Front MatterSource: Philosophical Transactions: Biological Sciences, Vol. 353, No. 1368 (Apr. 29, 1998)Published by: The Royal SocietyStable URL: http://www.jstor.org/stable/56936 .

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The Early Triassic rhynchosaur Mesosuchus

browni and the interrelationships of basal

archosauromorph reptiles

David W. Dulkes* Bernard Price Institutefor Palaeontological Research, University of the Witwatersrand, Private Bag 3, Wits 2050, Johannesburg, South Africa

CONTENTS PAGE

1. Introduction 501 2. Systematic Palaeontology 503 3. Description 503

(a) Skull 503 (b) Postcranial skeleton 512 (c) Reconstruction 519

4. Phylogenetic Relationships 519 (a) Taxonomic history of rhynchosaurs 519 (b) Materials and methods 520 (c) Results 522

5. Discussion 524 (a) Topological constraints 524 (b) Deletion of Trilophosaurus 526 (c) Definitions and diagnoses 526 (d) Taxonomic status of Noteosuchus colletti 529 (e) Stratigraphic calibration of phylogeny 530

6. Conclusions 531 References 531 Appendix 1 534 Appendix 2 536 Appendix 3 537 Appendix 4 537

Restudy of the unique diapsid reptile Mesosuchus browni Watson, from the Cynognathus Assemblage Zone (late EarlyTriassic to early MiddleTriassic) of the Burgersdorp Formation (Tarkastad Subgroup; Beaufort Group) of South Africa, confirms that it is the most plesiomorphic known member of the Rhynchosauria. A new phyloge- netic analysis of basal taxa of Archosauromorpha indicates that Choristodera falls outside of the Sauria, Prolacertiformes is a paraphyletic taxon with Prolacerta sharing a more recent common ancestor with Archosaur- iformes than with any other clade, Megalancosaurus and Drepanosaurus are sister taxa in the clade Drepanosauridae within Archosauromorpha, and are the sister group to the clade Tanystropheidae composed of Tanystropheus, Macrocnemus, and Langobardisaurus. Combination of the phylogenetic relationships of basal archosauromorphs and their known stratigraphic ranges reveals significant gaps in the fossil records of Late Permian and Triassic diapsids. Extensions of the temporal ranges of several lineages of diapsids into the Late Permian suggests that more groups of terrestrial reptiles survived the end-Permian mass extinction than thought previously.

Keywords: fossil; phylogeny; reptile; South Africa; diapsid; Gondwana

1. INTRODUCTION

In 1911, D. M. S. Watson had the opportunity to examine a block of sandstone with the intermingled partial skeletons

*Address for correspondence: Department of Zoology, Erindale College, The University of Toronto, 3359 Mississauga Road, Mississauga, Ontario, Canada L5L 1C6 (ddilkes@credit. erin. utoronto. ca).

of several small reptiles in the private collection of Mr Alfred Brown. This block had been found in the Cynog- nathus Assemblage Zone near the town of Aliwal North in the Cape Province (now Eastern Cape Province) of South Africa (figure 1). Watson considered the skeletons to belong to a single new species that he named Mesosuchus browni in a preliminary note (Watson 1912a). However, it was

Phil. Trans. R. Soc. Lond. B (1998) 353, 501-541 501 ? 1998 The Royal Society Received 24 October 1996 Accepted 10 March 1997

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