Zoological Journal of the Linnean Society, 2002, 136, 77–95. With 7 figures © 2002 The Linnean Society of London, Zoological Journal of the Linnean Society, 2002, 136, 77–95 77 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 Correspondence. Hans-Dieter Sues. E-mail: hds@rom.on.ca 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 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 In two papers that laid the foundation for our under- standing of interrelationships among crocodile-like archosaurs, Walker (1968, 1970) formally established Crocodylomorpha as a group comprising Crocodylia (in traditional usage) and a host of early Mesozoic taxa previously placed in the grade group ‘Thecodontia’. The best known among the latter taxa is Sphenosu- chus acutus, which Walker studied in great detail over the course of three decades, culminating in his magis- terial monograph (Walker, 1990). Subsequent phyloge- netic analyses (e.g. Clark in Benton & Clark, 1988; Parrish, 1991; Clark et al., 2001) have consistently corroborated the monophyly of the Crocodylomorpha but arrived at different conclusions about the interre- lationships of its constituent taxa. In particular, it has been unclear whether basal crocodylomorphs form a monophyletic grouping Sphenosuchia or whether some are more closely related to crocodylians than are others. In this paper we describe two new basal cro- codylomorph reptiles from the Lower Jurassic and reassess the monophyly of the Sphenosuchia. The first is based on a skull and skeleton from the upper Elliot Formation (Stormberg Group) of South Africa that was briefly described and identified as Pedeticosaurus sp. by Gow & Kitching (1988). The second is based on a skull and skeleton from the Kayenta Formation (Glen Canyon Group) of Arizona and has previously been referred to as the ‘Kayenta Form’ (Clark in Benton & Clark, 1988; see also Sues et al., 1994). The first phylogenetic analyses of crocodylomorph relationships concluded that sphenosuchians are a paraphyletic grouping (Clark in Benton & Clark, 1988; Parrish, 1991), with some being more closely related to Crocodyliformes ( sensu Clark, 1986 = Cro- codylia of traditional usage) than others. However, two subsequent studies independently supported the monophyly of Sphenosuchia (Sereno & Wild, 1992; Wu & Chatterjee, 1993). Recently we have presented a cri- tique of these analyses and reassessed relationships among sphenosuchians (Clark et al., 2001), with the result that most sphenosuchians form a monophyletic group with the possible exception of the taxon repre- sented by a skeleton referred to Pedeticosaurus by Gow & Kitching (1988). However, that analysis did not include the Kayenta form and we had not yet had the opportunity of first-hand examination of the specimen reported by Gow & Kitching. In this paper, we redescribe the skull of the latter, describe the Kayenta