The origin, early history and diversification of Lepidosauromorph reptiles

Abstract

Lepidosauria was erected by Romer (1956) to encompass diapsids that lacked diagnostic archosaurian characters. The resulting assemblage was paraphyletic. In the intervening 50 years, new fossils and new phylogenetic approaches have transformed our concepts (e.g., Evans, 1980, 1984, 1988; Benton, 1985;Whiteside, 1986; Gauthier et al., 1988). Lepidosauria is now restricted to the last common ancestor of Squamata (lizards, snakes and amphisbaenians) and Rhynchocephalia (represented by Sphenodon), and all descendants of that ancestor (e.g., Gauthier et al., 1988). The clade is robustly diagnosed by hard and soft characters (e.g., Gauthier et al., 1988; de Braga and Rieppel, 1997; Evans, 2003; Hill, 2005) and is recognized by recent molecular phylogenies (e.g., Gorr et al., 1998; Rest et al., 2003; Townsend et al., 2004; Vidal and Hedges, 2005). Extant lepidosaurs are globally distributed with more than 7,000 species ranging from desert lizards to marine snakes. The fossil record provides evidence of their history and radiation but, despite advances, that record is patchy. It relies mainly on microvertebrate assemblages, supplemented by rare skeletons from lacustrine and other fine grained deposits. Inevitably, the record is geographically and geologically biased.