Two New Basal Crocodylomorph Archosaurs from The

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Blackwell Science, LtdOxford, UKZOJZoological Journal of the Linnean Society0024-4082The Linnean Society of London, 2002September 2002 1361 7795 Original Article

TWO NEW CROCODYLOMORPHS

J. M. CLARK and H.-D. SUES Zoological Journal of the Linnean Society, 2002, 136, 77–95. With 7 figures

Archosaurian anatomy and palaeontology. Essays in memory of Alick D. Walker. Edited by D. B. Norman and D. J. Gower

Two new basal crocodylomorph archosaurs from the Lower Jurassic and the monophyly of the Sphenosuchia Downloaded from https://academic.oup.com/zoolinnean/article/136/1/77/2624221 by guest on 23 November 2020 JAMES M. CLARK* and HANS-DIETER SUES FLS†

*Department of Biological Sciences, George Washington University, Washington, DC 20052, USA, †Department of Palaeobiology, Royal Ontario Museum, 100 Queen’s Park, Toronto, ON M5S 2C6, and Department of Zoology, University of Toronto, Toronto, ON M5S 3G5, Canada

We report on and name two new taxa of basal crocodylomorph archosaurs from the Lower Jurassic, Litargosuchus leptorhynchus gen. et sp. nov., from the upper Elliot Formation (Stormberg Group) of South Africa, and Kayen- tasuchus walkeri gen. et sp. nov., from the Kayenta Formation (Glen Canyon Group) of Arizona, USA. Exami- nation of this material led to a reconsideration of basal crocodylomorph interrelationships. A phylogenetic analysis found no support for the monophyly of Sphenosuchia. © 2002 The Linnean Society of London. Zoological Journal of the Linnean Society, 2002, 136, 77–95.

ADDITIONAL KEYWORDS: Reptilia – Crocodylomorpha – Sphenosuchia – anatomy – phylogeny – Jurassic.

INTRODUCTION Formation (Stormberg Group) of South Africa that was briefly described and identified as Pedeticosaurus In two papers that laid the foundation for our under- sp. by Gow & Kitching (1988). The second is based on standing of interrelationships among crocodile-like a skull and skeleton from the Kayenta Formation archosaurs, Walker (1968, 1970) formally established (Glen Canyon Group) of Arizona and has previously Crocodylomorpha as a group comprising Crocodylia been referred to as the ‘Kayenta Form’ (Clark in (in traditional usage) and a host of early Mesozoic taxa Benton & Clark, 1988; see also Sues et al., 1994). previously placed in the grade group ‘Thecodontia’. The first phylogenetic analyses of crocodylomorph The best known among the latter taxa is Sphenosu- relationships concluded that sphenosuchians are a chus acutus, which Walker studied in great detail over paraphyletic grouping (Clark in Benton & Clark, the course of three decades, culminating in his magis- 1988; Parrish, 1991), with some being more closely terial monograph (Walker, 1990). Subsequent phyloge- related to Crocodyliformes (sensu Clark, 1986 = Cro- netic analyses (e.g. Clark in Benton & Clark, 1988; codylia of traditional usage) than others. However, Parrish, 1991; Clark et al., 2001) have consistently two subsequent studies independently supported the corroborated the monophyly of the Crocodylomorpha monophyly of Sphenosuchia (Sereno & Wild, 1992; Wu but arrived at different conclusions about the interre- & Chatterjee, 1993). Recently we have presented a cri- lationships of its constituent taxa. In particular, it tique of these analyses and reassessed relationships has been unclear whether basal crocodylomorphs form among sphenosuchians (Clark et al., 2001), with the a monophyletic grouping Sphenosuchia or whether result that most sphenosuchians form a monophyletic some are more closely related to crocodylians than are group with the possible exception of the taxon repre- others. In this paper we describe two new basal cro- sented by a skeleton referred to Pedeticosaurus by Gow codylomorph reptiles from the Lower Jurassic and & Kitching (1988). However, that analysis did not reassess the monophyly of the Sphenosuchia. The first include the Kayenta form and we had not yet had the is based on a skull and skeleton from the upper Elliot opportunity of first-hand examination of the specimen reported by Gow & Kitching. In this paper, we Correspondence. Hans-Dieter Sues. E-mail: [email protected] redescribe the skull of the latter, describe the Kayenta

78 J. M. CLARK and H.-D. SUES specimen, and present a reanalysis of sphenosuchian paration, and at this time we cannot significantly interrelationships. add to the brief account provided by Gow & Kitching (1988). A NEW CROCODYLOMORPH FROM THE LOWER JURASSIC OF SOUTH AFRICA CROCODYLOMORPHA HAY, 1930 SENSU WALKER, 1970 Gow & Kitching (1988) figured and briefly described SPHENOSUCHIDAE HAUGHTON, 1924 much of the skeleton, including a substantially com- LITARGOSUCHUS GEN. NOV plete skull and mandible, of a small, gracile crocody- Etymology. From Greek litargos, running fast, and lomorph archosaur from the upper Elliot Formation Greek soukhos, crocodile, in reference to the inferred (Stormberg Group; Lower Jurassic) of South Africa. cursorial habits of this crocodylomorph reptile.

The specimen was collected by James W. Kitching Downloaded from https://academic.oup.com/zoolinnean/article/136/1/77/2624221 by guest on 23 November 2020 (Bernard Price Institute for Palaeontological Re- Type species. Litargosuchus leptorhynchus sp. nov. (by search, University of the Witwatersrand, Johan- monotypy). nesburg) from strata just 2 m below the contact with Diagnosis. As for the type and only known species, the Clarens Formation, on the farm Eagles Crag, given below. Barkley East. Gow and Kitching referred the skeleton (Bernard Price Institute for Palaeontological Research, BP/1/5237) to Pedeticosaurus, identifying it LITARGOSUCHUS LEPTORHYNCHUS SP. NOV. as Pedeticosaurus sp. The type species of Pedeticosau- 1988 Pedeticosaurus sp. Gow & Kitching, p. 518. rus, P. leviseuri, was described by Van Hoepen (1915) Etymology. From Greek leptos, thin, delicate, and on the basis of a natural mould that mainly preserves Greek rhynchos, snout, muzzle. the impression of the right side of a skeleton from the Lower Jurassic Clarens Formation of Lesotho (for- Diagnosis. Parietals partially fused and devoid of merly Orange Free State). That specimen is housed sagittal cresting. Squamosal broad transversely and in the collections of the National Museum in without dorsolateral crest. Dentaries forming exten- Bloemfontein, where it is now catalogued as QS 606 sive symphysis, with little or no splenial involvement. (Bonaparte, 1972b). Van Hoepen placed Pedeticosau- Holotype. BP/1/5237, skull, mandible and much of the rus in its own family, Pedeticosauridae, and consid- postcranial skeleton, first identified as Pedeticosaurus ered it “only closely allied to one of the four known sp. by Gow & Kitching (1988). The postcranium is rep- families of the Pseudosuchians, i.e. the Ornitho- resented by the mostly articulated presacral vertebral suchidae”. Subsequently, this taxon has variously column and scattered parts of caudal series, both scap- been referred to the Protosuchia (Haughton & Brink, ulae and coracoids, both humeri, left radius and ulna, 1954; Romer, 1956; Bonaparte, 1972a,b; Clark, 1986) part of the left ilium, both ischia, left hindlimb (with or Sphenosuchia (‘Pedeticosauria’) (Walker, 1968, the exception of the proximal portion of the femur and 1970; Gow & Kitching, 1988). Walker (1970) and most of the pes), and distal portion of right femur. Clark (1986) based their observations and interpreta- In view of its small size and gracile build, BP/1/5237 tions on casts of the holotype, whereas Bonaparte possibly represents a juvenile. Closure of the neuro- (1972b) re-examined the actual fossil. Bonaparte central sutures along the vertebral column provides a interpreted P. leviseuri as a protosuchian primarily on particularly useful osteological criterion for ontoge- the basis of the broad, laterally overhanging squamo- netic assessment (Brochu, 1996). Open neurocentral sal. However, Clark (1986) pointed out that the latter sutures are apparent on the cervical vertebrae, but character was more widely distributed among Cro- preservation and current state of preparation do not codylomorpha, but he regarded the relatively broad permit identification of this feature in the dorsal col- scapula of P. leviseuri with its strongly concave ante- umn. rior margin as suggestive of crocodyliform affinities. He noted that this taxon may well be synonymous Type horizon and locality. Upper Elliot Formation with the protosuchid crocodyliform Protosuchus (Stormberg Group), 2 m below the contact with the haughtoni, which is known from the upper Elliot For- Clarens Formation, on the farm Eagles Crag, Barkley mation of South Africa. In view of the poor preserva- East, South Africa. Age: Early Jurassic. tion of and absence of clearly diagnostic features in the holotype of P. leviseuri, Clark (1986) considered that binomen a nomen dubium. SKULL We have re-examined the skull of BP/1/5237 after Gow & Kitching (1988) provided only a brief account careful additional cleaning of some regions. The of the structure of the skull, and examination of the postcranial skeleton requires much additional pre- specimen revealed much additional detail.

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Figure 1. Litargosuchus leptorhynchus gen. et sp. nov. Skull in (A) dorsal and (B) ventral views. Abbreviations for Figs 1, 2: ao.f = antorbital fenestra; ar = articular; cb = ceratobranchial I; d = dentary; e.m = external mandibular fenestra; ec = ectopterygoid; en = external naris; f = frontal; j = jugal; l = lacrimal; m = maxilla; n = nasal; or = orbit; p = parietal; pl = palatine; pm = premaxilla; prf = prefrontal; po = postorbital; po.p = paroccipital process; pt = pterygoid; q = quadrate; sq = squamosal; sp. = splenial; v = vomer. Scale bar = 1 cm.

The skull (Figs 1, 2) was dorsoventrally flattened It is 63 mm long (measured along the midline of the during fossilization. As a result of this crushing, the skull roof from the anterior tip of the snout to the mandibular rami are now tightly appressed to the anteromedial end of the occipital embayment). The skull. The individual bones, with the exception of those orbit is large, with an anteroposterior diameter of constituting the palate and ventral portion of the about 16 mm. The supratemporal fossae are delimited braincase, are well-preserved, but some are traversed medially and posteriorly by faint ridges on the parietal by fractures. They are delicate, smooth and devoid of and squamosal. The supratemporal fenestrae are sculpturing. The specimen was preserved in a hard, much longer than wide, resembling those of Terres- haematite-rich matrix, and removal of the encrusting trisuchus (Crush, 1984). haematite layer by mechanical means resulted in local On the better preserved left side, the recurved pos- loss of surficial bone. The occipital region is partially terolateral process of the small premaxilla overlaps obscured by unidentified pieces of bone. the nasal and maxilla on the side of the snout, exclud- In dorsal view, the skull has a narrow snout and a ing the latter element from participation in the poste- transversely broad temporal region (although its rior margin of the laterally directed external naris. width was accentuated by dorsoventral compression). The anterior ends of the premaxillae appear to be

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Figure 2. Litargosuchus leptorhynchus gen. et sp. nov. Skull in (A) left lateral and (B) right lateral views. Scale bar = 1 cm.

drawn out into a point. The left premaxilla holds four The lacrimal has the shape of an inverted L and is teeth, the ﬁrst of which is the smallest; three teeth are inclined forward in lateral view. It forms the preorbital preserved in the more incomplete right premaxilla. bar and contributes a broad medial lamina to the Contra Gow & Kitching (1988), the presence of a lat- medial wall of the antorbital fossa. The lateral surface eral notch between the premaxilla and maxilla cannot of its vertical portion bears a thin but distinct ridge. be ascertained due to poor preservation of this region Posteriorly, the lacrimal forms an extensive lateral on either side of the snout. contact with the prefrontal along the preorbital bar. The low but long maxilla forms most of the rostral Dorsally, it is narrowly exposed on the skull roof. portion of the skull. In lateral view, its alveolar margin The prefrontal forms the anteromedial portion of is almost straight. The facial portion of the maxilla is the dorsal rim of the orbit. It is overlapped by the vertical. Its ascending process projects posteriorly as frontal posterolaterally. The dorsal surface of the pre- well as slightly dorsally and contacts the anterior frontal is subtriangular in outline. ramus of the lacrimal half way along the dorsal rim of The posterior process of the jugal is deep dorsoven- the antorbital fenestra, excluding the nasal from par- trally and faces ventrolaterally (although this may be ticipation in the dorsal margin of the antorbital fossa. due to dorsoventral compression of the skull). Its dor- The ventral margin of the large, subtriangular antor- sal process for contact with the descending process of bital fossa is deeply recessed relative to the remainder the postorbital is short and delicate. The anterior pro- of the lateral surface of the maxilla. The antorbital cess of the jugal forms the ventral margin of the orbit fenestra is situated in the posteroventral corner of the but does not extend to the posteroventral corner of the antorbital fossa. It is long anteroposteriorly but low antorbital fenestra and fossa anteriorly. dorsoventrally. The more completely preserved left The dorsoventral crushing of the skull has pushed maxillary tooth row comprises at least 18 teeth (16 of the quadrates up through the supratemporal fenes- which are completely or partially preserved) and ter- trae. Few details are visible. minates posteriorly just behind the anterior margin of The frontal is much longer than wide and forms the orbit. most of the skull roof as well as the slightly raised dor- The nasal extends back almost to the level of the sal rim of the orbit. Its dorsal surface is concave trans- anterior margin of the orbit. Its lateral sutural contacts versely. Although the frontals are somewhat thicker with the maxilla, lacrimal and prefrontal are nearly along their median sutural contact they do not form a straight. Its tapered anterior portion forms most of the distinct ridge as in Hesperosuchus (Clark et al., 2001) dorsal margin of the narial fenestra. The dorsal surface and Sphenosuchus (Walker, 1990). Anteriorly, the fron- of each nasal bears several neurovascular foramina, tals extend forward for a short distance between the especially a large one in the posterior quarter. The con- posterior ends of the nasals along the midline of the tact between the ascending process of the maxilla and skull roof. Posteriorly, they contact the parietals along the anterior process of the lacrimal excludes the nasal a transverse suture. The frontal does not participate from the dorsal margin of the antorbital fossa. in the anterior margin of the supratemporal fenestra.

TWO NEW CROCODYLOMORPHS 81

The interparietal suture is present only on the or contributed only minimally to its formation. The anterodorsal portion of the skull roof and cannot be articular forms a distinct, dorsomedially directed traced more posteriorly. The parietals lack extensive process. posterolateral wings and form a weakly concave embayment in the occipital margin of the skull roof. Their dorsal surface is very slightly concave trans- DENTITION versely between the medial margins of the supratem- All teeth have labiolingually ﬂattened crowns with poral fossae. The sutural contact betwen the parietal anterior (mesial) and posterior (distal) carinae. Pres- and squamosal posterior to the supratemporal fenes- ervation of individual teeth is poor, and it cannot be tra is short. determined whether the carinae were serrated or The postorbital is triradiate in lateral view. It forms smooth; the carinae are serrated in all other known

the anterior half of the dorsal margin of the supratem- basal crocodylomorphs. The premaxillary and anterior Downloaded from https://academic.oup.com/zoolinnean/article/136/1/77/2624221 by guest on 23 November 2020 poral bar and overlaps the squamosal posteriorly. maxillary teeth have slender and distinctly recurved Anteromedially, the postorbital contacts the postero- crowns. In the left maxilla, the teeth in positions 4–6 lateral end of the frontal. Its ventral process for con- appear to have the tallest crowns. The more posterior tact with the ascending process of the jugal is delicate. teeth have shorter and less recurved crowns. No palpebral bones are preserved. The rather broad squamosal forms the posterolateral corner of the skull roof and resembles the homo- A NEW CROCODYLOMORPH FROM THE logous element in Crocodyliformes. It is thin and LOWER JURASSIC OF ARIZONA ventrally somewhat concave. The lateral edge of the A specimen of a basal crocodylomorph from the Early squamosal is deflected and overhangs the infratempo- Jurassic Kayenta Formation collected by J.M.C. in ral region and suspensorium laterally. Anteriorly, the 1983 represents a new taxon. It consists of a single squamosal extends ventral to the postorbital to par- articulated skeleton that includes examples of most of ticipate in the formation of the postorbital bar. The the skeletal elements and was found in the ‘silty facies’ dorsal surface of the squamosal is broad and gently of the Kayenta Formation near Willow Springs, some convex transversely. It lacks the posterolateral crest 50 km north-east of Flagstaff, Arizona. The specimen bordering the supratemporal fossa found in most occurred in a channel sandstone 3 m above the level of basal crocodylomorph archosaurs except Terrestrisu- the localities identified in Clark & Fastovsky (1986: chus (Crush, 1984). fig. 7). It is preserved in a red sandy siltstone rather The distal end of the paroccipital process formed by than the blue or green-coloured siltstones or mud- the otoccipital (fused exoccipital and opisthotic) is stones from which most vertebrate fossils in the silty expanded dorsoventrally. The post-temporal foramen facies are derived. Most bones are encrusted by a thin is located at the sutural contact between the squamo- layer of haematite. Nearly all of the skeletal elements sal, otoccipital, and supraoccipital and is very small. appear to represent a single individual; however, a The palate is poorly preserved; it is represented by fragmentary left premaxilla removed from the speci- the posterior portions of the vomers, the palatines and men during its excavation duplicates that on the fragments of the pterygoids. The vomers contact each articulated rostral fragment and thus represents a other along the midline. The long medial portion of the second individual. No other fossils were found within ectopterygoid extends posteriorly along the anterolat- several metres of the specimen; however, a number of eral edge of the transverse flange of the pterygoid. specimens of turtles (Kayentachelys), ornithischian Long, rod-like bones preserved on both sides of the dinosaurs (Scutellosaurus), and tritylodontids were palate probably represent the ceratobranchialia I of recovered from within 100 m of the specimen from a the hyoid apparatus, as in extant crocodylians. They stratigraphic level 3 m below it. have been somewhat warped during fossilization.

MANDIBLE KAYENTASUCHUS GEN. NOV. The mandibular rami are long and very slender. The Etymology. Kayenta, in reference to the formation external mandibular fenestra is long and low. The from which the holotype was collected, and Greek number of dentary teeth cannot be determined due to soukhos, crocodile. the tight contact between the mandibular rami and Type species. Kayentasuchus walkeri sp. nov. (by the skull. monotypy) The dentaries form a rather long symphysis, which extends back to the level of the third maxillary tooth. Diagnosis. As for the type and only known species, The splenial either did not enter into the symphysis given below.

KAYENTASUCHUS WALKERI SP. NOV. lary portion is no longer preserved). Each naris narrows posterodorsally and thus has a slightly oval Etymology. In memory of Alick D. Walker for his many outline. contributions to our understanding of Sphenosuchus An antorbital fenestra is present just anterior to the and other archosaurs. orbit. It forms a roughly equilateral triangle in out- Holotype. University of California Museum of Palae- line, with a vertical posterior margin, an horizontal ontology (UCMP) 131830, a nearly complete but dorsal edge, and an oblique anteroventral margin; fragmented skeleton including an incomplete skull the dorsal edge descends to a slight degree anteri- with articulated mandibular rami, articulated trunk orly. The maxilla forms the ventral margin, the lacri- region, articulated right ilium and femur, and other as mal the posterior, and the two bones meet midway yet unprepared postcranial bones. along the dorsal edge; the jugal may enter into the

posterior margin of the fenestra, but, if this is indeed Downloaded from https://academic.oup.com/zoolinnean/article/136/1/77/2624221 by guest on 23 November 2020 Type horizon and locality. Near the middle of the the case, it forms only a very small part of that mar- Kayenta Formation (Glen Canyon Group) in the gin. The fenestra, which is about one third the length ‘silty facies’ of that unit (Clark & Fastovsky, 1986). of the maxilla, is relatively shorter than in Saltoposu- Badlands at Willow Springs, Rock Head 7.5 Minute chus and Pseudhesperosuchus, but is similar in length Quadrangle, NE Arizona, USA. Age: Early Jurassic to the opening in Sphenosuchus and Dibothrosuchus. (Sues et al., 1994). Its shape differs from that in the latter, which is more Diagnosis. Anterior process on maxilla projecting into nearly circular, and those of the other three, which are well-developed, slit-like recess between premaxilla more elongate and oval. A fossa is present in the and maxilla. Outline of antorbital fenestra forming maxilla anterior to the fenestra. equilateral triangle. Squamosal descending along lat- The squamosals are broadened to form a ‘skull table’ eral edge of paroccipital process. Elongate mandibular as in crocodyliforms, but, unlike the ﬂat surface of cro- symphysis with only minimal involvement of splenial. codyliform squamosals, that of Kayentasuchus bends Dentary without enlarged anterior caniniform tooth ventrally lateral to the quadrate and faces laterally. and lacking teeth at anterior tip. Shares with Cro- This may be due to some extent to lateral compression codyliformes presence of a groove along lateral edge of during fossilization, but a ridge along the edge of the squamosal on dorsal surface. occiput at the bend in the squamosal indicates that the bend is natural. The supratemporal fenestrae are relatively elon- SKULL gate, similar in length to those of other sphenosu- The skull of the specimen (Figs 3, 4) was compressed chians except for Dibothrosuchus, in which the laterally during fossilization but otherwise appears fenestrae are shorter. The fenestrae of Kayentasuchus undistorted. It broke into several fragments during are much longer than wide, and although this has excavation. The left side of the rostrum is well- been accentuated by the lateral compression of the preserved and intact, and is preserved in articulation specimen the original dimensions could not have been with the left dentary. The right nasal is preserved with signiﬁcantly different from the observed condition. this piece, but the fragmentary right maxilla, premax- The post-temporal fenestra is small but is not illa and dentary and a large fragment of the frontals absent (as in Dibothrosuchus). It lies at the junction of were recovered separately. The posterior portions of the squamosal, parietal, otoccipital, and supraoccipi- the right and left mandibular rami are also preserved tal. This area is crushed on the better preserved left separately. The dorsal part of the braincase and skull side of the skull, but the smooth ventral edge of the roof have been assembled from individual fragments fenestra is present on the right side. On the left side into right and left halves, preserving most details; the the squamosal appears to form a groove which enters ventral part of the prootic and part of the basisphenoid the lateral edge of the fenestra, but this may be due to are preserved on the right side only. crushing. The snout (Fig. 3) is relatively deep and narrow; The surfaces of most of the skull bones, with the even allowing for distortion, it is at least four times exception of the frontal and squamosal, are smooth higher than wide at the level of the antorbital fen- and devoid of sculpturing. The dorsal surface of the estra. It is comparable in length to Sphenosuchus frontal bears weakly developed pitting along the mid- (Walker, 1990) and Dibothrosuchus (Wu & Chatterjee, line. The squamosal is rugose near its lateral edge. 1993) and shorter than in Pseudhesperosuchus The sculpturing composed of small pits and grooves (Bonaparte, 1972a) and Terrestrisuchus (Crush, 1984). typical of crocodyliform cranial bones is absent. The external nares are terminal and laterally The premaxilla is a small and slender bone forming directed. They are divided by a bony bar composed of most of the border of the external naris (Fig. 3). A slen- the nasals and premaxillae (although the premaxil- der posterodorsal process overlies the nasal and max-

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Figure 3. Kayentasuchus walkeri gen. et sp. nov. Holotype skull. A, left lateral view of reconstructed skull; shape of dentary probably distorted during fossilization. B, posterior view of occiput as preserved. Abbreviations: ao.f = antorbital fenestra; d = dentary; e.m = external mandibular fenestra; f. m = foramen magnum; g = lateral groove on squamosal; j = jugal; l = lacrimal; m = maxilla; n = nasal; or = orbit; ot = otoccipital; p = parietal; pm = premaxilla; po.p = paroccipital process; pt.f = post-temporal fenestra; so = supraoccipital; sq = squamosal. Scale bar = 1 cm. illa in what appears to be a weak suture behind the of the antorbital fenestra and the nares, the lateral naris, rather than abutting against them as in cro- part of the nasal is bent ventrolaterally and faces dor- codylians. The body of the premaxilla forms the ante- solaterally. A longitudinal ridge occurs where the bone rior edge of a laterally open notch between it and the bends. More posteriorly, the entire bone faces dorsally maxilla; this edge is gently convex posteriorly, and the and meets the frontal at the level of the anterior end of premaxilla and maxilla do not meet below the notch. A the orbit. It presumably also contacted the prefrontal process must have ascended from the anterior part of in this region, but neither prefrontal has been pre- the premaxilla near the midline to form the ventral served on the rostral fragment. The nasal does not half of the internarial bar, but it has been broken away. form any part of the fossa associated with the antor- The premaxillae meet only at the tip of the rostrum bital fenestra. and do not meet posterior to the incisive foramen, so The maxilla forms most of the facial region of the they do not form part of the secondary bony palate. snout as well as a short secondary bony palate (Fig. 3). The nasals form the dorsal surface of the snout Its facial portion is vertical. The length of the maxilla between the naris and the frontals. Each extends is more than twice its maximum height. It is lower anteriorly to form the posterodorsal half of the inter- anteriorly and gradually increases in depth posteri- narial bar, although the tips are broken off. The nasal orly. The combined length of the antorbital fossa and borders the maxilla and lacrimal along their medial fenestra is approximately one-half that of the maxilla. edges, and this contact is straight. Between the level The fossa has the same shape as the fenestra but is

© 2002 The Linnean Society of London, Zoological Journal of the Linnean Society, 2002, 136, 77–95 84 J. M. CLARK and H.-D. SUES longer anteriorly and shorter posteriorly. The anterior surface and broadens medially. The lacrimal broadens end of the fossa narrows to a rounded end opposite the ventrally at the contact with the maxilla (and possibly sixth tooth. The anterior tip of the fossa enters into a jugal), and it may also meet the palatine in this area. large foramen which communicates with the interior The contact between the lacrimal and prefrontal is not surface of the maxilla. The anterior edge of the maxilla preserved. The posterior entrance of the lacrimal forms the posterior part of the notch with the premax- canal could not be identiﬁed. illa and has a short anterior process that projects into The jugal is represented only by the anterior end of the notch. The dorsal part of the maxilla contacts the the left element lying beneath the orbit. It is rela- lacrimal half way along the dorsal edge of the antor- tively narrow compared with that of crocodylians. Its bital fenestra and at the posteroventral angle of the contact with the lacrimal is not evident, but it clearly fenestra. The full extent of the contact between the did not ascend far dorsally as in some basal archo-

maxilla and jugal is not obvious on the specimen, but saurs. The medial surface of the anterior end is Downloaded from https://academic.oup.com/zoolinnean/article/136/1/77/2624221 by guest on 23 November 2020 most of it lies ventral to the lacrimal so that the max- concave, wrapping around the posterior end of the illa does not extend posteriorly beneath the orbit. At maxilla. its contact with the jugal the ventrolateral part of the The squamosal lies at the posterolateral corner of maxilla has a thin lamina which ascends dorsally to the upper temporal region, extending laterally over overlie part of the jugal, although the jugal overlies the quadrate. It is thin and similar to that of Saltopo- the maxilla along most of the contact. The ventral bor- suchus (Sereno & Wild, 1992) and Terrestrisuchus der of the maxilla is straight, lacking the ‘festooning’ (Crush, 1984). Laterally, it bends downward so that commonly found in crocodyliforms. Small neurovascu- this part of the bone is orientated vertically (Fig. 3). lar foramina are present on the lateral surface of the This may be partly owing to the lateral compression of maxilla dorsal to the tooth row; there are slightly the fossil, but the shape of the occipital portion of the fewer foramina than teeth. bone suggests that the bend is for the most part a nat- The anterior halves of the maxillae form a second- ural feature. The border of the occipital portion of the ary bony palate, which extends back to the level of the bone has a smoothly curved edge that follows the bend sixth maxillary tooth. From here it continues posteri- in the body of the bone, so that, had the body of the orly as a narrow palatal shelf. The palatine contacts bone been essentially horizontal before crushing, the the maxilla posterior to this narrow shelf. The ventral fragmentation of the occiput would have been more surface of the secondary palate is covered with many severe. The medial part of the squamosal also bends tiny pits in a pattern similar to that seen on the occip- downward abruptly along the lateral edge of the ital surface of the squamosal. At the midline, the bone supratemporal fenestra, although a true descending rises dorsally to form a longitudinal ridge along the process as seen in primitive archosaurs and dinosaurs dorsal surface of the secondary palate. Slightly poste- is absent. This portion of the bone is relatively short rior to the secondary bony palate, a ridge arises from and of an even height throughout. the dorsal surface of the palatal shelf and ascends a The contact between the quadrate and squamosal short distance anterodorsally onto the medial surface lies along this part of the bone. Anteriorly, lateral to of the facial part of the maxilla; possibly soft tissue the supratemporal fenestra, this contact is a lap joint, forming the dorsal roof of the narial passage attached with the squamosal lying medial to the quadrate. Pos- to this ridge. The vomer articulates bluntly with the teriorly, in the area where the quadrate contacts the maxilla at the posterodorsal edge of the secondary prootic, the quadrate abuts directly against the ven- bony palate along the midline. tral surface of the squamosal, although there is a The vertically oriented lacrimal separates the small ventral extension of the squamosal lateral to the antorbital fenestra and orbit (Fig. 3). Most of the left quadrate. The dorsal part of the quadrate continues element is preserved on the rostral fragment except posteriorly beneath the squamosal to contact the ante- for its posterodorsal part near the contact with the rior surface of its occipital part. There is no indication prefrontal. The ventral portion of the lacrimal is ver- of a socket within the squamosal for the quadrate, as tical and forms the posterior border of the antorbital in Sphenosuchus (Walker, 1990) and more primitive fenestra and the anterior border of the orbit. The dor- archosaurs. As in crocodyliforms (with the exception of sal portion of the bone is horizontal and extends ante- Eopneumatosuchus; Crompton & Smith, 1980), the riorly dorsal to the antorbital fenestra. It is narrow, as anterior part of the quadrate is not sutured to the in Sphenosuchus, rather than having a broad ventral squamosal, but merely underlies it. However, a break lamina extending into the antorbital fossa, as in in the right squamosal reveals that, unlike in cro- Pseudhesperosuchus (Bonaparte, 1972a) and Terres- codyliforms, the quadrate is not sutured to the squa- trisuchus (Crush, 1984). The ventral part of the lacri- mosal posterior to the supratemporal fenestra. The mal is gently concave posteriorly and gently convex anteroposterior development of the quadrate beneath anteriorly. It bears a thin vertical ridge on its lateral the squamosal suggests that little, if any, movement

© 2002 The Linnean Society of London, Zoological Journal of the Linnean Society, 2002, 136, 77–95 TWO NEW CROCODYLOMORPHS 85 was possible along this contact, especially in an along an open suture, but posteriorly the break is not anteroposterior direction. directly through the midline and no suture is appar- The occipital portion of the squamosal (Fig. 3) is ent. It is possible that, as in Litargosuchus, the pari- extensive, being equal in height to the supraoccipital etals were fused posteriorly but suturally separated bone. It descends ventrally along the posterior surface more anteriorly. The anterior end of the bone is miss- of the paroccipital process to opposite the dorsal bor- ing from the braincase pieces, but a fragment contain- der of the foramen magnum. Its ventral edge is ing the anterior end of the left parietal and the straight and horizontal. The squamosal appears to posterior end of the frontal is preserved. In dorsal underlie the parietal posteriorly on the occipital sur- view, the parietal broadens posteriorly and, to a lesser face. The two bones meet along an extensive contact so extent, anteriorly; thus the lateral edge of the bone is that the squamosal has no, or a very slight, contact concave where it borders the supratemporal fenestra.

with the supraoccipital. In posterior view, the contact Anteriorly, near the frontal contact, the lateral edges Downloaded from https://academic.oup.com/zoolinnean/article/136/1/77/2624221 by guest on 23 November 2020 between the squamosal and parietal is oblique, become parallel. The parietal is similar in length to extending ventromedially from the dorsal surface of that of Sphenosuchus, Saltoposuchus, Terrestrisuchus, the skull. The occipital surface of the squamosal is and Pseudhesperosuchus. A distinct rugose ridge along covered with tiny pits. the lateral edge of the parietal clearly marks the The lateral surface of the squamosal is broadest pos- dorsal limit of m. adductor mandibulae within the teriorly, its ventral edge being orientated obliquely at supratemporal fenestra. These ridges are separated an angle of about 45 °. The occipital portion of the by a broad expanse of bone on the skull roof, in con- squamosal extends ventrally along the lateral edge of trast with Sphenosuchus and Dibothrosuchus in which the paroccipital process to cover its lateral surface. a very narrow sagittal crest is formed along the dorsal The lateral edge of the squamosal on the occiput forms midline. The dorsomedial surface is broadly rounded a strong ridge that extends posteriorly. It has a rough transversely, and the lateral edge of the dorsal surface surface, especially dorsally. The lateral surface of the is turned upward. The parietal extends ventrally from squamosal is sculptured in a complex pattern. The its lateral ridge to meet the endochondral bones of the area along the anteroventral edge is roughened, and a braincase (Fig. 4). It contacts the laterosphenoid ven- low ridge is developed paralleling this roughness pos- trally along the medial surface of the supratemporal terodorsally. Together these two features form a fenestra, and in this area the lateral surface of the groove extending most of the length of the bone parietal is relatively flat. Posterior to the supratempo- (Fig. 3). Anteriorly, this groove extends onto the dorsal ral fenestra the parietal contacts the prootic. Here its surface of the bone as the descending portion of the lateral surface is concave, with the ventral edge flar- bone gradually narrows. The ridges and groove termi- ing laterally at the prootic contact. The parietal con- nate posteriorly opposite the level of the occiput where tacts the supraoccipital at the posterior end of the the groove turns downward and reaches the ventral braincase, where it entirely overlies the supraoccipital edge of the bone. The groove may have served for the dorsally. The extensive occipital portion of the parietal attachment of muscles for an ear flap as in extant cro- (Fig. 4) is wedge-shaped, thinning ventrally. It has codylians (Shute & Bellairs, 1955). A raised area is sit- broad contacts with the squamosal laterally and the uated within the groove at its posterior end, as seen on supraoccipital medially on the occiput, and it has only the right side. Posterior to the groove, the lateral sur- limited (if any) ventral contact with the otoccipital. In face of the squamosal is roughened in a more regular dorsal view, the posterior edge of the parietal is con- pattern. cave posteriorly. The area dorsal to the supraoccipital The contact between the parietal and squamosal is strongly concave, but flattens out laterally. posterior to the supratemporal fenestra on the dorsal The frontals roof the orbits. They are incompletely surface of the skull is very short, especially in compar- preserved; the medial parts of both bones are pre- ison with crocodyliforms. It is less than one quarter served together as an isolated fragment, and the pos- the length of the squamosal, compared to about half terior region of the left frontal forms another isolated the length of the squamosal in crocodylians. The squa- fragment with the anterior part of the left parietal. mosal does not appear to border the anterior temporal The parietal extends anterolaterally along the edge of foramen (for the passage of a. temporo-orbitalis) as the supratemporal fenestra to separate it from the it does in Dibothrosuchus and crocodyliforms. The frontal. The ridge on the dorsal midline of the parietal contact of the squamosal with the postorbital is not continues anteriorly onto the frontals. The ridge preserved. becomes broader anteriorly, and its surface is slightly The parietals appear to be fused, but this is difficult sculptured with narrow grooves. The lateral portion of to determine with certainty because they have sepa- the frontals is not preserved, but the broken edges are rated along the midline and the contact surface is thinner than the medial part of the bones. Thus it is damaged. Anteriorly, they appear to have separated likely that the frontals are similar to those of Spheno-

© 2002 The Linnean Society of London, Zoological Journal of the Linnean Society, 2002, 136, 77–95 86 J. M. CLARK and H.-D. SUES Downloaded from https://academic.oup.com/zoolinnean/article/136/1/77/2624221 by guest on 23 November 2020

Figure 4. Kayentasuchus walkeri gen. et sp. nov. Holotype skull. A, ventral view of the braincase with its ﬂoor removed. B, medial view of the side wall of the braincase. Abbreviations: bs.s = space within the body of the basisphenoid; en.d = endolymphatic duct; ls = laterosphenoid; m.an = mastoid antrum; ot = otoccipital; p = parietal; po.p = paroccipital process; pt.f = post-temporal foramen; pr = prootic; q = quadrate; so = supraoccipital; sq = squamosal; ve = vestibule; VIII = foramen for cranial nerve VIII (n. vestibulo-cochlearis). Scale bar = 1 cm.

suchus and Hesperosuchus (Walker, 1970) in having The ventral surface of the frontals is poorly pre- depressions lateral to a midline ridge. The frontals of served, but the cristae cranii bordering the olfactory Kayentasuchus lack the three longitudinal ridges on tracts were well-developed. A single small foramen their dorsal surface that are diagnostic for Dibothro- marks the frontal lateral to the right crista. A frag- suchus (Wu & Chatterjee, 1993). ment underlying the right nasal is probably part of the

© 2002 The Linnean Society of London, Zoological Journal of the Linnean Society, 2002, 136, 77–95 TWO NEW CROCODYLOMORPHS 87 frontal, so that the frontal extended anteriorly beyond terygoid vacuity does not appear to be present at this the level of the orbit. The anterolateral and postero- end, but this might be due to the postmortem trans- lateral edges of the frontals, and thus the contacts verse crushing of the skull. with the prefrontal and postorbital, are not preserved. Portions of the ectopterygoids are preserved adher- The postorbitals are no longer attached to the fron- ing to the two pieces of the posterior parts of the two tal, jugal or squamosal, but isolated fragments are mandibular rami. They exhibit few details but do not tentatively identiﬁed as the body of each bone. These appear unusual. remnants reveal little of the structure of the elements There is no evidence of palpebral bones, but the other than the presence of a spherical protuberance on orbital region is poorly preserved. their anterolateral corner. Only the dorsal portion of either quadrate is pre- The right quadrate has some fragments of bone served. Comparisons with Sphenosuchus and Hespero-

adhering to its anterior edge; these pieces probably suchus indicate that only approximately half the bone Downloaded from https://academic.oup.com/zoolinnean/article/136/1/77/2624221 by guest on 23 November 2020 represent the quadratojugal. The dorsal part of the is represented. The bone is solid, and the area that anterior margin of the quadrate has no fragments bears a depression in Saltoposuchus and other related adhering to it (although a substantial amount of taxa is not preserved. The dorsal part of the quadrate matrix was still present in this region prior to prepa- is relatively long anteroposteriorly and extends ration), and the quadratojugal may not have extended beneath the squamosal from the occiput to a point dorsally to reach the top of the lateral temporal fenes- opposite the trigeminal foramen. It contacts the ante- tra. Thus this region of the skull appears to resemble rior surface of the occiput posteriorly and is slightly the condition in Dibothrosuchus, Hesperosuchus, and expanded at that contact (Fig. 4). It mainly contacts Sphenosuchus, as reinterpreted by Clark et al. (2001). the squamosal posteriorly, but it also contacts the The rod-like vomers unite along the midline and lateral surface of the paroccipital process. extend between the secondary bony palate formed by Medially, the quadrate broadly contacts the prootic the maxillae. The articulation with the maxilla along (Fig. 4), and together the two bones form the posterior the posterodorsal edge of the secondary bony palate is surface of the supratemporal fenestra. The medial somewhat damaged, but there is a matrix-filled area surface of the quadrate bears a prominent ridge that that probably represents this contact. The anterior begins dorsally at the anterior end of the prootic con- end of the vomer has a flat ventral surface and tact and extends ventrally to the broken edge. The appears to fit around a projection of the maxilla at pterygoid ramus was not preserved, but it probably their contact. The central part of each vomer is hemi- extended anteriorly from this ridge further ventrally. cylindrical so that the vomers together form a cylin- The dorsal end of the ridge lies slightly anterior to the der, and there is a short lateral flange on the dorsal middle of the quadrate, and ventrally it moves poste- edge of each. The posterior part of the vomer has a dor- riorly until at the broken ventral edge of the right sally projecting ridge on its medial edge that meets its element it is situated midway between the anterior counterpart along the midline. The bones flatten out and posterior edges. The medial surface of the quad- posteriorly and diverge as they meet the ventral sur- rate anterior to this ridge likely served as the origin of face of the palatines. It is not clear whether the vomer mm. adductor mandibulae externus profundus and meets the pterygoid, which is the plesiomorphic con- adductor mandibulae posterior (Busbey, 1989). The dition for Archosauria and is retained in Sphenosuchus preserved portion of the quadrate extends in a (Walker, 1990) and Dibothrosuchus (Wu & Chatterjee, parasagittal plane, so the ventral part of the bone 1993). must have twisted in order to form the transversely The palatines are poorly preserved, but they clearly orientated condyles. do not form part of the secondary bony palate. The The supraoccipital and epiotic bones are indistin- anterior end of the palatine articulates with the max- guishably fused together and are referred to as the illa medially and extends anteriorly to underlie the supraoccipital. The supraoccipital forms the mid- posterior part of the palatal shelves of the maxilla for dorsal portion of the occiput, the dorsal part of the otic a short distance. The palatine forms the anterior bor- capsule, and the posterodorsal roof of the braincase der of the suborbital fenestra, as is visible on the beneath the parietal (Figs 4, 5). It is slightly higher impression of the right element associated with the than wide on the occiput, so that, allowing for the lat- right dentary fragment, but little detail is preserved. eral compression of the specimen, the two dimensions Strong ridges of the type found in Sphenosuchus were probably more or less equal. The supraoccipital (Walker, 1990) are apparently absent on the ventral narrows above and below the level at which the squa- surface of the palatine posterior to the choana. mosal, parietal, and otoccipital come together. The The pterygoids are poorly preserved. Impressions of ventral narrowing is abrupt, but the dorsal narrowing the anterior parts of the bones are preserved in asso- is more gradual, so that the dorsal part of the bone is ciation with a fragment of the right dentary. An interp- about twice as high as the ventral. The supraoccipital

© 2002 The Linnean Society of London, Zoological Journal of the Linnean Society, 2002, 136, 77–95 88 J. M. CLARK and H.-D. SUES is overlain dorsally by the parietal and contacts the otoccipital. Posterior to the cochlear prominence, the otoccipital ventrolaterally. The occipital surface of the lateral surface of the prootic has several depressions bone is pitted like that of the squamosal, but the similar to those in Sphenosuchus that Walker (1990) surface is otherwise smooth. interpreted as pneumatic spaces. Ventrally, the prootic On the internal surface of the braincase, a thick ver- articulates with the basisphenoid. The anterior part of tical ridge extends along the ventral midline surface of this contact suggests that, as in Sphenosuchus, the the supraoccipital. The supraoccipital forms the dorsal basisphenoid rises anteriorly and the ventral edge of third of the otic capsule, contacting the otoccipital and the prootic rises with it. A groove extends on the prootic. A well-developed subarcuate fossa is present medial surface of the capsular portion of the (right) in the bone posterior to the otic capsule. The superior prootic, and at its anterodorsal end lies a foramen tympanic recess does not extend into the supraoccipi- for one branch of n. vestibulo-cochlearis (VIII). The

tal; thus, the horizontal lamina of bone between the prootic continues forward from the otic region to con- Downloaded from https://academic.oup.com/zoolinnean/article/136/1/77/2624221 by guest on 23 November 2020 posterior ends of the otic capsules on crocodyliform tact the laterosphenoid. This portion of the prootic is supraoccipitals is absent. The supraoccipital may longer than that of crocodylians but is similar in size barely have entered into the dorsal margin of the to that of basal crocodyliforms. Its dorsal edge contacts foramen magnum. the parietal along a straight, horizontal suture. The The exoccipital and opisthotic appear to be indistin- lateral surface of the prootic below its contact with the guishably fused together and are here referred to as parietal forms the medial part of a shelf in the poste- the otoccipital. The otoccipital forms the ventrolateral rior part of the supratemporal fossa. The medial sur- portion of the occiput (Fig. 3) and the posterior part of face of the prootic on this shelf forms the medial the otic region (Fig. 4). The paroccipital processes are surface of a long groove leading into the anterior tem- poorly documented, and only their dorsal part is pre- poral foramen (for the passage of a. temporo-orbitalis). served on each of the two braincase pieces. Part of the Laterally, the prootic forms a broad contact with the ventral portion of the right paroccipital process is quadrate. The prootic is hollowed out and supported present on a separate piece attached to the right only by a series of thin transverse struts between this prootic. A bend in this piece suggests the possible pres- contact and the otic capsule; these spaces appear to be ence of a suture between the paroccipital part of the parts of the mastoid antrum. As best seen on the right opisthotic laterally and the exoccipital medially, but side, there are three spaces separated by two struts. no such suture is discernable on the dorsal part of the The spaces extend dorsally well into the dorsal part of bone. A cast of the right quadrate on the matrix the bone. The foramen for the passage of n. trigeminus around this piece allows it to be ﬁtted with the actual (V) is not preserved. quadrate on the braincase piece. This indicates that The laterosphenoids are poorly preserved. As dis- the paroccipital process was relatively broad verti- cernable on the right side, the laterosphenoid is hol- cally. The dorsal part of the otoccipital is preserved on low, but it probably was not connected with the both braincase pieces, and the ventral part of the otic pneumatic cavities of the middle ear. It is thick at its region of the otoccipital is preserved in articulation posterior contact with the prootic but not at its dorsal with the right prootic (Fig. 4). The structure of the otic contact with the parietal. region is nearly identical to that described for Sphe- A fragment of the right side of the basisphenoid is nosuchus by Walker (1990). The otoccipital portion of preserved in articulation with the prootic (Fig. 4). A the cochlear prominence is a thick, arched structure large space lies within the bone immediately ventral that broadly meets the prootic below the otic capsule. to the prootic; in comparison with Sphenosuchus It is broken dorsally at the base of the crista inter- (Walker, 1990), it is situated within the body of the fenestralis on the prootic piece, and the braincase bone posterior to the postcarotid recess. piece preserves the posterodorsal base of the crista. The basioccipital is not preserved. The anterior wall of the opening for the foramen per- ilymphaticum and fenestra pseudorotunda is well preserved on the prootic piece, but the posterior wall MANDIBLE is not preserved. The subcapsular process is also The dentary forms the anterior portion of the mandib- missing. ular ramus (Fig. 3). It takes part in a relatively long The prootic forms the lateral wall of the braincase symphysis, extending from the anterior end of the between the otoccipital and laterosphenoid (Fig. 4). Its ramus back to the level of the fourth maxillary tooth. dorsal portion is preserved on both braincase pieces, The dentary narrows gradually anteriorly and is slen- and the posteroventral part of the right prootic is der at its tip. It is bent at the posterior end of the sym- preserved in articulation with the otoccipital and physis, so that its dorsal edge is concave. The left basisphenoid. Ventrally, the prootic portion of the dentary is preserved with its posterior part projecting cochlear prominence is much thinner than that of the upward into the jugal and its symphyseal region

© 2002 The Linnean Society of London, Zoological Journal of the Linnean Society, 2002, 136, 77–95 TWO NEW CROCODYLOMORPHS 89 turned upward into the premaxillae, but this was The dentary holds at least but probably no more probably not the original orientation of the lower jaw. than 13 teeth. The ﬁrst centimetre of its anterior end The posterior contacts of the dentary may be present is devoid of teeth, representing the length of approxi- on a block preserving the posterior part of the left mately three or four alveoli. Posterior to this edentu- mandibular ramus, but they are not obvious. lous segment, the alveoli are similar in size, and, The splenial is a broad sheet of bone covering the unlike in other basal crocodylomorphs, there is no medial surface of the dentary. It barely enters into the trace of a large caniniform tooth opposite the notch long symphysis anteriorly. Anteriorly, the dorsal part between the premaxilla and maxilla. The alveoli of the splenial ends short of the symphysis and only increase slightly in size posteriorly to about the ﬁfth the ventral part continues forward. Thus a small, elon- tooth position. The teeth are identical to those of the gate fenestra is formed on the medial surface of the maxilla; they are nearly conical and constricted at the

mandibular ramus opening into the Meckelian groove base. The alveoli are separated by septa, as most Downloaded from https://academic.oup.com/zoolinnean/article/136/1/77/2624221 by guest on 23 November 2020 on the dentary. clearly seen on the right dentary. The postdentary bones are preserved on two fragmentary pieces, one from each side. The large external mandibular fenestra is best preserved on the piece ILIUM AND FEMUR from the left side. It has sharp anterior and posterior The right ilium and femur are preserved in articula- ends, but its upper and lower margins are smoothly tion (Fig. 5); fragments of the left ilium and femur are curved. However, few details are preserved on these pieces, and the articular and prearticular are apparently not preserved.

DENTITION The premaxilla holds four teeth (Fig. 3). The ﬁrst tooth is smaller than the others, but all are similar in shape. The crowns are nearly conical but are slightly compressed labiolingually and have distinct but nonser- rated anterior and posterior cutting edges. The second and third teeth are slightly constricted at the base of the crown. The third tooth on the right side was in the process of replacement; replacement was typically cro- codylian, with the replacement tooth emerging lingual to its predecessor. There are positions for at least 12 and probably no more than 13 maxillary teeth were present. The tooth crowns increase in diameter back to the sixth tooth and decrease in diameter posterior to the ninth. The tooth row terminates posteriorly at the level of the posterior margin of the antorbital fenestra. The individual alveoli are separated from each other by septa (e.g. between the ﬁfth and sixth alveolus on the left side), and interdental plates are absent on the lingual surface of the maxilla. The tooth crowns are nearly conical, slightly compressed labiolingually,and have distinct anterior and posterior cutting edges. They are thus similar to those of Sphenosuchus, which Walker (1970, 1990) described as ‘lanceolate’. The cutting edges lack serrations, and there are longitudinal crenulations on the lingual and labial surfaces that are coarser near the tip. The enamel on all teeth is very thin. Broken surfaces on isolated pieces of the Figure 5. Kayentasuchus walkeri gen. et sp. nov. right maxilla reveal that the teeth are separated from Holotype. Lateral view of right ilium and femur. Abbre- the bone by matrix, suggesting that they were held viations: at = ?antitrochanter; tq = fourth trochanter; pi.t in their bony alveoli by periodontal ligaments in the = possible homologue of pseudointernal trochanter in typical archosaurian manner. Hallopus (Walker, 1970). Scale bar = 1 cm.

© 2002 The Linnean Society of London, Zoological Journal of the Linnean Society, 2002, 136, 77–95 90 J. M. CLARK and H.-D. SUES also preserved but have not yet been prepared. The two trochanters deﬁne a distinct longitudinal groove right ilium is represented only by the portion of the on the lateral surface of the femur. The fourth tro- bone surrounding the acetabulum, and the iliac blade chanter is situated approximately one-fourth of the as well as its anterior and posterior processes are not distance down the shaft on its posteromedial edge. It preserved. The acetabulum is deeply concave and is not as pronounced as the other two trochanters. overhung by a broad supra-acetabular crest. The crest The shaft of the femur is remarkably slender is broadest anteriorly and does not extend to the pos- and similar to that of Terrestrisuchus (Crush, 1984). terior edge of the acetabulum. The medial wall of the Although it has been distorted by lateral compression, acetabulum is perforated, as indicated by a concave it appears to have been more cylindrical distally and notch in the ventral edge of the ilium. This notch is laterally compressed at its dorsal end. The proximal somewhat broader and deeper than that on the ilium quarter of the shaft is nearly straight, but its distal

of crocodylians, but it is not as large as in dinosaurs. three-quarters are distinctly curved so that its poste- Downloaded from https://academic.oup.com/zoolinnean/article/136/1/77/2624221 by guest on 23 November 2020 Unlike the condition in Terrestrisuchus (Crush, 1984), rior edge is broadly concave. Thus its shape is not the posterior edge of the iliac crest projects posteriorly truly sigmoidal as in crocodyliform femora because its without forming a posteriorly facing notch with the anterior edge lacks a concavity in its dorsal part. The acetabular portion of the bone. The posteroventral sur- distal condyles of the femur are poorly preserved, face for the contact with the ischium is broad and although the medial condyle is fairly complete. It is becomes much thicker laterally. Immediately above laterally compressed, but this may be an artifact of the lateral edge of the ischial contact lies a thin ridge preservation. forming a groove along its posteroventral edge. This is more or less in the same position as the antitrochanter of birds and theropod dinosaurs, but differs from the OSTEODERMS AND VERTEBRAE latter in shape. Several sections of poorly preserved dorsal osteoderms Fragments of two sacral vertebrae are preserved are preserved with the specimen. Most of the bone has articulating with the medial surface of the ilium. shattered, but the impressions are preserved in iron- There is no indication that additional vertebrae were stone. A series of three nearly complete sections of involved in the formation of the sacrum. The rib of the body armour is preserved as impressions and sur- second sacral vertebra is broader than that of the first rounding vertebrae. It is unclear what part of the body (although the latter is incomplete). It contacts the these are derived from, but, based on the width of the ilium from a point behind the middle of the acetabu- dorsal osteoderms and the compactness of the verte- lum posteriorly and extends well onto the broken brae, they are probably from the trunk rather than the posterior process. The rib of the first sacral vertebra caudal or cervical region. articulates in a longitudinal groove medial to the ante- A pair of longitudinal rows of broad dorsal osteo- rior process. derms is preserved. The best preserved plates, from The proximal end of the femur has a well-developed the right side, are rectangular, about twice as wide as inturned head. The articular surface of the head long, and on the lateral part of the anterior edge is an extends over its convex, ball-shaped medial surface impression of an anterior process similar to that found and laterally across its posterodorsal surface. The on many crocodyliform osteoderms. The dorsal osteo- articular surface does not extend onto the flat anterior derms on the left side are strongly bent, unlike those surface of the head. The head is orientated at a right on the right which are more gently downturned; the angle to the shaft, so that the hindlimb appears to actual condition was presumably between these two have been fully erect. The ‘lesser trochanter’ (Walker, extremes, which are probably the result of postmor- 1970) is well developed on the anterior part of the lat- tem distortion. In any case, the lateral portion of each eral surface of the shaft. It is relatively long and is ori- osteoderm is deflected to some extent. entated along the long axis of the bone, descending The ventral osteoderms are subquadrangular and from the lateral surface of the femoral head. A second apparently not imbricated. They are much smaller well-developed trochanter on the posterior edge of the than the dorsal osteoderms, about half the anteropos- lateral surface opposite the lesser trochanter (Fig. 5) terior length and one quarter of the transverse width. may correspond to a similar feature in Hallopus that Two longitudinal rows are well preserved, and there Walker (1970) termed the ‘pseudointernal trochanter’ appear to be additional rows folded under the dorsal for the insertion of m. puboischiofemoralis externus osteoderms. A separately preserved ventral osteoderm (Romer, 1923; Hutchinson, 2001), but the trochanter exhibits a finely sculptured surface of pits and ridges. on the femur of Kayentasuchus is situated further from Few vertebrae are preserved, and none is as yet the posterior edge of the bone. This structure parallels completely prepared. Those examined all belong to the the lesser trochanter, but does not extend as far dor- trunk region. They are amphicoelous and relatively sally and its ventral end is more robust. Together the stout.

THE PHYLOGENETIC STATUS OF SPHENOSUCHIA

The relationships among sphenosuchians remain poorly understood, with several analyses having reached conﬂicting conclusions. Our recent analysis (Clark et al., 2001) found little resolution among basal Crocodylomorpha. In order to investigate the interrelationships of sphenosuchians, we modiﬁed the character-taxon matrix compiled and used by Clark et al. (2001) by adding Kayentasuchus walkeri as well

as an additional character concerning the presence or Downloaded from https://academic.oup.com/zoolinnean/article/136/1/77/2624221 by guest on 23 November 2020 absence of a groove on the lateral edge of the squamosal (character 13). The character-states for BP/1/5237, which is designated as the holotype of Litargosuchus leptorhynchus in this paper, were rescored based on re- examination of the specimen. Analysis of the modified character-taxon matrix was undertaken using PAUP 3.1.1 (Swofford, 1993), implemented with equal weights and with four characters treated as ordered (as indicated in the character descriptions; see Appen- dix). Two of the ordered characters (characters 22 and 23) were divided into pairs of additive binary characters in some runs as an alternative coding scheme. The results of these new analyses were disappoint- ing, showing even less resolution than the previous analysis by Clark et al. (Fig. 6). The analysis of the pri- mary data set produced 57 equally most parsimonious trees (MPTs). The strict consensus (Fig. 6) showed no resolution except for three groupings, Protosuchus + Alligator (representing Crocodyliformes), Dibothrosu- chus and Sphenosuchus, and the three specimens referred to Hesperosuchus agilis (Clark et al., 2001). Figure 6. Strict consensus (A) and Adams consensus (B) of The Adams consensus (Fig. 6) was little better, with 151 most parsimonious trees (MPTs) resulting from the only the addition of a group including the Hesperosu- PAUP analysis of the data matrix in Table 1 (outgroups chus set, Sphenosuchus and Saltoposuchus. omitted in figure). Each MPT has a length of 64 steps, a Analysis of the data set with two of the multistate Consistency Index (C.I.) of 0.609, and a Retention Index characters recoded as binary additive characters (R.I.) of 0.679. Reanalysis with characters 22 and 23 yielded 83 equally most parsimonious trees, with less recoded as pairs of additive binary characters recovered 38 resolution in the strict consensus but greater resolu- MPTs, each with a length of 62 steps, and with a less tion in the Adams consensus than the analysis with resolved strict consensus, but the Adams consensus, C, ordered multistate characters. The strict consensus shows much more resolution. has only two groups, the Hesperosuchus group and the Protosuchus-Alligator group. The Adams consensus, however, resolves a group comprising Hesperosuchus, sus typically identifies multiple subtrees for a given Saltoposuchus, Dibothrosuchus, and Sphenosuchus set of MPTs. (Fig. 7). Analysis of the MPTs from both phylogenetic anal- To explore further the stability of relationships yses (i.e. either with characters 22 and 23 ordered or among sphenosuchians, we performed a reduced con- with those characters each replaced with binary char- sensus analysis using the program RadCon (Thorley & acters) with RadCon resulted in four subtrees. Both Page, 2000). Reduced consensus analysis finds subsets sets of subtrees are similar except that the subtrees of taxa whose relationships are present in all MPTs from the analysis with ordered multistate characters (Wilkinson, 1994, 1995). A reduced consensus tree will all include a Dibothrosuchus-Sphenosuchus clade not thus exclude those taxa whose relationships are found in the other analysis. Of particular interest is unstable among all MPTs. Because more than one that the reduced consensus of the analysis with combination of stable taxa is possible, reduced consen- ordered multistates includes one subtree in which Ter-

Table 1. Modiﬁed character-taxon matrix used in this study for the analysis of the interrelationships of basal crocodylomorph archosaurs. See Clark et al. (2001) for further details and discussion

Character

1 2 3 22 23 Taxon 12345 67890 12345 67890 12345 67890 1234 ab ab

Outgroup taxa Stagonolepis 00000 00000 00010 00010 00000 00000 0000 0? 0? Gracilisuchus ?1?10 ??000 01010 1000? ???0? ?000? 00?1 ?? ?? Postosuchus 01000 ??000 1?000 01100 00000 00000 00?? 0? 0?

Ingroup taxa Downloaded from https://academic.oup.com/zoolinnean/article/136/1/77/2624221 by guest on 23 November 2020 Litargosuchus 00?1? ?1101 ?00?? 1100? ???0? ?011? ???? ?? ?? Pseudhesperosuchus 01??1 1?101 110?? 0?10? ????0 00?1? ?0?? ?? ?? Hesperosuchus AMNH 6758 ????? ???1? ????? ????? ???0? ?1?1? 1?11 ?? ?? CM 29894 00?1? ?1111 1101? 0?10? ???00 111?1 ??11 ?? ?? UCMP 129470 ????? ????? ????? ????? ????? ?1??? 1?11 ?? ?? Combined* 00?1? ?1111 1101? 0?10? ???00 11111 1?11 ?? ?? Saltoposuchus 00?1? ?1101 110?? 0?10? ????? ?0??1 1011 ?? ?? Terrestrisuchus ?111? ?1101 100?? 0?001 1??0? ?011? 11?? ?? ?? Dibothrosuchus 00111 10111 1?011 21111 12000 10111 ??00 11 0? Sphenosuchus 00111 01111 11011 21111 11100 1011? ???? 10 10 Kayentasuchus 0010? ???11 111?1 ?1001 11??? ?0??? 1?11 10 ?? Protosuchus 11111 0?101 10101 21012 12211 N012? 1011 11 11 Alligator 1N1N1 10101 10101 21012 12011 N0020 1000 11 0?

0 = plesiomorphic character-state 1, 2 = derived character-states N = inapplicable due to transformation, treated as unknown. * = coding combining the three known specimens; run separately in the analysis.

restrisuchus is closer to Protosuchus and Alligator than are several other sphenosuchians (Fig. 7), indicating that this relationship holds in all of the MPTs. How- ever, in the reduced consensus of the analysis with no multistate characters none of the subtrees shows this relationship. Most of the lack of resolution among sphenosuchian taxa is due to conflicting character support rather than missing data. This is reflected in the Retention Index of 0.679, which is relatively low in view of the large number of missing data. Some of this conflict probably results from the different ontogenetic stages of the various taxa, but, until more specimens become available documenting variation due to growth in Figure 7. One subtree from a reduced consensus analysis these forms, little can be done to identify the factors using the RadCon program (Thorley & Page, 2000). The causing the ‘noise’ in the analysis. MPTs from the phylogenetic analyses with characters 22 and 23 ordered or replaced by binary characters produced slightly different sets of reduced consensus subtrees. This ACKNOWLEDGEMENTS subtree, from the analysis with 22 and 23 ordered, shows the sphenosuchian Terrestrisuchus closer to the crocodyli- We dedicate this paper to the memory of Alick D. forms Protosuchus and Alligator, a relationship not found Walker. Alick not only set high standards through his in any subtree of the other analysis. monographic studies of several early Mesozoic archo-

© 2002 The Linnean Society of London, Zoological Journal of the Linnean Society, 2002, 136, 77–95 TWO NEW CROCODYLOMORPHS 93 saurs, but also provided both of us with encourage- Gow CE, Kitching JW. 1988. Early Jurassic crocodilomorphs ment and much unpublished information over the from the Stormberg of South Africa. Neues Jahrbuch für years. H.-D.S. thanks Michael A. Raath and Bruce Geologie und Paläontologie, Monatshefte 1988: 517–536. Rubidge (Bernard Price Institute for Palaeontological Haughton SH. 1924. The fauna and stratigraphy of the Research, University of the Witwatersrand) for the Stormberg Series. Annals of the South African Museum 12: loan of the holotype of Litargosuchus leptorhynchus, 323–497. and Robert R. Reisz and Sean P. Modesto (Erindale Haughton SH, Brink AS. 1954. A bibliographical list of Rep- College, University of Toronto) for safely transporting tilia from the Karroo Beds of Africa. Palaeontologia Africana 2: 1–187. it to Toronto. The holotype of Kayentasuchus walkeri Hutchinson JR. 2001. The evolution of femoral osteology and was collected by J.M.C. with the support from the soft tissues on the line to extant birds (Neornithes). Zoolog- National Geographic Society and with permission of ical Journal of the Linnean Society 131: 169–197.

the Navajo Tribal Council. Figures 1, 2 and 5 were Downloaded from https://academic.oup.com/zoolinnean/article/136/1/77/2624221 by guest on 23 November 2020 Parrish JM. 1991. A new specimen of an early crocodylo- drawn by Diane Scott (Erindale College, University of morph (cf. Sphenosuchus sp.) from the Upper Triassic Chinle Toronto) and Figures 3 and 4 by Claire Vanderslice Formation of Petrified Forest National Park. Journal of (formerly University of Chicago). Vertebrate Paleontology 11: 198–212. Romer AS. 1923. Crocodilian pelvic muscles and their avian and reptilian homologues. Bulletin of the American Museum of Natural History 48: 533–552. Romer AS. 1956. Osteology of the Reptiles. Chicago: The REFERENCES University of Chicago Press. Benton MJ, Clark JM. 1988. Archosaur phylogeny and Sereno PC, Wild R. 1992. Procompsognathus: theropod, the relationships of the Crocodylia. In: Benton MJ, ed. The ‘thecodont’ or both? Journal of Vertebrate Paleontology 12: Phylogeny and Classification of the Tetrapods, Vol. 1: 435–458. Amphibians, Reptiles, Birds. Systematics Association Spe- Shute CCD, Bellairs A. 1955. The external ear in Crocodilia. cial, Vol. 35A. London: Clarendon Press, 295–338. Proceedings of the Zoological Society of London 124: 741–749. Bonaparte JF. 1972a. Los tetrápodos del sector superior de Sues H-D, Clark JM, Jenkins FA Jr. 1994. A review of the la Formación Los Colorados, La Rioja, Argentina. Opera Lil- Early Jurassic tetrapods from the Glen Canyon Group of the loana 22: 1–183. American Southwest. In: Fraser NC, Sues H-D, eds. The Bonaparte JF. 1972b. Pedeticosaurus leviseuri Van Hoepen, Shadow of the Dinosaurs: Early Mesozoic Tetrapods. Cam- a probable protosuchian. Navorsinge van die Nasionale bridge and New York: Cambridge University Press, 284–294. Museum, Bloemfontein 2 (10): 301–305. Swofford D. 1993. PAUP, Phylogenetic Analysis Using Brochu CA. 1996. Closure of neurocentral sutures during Parsimony, version 3.1.1. Washington, DC: Smithsonian crocodilian ontogeny: Implications for maturity assessment Institution. in fossil archosaurs. Journal of Vertebrate Paleontology 16: Thorley JL, Page RDM. 2000. RadCon: Phylogenetic tree 49–62. comparison and consensus. Bioinformatics 16: 486–487. Busbey AB III. 1989. Form and function of the jaw apparatus Van Hoepen ECN. 1915. Contributions to the knowledge of of Alligator mississippiensis. Journal of Morphology 202: the reptiles of the Karroo Formation. 4. A new pseudosu- 99–127. chian from the Orange Free State. Annals of the Transvaal Clark JM. 1986. Phylogenetic relationships of the crocodylo- Museum 5 (1): 83–87. morph archosaurs. Unpublished PhD Dissertation, The Uni- Walker AD. 1968. Protosuchus, Proterochampsa, and the versity of Chicago, Chicago. origin of phytosaurs and crocodiles. Geological Magazine Clark JM, Fastovsky DE. 1986. Vertebrate biostratigraphy 105: 1–14. of the Glen Canyon Group in northern Arizona. In: Padian K, Walker AD. 1970. A revision of the Jurassic reptile Hallopus ed. The Beginning of the Age of Dinosaurs: Faunal Change victor (Marsh), with remarks on the classification of croco- across the Triassic–Jurassic Boundary. New York: Cam- diles. Philosophical Transactions of the Royal Society of bridge University Press, 285–301. London B 257: 323–372. Clark JM, Sues H-D, Berman DS. 2001. A new specimen of Walker AD. 1990. A revision of Sphenosuchus acutus Hesperosuchus agilis from the Upper Triassic of New Mexico Haughton, a crocodylomorph reptile from the Elliot Forma- and the interrelationships of basal crocodylomorph archo- tion (late Triassic or early Jurassic) of South Africa. Philo- saurs. Journal of Vertebrate Paleontology 20: 683–704. sophical Transactions of the Royal Society of London B 330: Crompton AW, Smith KK. 1980. A new genus and species of 1–120. crocodilian from the Kayenta Formation (Late Triassic?) of Wilkinson M. 1994. Common cladistic information and its Northern Arizona. In: Jacobs LL, ed. Aspects of Vertebrate consensus representation: reduced Adams and reduced History. Flagstaff: Museum of Northern Arizona Press, 193– cladistic consensus trees and profiles. Systematic Biology 43: 217. 343–368. Crush PJ. 1984. A late upper Triassic sphenosuchid cro- Wilkinson M. 1995. More on reduced consensus methods. codilian from Wales. Palaeontology 27: 131–157. Systematic Biology 44: 436–440.

Wu X-C, Chatterjee S. 1993. Dibothrosuchus elaphros, a 16. In presumed adults, parietals separate (0), inter- crocodylomorph from the Lower Jurassic of China and the parietal suture partially obliterated (1) or inter- phylogeny of the Sphenosuchia. Journal of Vertebrate parietal suture absent (2). [ordered] Paleontology 13: 58–89. 17. Posteroventral edge of parietals extends more than half the width of occiput (0) or less than half the width of occiput (1). APPENDIX 18. Medial extents of supratemporal fossae on lateral surface of parietal separated on midline by broad, Characters and character-states for selected taxa of ﬂat or gently rounded area (0) or by ‘sagittal’ crest Crocodylomorpha and three outgroup taxa. Modiﬁed (which may be divided by interparietal suture) (1). from Clark et al. (2001), with the addition of character 19. Occipital margin of parietals V-shaped in dorsal 13.

view (0) or straight (1). Downloaded from https://academic.oup.com/zoolinnean/article/136/1/77/2624221 by guest on 23 November 2020 20. Exoccipitals broadly separated dorsal to foramen magnum (0), approach midline without contact- SKULL ing (1), or contacting below supraoccipital (2). 1. Posterodorsal process of premaxilla overlapping [ordered] anterodorsal surface of maxilla (0) or dorsal 21. Prootic broadly contacting anterior surface of process of premaxilla vertical, strongly sutured paroccipital process (0) or not in broad contact (1). to maxilla (1). 22. Depression for mastoid antrum: absent (0), 2. Facial portion of maxilla anterior to anterior edge present on lateral surface of prootic dorsal to otic of antorbital fenestra equal in length to or longer capsule (1), or entering into prootic and con- than portion posterior to anterior edge of fenestra necting with opposite through supraoccipital (2). (0) or shorter than posterior portion (1). [ordered] 3. Maxillae do not meet on palate (0) or meet on 23. Depression for posterior tympanic recess: absent palate to form secondary bony palate anterior to (0), depression posterior to fenestra ovalis on choana (1). anterior surface of the paroccipital process (1), or 4. Jugal participates in posterior edge of antorbital penetrating prootic and paroccipital process (2). fenestra (0) or is excluded by lacrimal or maxilla [ordered] (1). 24. Paroccipital process dorsoventrally tall and dis- 5. Descending process of prefrontal absent (0), or tinctly expanded distally (0) or process narrower present (1). dorsoventrally, distal end only slightly expanded 6. Descending process of prefrontal not contacting (1). palate (0) or contacting palate (1). 25. Basipterygoid processes of basisphenoid present 7. Prefrontal not underlying anterolateral edge of (0) or absent (1). frontal to a significant degree (0) or with distinct 26. Basipterygoid processes simple, without large posterior process underlying frontal dorsal to orbit cavity (0) or greatly expanded, with large cavity (1). (1). 8. Postfrontal present (0) or absent (1). 27. Symphyseal region of dentary with straight 9. Dorsal surface of frontal flat (0) or with longitudi- ventral margin (0) or with deep ‘swelling’ extend- nal midline ridge (1). ing ventrally below level of ventral margin of 10. Squamosal not significantly overhanging lateral postsymphyseal portion of dentary (1). temporal region (0) or with broad lateral expan- 28. Articular without dorsomedial projection poste- sion overhanging lateral temporal region (1). rior to the glenoid fossa (0) or with dorsomedial 11. Descending process of squamosal anterior to projection (1). quadrate present (0) or absent (1). 12. Squamosal without ridge on dorsal surface along edge of supratemporal fossa (0) or with ridge (1). POSTCRANIAL SKELETON 13. Lateral edge of squamosal without longitudinal 29. Coracoid subcircular in lateral view (0), with elon- groove (0) or with longitudinal groove (part of the gate postglenoid process posteromedially (1), or area of attachment of the upper ear flap in extant with elongate ventromedial process expanded crocodylians) (1). ventrally (2). [unordered] 14. Quadratojugal extends anterodorsally to contact 30. Proximal ends of metacarpals overlap (0) or abut postorbital (0) or does not contact postorbital one another without overlapping (1). (1). 31. Proximal head of femur confluent with shaft (0) or 15. Quadrate does not contact prootic (0) or contacts with distinct, medially directed head set off from prootic (1). shaft (1).

32. Tibia/femur length ratio: less than 1 (0) or more 22b. Depression for mastoid antrum only on lateral than 1 (1). surface of prootic dorsal to otic capsule (0) or 33. Anterior edge of paramedian dorsal osteoderms entering into prootic and connecting with oppo- straight (0) or with anterior process (1). site side through supraoccipital (1). 34. Paramedian dorsal osteoderms ﬂat (0) or with 23a. Depression for posterior tympanic recess absent distinct longitudinal bend near lateral edge (1). (0) or present (1). 23b. Depression for posterior tympanic recess posterior to fenestra ovalis only on anterior surface of RECODING OF ORDERED MULTISTATE CHARACTERS the paroccipital process (0) or penetrating prootic 22a. Depression for mastoid antrum absent (0) or and paroccipital process (1). present (1). Downloaded from https://academic.oup.com/zoolinnean/article/136/1/77/2624221 by guest on 23 November 2020