Ebrachosuchus neukami, KUHN, 1936

Butler, Richard J., Rauhut, Oliver W. M., Stocker, Michelle R. & Bronowicz, Robert, 2014, Redescription of the phytosaurs Paleorhinus (‘ Francosuchus’) angustifrons and Ebrachosuchus neukami from Germany, with implications for Late Triassic biochronology, Zoological Journal of the Linnean Society 170 (1), pp. 155-208 : 180-197

EBRACHOSUCHUS NEUKAMI KUHN, 1936

‘ Ebrachosuchus neukami nov. gen. nov. spec.’; Kuhn, 1936: 77, figs 4, 5, pl. 8, 10

‘ Ebrachosuchus neukami Kuhn’; Kuhn, 1938: 318

‘ P. broilii ( Kuhn, 1933) ’; Gregory, 1962: 670, fig. 2B

‘ P. (F.) neukami O. Kuhn 1936 ’; Westphal, 1976: 109, fig. 7D

‘ Francosuchus broilii Kuhn, 1932 ’; Chatterjee, 1978: fig. 16B

‘ P. neukami Kuhn, 1936 ’; Hunt & Lucas, 1991: 489

‘ Paleorhinus neukami Kuhn, 1936 ’; Long & Murry, 1995: 36

Holotype: BSPG 1931 X 501, complete skull missing the lower jaws ( Kuhn, 1936: textfigs 4, 5, pl. 8, fig. 1a–e, pl. 10, fig. 4; Figs 9–14 ).

Locality and horizon: Bed 9 ( Kuhn, 1933, 1936) of the Ebrach quarry, Bamberg district, Upper Franconia region of northern Bavaria, Germany. Blasensandstein of the Sandsteinkeuper, laterally equivalent to the Hassberge Formation of the Middle Keuper (Late Triassic: late Carnian).

Previous diagnosis: Occiput strongly compressed dorsoventrally; orbit directed dorsally; interpterygoid vacuity large, elongate; rostral elongation extreme (prenarial length twice that of postnarial length); upper dentition with 58 teeth [i.e. in combined premaxilla and maxilla] ( Long & Murry, 1995: 36).

Emended diagnosis: Characterized by the following autapomorphic features: (1) preorbital length more than 3.8 times that of the orbit + postorbital length (convergently present in the pseudopalatine phytosaur Mystriosuchus planirostris ); (2) more than 50 teeth in the premaxilla and maxilla combined; (3) pronounced, sharp flange extending along the lateral surface of the dorsal (postorbital) process of the jugal and the ventral (jugal) process of the postorbital that is continuous posteriorly with the lateral margin of the postorbital–squamosal bar; (4) infratemporal fenestra is substantially longer anteroposteriorly than deep dorsoventrally, terminates anteriorly beneath the midpoint of the orbit; (5) quadrate foramen very large, approximately two-thirds of width of foramen magnum; (6) alveolar ridges absent from the anterior maxilla and only poorly developed on the premaxilla.

DESCRIPTION OF HOLOTYPE OF EBRACHOSUCHUS NEUKAMI

General: The skull ( Figs 9–14 ) is essentially complete (missing lower jaws) although the teeth are mostly missing and there is minor damage to some areas (e.g. lateral rims of the external nares, ectopterygoid). As in Paleorhinus angustifrons , most of the cranial sutures are tightly closed or fused. The skull has been crushed dorsoventrally, exaggerating its apparently low profile ( Figs 9C, D , 10D ). The rostrum is very long and slender, with the preorbital length being nearly 3.9 times as long as the orbit + postorbital length (skull length ∼ 635 mm; preorbital length ∼ 505 mm; orbit + postorbital length ∼ 130 mm; transverse width across squamosals = 144 mm). Among phytosaurs, a similarly elongate and slender rostrum is only known in Mystriosuchus planirostris (e.g. Hungerbühler, 1998, 2002), in which the ratio of preorbital length to orbit + postorbital length may approach 3.9–4.0 (e.g. SMNS 9134). The skull roof of Ebrachosuchus is strongly ornamented, particularly on the lateral portions of the nasals, the prefrontals, dorsal parts of the lacrimals, frontals, parietals, postfrontals and dorsal parts of the postorbitals.

Fenestral morphology: The external nares ( Figs 9 , 10A, D , 11C, D: ‘en’) have a sub-triangular outline, being broad and rounded posteriorly and tapering anteriorly. Their lateral rims (formed by the nasals) are broken on both sides, although the lateral rim is more complete on the left side. The nares face dorsally and slightly laterally. By comparison with Paleorhinus angustifrons , the nares are relatively short and broad (maximum width of the external naris is ∼60% of the narial length in Ebrachosuchus neukami and ∼33% of the narial length in Paleorhinus angustifrons ) with a much broader internarial septum. The external naris of Paleorhinus bransoni appears more similar in its proportions to Paleorhinus angustifrons than to Ebrachosuchus ( Lees, 1907; Stocker, 2010). The external nares of Ebrachosuchus are positioned notably proportionately more posteriorly than those of Paleorhinus angustifrons , Paleorhinus bransoni ( Lees, 1907; Stocker, 2010), and ‘ Paleorhinus ’ sawini ( Long & Murry, 1995): the posterior rim of the external naris in Ebrachosuchus is still positioned anterior to the anterior corner of the internal antorbital fenestra, but is only separated from it by a very short distance (c. 7 mm; see above). The posterior rims of the external nares of Ebrachosuchus are not so strongly rugose and raised as in Paleorhinus angustifrons , and, in contrast to the latter species, are not raised above the surface of the nasals.

The internal antorbital fenestra ( Figs 9 , 10A, D , 11D–F: ‘afen’) of Ebrachosuchus faces laterally and has a lenticular or eye-shaped outline (c. 43 mm long; 16 mm deep). The fenestra is absolutely and proportionally smaller than in Paleorhinus angustifrons (the anteroposterior lengths of the internal antorbital fenestra and the orbit are nearly identical in Ebrachosuchus , whereas the anteroposterior length of the internal antorbital fenestra is 140% or more of the length of the orbit in Paleorhinus angustifrons , Paleorhinus bransoni , the Krasiejów phytosaur specimens, and Parasuchus hislopi: Chatterjee, 1978 ; Dzik & Sulej, 2007; Stocker, 2010), despite the fact that the skulls of Ebrachosuchus and Paleorhinus angustifrons are closely similar in size ( Ebrachosuchus is very slightly larger, based on width across the squamosals and the orbital size). In Ebrachosuchus the antorbital fossa is greatly reduced: it is limited to an area on the lacrimal at the posteroventral corner of the internal antorbital fenestra. On the maxilla, there is only a slight transverse expansion of the anteroventral margin of the border of the internal antorbital fenestra, which might represent a remnant of the maxillary antorbital fossa. Similar reduction of the antorbital fossa occurs in ‘ Paleorhinus ’ sawini and most phytosaurids ( Stocker, 2010).

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The orbit of Ebrachosuchus ( Figs 9 , 10A, D , 11F, G: ‘orb’) faces dorsolaterally and is oval in outline (left orbit: anteroposterior length = 44 mm; dorsoventral depth = 33 mm). As in Paleorhinus angustifrons and other basal phytosaurs (see above) the ventral margin of the orbit of Ebrachosuchus is positioned slightly ventral to the dorsal margin of the internal antorbital fenestra.

The laterally and slightly dorsally facing infratemporal fenestra of Ebrachosuchus ( Figs 9 , 10A, D , 12A : ‘itf ’) is highly distinctive and differs greatly from that of Paleorhinus angustifrons and other basal phytosaur taxa. Rather than having a subquadrate outline it is strongly extended anteriorly (anteroposterior length = 68 mm; maximum dorsoventral height = 37 mm), tapering in length towards its anteroventral corner, and terminates anterior to the midpoint of the orbit. The infratemporal fenestra is therefore much larger than the orbit, contrasting strongly with the typically trapezoidal infratemporal fenestra of Paleorhinus angustifrons , Paleorhinus bransoni , the Krasiejów phytosaur specimens, ‘ Paleorhinus ’ sawini, and Parasuchus hislopi , which in all cases is subequal in size to the orbit and terminates anteriorly beneath the posterior margin of the orbit ( Chatterjee, 1978; Long & Murry, 1995; Dzik & Sulej, 2007; Stocker, 2010). By contrast, the infratemporal fenestra is greatly enlarged and extends beneath the orbit in all phytosaurids, including Angistorhinus ( Mehl, 1913, 1915), although in these taxa the infratemporal fenestra is also proportionately much deeper dorsoventrally. The most dorsal part of the infratemporal fenestra of Ebrachosuchus is positioned somewhat below the mid-height of the orbit.

The dorsally facing supratemporal fenestra of Ebrachosuchus ( Figs 9A , 10A , 11H: ‘stf’) has a teardrop-shaped outline that tapers to an apex posterolaterally. As in Angistorhinus , Brachysuchus megalodon , and non-phytosaurid phytosaurs such as Paleorhinus angustifrons (see above), the supratemporal fenestrae are in the same horizontal plane as the skull roof and completely open dorsally. Although a true supratemporal fossa is absent, the posterior temporal bars (the parietal–squamosal bars) are strongly inclined posterodorsally, so that their anterodorsal surfaces form somewhat depressed surfaces that are continuous with the posterior rims of the supratemporal fenestrae. The posterodorsally orientated parietal–squamosal bars contrast with the condition in Paleorhinus angustifrons , in which the bars are essentially vertically orientated.

The posttemporal fenestra ( Figs 9E , 10C , 12B, C : ‘ptf ’) is elongate and slit like, with margins formed by the otooccipital ventrally, and probably the squamosal and supraoccipital dorsally, although sutures are not clearly identifiable. As in Paleorhinus angusifrons , the posttemporal fenestra is placed dorsal to the foramen magnum and approximately halfway between the foramen magnum and the lateral tip of the paroccipital process. A notable groove extends medially and slightly ventrally along the supraoccipital–otooccipital suture from the posttemporal fenestra towards the dorsal margin of the foramen magnum, fading out shortly before the margin of the foramen magnum ( Fig. 12B ). A groove extending laterally from the lateral margin of the posttemporal fenestra is bordered by the overhanging squamosal shelf and the posterodorsally facing paroccipital process. Similar grooves are present in Paleorhinus angustifrons , but are less strongly defined.

No single large post-parietal foramen is present, although much smaller paired openings are present ( Fig. 12B : ‘for’) in an equivalent position to the large post-parietal foramen of Paleorhinus angustifrons (see above).

The foramen magnum ( Figs 9E , 10C , 12B : ‘fm’) is broad and oval in outline, with a straight dorsal margin, although the very low and broad shape has probably been exaggerated by dorsoventral compression of the skull. As in Paleorhinus angustifrons , the foramen magnum is bordered by the otooccipitals dorsolaterally, laterally, and ventrolaterally, with the supraoccipital forming only a small median part of the dorsal rim. Whether the basioccipital participates in the ventral margin of the foramen cannot be established with certainty, although it seems likely that any basioccipital contribution was very small.

The subtemporal fenestrae ( Figs 9B , 10B ) are also very similar to those of Paleorhinus angustifrons , in both their shape and their relative size. The suborbital fenestra ( Figs 9B , 10B , 13B, C : ‘sub’) is elongate and slit-like, with its long axis extending anterolaterally-to-posteromedially. It is proportion- ately narrower and lacks the curvature seen in Paleorhinus angustifrons . The margins of the suborbital fenestra are formed predominantly by the ectopterygoid posterolaterally and the palatine anteromedially, with the maxilla forming its lateral corner. The choanae ( Figs 9B , 10B , 13B : ‘cho’) are slit-like with rounded anterior margins, but their posterior margins appear to have broken away. The choanae are positioned medial to the antorbital fenestra and posterior to the external nares.

Premaxilla: The premaxilla is strongly compressed dorsoventrally ( Figs 9 , 10 : ‘pm’), with a dorsal surface that is gently convex transversely. The external surface is generally smooth and unornamented, with the exception of a number of longitudinally extending grooves and lineations, which are more common and clearly defined along the posterior half of the element. The interpremaxillary suture is open and the premaxillae have slightly separated from one another post-mortem such that a clear line of sediment, 3 mm thick, divides them on the dorsal surface. The anterior termination of the premaxilla is slightly downturned in lateral view, and is rounded and expanded transversely to form the terminal rosette or bulb, as occurs in many other phytosaurs. The terminal rosette ( Fig. 11A) is as wide as long, as in Paleorhinus bransoni ( Long & Murry, 1995) , the Krasiejów phytosaur specimens ( Dzik & Sulej, 2007), Parasuchus hislopi ( Chatterjee, 1978) , and Mystriosuchus westphali ( Hungerbühler, 2002) , but differing from the rosettes of Angistorhinus ( Mehl, 1915) and Pravusuchus (AMNH FR 30646; Stocker, 2010), which are wider than long. Immediately posterior to the rosette, the premaxillae of Ebrachosuchus are slightly contracted transversely in dorsal view to a minimum width of the snout of 22 mm. From this point on, the articulated premaxillae gradually expand posteriorly to a width of some 40 mm at the anterior end of the suture with the maxilla. The dorsal and ventral margins of the premaxilla are straight in lateral view along most of its length, but the dorsal margin becomes slightly concave and the ventral margin slightly convex posteriorly as the premaxilla arches gently upwards towards the external nares. There is no ‘rostral crest’, unlike the condition in most pseudopalatine phytosaurs ( Stocker, 2010). In dorsal view, the lateral margins of the premaxillae are straight.

The exact number of premaxillary teeth (none of which is preserved) is uncertain, because the exact position of the premaxilla–maxilla contact cannot be determined [there is no constriction at this contact, unlike the condition in some other phytosaurs (e.g. Hungerbühler, 2000) and no identifiable change in alveolar diameter that might correspond to the transition], and the premaxillary alveoli and palate are poorly preserved. However, there appear to be at least 30 premaxillary alveoli posterior to the terminal rosette. The terminal rosette clearly contains two large (7–8 mm diameter) alveoli that open ventrally and slightly posteriorly on the anterior margin ( Figs 11A, 14A : ‘1’, ‘2’). Posterior to these enlarged alveoli, two additional ventrolaterally opening alveoli are clearly visible in CT data ( Fig. 14A : ‘3’, ‘4’) but are poorly preserved on the external surface, and are followed by a short edentulous region (where the premaxillae are constricted transversely; Figs 11A, 14A : ‘edt’). Hungerbühler (2000) identified Ebrachosuchus as possessing a ‘bipartite’ upper dentition, in which the dentition is divided into a ‘tip-of-snout set’ and a large ‘post-tip set’, encompassing the entire post-rosette dentition. Thus, the complete premaxillary tooth count is estimated at 34–35. This count is higher than that reported for most other phytosaurs (see Gregory, 1962: table 1). The premaxillary alveoli are subcircular and gradually increase in size posteriorly: the first postrosette alveolus in the left premaxilla has a diameter of 3 mm, whereas a posterior alveolus (estimated as the 25th post-rosette alveolus) has a diameter of 6 mm. The alveoli face ventrally and slightly laterally. The teeth were well separated, with the interalveolar septa generally being at least half the anteroposterior width of the alveoli or even more; there is some irregularity in the spacing of the teeth. There also seems to be slight left–right asymmetry both in the spacing of the teeth and in the size of the alveoli, although the latter might be influenced by preservation.

On the ventral surface, the premaxillary palate is formed by medially extending shelves that have been damaged and become displaced and deformed along much of their length ( Figs 9 , 10 , 11B, 14B ). At their lateral margins, adjacent to the alveoli, these shelves are slightly thickened into weakly developed alveolar or palatal ridges along some parts of the premaxilla, but in other areas alveolar ridges appear to be absent. Alveolar ridges are also only weakly developed on the better-preserved palatal surfaces of the maxillae. The relatively weak development of the alveolar ridges distinguishes Ebrachosuchus from other phytosaurs, in which alveolar ridges are generally well developed, and is therefore considered autapomorphic. The premaxillary palate tapers in transverse width towards its posterior termination where it contacts the vomers, although sutures are difficult to trace in this area. Nevertheless, the preserved portions of the suture with the maxilla on the palate show this suture to be straight.

Dorsally, the premaxillae possess posteromedial processes ( Fig. 11C: ‘pmp’) that project between the ‘septomaxillae’ but do not appear to form any more than the anterior base of the internarial septum. This is similar to the condition in Paleorhinus angustifrons (see above). The exact nature of the contacts in the region where the premaxilla, maxilla, and nasals converge is unclear in Ebrachosuchus .

CT data show that a median premaxillary cavity similar to that of Paleorhinus angustifrons , presumably housing a pneumatic diverticulum of the antorbital air sinuses ( Witmer, 1997a), extends for the complete length of the premaxilla ( Fig. 14B : ‘mvc’). Along much of the length of the premaxilla, the bases of the alveoli are continuous with, or incomplete separated from, this cavity, and a discrete alveolar neurovascular canal (as seen along at least part of the posterior premaxilla of Paleorhinus angustifrons ) does not appear to be present, suggesting that the neurovascular bundle may have been carried within the median cavity. More posteriorly, the median sinus is continuous with the airway, external nares, and antorbital fossa. CT data indicate that each premaxilla is slightly dorsoventrally thickened adjacent to the midline interpremaxillary suture on the dorsal surface ( Fig. 14B ).

Maxilla: As in Paleorhinus angustifrons , the maxilla of Ebrachosuchus is an anteroposteriorly elongate and dorsoventrally shallow bone ( Figs 9 , 10A, D , 11E: ‘max’), although the exact positions of its sutures with the premaxilla and nasals anteriorly are unclear on the external surface. Eighteen alveoli on the left side and 19 on the right side appear to belong to the maxillae. As a result, the complete tooth count for the upper jaw of Ebrachosuchus exceeds 50; this extremely high tooth count seems to be autapomorphic for this species ( Gregory, 1962). Two complete maxillary crowns are preserved in situ in the left maxilla, and one is preserved in the right maxilla. In lateral view, the ventral margin of the maxilla is very subtly concave anteriorly, and then is nearly straight along its posterior half.

Externally, the maxilla contacts the premaxilla anteriorly, the nasal dorsally, the lacrimal posteriorly (ventrally and dorsally to the internal antorbital fenestra), and the jugal posteriorly. The maxilla forms the anteroventral and anterodorsal rims of the antorbital fenestra ( Fig. 11E) – in this area of the skull the internal and external antorbital fenestrae are essentially synonymous because no maxillary antorbital fossa is present. The maxilla is slightly thickened into a ridge where it forms the ventral rim of the antorbital fenestra. Below this ridge, the lateral surface of the maxilla is dorsoventrally concave, with the alveolar margin being drawn out laterally as a lateral ridge (best seen on the right side; the left side is distorted). The ascending process of the maxilla is slender and strongly posterodorsally directed. It slightly tapers posteriorly and meets the anterior process of the lacrimal dorsal to and at about the mid-length of the antorbital fenestra. The lateral surface of the ascending process is strongly sculptured, as is the case with the lateral parts of the nasals, prefrontals, and the dorsal part of the lacrimal. The ventral margin of the posterior half of the internal antorbital fenestra is formed by the medially inset anteroventral expansion of the lacrimal, with the suture between the lacrimal and the maxilla running along the lateral margin of the antorbital fossa.

On the ventral surface, the alveoli generally have a subcircular outline ( Fig. 13B ). All of the alveoli, with the exception of those at the posterior end of the tooth row, are similar in size, with a diameter of ∼ 7 mm. The smallest alveoli at the posterior end of the tooth row have a diameter of 4–5 mm. The consistent alveolar size along the maxillary tooth row differs from the condition in Paleorhinus angustifrons , in which there is greater heterodonty in tooth size along the maxilla (inferred from variation in alveolar size). Furthermore, the largest alveoli in Paleorhinus angustifrons are considerably larger in absolute size than those of Ebrachosuchus (9 mm vs. 7 mm in diameter), although both skulls are of closely comparable overall size. Medial to the tooth row, the alveolar ridge is almost absent, and is only indicated by a slight thickening of the medial alveolar margins in a few places. As in the premaxilla, the alveoli are well spaced, with a notably wider spacing occurring between several teeth that are placed just in front of the level of the external nares.

The maxilla is contacted by the ectopterygoid immediately posterior and medial to the last alveolus ( Fig. 13C ). The maxilla forms the anterolateral margin of the slit-like suborbital fenestra ( Fig. 13B, C ); this fenestra is more broadly separated from the maxillary alveoli than in Paleorhinus angustifrons . Anterior to the suborbital fenestra, the medial palatal margin of the maxilla is drawn out medially into a palatal flange that is elongate and triangular in outline in ventral view ( Fig. 13B ). At its broadest extent, this medial flange forms the anterolateral margin of the choana, thus separating the palatine from the anterior expansion of the vomer and the premaxilla.

‘Septomaxilla’: The ‘septomaxillae’ appear to form the anterior half of the internarial septum ( Figs 9 , 10A, D , 11C: ‘sm’). Their posterior extensions terminate anterior to the point indicated by Kuhn (1936), although the exact position of the suture with the nasals is difficult to determine. The ‘septomaxillae’ articulate with one another along the midline posteriorly, and their anterior processes terminate a short distance anterior to the external nares. They are separated from one another on the midline anteriorly by posteromedial processes of the premaxillae ( Fig. 11C), as in Paleorhinus angustifrons , the Krasiejów phytosaur specimens (ZPAL Ab III 200, 1943, Dzik & Sulej, 2007), and Paleorhinus bransoni (TMM 31100-101; Stocker, 2010). Anterolaterally, the ‘septomaxillae’ are separated from the nasals by a groove that extends anteriorly from the anterior corner of the external naris ( Fig. 11C: ‘gr’). This groove is longer than that in Paleorhinus angustifrons .

Nasals: The nasals are elongate and transversely expanded elements that form the very broad, nearly flat area (only slightly convex transversely) of the skull roof between the orbits and the external nares ( Figs 9 , 10A, D , 11C–G: ‘na’). Their maximal transverse width (c. 48.5 mm) is more than 1.7 times the transverse width of the frontals between the orbits (c. 28 mm), rather than being subequal in width as in Paleorhinus angustifrons and Paleorhinus bransoni ( Stocker, 2010) .

Anteriorly, the nasals apparently form the posterior half of the broad internarial septum and the posterior and lateral margins of the external nares, and appear to terminate at a point approximately level with the anterior termination of the ‘septomaxillae’. The internarial septum is broad and has a flattened dorsal surface. Unlike the condition in Paleorhinus angustifrons , the posterior rims of the external nares are not raised into rugose ridges and are not raised above the level of the main bodies of the nasals ( Fig. 11C). The depression on the anterior portion of the nasal immediately posterior to the naris, which is present in Paleorhinus angustifrons , is absent in Ebrachosuchus ( Fig. 11C). The nasals are broken along the lateral rims of the external nares on both sides; however, the left rim is sufficiently well preserved to indicate that this rim was raised and rugose along nearly its entire length, rather than just posteriorly as in Paleorhinus angustifrons . The posterolateral parts of the narial rims flare abruptly laterally in the posteriormost quarter of the nares, and the lateral narial rims slightly overhang the lateral surfaces of the anterior ends of the maxillae along their entire length ( Fig. 11C). Laterally, the nasal contacts the maxilla, lacrimal, and prefrontal, and is excluded from the rim of the antorbital fenestra by a maxilla–lacrimal contact. The nasals are gently convex transversely, and their external surfaces are rugosely ornamented laterally but relatively smooth at the midline internasal suture ( Fig. 11C). The exact position of the suture with the frontals is not clear, but appears to be positioned between the prefrontals some 7 mm anterior to the anterior margin of the orbit – there is some evidence for an interdigitating transverse suture at this point.

In CT data, a subtle longitudinal concavity is present on the ventral surface of each nasal ( Fig. 14E : ‘naconc’), immediately adjacent to the internasal suture, and is visible for approximately 40 mm of nasal length, beginning shortly posterior to the external nares and reaching close to the posterior margin of the internal antorbital fenestra. This concavity covers approximately half of the width of the ventral surface of each nasal; in this area, the bone is dorsoventrally thick, whereas it is notably thinner more laterally. Furthermore, the lateral margin of the concavity seems to coincide roughly with the distinction between the rugose lateral part and the more smooth medial part of the external surface of the nasal. It is not clear what soft tissue structure this concavity represents, although Walker (1961) and Witmer (1997a) identified a median concavity on the ventral surface of the nasals of the aetosaur Stagonolepis as the impression of the nasal gland. The CT data for Paleorhinus angustifrons show only a single, very subtle median concavity spanning both nasals, which is mainly marked in its posterior part and is missing the distinction between a thickened medial and thinner lateral part.

Prefrontal: The prefrontal forms the anteromedial and most of the anterior margin of the orbit ( Figs 9 , 10A, D , 11E–G: ‘prf’). It has convex lateral and medial margins in dorsal view, giving it a broadly oval outline. Its dorsal and lateral surfaces are strongly rugose and deeply pitted; as in Paleorhinus angustifrons , the prefrontal of Ebrachosuchus is one of the most strongly ornamented of the skull elements and is strongly thickened at its orbital margin. Also as in Paleorhinus angustifrons , the thickened orbital margin is distinctly offset from the rest of the surface of the bone, and a crescentic ‘pre-orbital depression’ ( Hungerbühler, 2002) is present anterior to the orbit ( Fig. 11E–G: ‘prod’). In contrast to Paleorhinus angustifrons , several irregularily arranged ridges subdivide this depression. Laterally, the prefrontal is broadly separated from the margin of the antorbital fenestra by the lacrimal. There is a small foramen in the prefrontal–lacrimal suture close to the anterior end of the prefrontal. This foramen pierces the skull roof and opens ventrally into the antorbital cavity (visible in CT data). The suture with the frontal and nasal is curved along its length.

Frontal: The anterior contact of the frontals ( Figs 9 , 10A , 11G, H: ‘fr’) with the nasals is poorly defined but is placed between the prefrontals (see above). The paired depressions present on the anterior frontals of Paleorhinus angustifrons are absent in Ebrachosuchus . Laterally the frontal forms clear sutures with the pre- and postfrontal, and contributes to the dorsomedial rim of the orbit. Posteriorly the frontals form a transversely extending interdigitated suture with the parietals. The dorsal surfaces of the frontals are covered with rugose and pitted ornamentation similar to that of the prefrontal and other skull roof bones. Transversely, the frontals are slightly raised at the midline interfrontal suture, concave lateral to this suture, and then strongly raised and thickened at their orbital margins, much more so than in Paleorhinus angustifrons . The width of the frontals between the orbits is relatively narrow: it is approximately equal to the transverse width of the parietals. By contrast, in Paleorhinus angustifrons and the Krasiejów phytosaur specimens (ZPAL Ab III 200, Dzik & Sulej, 2007) the frontals are substantially broader than the transversely narrow parietal. In CT data a marked transverse concavity for the olfactory bulbs is visible on the ventral surface of the frontals ( Fig. 14H ).

Lacrimal: The lacrimal forms the anteroventral margin of the orbit and the posteroventral, posterior, and posterodorsal rims of the internal antorbital fenestra, contacting the maxilla both dorsal and ventral to the fenestra ( Figs 9 , 10A, D , 11E–G). The lacrimal additionally contacts the prefrontal and nasal dorsally, and the jugal ventrally. The lacrimal is extensively excavated on its lateral surface by the antorbital fossa, which is deepest anteriorly and shallows posteriorly. The posterior margin of the lacrimal antorbital fossa is not defined by a sharp rim, but rather merges smoothly with the lateral surface of the lacrimal adjacent to the orbit. The lateral surface of the lacrimal adjacent to the orbit has a smooth surface texture, but more dorsally and anteriorly the lacrimal is rugose and forms a rim that overhangs the antorbital fossa. The contact of the lacrimal with the maxilla appears to run anteroposteriorly, and is positioned medial to the ridge on the maxilla that forms the ventral margin of the antorbital fossa and fenestra. The nasolacrimal foramen is visible in CT data on the internal surface of the orbit just ventral to the midheight of the orbit, and is placed on the suture between the lacrimal laterally and the prefrontal medially. The narrow nasolacrimal canal extends anteriorly within the lacrimal ( Fig. 14F : ‘lccn’), exiting the lacrimal dorsomedially, just posterior to the posterior rim of the internal antorbital fenestra. Two smaller canals branch off the main nasolacrimal canal ( Fig. 14F ), one exiting laterally just ventral to the dorsal rim of the lacrimal antorbital fossa, and one exiting ventrally. CT data also demonstrate that the medial margin of the lacrimal has a strongly developed ventral flange ( Fig. 14F : ‘lcfl’), medioventral to the nasolacrimal canal. This flange defines a clearly defined and deep ventral fossa on the lacrimal, into which the second of the small canals extending from the nasolacrimal duct opens. Anteriorly, this flange converges upon and merges with the main body of the lacrimal medial to the lacrimal antorbital fossa. Posteriorly, this flange is continuous with a low ridge on the ventral surface of the prefrontal. A similar medioventral flange of the lacrimal is not present in Paleorhinus angustifrons .

Jugal: The triradiate jugal has a distinctive morphology that reflects the anterior extension of the infratemporal fenestra beneath the orbit ( Figs 9 , 10A, D , 11F, 12A ). The dorsal process of the jugal begins anterior to the midpoint of the orbit and extends primarily posteriorly and slightly dorsally. Rather than facing laterally, the dorsal process of the jugal is twisted along its length to face primarily dorsally and is expanded transversely. Its lateral margin forms a sharp flange that overhangs the infratemporal fenestra and that is continuous with a similar flange on the lateral margin of the postorbital ( Fig. 11F: ‘por’). The dorsal process forms the ventral and posteroventral margins of the orbit and the anterodorsal corner of the rim of the infratemporal fenestra. The dorsal process is overlapped dorsally by the ventral process of the postorbital. As in Paleorhinus angustifrons and some other phytosaurs (see above), the infratemporal fenestra extends as a shallow fossa onto the jugal at the point at which the dorsal process of the jugal connects to the posterior process of the jugal ( Fig. 11F: ‘fo’). In Ebrachosuchus , the margin of this fossa is defined by a sharp ridge (preserved on the left jugal; the right jugal is reconstructed in this region) that is continuous with the lateral flange of the dorsal process, unlike the subtle break-in-slope present in Paleorhinus angustifrons . A shallow, triangular depression extends anterior to this ridge on the lateral side of the jugal below the lacrimal antorbital fossa ( Fig. 14G : ‘jgfo’), being separated from the lacrimal antorbital fossa by a broad, swollen area at the suture between the lacrimal and jugal.

The elongate posterior process of the jugal is shallow dorsoventrally ( Fig. 12A ), much shallower relative to its length than in other basal phytosaurs (e.g. Dzik & Sulej, 2007; Stocker, 2010) including Paleorhinus angustifrons . The posterior process forms the anterior half of the ventral margin of the infratemporal fenestra, and tapers posteriorly. It forms an elongate, posteroventrally sloping suture with the quadratojugal and terminates anterior to the quadrate. Its lateral surface is reconstructed on the left side.

The short and dorsoventrally deep anterior process of the jugal contacts the maxilla along a deep anterodorsally-to-posteroventrally extending suture, which begins at the posteroventral corner of the antorbital fenestra and reaches to the posterior end of the maxillary tooth row. The anterior process also forms an elongate posterodorsally-to-anteroventrally extending suture with the lacrimal, although the exact position of this suture is unclear; it probably coincides with the ventral margin of the lacrimal antorbital fossa. The lateral surface of the anterior process is rugose, and possesses a strong anteroposteriorly extending ridge ( Fig. 14G : ‘jgri’) ventral to the concavity described above, which is continuous with the posterior process of the jugal; this ridge is similar to that present in Paleorhinus angustifrons . However, Ebrachosuchus lacks the discrete row of nodes on the lateral surface of the jugal that is present in Paleorhinus angustifrons .

Medially, the jugal is contacted by the ectopterygoid adjacent to the jugal–maxilla contact as in other phytosaurs ( Fig. 13C ). The medial surface of the jugal is not visible due to sediment infilling the subtemporal fenestra.

In CT data, an anteroposteriorly extending canal is visible within the jugal ( Fig. 14G : ‘jgc’), as in Paleorhinus angustifrons (see above). Anteriorly, this canal enters the bone from the dorsomedial side adjacent to the ectopterygoid–jugal contact, a short distance posterior to the last maxillary alveolus and lateral to the midpoint of the suborbital fenestra. It extends posterolaterally into the jugal for less than 10 mm, and exits the bone via a ventral and posteriorly facing opening situated on the suture between the posterolateral process of the ectopterygoid (see below) and the jugal ( Fig. 13C : ‘for’). The canal differs from that preserved within the jugal of Paleorhinus angustifrons in being relatively shorter, and in not extending as a groove along the medial surface of the posterior process of the jugal. In addition, there do not appear to be additional narrower canals branching off the main canal in Ebrachosuchus , unlike the condition in Paleorhinus angustifrons (see above).

Postorbital: The postorbital is triradiate with long anterior and posterior processes and a short and broad medial process ( Figs 9 , 10A, D , 11F, H, 12A : ‘po’). It is ornamented on its dorsal surface with small, irregular pits. This ornamentation becomes less marked towards the sutures with the jugal, squamosal, and parietal. The postorbital forms the majority of the posterior rim of the orbit (where it is not strongly thickened relative to the rest of the bone), the anterodorsal rim of the infratemporal fenestra, and the anterolateral rim of the supratemporal fenestra. The ventral (descending) process of the postorbital is directed more anteriorly than ventrally, and is folded outwards at its lateral margin so that it forms a partly dorsally facing and nearly horizontal surface. The lateral margin of this horizontal surface of the ventral process forms a sharply developed flange that overhangs the anterodorsal part of the infratemporal fenestra ( Figs 11F, 12A : ‘por’) and is continuous with a flange on the dorsal process of the jugal (see above) and the anterior process of the squamosal. The ventral process becomes thickened dorsoventrally towards the orbital margin. CT data show that the ventral process of the postorbital is very massive at its base.

The interdigitating contact between the postorbital and the postfrontal is best seen on the right side, with the suture curving posteromedially away from the orbital rim. The postfrontal suture forms approximately two-thirds of the medial sutural contacts of the postorbital. With the parietal, the medial process of the postorbital forms a short, anteroposteriorly extending suture anterior to the most anterior point of the supratemporal fenestra. The posterior process of the postorbital terminates approximately at the level of the posterior margin of the infratemporal fenestra. The postorbital–squamosal bar is slightly more expanded transversely than in Paleorhinus angustifrons , with its lateral margin being developed into a distinct flange, continuous with the lateral flange of the ventral process, which overhangs the infratemporal fenestra ( Fig. 14A ). The posterior process of the postorbital tapers to a rounded tip in dorsal view in Ebrachosuchus , and this point appears to fit into a slot in the anterior process of the squamosal, as in other basal phytosaurs (see above). The postorbital–squamosal bar is strongly compressed dorsoventrally.

The medial surface of the postorbital is not exposed. CT data suggest that contact between the laterosphenoid and postorbital is absent.

Postfrontal: The postfrontal is a nearly circular element that forms the posteromedial rim of the orbit, contacting the postorbital laterally and posterolaterally, the parietal posteromedially, and the frontal anteromedially ( Figs 9 , 10A , 11H: ‘pof ’). Its external surface is strongly rugose on the medial side of the bone, but smooth towards the postorbital contact. It is thickened and slightly raised at its orbital margin. CT data suggest that at least a point contact between the laterosphenoid and the postfrontal is present ventrally.

Parietal: The parietals contact the postorbitals laterally, the postfrontals anterolaterally, and the frontals anteriorly, and form the medial, anteromedial, and much of the posterior rims of the supratemporal fenestrae ( Figs 9 , 10A , 11H). Posteriorly, they contact the supraoccipital on the occiput and have long posterolateral processes for the contact with the squamosal. The dorsal surfaces of the parietals are strongly ornamented, with a shallow, broad fossa present on each parietal anteriorly, and a deeper arcuate pit present on each parietal posteriorly ( Fig. 11H: ‘dpa’). The parietals are slightly thickened at their medial margins where they articulate with one another, although there is no development of a distinct sagittal crest. A parietal foramen is absent. The main bodies of the parietals expand laterally anteriorly, forming the anteromedial rims of the supratemporal fenestrae. The dorsal surface of the parietal forms a sharp, overhanging edge above the lateral braincase wall on the medial margin of the supratemporal fenestra. This morphology is mainly caused by the presence of a marked depression on the parietal–prootic suture on the lateral braincase wall. Posteriorly, the posterolateral corner of each parietal is drawn out to form the parietal components of the parietal–squamosal bars, which, as described above, are strongly inclined posterodorsally, so that their anterodorsal surfaces form somewhat depressed surfaces that are continuous with the posterior rims of the supratemporal fenestrae. The posterolateral parietal wing dorsally overlaps a medial process of the squamosal, and tapers to a point posterolaterally. It extends laterally up to the level of the lateralmost point of the supratemporal fenestra.

In posterior view, the posterolateral wings of the parietals form the dorsal margin of the occiput, which they slightly overhang posteriorly. They contact the supraoccipital along most of their length, but laterally each wing overlaps a medial process of the squamosal. Whether the posterolateral wings contribute to the dorsal margins of the posttemporal fenestra is unclear. Medially, the parietals appear to form the dorsal margins of the paired small postparietal fenestrae.

Squamosal: As in Paleorhinus angustifrons , the squamosal possesses four processes (postorbital, parietal, anteroventral, opisthotic), but lacks a posterior process extending posteriorly beyond the paroccipital process of the opisthotic ( Figs 9 , 10 A, C, D , 11H, 12A, C : ‘sq’).

The postorbital process of the squamosal forms the posterior part of the postorbital–squamosal bar, the posterodorsal margin of the infratemporal fenestra, and the posterolateral rim of the supratemporal fenestra. The postorbital–squamosal bar is strongly compressed dorsoventrally and expanded transversely. In dorsal view, its anterior end is forked, with the lateral processes almost reaching the level of the anterior end of the supratemporal fenestra, whereas the medial process ends just posterior to the midlength of this opening. There is a shallow concavity on the dorsal surface of the squamosal, lateral to the contact between its parietal and postorbital processes, but Ebrachosuchus lacks the well-developed, anteroposteriorly extending furrow that is present in Paleorhinus angustifrons , Paleorhinus bransoni (TMM 31025-172; Stocker, 2010), and the Krasiejów phytosaur specimens (ZPAL Ab III 200, Dzik & Sulej, 2007). Most of the dorsal ornamentation is placed within this concavity, whereas the rest of the surface of the squamosal is rather smooth. The lateral edge of the postorbital–squamosal bar is a sharp flange that overhangs the infratemporal fenestra and extends along the lateral margins of the postorbital and squamosal to reach the most posterolateral corner of the squamosal. This ridge does not bifurcate posteriorly, unlike the condition in Paleorhinus angustifrons , referred specimens of Paleorhinus bransoni ( Stocker, 2010: fig. 9), and the Krasiejów phytosaur specimens (ZPAL Ab III 200, Dzik & Sulej, 2007), but it is somewhat thickened in this region.

The main body of the squamosal is dorsoventrally shallow in lateral view, as in other basal phytosaurs (e.g. Paleorhinus bransoni, TMM 31025-172; the Krasiejów phytosaur specimens, ZPAL Ab III 200). In lateral view, the squamosal extends beyond the quadrate head posteriorly, but only slightly posterior to the quadrate condyles. In dorsal view, the squamosal tapers posterolaterally but is rounded, rather than pointed at its posterolateral corner as occurs in Paleorhinus angustifrons . The squamosal is drawn out posteroventrally into a short opisthotic process ( Fig. 12A, C : ‘opsq’), the posterior surface of which articulates with the paroccipital process and extends slightly further laterally than the latter.

The anteroventral process of the squamosal tapers along its length and forms nearly the entire posterior margin of the infratemporal fenestra, articulating with the quadratojugal ventrally and the quadrate posteriorly ( Fig. 12A : ‘avpsq’). The anteroventral process is transversely compressed, smooth, and unornamented on its lateral surface. Dorsally, the process is separated from the dorsal surface of the squamosal by the lateral ridge extending posteriorly from the dorsal rim of the infratemporal fenestra, which laterally overhangs the base of the anteroventral process.

Medially, the parietal process forms the most posterolateral part of the parietal–squamosal bar and at least the lateral part of the dorsal margin of the slit-like posttemporal fenestra. The process tapers medially, and is dorsally overlapped by the posterolateral wing of the parietal. The parietal process reaches almost to the medial margin of the supratemporal fenestra. The contacts of the squamosal with the supraoccipital and parietal above the posttemporal fenestra on the occiput are unclear.

Quadratojugal: The quadratojugal is a hook-shaped element ( Figs 9 , 10A, D , 12A : ‘qj’) that has an elongate, dorsoventrally compressed, tapering anterior process (broken off on the left side and reconstructed, but complete on the right side), which forms the posterior half of the ventral rim of the infratemporal fenestra. The process articulates with the posterior process of the jugal along an elongate anterodorsalto-posteroventrally inclined suture. The posterior process of the jugal overlaps the ventral part of the quadratojugal laterally and ends at about the level of the ventral process of the squamosal, a short way anterior to the quadrate condyles. The lateral surface of the anterior process of the quadratojugal is gently concave dorsoventrally, and it is thickened slightly at its dorsal margin. Posteriorly, the quadratojugal contacts the quadrate, separating it from the jugal. Dorsally the quadratojugal articulates with the anteroventral process of the squamosal, and forms a small ventral part of the posterior margin of the infratemporal fenestra. Posterodorsally it articulates with a laterally extending tongue of the quadrate that forms the roof of the quadrate foramen ( Fig. 12C : ‘ltqd’). The quadratojugal forms the lateral margin of the large, posteriorly facing, quadrate foramen ( Fig. 12A, C : ‘qf ’), which is considerably larger than that of Paleorhinus angustifrons or other phytosaurs. In Ebrachosuchus the quadrate foramen is ∼66% of the width of the foramen magnum, whereas it is 50% or less in other phytosaurs including Paleorhinus angustifrons , Mystriosuchus westphali ( Hungerbühler, 2002, GPIT 261/001), Angistorhinus grandis ( Mehl, 1915, FMNH UC 631), and Parasuchus hislopi ( Chatterjee, 1978) . The enlargement of the quadrate foramen appears therefore to be autapomorphic for Ebrachosuchus . On the right side, a short, narrow canal is present within the quadratojugal anterolateral to the quadrate foramen, and opens medially into the subtemporal fenestra (visible in CT data).

Quadrate: The main body of the quadrate is triangular in posterior view ( Figs 9E , 10C , 12C : ‘qd’), being transversely expanded at the ventral margin to form the articular condyles for the mandible and becoming narrower dorsally where it is tightly sutured with the squamosal and the paroccipital process. The dorsal end of the bone is remarkably broad and CT data show that it contacts the ventral surface of the squamosal in a saddle-shaped suture, with a broader medial condyle being separated from a lateral condyle by a marked concavity. At the mandibular articulation, the medial condyle extends slightly further ventrally in posterior view than does the lateral condyle ( Fig. 12C : ‘qdc’). The width of the skull across the quadrate condyles (185 mm) is greater than that across the squamosals (145 mm), giving the skull a somewhat trapezoidal outline in posterior view. In ventral view the quadrate condyles are anteroposteriorly narrow, and their articular surface appears somewhat saddle-shaped, with shallow medial and lateral concavities separated by a median convexity, although this morphology has probably been distorted by crushing. As in Paleorhinus angustifrons , the medial condyle is set slightly more posteriorly than the lateral condyle.

The quadrate articulates laterally with the quadratojugal and forms the ventral, medial, and dorsal margins of the quadrate foramen. The dorsal margin of the foramen is formed by a lateral flange of the quadrate that articulates with the quadratojugal and the anteroventral process of the squamosal ( Fig. 12C : ‘ltqd’). Medial to the foramen the main body of the quadrate is thickened. The quadrate foramen passes directly anteriorly through the skull, opening into the subtemporal fenestra (visible in CT data).

The pterygoid wing of the quadrate extends anteromedially as a robust flange ( Fig. 12C : ‘ptqd’). It forms an extensive suture with the posterior wing of the pterygoid, with the pterygoid medially overlapping the quadrate. The ventral margin of the pterygoid wing is placed dorsal to the quadrate condyles and is flexed medially, to form an expanded medial shelf that extends along the full length of the pterygoid–quadrate plate. In ventral view, the articulation of the quadrate with the pterygoid along the pterygoid–quadrate plate is marked by a small swelling. Dorsal to the medial shelf, the medial surface of the pterygoid wing is strongly concave dorsoventrally.

Pterygoid and epipterygoid: The posterior wing or quadrate process of the pterygoid ( Figs 9 , 10B , 13A, C : ‘pt’) curves posterolaterally from the midline, and its lateral surface overlaps the pterygoid wing of the quadrate. The posterior wing is strongly concave dorsoventrally in medial or posterior view ( Fig. 12C ), and its ventral margin is drawn out posteromedially as a horizontal medial shelf that is continuous with the medial shelf of the ventral margin of the pterygoid wing of the quadrate. Unlike the situation in Paleorhinus angustifrons , the wing does not appear to be strongly forked at its posterior margin. At the proximal end of the posterior wing of the pterygoid, the pterygoid is drawn out medially to form a subquadrangular, medially extending plate ( Fig. 13A : ‘mppt’), the posteromedial corner of which is slightly drawn out posteriorly (best preserved on the right side) as in Paleorhinus angustifrons . The posterior part of this medial plate forms a cup-like articulation on its dorsal surface for the anteroposteriorly broad basipterygoid process of the basisphenoid. As in Paleorhinus angustifrons , an interpterygoid vacuity is present, through which the cultriform process of the parabasisphenoid can be seen, although this vacuity is wider and extends further anteriorly in Ebrachosuchus neukami (see below) and so proportionally more of the cultriform process is exposed.

Anterior to the basipterygoid articulation, a short lateral flange of the pterygoid extends anterolaterally and ventrally to contact the ectopterygoid and palatine ( Fig. 13A : ‘lfpt’); the posterolateral extremity of this flange is missing on both sides. Medial and anterior to this, flanges of the pterygoid extend dorsomedially to form the roof of the palate, and articulate with one another along the midline ( Fig. 12A, C : ‘afpt’). These anterior flanges have been damaged badly and mostly lost, so their articular contacts with the palatines are unknown. Posteriorly, they are offset sharply dorsally from the basipterygoid articulation by a curved ridge extending from this articulation laterally onto the lateral flange of the pterygoid. At their medial margins the anterior flanges are markedly thickened into sharp ridges that arise from the medial edges of the medial sheets that form the basicranial articulation, as in Paleorhinus angustifrons . These ridges are continuous anteriorly with the ridges of the vomers. The anterior flanges are broadly separated from one another for at least 50% of their length, rather than tightly appressed to each other as in Paleorhinus angustifrons . CT data show that these thickened medial parts of the pterygoid anterior flanges are also drawn out dorsally into short curved sheets that extend either side of the cultriform process ( Fig. 14G, H ). The nature of the contact between the vomers and the anterior flanges of the pterygoids is not clear.

CT data indicate that the epipterygoid is at least partially preserved on the right side. It articulates dorsally with a cup-like depression on the ventral margin of the laterosphenoid, and ventrally with the pterygoid, immediately anterior to the basipterygoid articulation. The element is a thin, triangular sheet of bone that seems to be somewhat inclined anteriorly.

Ectopterygoid: The ectopterygoids ( Figs 9 , 10B–D , 13C : ‘ect’) are damaged along their posterior margins and adjacent to their contacts with the pterygoids. The ectopterygoid extends anterolaterally as a broad bar of bone from its medial contact with the pterygoid and palatine to its lateral contact with the posterior end of the maxilla and the adjacent anterior part of the jugal. The ectopterygoid forms the entire posterior margin of the suborbital fenestra and the anterior margin of the subtemporal fenestra ( Fig. 13C ). On the right side, a narrow slit-like depression, smaller than that of Paleorhinus angustifrons , is present adjacent to the pterygoid–ectopterygoid contact, and forms a shallow, blind pit that does not extend extensively into the ectopterygoid ( Fig. 13C : ‘?ectf ’). At its distal end, the ectopterygoid is considerably expanded anteroposteriorly, and as a result has a more extensive contact with the medial surface of the jugal than in Paleorhinus angustifrons . Whereas the anterior expansion is robust, the posterior expansion is thin and rod-like ( Fig. 13C : ‘ppect’), and forms the medial border of the foramen in the jugal–ectopterygoid suture described above.

Palatine: The palatine ( Figs 9B , 10B , 13B, C : ‘pal’) is elongate with a main body that is orientated horizontally, forming most of the lateral region of the posterior portion of the palate. This horizontal main body forms a medially convex shelf with a sharply defined medial margin in ventral view that narrows the palatal vault and more strongly approaches the opposing palatine than in Paleorhinus angustifrons . This medial margin forms a projecting ridge that separates the lateral part of the palatine from the dorsomedial wing. Posteriorly, the palatine articulates with the pterygoid and ectopterygoid adjacent to the pterygoid/ectopterygoid suture and forms the entire anteromedial margin of the suborbital fenestra. Medially, the dorsomedial wings of the palatines appear to have broken away, and thus no contacts with the pterygoids are visible. Anterior to the suborbital fenestra the palatine tapers in transverse width as it articulates with a medially extending shelf of the maxilla ( Fig. 13B : ‘atpal’). This maxillary shelf excludes contact between the premaxilla and palatine.

Vomer: The vomers form the septum separating the choanae ( Figs 9B , 10B , 13B : ‘v’); anteriorly they are expanded to form a plate that contacts the maxilla and premaxilla, although the contacts in this area are unclear. The positions of the posterior contacts with the pterygoid are not clear.

Supraoccipital: The external surface of the supraoccipital faces posterodorsally ( Figs 9E , 10C , 12B : ‘so’), and is broadly exposed dorsally posterior to the parietal–squamosal bars. There is a low median ridge in the dorsalmost third of the bone that becomes less pronounced posteroventrally; either side of this ridge the surface of the supraoccipital is gently concave. Dorsally, the supraoccipital articulates with the main body of the parietal and the parietal component of the parietal–squamosal bar. Unlike the condition in Paleorhinus angustifrons , there is no large foramen at the junction between the supraoccipital and the parietals, although notable depressions are present in this area; however, CT data suggest that very narrow slit-like foramina exit the bone immediately ventral to the parietal–supraoccipital contact, on either side of the median ridge within the depressions and open anteriorly into a sinus dorsal to the endocast. Ventrally, the supraoccipital is thickened into a low, transversely extending ridge along the extensive articulation with the opisthotic. The supraoccipital forms only a small median part of the dorsal margin of the foramen magnum. At its most lateral corners, the supraoccipital forms the medial rim of the slit-like posttemporal fenestra. There is no sign of separate interparietal or tabular ossifications.

Otooccipital: The exoccipital portions of the otooccipitals (see discussion above) form the lateral and dorsolateral margins of the oval foramen magnum as well as most of the ventrolateral margin ( Fig. 12B : ‘oto’), although the contacts with the basioccipital are unclear. The parts lateral to the foramen magnum are offset from the dorsal portions by a posterior ridge that is continuous with the ventral margin of the paroccipital processes. On the lateral surface of the opisthotic portion, the metotic fissure and fenestra ovalis are visible as deep recesses separated by the ventral process of the opisthotic. The fenestra ovalis is placed more anteriorly and is roofed over dorsolaterally by a strongly expanded otosphenoidal crest (crista prootica), which continues anteroventrally towards the basisphenoid. A short and narrow stapedial groove is present lateral to the fenestra ovalis on the broad ventral surface of the paroccipital process. A large depression is present below the fenestra ovalis in the ventral part of the otosphenoidal crest; the internal carotid might have entered the braincase through a foramen (which is not visible) within this depression. The metotic fissure seems to be at least partially subdivided by a posterior projection of the opisthotic into a smaller dorsal and a larger ventral opening, the former corresponding to the foramen lacerum posterius for cranial nerves IX–XI, whereas the latter represents the jugular foramen. Posterior to the metotic fissure and separated from it by a low lateral ridge is a triangular depression on the lateral side of the neck of the occipital condyle, in which the foramen for cranial nerve XII is probably placed.

The paroccipital processes of the opisthotics extend posterolaterally ( Fig. 10C , 12C : ‘par’), with their external surfaces facing posterodorsally and broadly exposed in dorsal view, substantially more so than in Paleorhinus angustifrons . At their bases, the processes are anteroposteriorly expanded and dorsoventrally shallow, but distally they become more compressed anteroposteriorly and gently expanded dorsoventrally, with their tips being gently rounded in posterior view. The paroccipital process forms the ventral margin of the elongate, slit-like posttemporal fenestra. Laterally, the paroccipital process forms a suture with the quadrate along the anterior margin of the process. Distally, the paroccipital process is buttressed by the opisthotic process of the squamosal.

Basioccipital and parabasisphenoid: The basioccipital ( Figs 9B, E , 10B, C , 13A : ‘bo’) forms most of the dorsoventrally crushed occipital condyle, the ventral surface of which is transversely convex. The neck of the basioccipital separates the condyle from the basitubera, but it is only a few millimetres narrower than the widest point of the condyle. Anteroventrally, the basioccipital flares laterally to form the basioccipital tubera, which form the most posterior parts of the basitubera ( Fig. 13A : ‘bt’). The basitubera are separated posteriorly by a broad incision ( Fig. 13A : ‘slt’), but connected to one another on the ventral midline by a low transverse ridge of the basisphenoid.

The basitubera are expanded broadly, being mediolaterally wider than the occipital condyle, and extend slightly ventral to the condyle. They are proportionally larger, more robust, and broader than in Paleorhinus angustifrons : in Ebrachosuchus the mediolateral width of the basitubera is greater than the mediolateral width of the articular condyles of the left quadrate, whereas the basitubera are substantially narrower than the articular condyles of the quadrate in Paleorhinus angustifrons . The basitubera are flattened along their posteroventral surfaces, presumably for muscle attachment, although this might be a result of crushing.

The basisphenoid is an anteroposteriorly compressed element that is expanded transversely at its anterior and posterior ends; posteriorly it forms the anterior part of the basitubera, whereas anteriorly the basipterygoid processes extend laterally, ventrally, and slightly posteriorly to articulate with the pterygoid. The processes thus face anterolaterally and are much broader anteroposteriorly than in Paleorhinus angustifrons . The transverse width across the basitubera is slightly greater than the transverse width across the basipterygoid processes. There is a shallow concavity that covers the ventral midline of the basisphenoid adjacent to the contact with the basioccipital ( Fig. 13A : ‘conc’); this concavity is broader than long, rather than being subcircular as in Paleorhinus angustifrons , reflecting the anteroposterior compression of the basisphenoid. The depression is connected to the ventral surface of the cultriform process of the parasphenoid anteriorly by a broad ventral groove.

Anterior to the main body of the basisphenoid, the elongate cultriform process extends anterodorsally as a narrow process of the parabasisphenoid. Its anterior termination is hidden by the pterygoids, but CT data show that, as in Paleorhinus angustifrons , it has a V-shaped cross section and terminates a short distance posterior to the end of the maxillary tooth rows.

Dentition: Three maxillary teeth are preserved in situ, two in the left maxilla (one from the anterior part of the maxilla and one from the middle part) and one in the posterior half of the right maxilla, although none is well preserved. The maxillary teeth are similar in size to one another (total crown heights of approximately 10–12 mm), despite their differing positions along the tooth row, and are apicobasally short and robust. The apices of the crowns are curved both posteriorly (recurved) and medially. The posterior crown in the right maxilla possesses carinae that cover nearly the entire crown height on the mesiolingual and distolabial surfaces, but preservation is not sufficient to recognize the presence or absence of serrations.

Figures

Figure 9. Ebrachosuchus neukami Kuhn, 1936, BSPG 1931 X 501. Photographs of holotype skull in dorsal (A), ventral (B), left lateral (C), right lateral (D), and posterior (E) views. Asterisks show positions of transverse sections shown in Figure 14.

Figure 10. Ebrachosuchus neukami Kuhn, 1936, BSPG 1931 X 501. Interpretive line drawings of holotype skull in dorsal (A), ventral (B), posterior (C), and left lateral (D) views. Dark grey areas represent sediment. Light grey areas represent recessed areas of bone (antorbital fossa). Cross hatched areas are broken or restored surfaces. Abbreviations: afen, antorbital fenestra; afos, antorbital fossa; bo, basoccipital; bsp, basisphenoid; bt, basal tubera; cho, choana; cr, crown; ect, ectopterygoid; en, external naris; fm, foramen magnum; fo, fossa; fr, frontal; itf, infratemporal fenestra; jg, jugal; lc, lacrimal; max, maxilla; na, nasal; orb, orbit; pa, parietal; pal, palatine; par, paroccipital process; pm, premaxilla; po, postorbital; pof, postfrontal; prf, prefrontal; pt, pterygoid; ptf, posttemporal foramen; qd, quadrate; qf, quadrate foramen; qj, quadratojugal; sm, ‘septomaxilla’; so, supraoccipital; sq, squamosal; stf, supratemporal fenestra; sub, suborbital fenestra; v, vomer.

Figure 12. Ebrachosuchus neukami Kuhn, 1936, BSPG 1931 X 501. Close-up photographs of holotype skull. A, left infratemporal region in lateral view. B, foramen magnum and supraoccipital in posterior view. C, quadrate and distal end of paroccipital process in posterior view. Abbreviations: avpsq, anteroventral process of the squamosal; bo, basioccipital; bt, basal tuber; fm, foramen magnum; fo, fossa; for, foramina; itf, infratemporal fenestra; lfqd, lateral flange of the quadrate; opsq, opisthotic process of the squamosal; orb, orbit; oto, otooccipital; par, paroccipital process; po, postorbital; por, ridge along lateral margin of postorbital; ptf, posttemporal foramen; ptqd, pterygoid wing of the quadrate; qd, quadrate; qdc, quadrate condyles; qf, quadrate foramen; qj, quadratojugal; sq, squamosal; stf, supratemporal fenestra.

Figure 13. Ebrachosuchus neukami Kuhn, 1936, BSPG 1931 X 501. Close-up photographs of holotype skull. A, braincase and posterior palate in ventral view. B, choanae, vomers, and palatines in ventral view. C, right ectopterygoid, suborbital fenestra, and surrounding areas in ventral view. Abbreviations: afpt, anterior flange of the pterygoid; atpal, anterior termination of the palatine; bpt, basipterygoid process; brk, broken surface of palatal; bt, basal tuber; cho, choana; clt, cultriform process; conc, concavity on ventral surface of basisphenoid; dep, depression; ect, ectopterygoid; ectf, ectopterygoid foramen; for, foramen; ft, flattened posterior surface of basal tuber; lfpt, lateral flange of pterygoid; max, maxilla; mppt, medial process of pterygoid; occ, occipital condyle; pal, palatine; par, paroccipital process; pm, premaxilla; ppect, posterior process of ectopterygoid; qdpt, quadrate process of pterygoid; slt, median slot on basioccipital between basal tubera; stgr, stapedial groove; sub, suborbital fenestra; v, vomer.

Figure 14. Ebrachosuchus neukami Kuhn, 1936, BSPG 1931 X 501. A, cross section (from CT data) through premaxillary rosette. B–H, series of transverse cross sections (from CT data) in posterior view moving from anterior (B) to posterior (H). Positions of sections are shown in Figure 9. B, section across the premaxillae approximately 60 mm anterior to the external nares. C, section across the rostrum at a point level with the anterior end of the external nares. D, section across rostrum, immediately posterior to external nares. E, section across rostrum, choanae, and antorbital fenestra, at approximate midpoint of antorbital fenestra. F, section across frontal, prefrontal, lacrimal, and jugal, a short distance anterior to the anterior margin of the orbit. G, section across the anterior margin of the orbit. H, section across orbits at their midpoint. Bone is white to light grey in colour, sediment and reconstructed bone is dark grey in colour, air is black. Abbreviations: afen, antorbital fenestra; alv, alveolus; cho, choana; clt, cultriform process; cr, crown; ect, ectoptergoid; edt, edentulous region of premaxilla; en, external naris; fr, frontal; intpms, interpremaxillary suture; itf, infratemporal fenestra; jg, jugal; jgc, canal within body of jugal; jgfo, fossa on lateral surface of jugal; jgri, ridge on lateral surface of jugal; lc, lacrimal; lccn, lacrimal canal, with smaller canals branching off it ventrally and laterally; lcfl, medial flange of the lacrimal; max, maxilla; mcv, median cavity; na, nasal; nacon, concavity on ventral surface of nasal; nvc, neurovascular canal; orb, orbit; pal, palatine; pm, premaxilla; po, postorbital; prf, prefrontal; prod, pre-orbital depression; pt, pterygoid; sep, ‘septomaxilla’; sub, suborbital fenestra; v, vomer. Numbers indicate tooth positions in the premaxillary rosette.