The early Triassic rhynchosaur Mesosuchus browni and the interrelationships of basal archosauromorph reptiles

Abstract

Restudy of the unique diapsid reptileMesosuchus browniWatson, from theCynognathusAssemblage Zone (late Early Triassic to early Middle Triassic) 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 phylogenetic analysis of basal taxa of Archosauromorpha indicates that Choristodera falls outside of the Sauria, Prolacertiformes is a paraphyletic taxon withProlacertasharing a more recent common ancestor with Archosauriformes than with any other clade,MegalancosaurusandDrepanosaurusare sister taxa in the clade Drepanosauridae within Archosauromorpha, and are the sister group to the clade Tanystropheidae composed ofTanystropheus,Macrocnemus, andLangobardisaurus. 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.