Kansajsuchus extensus Efimov, 1975

Halliday, Thomas J. D., Andrade, Marco Brandalise De, Benton, Michael J. & Efimov, Mikhail B., 2015, A re-evaluation of goniopholidid crocodylomorph material from Central Asia: Biogeographic and phylogenetic implications, Acta Palaeontologica Polonica 60 (2), pp. 291-312 : 299-304

Kansajsuchus extensus Efimov, 1975

Holotype: PIN 2399-301 , a right premaxilla ( Fig. 5 ), approximately 11.5 cm in length and 5 cm wide at the widest point, though this only extends to the midline of the rostrum. The maxilla and nasal bones are also partially represented, with the sutures obviously present. It is broken along the midline.

Type locality: The Kansaj part of the Yalovachskaya Svita in the Fergana Basin, a region of northern Tajikistan. Coordinates are 40.5N, 69.7E. The depositional setting was a river delta of one of the major rivers flowing into the Tethys Ocean. The exact location within this general locality of any individual specimen is unrecorded either in publication, or, as far as can be ascertained, in any field notebooks at PIN .

Type horizon: This locality was referred to the Upper Cretaceous (lower Santonian) by Rozhdestvensky (1977) and everyone since ( Nessov 1995).

Material.— PIN 2399-301 (holotype) to PIN 2399-426 . There is a great deal of other material assigned to K. extensus , some 300 identifiable elements and fragments, all collected from the same locality on the same expedition. This additional material includes a large left premaxilla/maxilla complex, a right nasal bone, a right maxilla, a frontal ( Fig. 6 ), a right quadrate, a large complex of the skull roof and occipital region ( Figs. 7 , 8 ; this specimen was also figured in Efimov 1988b), a separate occipital condyle, parts of the lower jaw Fig. 9 ), a femur, vertebrae ( Fig. 10 ), several osteoderms, and over 100 teeth, all well preserved .

It is hard to determine how much of the supplementary material should be assigned to K. extensus . Several fragments are clearly not from the same individual because of size differences, but the collection data, bone preservation, and overall size range do not exclude the possibility that all specimens belong to the same species. This has been the assumption made by previous workers, who accepted that the numbering by PIN shows that all specimens with the primary number 2399 were collected from the same formation and locality at the same time, and presumably close together. Here, we describe the holotype, and then add comments on additional elements as appropriate .

Emended diagnosis.— Although largely possessing goniopholidid features, Kansajsuchus differs from all other goniopholidids in the following: (i) possessing an ornamentation in which grooves are present alongside the pits; (ii) lacking neurovascular foramina on the dorsal surface of the rostrum;

iii) possessing a frontal with concave, ridged margins; and iv) the skull roof forming a trapezoidal shape. The postorbital bar is slender, and the quadrate is relatively broad compared with other goniopholidids. The retroarticular process is more posteroventrally directed, and more strongly concave. Unlike all goniopholidids except Eutretauranosuchus , Kansajsuchus possesses a highly serrated premaxillo-maxillary suture. Kansajsuchus differs from Siamosuchus , Goniopholis , Nannosuchus , Anteophthalmosuchus , and other Europe- an goniopholidids in the extent to which the premaxillo-maxillary notch contacts the alveoli, and in the convexity of the margins of the nasal bone. Kansajsuchus resembles Europe- an goniopholidids in the morphology of the frontal, which is narrow with a narrow anterior projection, with the anterior and posterior surfaces at different heights, unlike Siamosuchus , Sunosuchus , Eutretauranosuchus , or Calsoyasuchus . The lateral processes of the frontal are arched, similarly to Goniopholis willetti , Dollo’s goniopholidid, and Anteopthalmosuchus hooleyi. There is a small sagittal crest on the frontal, like that of Sunosuchus junggarensis and Siamosuchus . The specific diagnosis is as that of the genus.

Description.— General features: Little can be elucidated about the general shape of the skull, since all fragments are of different sizes. However, some broad patterns are clear. The snout is relatively long, with a broadening of the premaxillae at the anterior end. The skull table is raised above the rostrum, but in general the skull is wider than high, and relatively flat. The whole surface posterior to the narial opening is covered in a series of pits and wrinkles. Though pits dominate, there are occasional ornamentations that would be better described as wrinkles or ridges; these are, however, rare. There is an expansion just anterior to the premaxillo-maxillary suture, giving the anterior edge of the snout a keyhole-shaped appearance. There are no teeth in the holotype, and the region surrounding the narial opening is slightly damaged, but otherwise preservation is good.

Premaxilla: Three fragments of premaxillae are preserved from three different individuals. They vary in quality of preservation, with most detail preserved in the holotype. In PIN 2399-301 half of the naris is seen ( Fig. 5 ), and its shape is somewhere between subtriangular and heart-shaped. There is a dorsally oriented projection resulting from an extension of the anterior rami of the premaxillae. This projection extends vertically to a point where the bone is broken off, and could be an intranarial bar or a completely vertical projection ( Fig. 5B ). As the bone is broken, the length of this projection cannot be established, or the extent to which it projects over the narial cavity .

The suture with the maxilla occurs at the same point as the lateral constriction of the snout, meaning that there is a shallow notch here. While it is far shallower than in other species, the constriction is clearly present ( Fig. 5A, B ). All goniopholidids possess this feature, and in many it houses an enlarged mandibular caniniform tooth. As the mandible is not preserved, this cannot be confirmed in Kansajsuchus . The premaxillo-maxillary suture is very roughly serrated, with a wedge of the premaxilla penetrating between the maxilla and nasal bones, giving a clear posterior process to the premaxilla.

The premaxillary section of the palate is only partially preserved, but what has survived is unornamented and raised with respect to the alveoli ( Fig. 5C ). Each tooth in the premaxilla is in its own separate alveolus, and there is a great disparity in size of teeth, with the third and fourth alveolus significantly larger than the others. There is a small diastema beyond the fifth alveolus, with the maxillary and premaxillary teeth separated from each other. There is a notch medially between the third and fourth alveolus that might have housed an enlarged mandibular tooth. The palate at the level of the premaxilla is entirely composed of premaxilla, with the two sides fully extending into the middle.

Maxilla: The anterior part of the maxilla is preserved in the holotype ( PIN 2399-301 ), as well as separately in PIN 2399-307 , which is composed of a right maxilla, now fractured into two pieces, unconnected to any other portion of the specimen ( Fig. 6B ). It is extremely damaged and thin, but the remains of six alveoli are visible in ventral view, with obvious festooning with an increase in size of the teeth. No sutures are apparent on either fragment .

Nasal: The nasal is incompletely preserved in the posteriormost part of the holotype, PIN 2399-301 , as well as more completely in PIN 2399-306 , which is just a nasal bone ( Fig. 6C ). The nasal is ornamented like other skull bones. In dorsal view, the nasal is rectangular and does not taper at either end; although one end is broken to suggest tapering, this is a break rather than a suture. At the anterior end, the nasal is separated from the maxilla by a posteriorly directed process. The angle at which the two unfused nasals contact each other is strongly convex ( Fig. 6C 1 ), implying that the snout itself was very steep-sided. The bone at the maxillary suture is much thicker than it is at the midline. Here it has a laminar appearance when the internal structure is visible—a direct result of several layers of interdigitating bone .

Frontal: One specimen ( PIN 2399-310 ) is a T-shaped piece of the skull including the dorsal and ventral surfaces of the frontal, with part of the palate and the external rim of the orbit ( Fig. 6A ). This bone has ornamentation unlike other specimens, comprising wrinkles and ridges rather than pits. This suggests that the frontal is possibly from anoth- er species, though it may simply be that this skull region showed different patterning. There is a major anteroposterior ridge down the midline ( Fig. 6A 2 ). The frontal is at a lower level than the orbits, the medial extremities of which are preserved. The suture with the nasal bones is extremely clear, and takes the form of a V, with frontal penetration into the nasal region. The frontal does not project strongly in front of the orbit, unlike the condition observed in Sunosuchus , which has an extremely anteriorly placed naso-frontal suture. There is only a single, fused frontal bone, which appears to comprise only a small proportion of skull width .

Parietal: The parietal is preserved as part of PIN 2399- 308, which includes all of the area surrounding the supratemporal fenestrae, as well as the occipital region ( Fig. 7 ). The parietal is a single fused element, as in other derived crocodyliforms, and is flat in lateral view, and relatively broad. The part of the parietal between the supratemporal fenestrae is covered in the same pitted ornamentation as the other dermal skull bones ( Fig. 7D ).

Orbit: The medial edges of the orbits are preserved on the ventral surface of PIN 2399-310 ( Fig. 6A ). The shape is unknown, but the size is reconstructed as larger than the supratemporal fenestrae, based on the curvature present in the preserved fragments. Having orbits larger than the supratemporal fenestrae is often seen in goniopholidids, although this feature is not exclusive of this group.

Postorbital: The right postorbital is complete in PIN 2399- 308, and the anterior half of the left postorbital is preserved in the same specimen ( Fig. 7 ), with the border of the left supratemporal fenestra missing. The jugal process of the postorbital bar is extremely short, being barely present. The bone surface is, as with the other skull roof bones, ornamented, and the postorbital fenestra is present at the anterolateral corner.

Squamosal: The right squamosal is visible in PIN 2399- 308, and like all other skull bones, is ornamented with a series of strong pits ( Fig. 7 ). The left squamosal has been lost through damage to that side of the skull. However, the squamosal does not extend back far enough to reach the ventrally directed squamosal prong ( Fig. 7E ). The region dorsal to the external auditory meatus, which is well preserved, shows the fossa for the muscles involved in the movement of the external ear flap, as in modern alligatorids.

The external auditory meatus is, as in most other crocodyliforms, subcircular in shape, and relatively large and obvious. The suture between the quadrate and the squamosal is deflect- ed anterodorsally ( Fig. 7E ), with the quadrate making up a large part of the distal edge of the external auditory meatus.

Quadrate: The right head of the quadrate is preserved in PIN 2399-468 ( Fig. 8B ). As in Sunosuchus , the medial condylar head is slightly ventrally directed, though the quadrate as a whole is horizontally oriented, and, like the condition in Sunosuchus , the medial condylar head is smaller than the lateral ( Fig. 8B 1 ). The groove on the ventral surface in “ Sunosuchus ” thailandicus is not present in Kansajsuchus , but there is a strongly angled ridge on the lateral edge of the ventral surface ( Fig. 8B 2 ), which may represent the same structure. The dorsal surface is, in comparison, convex, with an antero-posteriorly oriented ridge lying between the condylar heads. In lateral view, it is possible to see the internal structure of the bone, which contains the paths of several sinuses, some of which open onto the dorsal surface of the bone. The largest of these is the cranioquadrate canal, which has its opening near the posterior end of the quadrate, and curves along the length of the preserved specimen.

The anterior ends of the quadrate are also preserved in PIN 2399-308. The otic joint and the external auditory meatus are visible, though this region is slightly damaged around the foramen for cranial nerve VII. The quadrate is sutured simply to the quadratojugal, overlying it for the majority of its face.

Exoccipital: The entire occipital region is preserved in PIN 2399-308. In the exoccipital, all major foramina for the cranial nerves are extremely well preserved ( Fig. 8A ), and the bone damage reveals the spongy nature of the bone and the pattern of sinuses. As with Sunosuchus, Efimov (1975) dealt extensively with the paths of all the sinuses and air channels. The cranial nerves IX, X, and XII, as well as the jugular vein, pass through the largest of the preserved foramina ( Fig. 8A 1 ), and the smaller foramen for the path of a branch of cranial nerve XII is also present. A derived feature is the separate and very small foramen through which the carotid artery passes ( Fig. 8A 2 ), positioned between the foramen magnum and the other foramina. The area for the attachment of the epaxial musculature is large and more vertically oriented than in other forms. This is noted by Efimov (1975) who reports the “bold lateral ridges” on and around the basioccipital for muscle attachment.

Basioccipital: The occipital condyle, which is not dorsoventrally compressed, is subcircular in caudal view ( Fig. 8A 1 ), and has a rim running around the posterior end. There are no basal tubera. The basioccipital surface entirely obscures the underlying basisphenoid, and in this way the basioccipital resembles that of all neosuchians, including all goniopholidids and modern crocodyliforms.

Angular: The angular is preserved in PIN 2399-453, which consists of the rear portion of the right lower jaw ( Fig. 9 ). A suture with one of the neighbouring bones is apparent, and this appears to be the surangular, confirming that this is the rear part of the jaw behind the external mandibular fenestra. The angular is ornamented on the anterior edge with a pattern of pits just as in the bones of the skull, becoming less ornamented posteriorly. What is preserved of the surangular is unornamented. The whole of the preserved section of the mandible is 17 cm long and 8 cm high, which is a relatively large jaw. On the interior surface, there are large neurovascular foramina that housed the inferior alveolar branches of the mandibular nerve and associated blood vessels.

Teeth: The teeth of Kansajsuchus are distinctive and represent the majority of the preserved material from the Yalovachskaya Svita. There are two broad tooth morphologies. The anterior teeth are elongate, slender and pointed, and have extremely pronounced proximodistal ridges on all sides

1

2

( Fig. 4B ). These teeth are recurved slightly, and on the medial (concave) surface, there are two ridges that are thicker and larger than the others, making the shape of the tooth almost triangular in distal view. This double-ridged pattern (i.e., “bicarinate” in Storrs and Efimov 2000) constitutes a very distinctive morphology, so far unparalleled within Crocodylomorpha . The second tooth morphology is seen in the distal end of the dental series; these are shorter, thicker and blunter ( Fig. 4C ), and appear to be better adapted for crushing than the other teeth. The pattern of ridges in the anterior teeth is also present in this morphotype, which suggests that the two tooth morphotypes come from a single heterodont species rather than from two species, with the two tooth morphologies smoothly grading from one end of the dental series to the other. In the more posterior teeth, however, the largest ridges are not as pronounced as on the anterior teeth; they are nonetheless clearly present. The teeth are deep-rooted, descending well into the tooth-bearing bones, with the roots comprising about 60% of the length of the tooth. From the other bones preserved, including a mandibular fragment, the premaxillae and a maxillary fragment, it is clear that each tooth is situated apart from its neighbours in an individual alveolus, and not in a single groove. There is no constriction between the root and crown.

The teeth vary considerably in size, the largest being about 3 cm from the tip of the tooth to the base of the crown in caniniform teeth, and 2 cm in the blunter, slightly molariform teeth. The smallest of the teeth are slightly more than 1 cm long, and the average length seems to be about 2 cm. Local variation in tooth size is seen in PIN 2399-301 , the holotype, where neighbouring alveoli vary substantially in size .

Cervical vertebrae: The neural spine of the cervical vertebrae has a robust base, expanding ventrally to fit onto the neural arch. It is oriented only slightly posteriorly. The centrum is cylindrical, and the zygapophyses are robust, forming a rigid structure ( Fig. 10A ).

Femur: The right femur ( PIN 2399-318) has been damaged in mounting, being split by a metal spike. It is slightly sigmoid in shape, and twisted such that the heads are at 90° to one another ( Fig. 10B 1 ). A large process three-quarters of the way down the bone appears to be an attachment site for the lower leg musculature, apparently extremely enlarged. The bones are slender, being far longer than wide, although the femur is short with respect to the length of Kansajsuchus , which was estimated as 8 metres long by Efimov 1975). As previously discussed, however, this length may be an overestimate. Only one other Asian goniopholidid, “ Sunosuchus ” junggarensis , is in a complete enough state to include the femur, and it had relatively robust limb bones Wu et al. 1996), in contrast to Kansajsuchus . It may well be, then, that the femur attributed to Kansajsuchus belongs to a different species, and should not be included in the generic definition.

Osteoderms: Several dermal osteoderms are preserved, mostly from the dorsal shield, though others are possibly from the belly. The dorsal osteoderms are square, with a strongly pitted ornament. On the anterior edge of the osteoderm is a region that is unornamented, the overlap flange for the neighbouring osteoderm. An anteroventrally directed keel is present along the centre of the osteoderm, and its slope is gentlest at the anterior end. Some osteoderms lack a keel, and these also lack the region of overlap (e.g., Fig. 6D ), but have jagged edges and indications of a complexly arranged suture.

Remarks.—The presence of such a large number of isolated and identical teeth and osteoderms. The teeth in particular are distinctive, with their strongly ridged surface ( Fig. 4B ), which indicates that, while there are a large number of fragments, none of which can definitively be assigned to the same individual, the material is almost certainly from the same species. If there had been several crocodylomorphs in this deposits, other types of teeth and osteoderms should have been discovered. While crocodylomorphs are known from the northern part of the large Fergana Basin, including Peipehsuchus ( Nessov 1995) , which has been attributed to both Pholidosauridae ( Carroll 1988) and Teleosauridae ( Li 1993) , none besides Kansajsuchus extensus is known from the south, indicating that Kansajsuchus extensus should be considered a valid taxon.

Figures

Fig. 5. Crocodylomorph Kansajsuchus extensus Efimov, 1975, holotype, PIN 2399-301 from the Santonian (Upper Cretaceous) of Fergana, Tajikistan. Right premaxilla of an adult crocodilian in dorsal (A), lateral (B), and ventral (C) views. Photographs (A1–C1) and explanatory drawings (A2–C2).

Fig. 6. Crocodylomorph Kansajsuchus extensus Efimov, 1975 specimens from the Santonian (Upper Cretaceous) of Fergana, Tajikistan. A. Portion of frontal bone and posterior end of nasal, PIN 2399-310. B. Broken portion of a left maxilla, PIN 2399-307. C. Anterior section of right nasal bone, PIN 2399-306. D. Example of dorsal dermal osteoderm, PIN 2399-312. In ventral (A –D ) and dorsal (A –D ) views.

Fig. 7. Crocodylomorph Kansajsuchus extensus Efimov, 1975 frontoparietal region from the Santonian (Upper Cretaceous) of Fergana, Tajikistan, PIN 2399-308, in posterior (A), ventral (B), anterior (C), dorsal (D), and lateral (E) views, clearly demonstrating the trapezoidal shape of the skull roof, and the near-circular fenestrae.

Fig. 8. Crocodylomorph Kansajsuchus extensus Efimov, 1975 basioccipital region and quadrate, preserving several nerve and vascular foramina. Specimens from the Santonian (Upper Cretaceous) of Fergana, Tajikistan. A. PIN 2399-308 (second part) in posterior (A1), ventral (A2), and dorsal (A3) views. B. PIN 2399-468, a quadrate in posterior (B1), dorsal (B2), and ventral (B3) views.

Fig. 9. Crocodylomorph Kansajsuchus extensus Efimov, 1975 left angular region of the mandible. Specimens from the Santonian (Upper Cretaceous) of Fergana, Tajikistan, PIN 2399-453, in ventral (A), dorsal (B), medial (C), and lateral (D) views.

Fig. 10. Crocodylomorph Kansajsuchus extensus Efimov, 1975 postcranial material from the Santonian (Upper Cretaceous) of Fergana, Tajikistan. A. Cervical vertebra, PIN 2399-304, in anterior (A 1) and lateral (A 2) views. B. Left femur, PIN 2399-318, in posterior (B ) and lateral (B ) views.

Fig. 1. Adult crocodylomorph “Sunosuchus” thailandicus Buffetaut and Ingavat, 1980, PIN 4174-1, from the Tithonian (Upper Jurassic) of Shar Teeg, Mongolia. A. Rostrum, quadrates, and occipital condyle in dorsal aspect. B, C. Rostrum and mandible in left (B) and right (C) views. Photographs (A 1 –C 1) and explanatory drawings (A –C ).

Fig. 2. Crocodylomorph “Sunosuchus” thailandicus Buffetaut and Ingavat, 1980 dentition, PIN 4174-1, from the Tithonian (Upper Jurassic) of Shar Teeg, Mongolia. A. Rostrum in palatal aspect. Photograph (A1) and explanatory drawing (A2). B. Anterior mandible in dorsal view, from symphysis to the anterior edge of the external mandibular fenestra.

Fig. 4. Teeth of crocodylomorphs from the Cretaceous of Central Asia. A. “Sunosuchus” thailandicus Buffetaut and Ingavat, 1980, left mandibular tooth of PIN 4174-1. Tooth is from mid-mandible and is similar in size to all of the other mandibular teeth, which show little size variation. B, C. Kansajsuchus extensus Efimov, 1975. B. Caniniform tooth of PIN 2399-313 in anterior (B1), posterior (B2), and lateral (B3) views. The tooth is characterized by prominent ridges, including a distinctive “double keel” on the posterior side of the tooth. The tooth is from the anterior part of the jaw. C. Molariform tooth of PIN 2399-314 in posterior (C1), anterior (C2), and lateral (C3) views. The tooth shares the ridges characteristic of Kansajsuchus, including a less prominent version of the double keel, but is blunter, and derived from the posterior part of the jaw.