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Two New Basal Crocodylomorph Archosaurs from The 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 © 2002 The Linnean Society of London, Zoological Journal of the Linnean Society, 2002, 136, 77–95 77 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 skele- ton (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. © 2002 The Linnean Society of London, Zoological Journal of the Linnean Society, 2002, 136, 77–95 TWO NEW CROCODYLOMORPHS 79 Downloaded from https://academic.oup.com/zoolinnean/article/136/1/77/2624221 by guest on 23 November 2020 Figure 1. Litargosuchus leptorhynchus gen. et sp. nov. Skull in (A) dorsal and (B) ventral views. Abbreviations for Figs 1, 2: ao.f
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