apertura narium externa, like that seen in Phosphatochelys . The midline carina has a dorsal process where it intersects the apertura narium externa.

Structures on ventral surface: The labial ridge is inclined in Ummulisani , different from the vertical ridge in Phosphatochelys . The edge of the ridge is sharp and the bone is much thinner than in Phosphatochelys , and the more horizontal triturating surface produces a wider, flat area behind the labial ridge. The midline embayment in Ummulisani is wide as in Phosphatochelys , but it is much shallower. As on the dorsal surface, the labial ridge forms a pointed anterior protuberance in Ummulisani not seen in Phosphatochelys .

MAXILLA (figs. 204–207)

Preservation: Most of the right maxilla is present in AMNH 30563, but the ventral margin is missing some of its edges; its medial margin is missing posteriorly. There seems to be a natural edge just behind the premaxilla. The left maxilla only consists of the anterior half of the bone. Its ventral margin is a broken edge. Its medial edge seems to be natural anteriorly, as on the right side. Both maxillae have a posterior broken edge with a very similar shape that is close to where the palatine should be.

Contacts of vertical plate: The maxilla contacts the premaxilla anteriorly, the prefrontal anterodorsally, the jugal posterodorsally, and the quadrate posteroventrally. The jugal contact is only presumed, as the bone is ill defined. The quadrate suture is in a broken area, so its exact position is unclear, but it is not possible that another bone could be there.

Structures of vertical plate: The maxilla forms the ventral part of the orbital margin. There is a sharp rim with a concave pocket below the internal surface, as in Phosphatochelys and Rhothonemys . Anteriorly the maxilla forms the lateral wall and lateral part of the floor of the fossa nasalis. The orbitonasal bar in Ummulisani is narrow, as in Phosphatochelys , not wide, as in Taphrosphys and other Taphrosphyini .

The maxilla in Ummulisani is unusually deep, deeper than other Taphrosphyini except Phosphatochelys . Due to the greater snout foreshortening in Phosphatochelys , Ummulisani has a longer anterior part of the maxilla, as in the other Taphrosphyini . The narrow cheek emargination seen in Phosphatochelys is present but poorly preserved in the type skull of Ummulisani , but it is clearly present in the other two skulls of Ummulisani .

Contacts of horizontal plate: The only contact preserved in AMNH 30563 is anteriorly with the premaxilla, but it is possible that the posteromedial broken edge is close to the palatine contact.

Structures of horizontal plate: The triturating surface in Ummulisani is relatively narrow, as in other Taphrosphyini and in contrast to the wide surface of the Bothremydini . The labial ridge in Ummulisani is deep, as in Phosphatochelys , but it is very thin and curved, in contrast to the thicker, wedge shape in Phosphatochelys . The entire triturating surface is curved, as in Labrostochelys ; it is not a distinct labial ridge meeting a horizontal triturating surface at right angles.

The apertura narium interna is represented by a natural edge of the maxilla that is the anterolateral margin of the apertura. This is similar in position to the apertura in Phosphatochelys and Taphrosphys . The maxilla forms the lateral part of the floor of the fossa orbitalis. All the other bones are missing, but the maxilla in Ummulisani does form more of the floor than does the maxilla in Azabbaremys . There is a high, sharp rim to the orbital margin and a ventral pocket formed by the maxilla, as in Rhothonemys and Phosphatochelys .

VOMER

Preservation: Not preserved in AMNH 30563.

PALATINE

Preservation: Not preserved in AMNH 30563.

QUADRATE (figs. 204–207)

Preservation: Both quadrates are present in AMNH 30563; the right one is nearly complete except for damage along its anterior margin, and the left is missing its dorsal portions.

Contacts on lateral surface: The quadrate in Ummulisani contacts the quadratojugal dorsomedially and the postorbital anteromedially. The anterior margin of the quadrate is not well preserved and the sutures are not entirely clear. However, the quadrate does contact the jugal anterodorsally and the maxilla anteriorly, as in Phosphatochelys . The quadrate contacts the squamosal posterodorsally.

Structures: It is not clear whether the quadrate enters the temporal emargination in Ummulisani due to damage. The degree of emargination is similar in Ummulisani and Phosphatochelys , and Phosphatochelys has no quadrate exposure along the margin. The lateral surface of the quadrate in Ummulisani is expanded anteriorly as in Phosphatochelys , forming much of the cheek. Although the cavum tympani is clearly defined, there is a wider, shallow depression paralleling the anterior curved edge of the cavum. This depression extends well onto the cheek.

The cavum tympani in Ummulisani is similar to that in Phosphatochelys . The incisura columellae auris is the usual canal, with the deepest part of the cavum dorsal and anterior to it. The ventral shelf seen in many bothremydids is present, but not as deep or as well defined as in other taxa, such as Bothremys . The antrum postoticum is closed, although the area is a deep concavity posterodorsal to the incisura columellae auris. The sulcus eustachii is a V-shaped notch with a shallow groove extending toward the incisura columellae auris. There is a ventrally directed process on the dorsal edge of the sulcus, as in Phosphatochelys and Labrostochelys . There is also a broken base for a dorsally directed process on the lower margin of the sulcus eustachii on the right quadrate.

Contacts on dorsal and anterior surface: On the dorsal surface of the otic chamber, the quadrate contacts the prootic anteromedially, the opisthotic posteromedially, and the squamosal posteriorly. There is no supraoccipital contact, agreeing with the other Taphrosphyini .

Structures on dorsal and anterior surface: The foramen stapedio-temporale is only separated from the foramen nervi trigemini by a thin bar. Only a small part of quadrate seems to reach the margin of the foramen stapedio-temporale due to this very medial position. These relations are similar in both Ummulisani and Phosphatochelys .

Contacts on ventral surface: The quadrate in Ummulisani contacts the pterygoid anteromedially, the basisphenoid medially, the basioccipital posteromedially, and the exoccipital posteromedially as well. The basisphenoid contact is wide in Ummulisani , as in Taphrosphys and in contrast to the narrow contact of other Taphrosphyini .

Structures on ventral surface: There is no fossa pterygoidea in Ummulisani , although there is a slight concavity here. The condylus mandibularis is well anterior to the condylus occipitalis and the basisphenoid-basioccipital suture. On the posterior surface of the condylus mandibularis is a shallow depression for the depressor mandibulae, as in Phosphatochelys , not a deep depression, as in Labrostochelys . The foramen posterius canalis carotici interni is formed completely by the quadrate in Ummulisani . Ummulisani and Labrostochelys are the only pleurodires with the foramen posterius canalis carotici interni entirely formed by the quadrate.

Contacts on posterior surface: The quadrate in Ummulisani contacts the squamosal dorsolaterally, the opisthotic dorsomedially, the exoccipital medially, and the basioccipital ventromedially. The exoccipital suture is visible in only a few places.

Structures on posterior surface: The fenestra postotica in Ummulisani is fully enclosed by bone, being widely separated from the foramen jugulare posterius. The fenestra postotica is oval, roughly horizontal, with no sign of divisions.

PTERYGOID (figs. 204–207)

Preservation: Both pterygoids are present, but they lack the processus trochlearis pterygoideus and anterior edges. The left one is missing its lateral edge, which is present on the right.

Contacts on ventral surface: The pterygoid in Ummulisani contacts the quadrate posterolaterally, the basisphenoid posteromedially, and the other pterygoid medially. The palatine suture may be represented in a small part of the broken anterior edge, indicating that the pterygoid may not have been much longer than preserved.

Structures on ventral surface: There is no deep fossa pterygoidea, only a very shallow, ill-defined depression in the area. The quadrate ramus is slightly more extensive than in Phosphatochelys . There is no sign of the foramen palatinum posterius, as all of the anterior edges of the pterygoids are broken. The foramen posterius canalis carotici interni is entirely formed by the quadrate with no pterygoid participation.

Contacts on dorsal surface: The crista pterygoidea of the pterygoid contacts the parietal dorsally and the quadrate posteroventrally below the foramen nervi trigemini. The sutures around the foramen nervi trigemini are not clear, but there seems to be no prootic contact; the parietal enters the margin of the foramen between the pterygoid and prootic.

Structures on dorsal surface: The crista pterygoidea rises posteriorly to just anterior to the foramen nervi trigemini where it drops ventrally, and only a small part enters the foramen margin. The pterygoid bears a low, rounded ridge that is oriented anterodorsally–posteroventrally. It extends from a position anterior to the foramen nervi trigemini ventrally along the quadrate ramus paralleling the quadrate-pterygoid suture. In Phosphatochelys this ridge is larger and acute, defining a tubular space anterior to the ridge (see Phosphatochelys, Pterygoid ).

SUPRAOCCIPITAL (figs. 204, 207)

Preservation: The supraoccipital is present and nearly complete in AMNH 30563. There is some breakage along its right anterolateral margin.

Contacts: The supraoccipital in Ummulisani contacts the parietals anteriorly, the exoccipitals posteroventrally, the prootic anterolaterally, and the opisthotic posterolaterally. The sutures, however, are not clear on either side, but there is no quadrate contact, agreeing with other Taphrosphyini .

Structures: The crista supraoccipitalis in Ummulisani is a very short, blunt process, with little similarity to the usual flat, vertical plate seen in other turtles. Phosphatochelys has a short crista, but it has a clear vertical plate. Ummulisani has a low crista with a blunt posterior end that is only slightly raised above the foramen magnum. The supraoccipital in Ummulisani has a horizontal contribution to the skull roof that extends anteriorly and laterally more than in other bothremydids. Taphrosphys has a wide plate, but not as deep as in Ummulisani .

EXOCCIPITAL (figs. 204, 207)

Preservation: Both exoccipitals are present and nearly complete in AMNH 30563.

Contacts: The exoccipital in Ummulisani contacts the supraoccipital dorsally, the opisthotic laterally, the quadrate ventrolaterally, and the basioccipital ventrally.

Structures: The foramen magnum in Ummulisani is about the same as in other

Taphrosphyini . The condylus occipitalis is formed entirely by the exoccipitals. There is very little constriction to form a neck for the condyle. The foramen nervi hypoglossi consist of a larger, more medial foramen and a much smaller, more lateral one, as in other Taphrosphyini . As in Phosphatochelys , the more lateral one is very close to the foramen jugulare posterius, although in Ummulisani it is not actually within the margin of the foramen jugulare posterius as it is in Phosphatochelys . The foramen jugulare posterius is completely closed laterally by the opisthotic-exoccipital contact. The foramen is recessed, with a blunt shelf below, so that it faces more laterally than the foramen does in Phosphatochelys .

BASIOCCIPITAL (figs. 204–207)

Preservation: The basioccipital in AMNH 30563 is nearly complete.

Contacts: The basioccipital in Ummulisani contacts the basisphenoid anteriorly, the quadrate in a wide suture laterally, and the exoccipital posterolaterally.

Structures: Ummulisani has a blunt, low tuberculum basioccipitale formed by the basioccipital and exoccipital that is similar in size and extent to that in Labrostochelys and is lower than that in Phosphatochelys . There is a shallow concavity on the midline, much the same as in other Taphrosphyini .

PROOTIC (figs. 204, 207)

Preservation: Both prootics in AMNH 30563 are present and nearly complete, but some of the sutures are dim.

Contacts: The prootic in Ummulisani contacts the parietal dorsomedially, the quadrate laterally, the supraoccipital posterodorsally, and the opisthotic posteriorly.

Structures: The prootic forms a thin bar separating the foramen nervi trigemini from the foramen stapedio-temporale. In Ummulisani the two foramina are not sunk into a common recess, as in Taphrosphys , but are still very close, as in Phosphatochelys . The prootic forms most of the foramen stapedio-temporale. The foramen stapedio-temporale faces mostly anteriorly and the foramen nervi trigemini faces mostly laterally.

OPISTHOTIC (figs. 204–207)

Preservation: Both opisthotics are present in AMNH 30563. The left one is damaged along its posterolateral margin; the right one is also damaged posterolaterally and medially as well, so that some of the sutures are obscured.

Contacts: The opisthotic in Ummulisani contacts the supraoccipital anteromedially, the prootic anteriorly, the quadrate anterolaterally, the exoccipital posteromedially, and the squamosal posterolaterally, although much of this latter contact is obscured by breakage.

Structures: The opisthotic enters into the fenestra postotica (see Quadrate) and the foramen jugulare posterius. The opisthotic is part of a posterior flange that, along with the squamosal, forms a ventrally open trough similar to that seen in Labrostochelys and Taphrosphys , and, to a lesser extent, in Phosphatochelys .

BASISPHENOID (figs. 204–207)

Preservation: The basisphenoid in AMNH 30563 is present and complete ventrally. Its dorsal surface has some damage and is partially obscured by matrix.

Contacts on ventral surface: The basisphenoid in Ummulisani contacts the pterygoids anterolaterally, the basioccipital posteriorly, and the quadrate in a wide suture laterally.

Structures on ventral surface: The basisphenoid in Ummulisani is pentagonal and similar in shape to that in Taphrosphys . However, its anterior margin does have a point on the midline, similar to that in Phosphatochelys .

Contacts on dorsal surface: Not determinable.

Structures on dorsal surface: The rostrum basisphenoidale is fused into a single rod anterior to the sella turcica. The sella seems to be wide, not narrow as in Taphrosphys congolensis . The dorsum sellae seems to be damaged, but was probably higher than in T. sulcatus .

Rhothonemys brinkmani

The single skull representing this species is incomplete, lacking most of the palate and basicranium. Rhothonemys is the sister group to Phosphatochelys + Ummulisani .

PREFRONTAL (figs. 208–211)

Preservation: Both prefrontals are present in AMNH 30521, with both surfaces visible. The left prefrontal lacks its anteromedial edge and the right one has a small broken area ventrally. The right prefrontal is missing some of the ventral margin of its ventral process.

Contacts: The prefrontal in Rhothonemys contacts the maxilla anteroventrally, the frontal posteriorly, and the other prefrontal medially. There is no parietal contact, as in Phosphatochelys , or a palatine contact, as in Bothremys and Chedighaii .