Ctenomastax parva, KEQIN & NORELL, 2000

KEQIN, GAO & NORELL, MARK A., 2000, Taxonomic Composition And Systematics Of Late Cretaceous Lizard Assemblages From Ukhaa Tolgod And Adjacent Localities, Mongolian Gobi Desert, Bulletin of the American Museum of Natural History 2000 (249), pp. 1-118 : 11-32

IGUANIDAE (SENSU LATO: NONACRODONTAN IGUANIANS)

Ctenomastax parva , new genus and species Figures 3–4

ETYMOLOGY: ktenos + mastax (Gr., f.), comb­jaw; referring to the comblike arrangement of the marginal teeth of this lizard; parvus (L.), meaning ‘‘little.’’

HOLOTYPE: IGM 3 /61 (MAE 89/93­70), incomplete skull with partial right and clear impression of the left mandible; preserved in red fine­grained sandstones.

TYPE LOCALITY AND HORIZON: Zos, Nemegt Basin, Mongolian Gobi Desert; Upper Cretaceous Djadokhta Formation.

KNOWN DISTRIBUTION: Zos and Khulsan localities, Djadokhta and Barun Goyot formations.

DIAGNOSIS: Distinguished from other nonacrodontan iguanians (or iguanids) in having the following derived character states: slen­ der, fine teeth arranged in a ‘‘comb­like’’ configuration along the tooth row; tooth crowns short and peglike; maxillary tooth row slightly heterodont with anterior and posterior teeth larger than those in the middle part of the tooth row; anterior one third of Meckelian canal enclosed without fusion of the dentary tube; retracted splenial covering only the posterior two thirds of Meckelian canal.

REFERRED SPECIMEN: IGM 3/62 (MAE 131), incomplete skull with mandibles, first nine vertebrae and an incomplete scapula; from Khulsan (preserved in gray fine­grained sandstones); Upper Cretaceous Barun Goyot Formation.

DESCRIPTION

The new taxon is known from two specimens. The diagnostic features of the teeth and jaw structures are best shown on the holotype (fig. 3), whereas the skull roof and the palatal region are well preserved on the referred specimen. The following description is based on both specimens.

SKULL ROOF: Skull is delicately built with Fig. 3 . Continued. a pointed snout. The premaxillae are fused as a single element and exhibit a prominent dorsal spine separating the nares. Six small unicuspid premaxillary teeth are present. The nasals are paired and extend posteriorly to the level of the posterior borders of the prefrontal bosses. As in other iguanians, the frontals are fused as a single bone and are constricted between the orbits. Ventrally, shallow subolfactory flanges form a trough for the olfactory tract. The dorsal surface of the frontal is smooth anteriorly, but posteriorly is lightly ornamented with rugosities anterior to the parietal foramen. The frontoparietal suture is transverse, with a small parietal foramen opening at the suture (best shown on IGM 3/62; see fig. 4).

The prefrontal is overlapped anteriorly by the dorsal process of the maxilla. The prefrontal is exposed primarily on the dorsal table of the skull and carries a prefrontal boss. It also has a well­developed frontal process, which medially articulates with the frontal and posteriorly extends to the midlevel of the orbit. The anteroventral (orbital) process forms the anterior wall of the orbit, but ventrally does not contact the palatine. This process medially borders the orbitonasal fenestra (term sensu Oelrich, 1956). The prefrontal contacts the lacrimal. Along this suture lies a small notch (the lacrimal foramen).

The postorbital and postfrontal are unfused, separate elements. The left postfrontal on the holotype is slightly shifted medially beneath the frontal and parietal, but it shows a forked condition with a slender anterior process and a short posterior process clasping the frontoparietal suture. The postorbital slightly broadens posteriorly on the skull table where it intrudes into the supratemporal fenestra.

The parietal table is short and roughly trapezoidal. Laterally the parietal table is strongly concave with a medial constriction Ventrolaterally it has a steep flange for the attachment of the temporal muscle, which extends continuously to the lateral surface of the supratemporal process of the parietal. The dorsal surface of the parietal table is ornamented with small bumps with rugosities. This sculpturing is more developed than that on the frontals. The posterior border of the parietal table is not a simple transverse margin. Rather, this margin consists of two lateral notches separated by a flat, posterior extension of the parietal table dorsal to the foramen magnum (fig. 4B). The supratemporal process of the parietal is longer than the parietal table. In dorsal view, the supratemporal process is triangular in cross­section adjacent to the main body of the parietal. Posteriorly it becomes laterally compressed, forming a crest as it turns posterolaterally to contact the quadrate. The supratemporal is preserved on both sides. It attaches to the lateral surface of the supratemporal process of the parietal, and extends anteriorly to the midlevel of the supratemporal process.

In lateral view, the maxilla has a relatively high dorsal process, which forms part of the posterior border of the narial opening. The premaxillary process of the maxilla is short, overlapping the lateral extension of the premaxilla. An even stronger anteromedial process extends and meets its counterpart behind the premaxilla (on both the holotype and the referred specimen). Such a contact was previously interpreted as an acrodontan syna­ pomorphy (Estes et al., 1988), but its occurrence in this and other nonacrodontan iguanians (see below) from the Gobi indicates that the character merits reevaluation. The maxilla carries 19 highly pleurodont teeth (see below) on the holotype and 18 on the referred specimen. Dorsal to the maxilla, the ventral rim of the orbit is formed by the anterovental process of the jugal and a small lacrimal. As in other iguanians, the posterodorsal process of the jugal extends to meet the squamosal ventral to the postorbital. The squamosal is missing on the holotype, but is preserved on both sides of the referred specimen. It has a slightly widened base that articulates with the quadrate, and a slender anterior process contacting the postorbital and abutting the jugal.

The quadrate is straight and lightly built. Its dorsal end expands posteriorly slightly. It has a well­developed cephalic condyle that is covered by the squamosal in the holotype. The anterior surface of the quadrate is a vertical plate with a smooth surface penetrated by a small quadrate foramen dorsal to the ventral condyle. This foramen forms the passageway for an anastomotic branch of the anterior tympanic vein and a small anastomotic branch of the posterior condylar artery (Oelrich, 1956). The lateral (tympanic) crest is vertical and curves slightly posteriorly forming the margin of the tympanic membrane. The medial border of the anterior surface of the quadrate is marked by the medial crest which ventrally has a small notch for insertion of the quadrate process of the pterygoid. The ventral condyle is much smaller than the cephalic condyle and sets in the articular fossa of the lower jaw, which has an anterior buttress enhancing the jaw joint (fig. 4A). The posterior crest is much more robust than the tympanic crest. It originates on the cephalic condyle as a prominent ridge that curves ventrally and disappears dorsal to the ventral condyle. Lateral to this crest is a dorsally expanded triangular fossa. The posteromedial surface of the quadrate is also triangular. The thin medial crest is oblique in posterior view. The posterior opening of the quadrate foramen is dorsal to the quadratepterygoid articulation.

PALATAL ELEMENTS: Much of the palatal region can not be examined on the type spec­ imen. However, preparation of the palatal region of the referred specimen (IGM 3/62) shows that the preserved left vomer has a clear midline edge separating it from the right vomer (not preserved). In iguanians vomer fusion occurs only in chamaeleonids (Rieppel, 1981), and the paired condition is a primitive character state for squamates generally (Estes et al., 1988). The suture between the vomer and the palatine cannot be clearly delimited, but the palatine is slightly widened and has a small lateral process that overlaps the palatal process of the maxilla The lateral edge of the palatine forms the entire medial border of the suborbital fenestra which is narrow and slightly elongated. The medial edge is slightly damaged, but shows no indication of a midline contact with its counterpart to close the interpterygoid vacuity. Posteriorly, the palatine has an irregular diagonal sutural contact with the pterygoid. Posterolaterally, the suture originates at the posterior border of the suborbital fenestra, but extends anteromedially, ending at the midlevel of the interpterygoid vacuity. The pterygoid has a short and wide anterior (or palatal) process, which is about half the length of the posterior (or quadrate) process Due to its oblique sutures with the palatine the anterior process of the pterygoid is roughly triangular. The lateral process of the pterygoid is even shorter and forms the weakly developed pterygoid flange. Dorsomedial to the lateral process, the epipterygoid sets in a small columellar fossa at the base of the quadrate process. All the palatal elements are toothless.

BRAINCASE: The floor of the braincase is well preserved on both specimens, but the dorsal part of the lateral wall of the braincase is not preserved. Only the ventral half of the right epipterygoid is preserved as a vertical pillar. The basipterygoid process of the basisphenoid is short and slender and articulates with the grooved medial surface of the pterygoid. The ventral surface of the basisphenoid is slightly depressed, as seen in many other iguanians. Posteriorly, the basisphenoid is sutured to the basioccipital. This suture is slightly arched anteriorly (fig. 3A, 4C). The basioccipital posterolaterally forms the small spheno­occipital tubercle, which is ventrally directed. Laterally it displays a roughly triangular occipital recess. Anterolateral to the occipital recess, the recessus vena jugularis (or vena capitis lateralis of others) is poorly preserved. It is a relatively shallow trough where the posterior opening to the Vidian canal is located anteriorly dorsal to the base of the basipterygoid process and within the basisphenoid. The foramen ovale lies anterior to the occipital recess. The facial foramen is not preserved on either side of the type.

Although the occiput is badly damaged, some elements are still identifiable on IGM 3/62. The supraoccipital is not preserved. The right paroccipital process is missing, and the left is displaced below the supratemporal arch and in front of the quadrate. The occipital condyle is formed predominately by the basioccipital, with little contribution from the exoccipitals. Dorsolateral to the occipital condyle, the exoccipital is partially preserved on both sides. It forms the posterior rim of the occipital recess, and contributes in small part to the spheno­occipital tubercle and the lateral part of the occipital condyle. The better preserved right side seems to show that the exoccipital is broken at the hypoglossal foramina.

MANDIBLE: Both mandibles are well preserved on the referred specimen, but the diagnostic medial side of the dentary and teeth are best exposed on the holotype, in which a matrix impression shows the sutures and enclosure of the Meckelian canal. Both the holotype and the referred specimen show that the canal is closed anteriorly for about one third of its length; the presence of a clear suture indicates that the dentary tube is enclosed but not fused. The posterior two thirds of the canal is medially covered by a narrow splenial. The anterior inferior alveolar foramen and the anterior mylohyoid foramen are located in close approximation. The former foramen is larger than the latter and is locat­ ed at the anterior end of the splenial, whereas the anterior mylohyoid foramen lies at the ventral border of the splenial. Location of the posterior mylohyoid foramen (= angular foramen of other authors) cannot be determined on either of the specimens, as a matter of preservation. The splenial terminates posteriorly at the level of the coronoid summit of the jaw.

Posterodorsal to the splenial, the medial exposure of the coronoid is triradiate, lacking the posterodorsal process seen in some extant iguanians (see Frost and Etheridge, 1989: fig. 4). Ventral to the coronoid, the anterior part of the angular is exposed as a tonguelike extension, which turns from lateral to the medial side of the jaw, separating the splenial and the dentary to the level of the anterior inferior alveolar foramen. Immediately behind the posteroventral process of the coronoid, the mandibular fossa opens as a narrow and shallow groove extending posteriorly towards the craniomandibular joint. As shown on both the holotype and the referred specimen, the angular process is strongly developed, directed medially and not hooked at all.

In lateral view, the dentary occupies the anterior half of the mandible and posteriorly terminates at the level of the anterior surangular foramen. This proportion is a derived condition among iguanians, as Sphenodon and some extant iguanians have a greater proportion of the dentary in relation to the postdentary part of the jaw. Neither of the two specimens has the lateral coronoid process preserved. But the referred specimen displays a clear articular surface anterior to the anterior surangular foramen, indicating that the lateral coronoid process has a triangular anterior border and covers the dorsal part of the dentary­surangular suture (fig. 4A). A small coronoid process of the dentary slightly covers the anterior surface of the dorsal process of the coronoid bone. The posterior extent of the dentary is not preserved on either specimen, but based on observation of the referred specimen, it seems to terminate below the anterior surangular foramen. The latter specimen seems to have a small notch on the dentary for articulation with the surangular and angular bones.

The posterior surangular foramen, much smaller than the anterior one, is located posteriorly near the dorsal border of the jaw and anterior to the craniomandibular joint. As in many other iguanian lizards, the articular and prearticular are fused. The retroarticular process is slightly stronger than the angular process and is directed posteriorly, in contrast to the deflected condition in several lizard groups including gekkotans, scincoids, and varanids (see Estes et al., 1988). The process has a depression on its dorsal surface, which provides the insertion for the dorsal fibers of the pterygomandibularis muscle (Oelrich, 1956).

DENTITION: The marginal teeth are generally peglike in lateral view, but are highly pleurodont, having over two thirds of the tooth height attached to the lateral parapet of the jaws. As the teeth have very slender shafts and are closely spaced, they show a comblike arrangement along the tooth row. The crowns are unicuspid, having no cuspules but displaying weak lateral crests.

The marginal teeth of Ctenomastax parva are weakly heterodont: the first two or three teeth on the maxillary and dentary tooth rows are enlarged and are more or less caniniform, the middle teeth are much smaller than the anterior ones, and a few posterior teeth are larger than those in the middle part of the tooth row. However, there is no differentiation of crown pattern along the tooth row. The complete maxillary tooth row includes 19 positions on the holotype and 18 on the referred specimen. The complete dentary tooth row is best shown on the holotype, in which a total of 23 teeth are preserved as clear impressions. As mentioned before, the premaxilla is a single element that bears six small unicuspid teeth.

COMPARISON AND DISCUSSION

The new taxon Ctenomastax parva shares the following characters with other iguanians: frontals are fused and constricted between the orbits; presence of a frontal shelf that anteriorly underlies the nasals; parietal foramen located anteriorly on the frontoparietal suture; and presence of an angular process on the retroarticular process of the lower jaw. Other characters listed in Estes et al. (1988) as iguanian synapomorphies are not preserved on the specimen.

Two nonacrodontan iguanians described by Borsuk­Bialynicka and Alifanov (1991) from Khulsan ( Igua and Polrussia ) have short, wide, and rectangular parietal tables. By contrast, Ctenomastax parva , known from the same locality, has a trapezoidal parietal table. All of the specimens of these three taxa are small and nearly equivalent in size, indicating that differences in the shape of the parietal table are not due to ontogenetic or allometric factors. Furthermore, Igua has tricuspid teeth that are very different from the peglike dentition of Ctenomastax parva . Polrussia has unicuspid teeth, that ‘‘protrude high above the parapet of the jaw’ (Borsuk­Bialynicka and Alifanov, 1991) Ctenomastax parva with its low crowned teeth clearly differs from Polrussia . Furthermore, the new taxon lacks the fusion of the dentary tube seen in Polrussia .

A notable character in Ctenomastax parva is the contact of the maxillae behind the premaxillary spine. This character was regarded as an acrodontan synapomorphy by Estes et al. (1988) based on its distribution in extant iguanians (but see Jollie, 1960). However the dentition of the new species is highly pleurodont, the postfrontal remains as a separate element from the postorbital, and the Meckelian canal is closed anteriorly. These characters strongly indicate that the new species represents a nonacrodontan iguanian (or iguanid), and cannot be classified in the Acrodonta. Furthermore, this same character occurs in several other nonacrodontan iguanians from the Gobi, and suggests such a contact could well be a primitive character state among iguanians.

The relationships of the new species with other nonacrodontan iguanians is currently unclear. Like some other nonacrodontan iguanians described from the Gobi Desert Ctenomastax parva shares a large number of characters with crotaphytine iguanians: (1) lacrimal foramen not enlarged; (2) skull roof not strongly rugose; (3) jugal and squamosal not broadly juxtaposed; (4) parietal table trapezoidal; (5) parietal foramen in frontoparietal suture; (6) supratemporal on lateral side of supratemporal process of parietal (7) dentary not expanded onto labial face of coronoid; (8) labial blade of coronoid absent; (9) anterior surangular foramen above posteriormost extent of dentary; (10) dentary tube not fused; (11) splenial relatively long anteriorly; (12) marginal teeth pleurodont. Many of these characters are plesiomorphic for the Iguania, providing little information regarding the relationships of the

new lizard except for possibly indicating its primitive status.

Temujinia ellisoni , new genus and species Figures 5–6

ETYMOLOGY: Temujin, Mongolian name of the world conqueror Genghis Khan; species epithet after Mick Ellison, Principal Artist at the American Museum of Natural History, who skillfully prepared the photographs and outline drawings for this work.

HOLOTYPE: IGM 3 /63 (MAE 121/93­93), incomplete skull with mandibles.

TYPE LOCALITY AND HORIZON: Ukhaa Tolgod, Nemegt Basin, Mongolian Gobi Desert; Upper Cretaceous Djadokhta Formation (Loope et al., 1998).

KNOWN DISTRIBUTION: Ukhaa Tolgod and Tugrugeen Shireh localities, Djadokhta Formation.

DIAGNOSIS: Differing from other iguanians in having the following derived character states: postfrontal forms slender bar between orbit and supratemporal fenestra; parietal foramen opens largely on frontal side of frontoparietal suture; posterior margin of parietal symmetrically notched for insertion of dorsal axial muscle; presence of vertical ridges and grooves on dorsal process of coronoid for insertion of mandibular adductor muscle; anterior surangular foramen opens dorsally behind dorsal process of coronoid; anterior half of Meckelian canal closed by dentary without fusion; mandibular fossa narrow and elongate; marginal teeth low crowned and strongly swollen; tooth crowns weakly tricuspid; angular process of mandible wide and strong, directed medially.

REFERRED SPECIMENS: IGM 3/64–3/69 (MAE 145/94­40, 75/93­89, 235/93­130, 319/93­147, 39/93­90, MAE 94­37), all topotypic incomplete skulls with mandibles (see discussion below); IGM 3/70 (MAE 19/ 93­6), fragmentary skull with mandibles from Tugrugeen Shireh (Tugrikin­Shireh).

DESCRIPTION

SKULL ROOF: The premaxillae are not preserved on the holotype, but are present on several referred specimens (IGM 3/64, 3/66, 3/68). The premaxillae are fused into a single element with a slender spine. None of the specimens preserve complete nasals, but impressions on the holotype and IGM 3/70 indicate that the nasals are paired and laterally in contact with the maxillae. The frontals are fused and have an interorbital constriction. The holotype shows a frontal shelf is present anteriorly to underlay the nasal and an anterolateral spike is developed between the nasal and prefrontal. The dorsal surface of the frontals is lightly ornamented with rugosities. The frontoparietal suture is transverse, with the parietal foramen slightly chipping the anterior margin of the parietal, but largely opening on the frontal side of the suture (see fig. 5A).

The parietal table is roughly trapezoidal, and the dorsal surface is weakly ornamented anteriorly with rugosities, as on the frontals. The maximum width of the parietal table is anteriorly at the frontoparietal suture and the minimum width at the posterior margin (slightly wider than half the width at the frontoparietal suture); therefore, the parietal table has no obvious constriction at the middle level. However, the parietal laterally develops a relatively deep flange, indicating a dorsal origin of the temporal muscle. As a distinct character of the species, the posterior margin of the table is symmetrically notched for the insertion of dorsal axial musculature (spinalis capitis). The supratemporal process of the parietal is slightly longer than the table and extends posterolaterally at a roughly 45° angle in relation to the midline of the skull. The process is strongly compressed laterally, having a dorsal crest and a deeply sloped lateral surface for attachment of temporal muscles.

The prefrontal has an elongate frontal process, which extends posteriorly along the lateral edge of the frontal to the midpoint of the dorsal border of the orbit. The new species shares this character with Ctenomastax (see above) and extant Oplurus (see Blanc, 1977: fig. 26), but the phylogenetic significance of this character state needs to be evaluated on the basis of a broader survey. Anterolaterally, the prefrontal forms a very weak prefrontal boss. The anteroventral (orbital) process is slightly concave anteriorly, forming the anterior wall of the orbit and ventrally contacts the widened palatine. This process medially borders the orbitonasal fenestra and laterally contacts the lacrimal bone. The lacrimal foramen is small, differing from the enlarged condition seen in acrodontans. The relationship of the prefrontal with the nasal is unclear, but at least the large part of the antero­ medial edge of the prefrontal is separated from the nasal by a slender anterolateral process of the frontal (figs. 5A, 6B).

The postfrontal and postorbital are clearly delimited by a V­ shaped suture, and a small wedge of the postorbital fits in the lateral edge of the postfrontal. The postfrontal is reduced, but is present as a slender bar separating the orbit from the supratemporal fenestra (not confined to the orbital rim); it is medially forked to clasp the frontoparietal suture. Such a postfrontal differs from that in extant iguanians, which is confined to the posterodorsal margin of the orbit (see de Queiroz, 1987; Estes et al., 1988). The posterior process is short and robust, fitting in a small notch on the parietal, but the anterior process is long and slender, almost twice the length of the posterior process. The body of the postfrontal is thickened and is more rodlike than platelike, differing from other iguanian species. The postorbital is subtriangular with a large, wide anterior process and a pointed posterior process that contacts the squamosal. The lateral edge of this element is slightly grooved for the posterodorsal process of the jugal, which contacts the anteroventral side of the squamosal (the posterior tip of the jugal process is preserved with the squamosal).

The squamosal is missing on the right side but completely preserved on the left. This element is also transversely expanded like the postorbital. It has no dorsal process, but its posterior end is hooked laterally in dorsal view. The supratemporal is not preserved on the holotype, but other specimens (e.g., IGM 3/66, 3/68) show a small splint, which lies between the squamosal and the supratemporal process of the parietal as in many other lizards.

The maxilla, jugal, and lacrimal are preserved on the right side of the holotype. These elements are also preserved on several referred specimens. The maxilla is relatively low and carries a dorsal process, the summit of which is slightly anterior to the midpoint of the tooth row. As in Ctenomastax parva , an anteromedial process of the maxilla contacts the opposite element behind the dorsal spine of the premaxillae (best shown in IGM 3/64, 3/68). The maxilla bears teeth and tooth spaces for 21–22 positions (see description of dentition below). The posterodorsal process of the jugal on the holotype is broken above the coronoid process and at the middle part of the postorbital rim. However, IGM 3/ 64 preserves a complete bar (see fig. 6B) that extends first posterodorsally then nearly horizontally to contact the postorbital and the squamosal. The anterovental process is mounted on the dorsal edge of the maxilla and forms most of the ventral rim of the orbit. Anterior to the jugal is a small lacrimal which forms the anteroventral corner of the orbit.

PALATAL ELEMENTS: The vomers are not preserved on the holotype, but the articular surface on the palatine indicates the vomers are paired as in other iguanians except for chamaeleonids. The palatine has a vomerine process. Posteriorly the palatine is wide forming most of the floor of the orbit. Anteromedially within the orbit, a small process meets its counterpart, forming the ventral border of the orbitonasal fenestra. Posteriorly it lacks sutural contact along the midline leaving a narrow opening of the interpterygoid vacuity (pyriform recess of Oelrich 1956; Estes et al., 1988). Anterolaterally within the orbit, a small lateral process of the palatine overlaps the palatal flange of the maxilla, and it is through this process that the infraorbital canal penetrates the palatine The palatine contributes the anterior two thirds of the medial border of the suborbital fenestra, with the posterior one third formed by the pterygoid. As in many other lizards the ectopterygoid forms both part of the posterior as well as the lateral border of the fenestra, and its anterolateral process does not extend to meet the palatine.

The anterior (palatine) process of the pterygoid has a wide base and contacts the palatine along a transverse suture when viewed dorsally. Ventrally, however, the suture is oblique with a short anterior extension of the pterygoid along the ventromedial edge of the palatine (fig. 5B). The short lateral process is articulated with the ectopterygoid, and ventrally forms a weak pterygoid flange. Dorsally near the base of the posterior (quadrate) process, a small socket (the fossa columella) is developed for the epipterygoid articulation. However, the epipterygoid on the holotype is displaced on both sides, so the ventral end of the left epipterygoid abuts the basipterygoid process, and the right epipterygoid lies horizontally across the ventral surface of the basioccipital (fig. 5B). A deep notch, forming the synovial joint, lies slight­ ly anteroventral to the basipterygoid process. As in many other lizards, the notch has an anterior buttress, preventing the process from sliding forward. Posterior to the joint, the laterally smooth and convex quadrate process is medially grooved, possibly allowing a sliding motion of the basipterygoid process. The posterior end of the process becomes laterally compressed and extends to support the quadrate.

BRAINCASE: The braincase floor is well preserved on the holotype and several of the referred specimens (e.g., IGM 3/68). On the holotype, the basisphenoid is complete except for the parasphenoid process, which is missing, possibly because it was cartilaginous in life. The basipterygoid process has a slender shaft but a strongly expanded condyle for articulation with the pterygoid. The main part of the basisphenoid has a small depression on its ventral surface, and carries a short posterolateral process extending to the base of the spheno­occipital tubercle. Owing to the development of this lateral process, the basisphenoid­basioccipital suture is laterally oblique rather than transverse. The basioccipital is roughly equivalent in size with the basisphenoid. Located laterally, at the midlevel of the basioccipital, the sphenooccipital tubercle is more ventrally than posteriorly directed. The occipital condyle is robust in relation to the size of the basioccipital. Corresponding lateral components of the exoccipital form two thirds of the occipital condyle, while a medioventral one third is composed of basioccipital.

Dorsolateral to the braincase floor is a deep and wide trough, which is the recessus vena jugularis (term of Oelrich, 1956). The lateral wall of the trough is formed by a welldeveloped crista prootica of the prootic, but the medial wall is composed of both the prootic and a dorsal extension of the basisphenoid (without contribution from the basioccipital). Anteriorly within the recessus, the posterior opening of the Vidian canal penetrates the basisphenoid and opens posterodorsal to the base of the basipterygoid process. The facial foramen for the facial nerve (VII) opens on the arched roof of the recessus. More posteriorly, the foramen ovale opens dorsolateral to the spheno­occipital tubercle, and is separated from the occipital re­ cess by a prominent ridge (crista interfenestralis of Säve­söderbergh, 1947; Oelrich, 1956). Within the occipital recess, two openings are clearly identifiable: dorsal to the recess is a smaller foramen perilymphaticus, and deep in the recess is the larger foramen rotundum.

The lateral wall of the braincase lacks a clearly defined alar process of the prootic (best shown on IGM 3/68, 3/70), and thus the dorsal part of the epipterygoid lays against the otic capsule directly (IGM 3/68). The alar process provides an origin of the pseudotemporalis profundus (see Oelrich, 1956). Lack of an alar process indicates fundamental differences in the development, or the origin, of these muscles compared to oth­ er iguanians that have this process. Ventral to the anterior semicircular canal, a weak trigeminal notch is developed as the passageway for the trigeminal nerve (V). Anteroventral to the notch, the inferior process of the prootic (best shown on IGM 3/70) is well developed and anteriorly sutures to the wellossified pila antotica. The posterior process of the prootic is triangular, extending posterolaterally along the anterior surface of the paroccipital process and terminating near the tip of the process. Dorsally at the base of the posterior process, a minute foramen (?endolymphatic foramen) opens near the prooticsupraoccipital suture on the prootic.

In posterior view, the supraoccipital is hexagonal, having a very low occipital crest limited to the anterodorsal part of the bone. Part of the anterior and most of the posterior semicircular canals are covered by the supraoccipital. The posterior dorsal surface of the supraoccipital is a slightly convex and smooth slope, and its posterior edge is arched anteriorly as the dorsal rim of the foramen magnum. The supraoccipital is sutured laterally with the prootic and posterolaterally with the exoccipital. Lateral to the foramen magnum, the exoccipital serves multiple functions as in many other lizards: it forms a posterolateral wall of the braincase, the lateral border of the foramen magnum, the basal part of the paroccipital process (fused with the opisthotic), the posterior rim of the occipital recess, and part of the occipital condyle. In posterior view, the exoccipital forms a triangular surface, which medially sutures with the spheno­occipital tubercle and laterally borders the occipital recess by its crista tuberalis (best shown on the holotype and IGM 3/68). Lateral to the occipital condyle, the triangular surface is penetrated by three foramina, which are arranged as a triangle: dorsally lies the foramen for the vagus nerve (X), and ventrally are two foramina for the hypoglossal nerve (XII). This condition is different from Anolis carolinensis and Ctenosaura pectinata , in which three rami of the hypoglossal nerve emerge through three separate foramina in the exoccipital bone (Willard, 1915; Oelrich, 1956).

MANDIBLE: The mandibles on the holotype are well preserved except for the anterior tips, which are missing due to breakage. In lateral view, the dentary makes up roughly the anterior half of the mandible, having a strongly convex lateral surface. The left dentary is better preserved than the right, and is broken anteriorly at the fourth or the fifth tooth position (determined by comparison with IGM 3/64). Posteriorly, the dentary is slightly notched for the short anterior extension of the surangular and angular. The posterior extremity of the dentary terminates at the level below the summit of the coronoid. The ventral border of the mandible is slightly flattened, as the jaw is not strongly compressed laterally, but is rather convex.

The coronoid has no lateral blade. Instead it displays a robust dorsal process with two prominent vertical ridges on its lateral surface for attachment of the mandibular adductor muscle. The surangular occupies the dorsal posterior half of the mandible and has an anterior process fitting into the posterior notch of the dentary together with the anterior process of the angular. The lateral surface of the surangular has a strong horizontal crest (adductor crest) for attachment of the jaw muscles. The anterior surangular foramen (figs. 5C, 6A) is located dorsal to the crest and right at the coronoid/surangular suture posteroventral to the dorsal process of the coronoid. The posterior surangular foramen is much smaller than the anterior foramen (about half the size of the latter), and is located below the adductor crest and anteroventral to the craniomandibular joint. Posterodorsally, the surangular bears a promi­ nent dorsal process, which forms the anterior buttress for the craniomandibular joint.

The angular is a narrow tonguelike element exposed ventral to the surangular. Anteriorly it fits into the posterior notch of the dentary below the surangular, and posteriorly it terminates well anterior to the angular process and ventral to the posterior surangular foramen. Sharply different from the condition in Anchaurosaurus gilmorei , the angular in this species forms part of the ventral bor­ der of the postdentary part of the jaw, but is not exposed on the medial side of the jaw.

In medial view, the anterior one third of the Meckelian canal on the holotype is closed by a strong medial and upward enrolling of the ventral edge of the dentary; however, the enclosure of the dentary tube is unfused Most of the referred specimens consistently show the same morphology as the holotype but IGM 3/69 has the canal slightly open medially. The splenial is reduced, restricted to the posterior two thirds of the Meckelian canal. Posteriorly, it terminates at the same level as the posteroventral process of the dentary. The anterior inferior alveolar foramen and the anterior mylohyoid foramen penetrate the splenial close to the midpoint of the tooth row.

The mandibular fossa is a very narrow and elongate slit, opening horizontally between the prearticular and the surangular; it has an anterior border immediately behind the posteroventral process of the coronoid and posteriorly extends to a point below a prominent process of the surangular anterior to the craniomandibular joint. At the posterior end of the mandible, the prearticular is entirely fused with the articular and is partially fused with the surangular; only a short suture posterior to the angular can be delimited from the latter element. Medial to the craniomandibular joint, the prearticular bears a wide and strong angular process, which is perpendicular to the retroarticular process in direction. The retroarticular process is best preserved on the holotype and IGM 3/69 (figs 5B, 6A). Both the specimens show that the process is posteriorly directed, having its lateral border curved medially at the base.

DENTITION: The premaxillary teeth are not preserved on the holotype, but other specimens (e.g., IGM 3/64, 3/68) show that the fused premaxilla carries five to six unicuspid teeth. The maxillary teeth are best preserved on IGM 3/69, which shows a nearly complete tooth row containing 20 positions. A complete maxillary tooth count can be estimated as 22 based on comparison of this specimen with IGM 3/64. The dentary teeth are best preserved on the holotype and IGM 3/69, and a complete dentary tooth row as shown on the latter specimen contains a total of 25 positions.

The tooth attachment is pleurodont, having about two thirds of the columnar tooth shaft attached to the relatively deep lateral parapet of the jaws. The teeth in lateral view have short crowns. The first two or three maxillary teeth are unicuspid, followed by several bicuspid teeth, then well­defined tricuspid teeth in the middle and posterior part of the tooth row. The tricuspid crowns are laterally swollen, having a prominent central cusp and smaller but symmetrical lateral cusps (see figs. 5C, 6A). From anterior to posterior along the tooth row, the teeth become increasingly stouter and the tricuspid cusps become more pronounced.

COMPARISON AND DISCUSSION

Recognition of the new taxon Temujinia ellisoni is primarily based on the holotype. Several specimens (e.g., IGM 3/68, 3/69, 3/ 70) can be confidently referred to the same species, whereas the referral of several other specimens (IGM 3/65, 3/66, 3/67) to the species is tentative. In comparison with the holotype, the latter three skulls are more slenderly built with a more pointed snout. However, these specimens possess most of the diagnostic features of the species (see above), supporting referral to the same species as the holotype. IGM 3/65 shows a frontal tab overlapping the parietal (indicating a less movable frontoparietal hinge) and the parietal foramen opens within the frontal tab (see fig. 6C). However, because this is the only specimen showing this feature and the other two specimens with similar skull configurations are poorly preserved, we cannot determine the significance of this feature.

The new species Temujinia ellisoni is clearly referable to the Iguania on the basis of the following diagnostic characters of the group (see Estes et al., 1988 for evaluation): frontals are fused and constricted between orbits; frontal shelf anteriorly underlies the nasals, with frontals exposed anterolaterally as prominent spikes; prefrontal bosses are present; postfrontal is reduced; parietal foramen is displaced anteriorly; and the presence of an angular process of the mandible. Possession of these iguanian synapomorphies, but lack of acrodontan autapomorphies (see Estes et al., 1988) indicate the nonacrodontan position of the new taxon within the Iguania.

Compared with other nonacrodontan iguanians from the Gobi, this taxon differs from Anchaurosaurus (Gao and Hou, 1995, 1996) in having the frontal process of the prefrontal extended to the middle level of the orbit, much weaker frontal bosses, and shortcrowned and swollen teeth. It differs from Igua and Polrussia in having a short, trapezoidal parietal table with longer supratemporal process, and differs from the abovedescribed Ctenomastax primarily in having short­crowned and tricuspid teeth.

Compared with extant nonacrodontan iguanians, it is worth noting that the new species shares the following characters with the Madagascan Oplurus (see Blanc, 1977): the frontal process of the prefrontal is strongly elongate; the parietal table is short and trapezoidal, with a lateral flange extending onto the lateral surface of the supratemporal process; the palatal elements are expanded transversally; the mandibular fossa opens as an elongate narrow slit. The phylogenetic significance of these shared characters merits further investigation.

One interesting cranial feature displayed in Temujinia ellisoni is the forked postfrontal (see also description of Ctenomastax parva ). A forked postfrontal that clasps the frontoparietal suture is absent in extant iguanids and this character has been interpreted as a synapomorphy of Scleroglossa (Estes et al., 1988; Scincogekkonomorpha of Sukhanov, 1961). However, presence of such a forked condition in the Late Cretaceous iguanids from the Gobi indicates that the status of this character in squamate evolution requires reevaluation. As these may represent basal iguanians, the forked condition may well be a primitive state for lizards generally, and the nonforked condition in extant iguanians is probably a derived condition within the clade.

Another notable feature about this new taxon is the maxillary contact behind the premaxillary spine. Among the Late Cretaceous iguanians from the Gobi, both Temujinia ellisoni and Ctenomastax parva show such a contact. As discussed above, occurrences of such a contact in these Cretaceous nonacrodontan iguanians raise the question about the apomorphic status of the character for acrodontans and indicate that the character merits further evaluation.

Zapsosaurus sceliphros , new genus and species Figure 7

ETYMOLOGY: zaps + sauros (Gr., m.), meaning storm lizard; skeliphros (Gr.), meaning thin or slender, in reference to the lightly built skull of the new species.

HOLOTYPE: IGM 3 /71 (MAE 255/92­10), incomplete skull articulated with mandibles.

TYPE LOCALITY AND HORIZON: Tugrugeen Shireh, Mongolian Gobi Desert; Upper Cretaceous Djadokhta Formation (Jerzykiewicz et al., 1993; Fastovsky et al., 1997).

KNOWN DISTRIBUTION: Only known from the type locality and horizon.

DIAGNOSIS: Distinguished from possibly closely related Anchaurosaurus gilmorei by having the following character states: prefrontal bosses weakly developed; posterior border of parietal strongly flanged for attachment of axial musculature; Meckelian canal closed below anterior three­fourths of tooth row; splenial strongly reduced, covering only posterior one fourth of Meckelian canal; lateral surface of coronoid dorsal process bears vertical crest associated with a ventral tubercle; presence of distinct medial flange of surangular anteromedial to craniomandibular joint; mandibular fossa strongly shortened, posteriorly terminating halfway between coronoid and craniomandibular joint; marginal teeth having short shafts, but strongly flared crowns.

REFERRED SPECIMEN: IGM 3/72 (MAE 20/ 93­15), left upper and lower jaws (topotypic).

DESCRIPTION

SKULL ROOF: The holotype skull is undistorted and is preserved in a dark brown coarse­grained sandstone concretion. The premaxillae are not preserved on the holotype or the referred specimen. The left nasal is incompletely preserved, but is the only remnant of this element present. Its posterior end is slightly displaced ventral to the frontal; however, a depression clearly indicates that the frontal has an anterior tab, which is overlapped by the nasal as in other iguanians The fused frontals are more slender than in Anchaurosaurus gilmorei , and the frontoparietal suture is slightly posterior to the level of the coronoid process of the lower jaw. As in Anchaurosaurus gilmorei , the parietal foramen opens at the frontoparietal suture, but is significantly enlarged on the parietal side Only an anterior rim occurs on the frontal (fig. 7C). The parietal table is short and trapezoidal. It differs from Anchaurosaurus gilmorei in having a strongly developed posterior shelf or flange, which is divided by a weak median ridge and is laterally extended onto the base of the supratemporal process The process is slender and strongly elongate bearing a sharp dorsal crest. Attached to the posterolateral surface of the supratemporal process, the supratemporal bone is a much stronger element than in Anchaurosaurus gilmorei , and it has a flat dorsal surface.

The prefrontal is preserved on both sides It has a weak prefrontal boss, contrary to the strong lateral projection seen in Anchaurosaurus gilmorei (see Gao and Hou, 1995: fig 1). Posteromedially, the prefrontal has a slen­ der frontal process whose posterior extent lies at the midlevel of the orbit. The postfrontal is probably separated from the postorbital (indicated by the articular surface on the frontal), but the actual status of this element cannot be ascertained because of poor preservation. Extant nonacrodontan iguanians normally retain a reduced postfrontal (Estes et al., 1988). A comparison with Anchaurosaurus gilmorei is impossible, as this region of the skull is not preserved on any known specimens of the latter species.

The squamosal is incompletely preserved on the right side, and it has been slightly displaced medially. The bone has a broad pos­ Fig. 7 . Continued. terior end, limiting the size of the supratemporal fenestra. Because the bone is poorly preserved, the contact of this element with the postorbital and the jugal cannot be identified. The quadrate is straight and is more slender than in Anchaurosaurus gilmorei . The cephalic condyle expands strongly medioposteriorly to form a triangular table and has a well­developed foramen penetrating its dorsal surface. The anterolateral surface of the quadrate is smooth and slightly convex. The quadrate foramen opens above the ventral condyle on this surface. However, the anteromedial surface is strongly concave to form a wide and vertical groove dorsal to the ventral condyle. In lateral view, the tympanic crest is thin, straight, and vertical. The tympanic crest is oriented at a 90° angle to the horizontal lateral border of the cephalic condyle, giving the lateral crest for the tympanic membrane an L­ shape. The posterior surface of the quadrate is divided into two surfaces by a vertical posterior crest, which is weakly arched anteriorly. The lateral part is strongly concave to form a deep fossa, and the medial part is slightly concave and forms an inverted triangular­shaped surface as the medial crest diminishes ventrally. The posterior opening of the quadrate foramen penetrates the medial surface on the lower one third of the bone, close to the posterior crest. The ventral condyle is transversely expanded and is saddle­shaped with a concave ventral surface. The right epipterygoid is preserved and exposed in dorsal view (fig. 7C). It attaches to the lateral surface of the prootic, but its contact with the parietal cannot be confidently determined as the bone may have been slightly displaced posteriorly.

Only the left maxilla is preserved, and it is incomplete. It has a low dorsal process that bends medially to contact the nasal, prefrontal, and the anterolateral process of the frontal. The posterior border of the process is notched for a well­developed lacrimal. The posterior process of the maxilla has a nearly transverse suture with the jugal, and in this aspect differs from Anchaurosaurus gilmorei (see Gao and Hou, 1995: fig. 1). The maxilla has 18 well­preserved teeth, and probably four to five additional anterior teeth are missing owing to breakage (see below).

The jugal is broken on the left side, but a clear impression allows the morphology of this element to be described. Its anteroventral process is relatively deep, roughly rectangular, and forms the ventral border of the orbit together with the lacrimal. The posterodorsal process forms the posterior bar of the orbit and dorsally contacts the postorbital.

PALATAL ELEMENTS: All of the palatal elements are toothless (fig. 7D). Better preserved on the right side than the left, the vomers are paired and slightly elongate. The palatines are wide, but have no midline contact. The suborbital fenestra is slightly elongate, extending to the midlevel of the palatine. The fenestra is medially bordered by the palatine and the pterygoid, and is laterally bordered by the maxilla and the ectopterygoid. The ectopterygoid in palatal view has a triangular base, which is sutured medially with the widened pterygoid, and has a ventral process forming small part of the weakly developed pterygoid flange. The ectopterygoid forms the posterior border of the suborbital fenestra, and the anterolateral process extends to the midlevel of the suborbital fenestra. The pterygoid has an elongate palatine process, which thins anteriorly and is sutured to the palatine along its medial edge to form the medial border of the interpterygoid vacuity. The posterior part of the process broadens and has an oblique lateral edge for articulation with the palatine. The posterior edge of the lateral process inflects dorsally to form the pterygoid flange. The quadrate process is essentially a blade that is convex laterally and concave medially. Like in many other iguanians, a notch is developed medially at the base of the process that forms the joint with the basipterygoid process of the basisphenoid. The posterior extremity of the process becomes a slender blade, attaching to the medial border of the quadrate.

BRAINCASE: The basisphenoid and the basioccipital form the braincase floor. These elements are unfused and separated by a clear suture (fig. 7D). The base of the rostrum of the basisphenoid is slightly thickened, and has a small depression posterior to it. Anterolaterally, the basipterygoid process is short, but has a strongly expanded condyle directed anterolaterally at a 45° angle to the midline. Posterolaterally, the basisphenoid bears a short process attaching to the ventral surface of the basioccipital and extending to the base of the spheno­occipital tubercle. The basioccipital forms the posterior part of the floor and ventral part of the lateral wall of the braincase, and a major part of the occipital condyle.

Dorsolateral to the floor of the braincase, the recessus vena jugularis is well preserved on both sides of the holotype. The lateral wall of the recessus is formed by the prootic with a sharp crest (crista prootica), but the medial wall is formed by three elements: dorsally by the prootic and ventrally by the basisphenoid and basioccipital. A posterior opening of the Vidian canal penetrates the medial wall of the recessus. It opens between the base of the basipterygoid process and the basisphenoid­basioccipital suture, with no involvement from the prootic. A small facial foramen penetrates the prootic and opens on the medial wall of the recessus. The foot of the right stapes as preserved covers the foramen ovale, but the shaft is not preserved. The foramen ovale is located dorsal to the occipital recess. A slender bone extends posteriorly from the occipital recess. Although similar in position to the stapes, it is long and slightly curved, indicating it is a dislocated hyoid element. Another hyoid element is preserved on the left side posteroventral to the braincase floor.

Most of the occipital aspect of the skull is not exposed, because the skull is articulated with several cervical vertebrae. However, some features of the occiput can be observed from dorsal and ventral views. In dorsal view, the supraoccipital carries a weakly developed median crest for attachment of the ligamentum nuchae (Oelrich, 1956). Laterally parallel to the crest, the posterior semicircular canal swells dorsally, but no suture can be delimited between the supraoccipital and the exoccipital. In ventral view, the paroccipital process is shorter than in Anchaurosaurus gilmorei and extends more laterally than posteriorly. The fissurelike vagus foramen (for cranial nerves X, XI) and the rounded hypoglossal foramen (for cranial nerve XII) are very close to one anoth­ er, and are both located dorsolateral to the occipital condyle.

MANDIBLE: The mandibles are well preserved on both sides, with slight damage to the right coronoid and the postdentary region. In lateral view, the dentary has a smooth surface and carries seven mental foramina. The last foramen is located at the midlevel of the tooth row. Like in Anchaurosaurus gilmorei (Gao and Hou, 1995) , the dentary is posteriorly bifurcated and notched for the blunt surangular with little involvement of the angular bone The posterodorsal (coronoid) process is shorter but stronger than the posteroventral (Meckeli­ an) process, which extends on the ventral bor­ der of the jaw and wedges between the surangular and the angular. The coronoid has a lightly built dorsal process, the lateral surface of which carries a vertical crest for the external jaw adductor. This crest ventrally ends with a prominent process. This condition is different in Anchaurosaurus gilmorei , where the coronoid process is robust, lacks a vertical crest but has a low and robust tubercle. Like in Anchaurosaurus gilmorei , the coronoid of the new species has no lateral blade, but a small wedge between the dentary and the surangular

The surangular occupies most of the postdentary part of the jaw in lateral view. It has a large lateral surface and a prominent crest for the attachment of the jaw adductor muscle As in Anchaurosaurus gilmorei , the anterior surangular foramen is located in a low position anteriorly in the middle of the bone, and the posterior surangular foramen opens on the crest posteriorly near the craniomandibular joint (fig. 7A, B). The angular is incompletely preserved on the left side, and left clear impressions on the right. This element is small and barely exposed in lateral view. It wedges between the surangular and the prearticular in ventral view and between the dentary and the splenial in medial view. The angular foramen (preserved on the left side) is extremely small and opens on the medial side of the jaw close to the posterior end of the splenial. The prearticular (fused with the articular) is the second largest element of the postdentary part of the jaw. Its contact with the surangular and the posteroventral process of the dentary is exposed, as the angular bone that normally covers this suture is not preserved. The prearticular medially carries a prominent and slightly hooked angular process, and a posteriorly directed retroarticular process. The articular fossa for the mandibular joint with the quadrate condyle lacks an anterior or posterior buttress therefore, the joint seems to be more freely

movable. Posterior to the jaw joint, the retroarticular process is weakly developed and posteriorly directed. The dorsal surface of the process is concave, but has no foramina opening in it.

In medial view, the anterior three­fourths of the Meckelian canal is closed, without fusion of the dentary tube. The anterior end opens near the symphysis. The posterior one fourth of the canal is medially covered by a greatly reduced splenial, which has its posterior extension terminating anterior to the angular foramen. The anterior process of the surangular extends and wedges between the splenial and the anteroventral process of the coronoid. The dorsal rim of the surangular is anteriorly rounded as commonly seen in other lizards, but posteriorly a distinct flange is strongly developed anteromedial to the craniomandibular joint and above the mandibular fossa (fig. 7C). Such a strong flange is absent in other lizards. Functionally, this flange may serve as an insertion of the pterygomandibularis muscle (see Oelrich, 1956). Also different from Anchaurosaurus gilmorei (see Gao and Hou, 1995: fig. 1), the mandibular fossa in Zapsosaurus sceliphros is strongly reduced into a short and shallow groove, extending only to the midpoint between the coronoid process and the craniomandibular joint.

DENTITION: The morphology of the marginal teeth is best observed on the incomplete left maxilla, which has 18 tricuspid teeth preserved. The teeth are much shorter and more slender than in Anchaurosaurus gilmorei , and the crowns are more strongly flared, having the small lateral cusp separated from the prominent central cusp by a clearly defined groove (fig. 7A). Owing to breakage of the maxilla, a complete tooth count of the upper dentition cannot be obtained, but can be estimated at 23–24 teeth. The right dentary contains 27 positions for the complete tooth row, and these are all tricuspid except for the anteriormost five that are unicuspid. The number and morphology of the premaxillary teeth cannot be determined.

VERTEBRAE: On the holotype (IGM 3/71), the first three cervicals (the atlas­axis complex and the third vertebra) and part of the fourth are preserved in articulation. The atlas is a simple ringlike structure, the elements of which remain unfused. The axis is elongate and has a low but well­developed crown, which extends posteriorly and overlaps part of the third cervical. Each of the cervicals has a well­defined ventral keel.

Several caudals are preserved in association with the skull. Two anterior caudals are dislocated to the left orbit, and each of these shows an autotomy fracture posterior to a single pair of transverse process. This condition corresponds with the so­called ‘‘ Sceloporus ­type’’ of caudal autotomy as described by Etheridge (1967).

COMPARISON AND DISCUSSION

The new taxon shares several characters with Anchaurosaurus gilmorei including: skull elongate with relatively pointed snout; parietal table trapezoidal, but with long, slen­ der supratemporal process; parietal foramen opens at the frontoparietal suture, but is enlarged on the parietal side. These indicate a close relationship of the two forms. However, Zapsosaurus sceliphros is clearly distinguishable from Anchaurosaurus gilmorei by the characters listed in the diagnosis.

Both Zapsosaurus sceliphros and Anchaurosaurus gilmorei are relatively large lizards in comparison with other Cretaceous iguanians known from the Gobi. These taxa are from the same geological formation (Djadokhta Formation), but do not co­occur at the same localities. Anchaurosaurus gilmorei is known from Bayan Mandahu near the southern border of the Gobi, and Zapsosaurus sceliphros from the Tugrugeen Shireh locality, which is some 400 km northwest of the former locality.

Although Gao and Hou (1995) noted that Anchaurosaurus gilmorei shares 11 character states with crotaphytines, the relationships of Anchaurosaurus gilmorei and Zapsosaurus sceliphros to other iguanians are unclear. Alifanov (1996) classified Anchaurosaurus in the Crotaphytidae together with the Eocene Arretosaurus Gilmore, 1943 . Examination of the known material of Arretosaurus , including the holotype (AMNH 6706), indicates no shared derived character states supporting the grouping of these taxa in the same family. Until a thorough study of the phylogenetic relationships of the Gobi and other basal ig­ uanians is completed, the interrelationships of several nonacrodontan iguanians including Anchaurosaurus and Zapsosaurus remain unclear.

Polrussia mongoliensis Borsuk­Bialynicka and Alifanov, 1991 Figure 8

HOLOTYPE: ZPAL MgR­I/119, incomplete skull with mandibles.

TYPE LOCALITY AND HORIZON: Khulsan, Nemegt Basin, Mongolia; Upper Cretaceous Barun Goyot Formation.

KNOWN DISTRIBUTION: Known only from the type locality and horizon.

REVISED DIAGNOSIS: Distinguished from

other nonacrodontan iguanians by the following derived character states: frontals slenderly elongate and strongly narrowed spheno­occipital tubercle greatly reduced as remnant knob; splenial retracted to slightly anterior to posterior end of tooth row; Meckelian canal entirely closed by fusion of dentary tube; posterior extension of dentary terminates at level of dorsal process of coronoid; marginal teeth having slenderly cylindrical shafts and pointedly unicuspid crowns

REFERRED SPECIMEN: IGM 3/73 (MAE 219/92­45), partial skull with mandibles and cervical vertebrae; collected from Khulsan.

REMARKS: IGM 3/73 is referred to Polrussia mongoliensis based on several diagnostic features of the species shown on the specimen: the splenial is retracted to slightly anterior to the posterior end of the dentary tooth row; the Meckelian canal is entirely closed by fusion of the dentary tube; posterior extension of the dentary terminates at the level of the coronoid dorsal process; and the marginal teeth are slenderly built, with point­ ed, unicuspid crowns.

Although fragmentary, IGM 3/73 is only the second specimen (other than the holotype) known for the species. The new specimen reveals some unknown morphology and clarifies some uncertainties about the species. The configuration of the parietal is uncertain on the holotype, but the new specimen shows the element is rectangular and has an unossified region indicating a fontanelle. In palatal view, the new specimen shows no midline contact of the palatines, contrary to the speculation ‘‘judging from the position of the right bone’’ on the holotype (Borsuk­Bialynicka and Alifanov, 1991: 338). Also from the new specimen, the pterygoid teeth are retained, but palatine teeth are absent. The spheno­occipital tubercle is greatly reduced into a small knob.

Regarding the relationships of Polrussia mongoliensis, Borsuk­Bialynicka and Alifanov (1991: 340) stated that ‘‘on the basis of the present knowledge the Opluridae , nonanole Polychridae , Tropidurinae and Leiocephalinae may not be excluded as possible relatives of Polrussia .’’ It is worth noting, however, that Polrussia mongoliensis shares with Igua minuta at least one character state: the parietal is rectangular with a large fontanel. Pending an actual phylogenetic analysis, this character state may indicate a closer relationship of the two species.

Figures

Fig. 3. Ctenomastax parva, new genus and species: A, B, IGM 3/61 (holotype), incomplete skull with mandibles from Zos, ventral and dorsal views.

Fig. 4. Ctenomastax parva, new genus and species: A–C, IGM 3/62 (referred specimen), incomplete skull with mandibles from Khulsan, lateral, dorsal, and ventral views.

Fig. 5. Temujinia ellisoni, new genus and species: A–C, IGM 3/63 (holotype), incomplete skull with mandibles from Ukhaa Tolgod, dorsal, ventral, and lateral views.

Fig. 6. Temujinia ellisoni, new genus and species (referred specimens, topotypic): A, IGM 3/69, incomplete skull with mandibles, right lateral view; B, IGM 3/64, incomplete skull with mandibles, dorsal view; C, IGM 3/65, incomplete skull with mandibles, dorsal view.

Fig. 7. Zapsosaurus sceliphros, new genus and species: A–D, IGM 3/71 (holotype), incomplete skull with mandibles from Tugrugeen Shireh, lateral, dorsal, and ventral views.

Fig. 8. Polrussia mongoliensis: A–C, IGM 3/73, incomplete skull articulated with mandibles and cervical vertebrae, dorsal, ventral, and lateral views.