Abstract
Sauria is the crown-group of Diapsida and is subdivided into Lepidosauromorpha and Archosauromorpha, comprising a high percentage of the diversity of living and fossil tetrapods. The split between lepidosauromorphs and archosauromorphs (the crocodile-lizard, or bird-lizard, divergence) is considered one of the key calibration points for molecular analyses of tetrapod phylogeny. Saurians have a very rich Mesozoic and Cenozoic fossil record, but their late Paleozoic (Permian) record is problematic. Several Permian specimens have been referred to Sauria, but the phylogenetic affinity of some of these records remains questionable. We reexamine and review all of these specimens here, providing new data on early saurian evolution including osteohistology, and present a new morphological phylogenetic dataset. We support previous studies that find that no valid Permian record for Lepidosauromorpha, and we also reject some of the previous referrals of Permian specimens to Archosauromorpha. The most informative Permian archosauromorph is Protorosaurus speneri from the middle Late Permian of Western Europe. A historically problematic specimen from the Late Permian of Tanzania is redescribed and reidentified as a new genus and species of basal archosauromorph: Aenigmastropheus parringtoni. The supposed protorosaur Eorasaurus olsoni from the Late Permian of Russia is recovered among Archosauriformes and may be the oldest known member of the group but the phylogenetic support for this position is low. The assignment of Archosaurus rossicus from the latest Permian of Russia to the archosauromorph clade Proterosuchidae is supported. Our revision suggests a minimum fossil calibration date for the crocodile-lizard split of 254.7 Ma. The occurrences of basal archosauromorphs in the northern (30°N) and southern (55°S) parts of Pangea imply a wider paleobiogeographic distribution for the group during the Late Permian than previously appreciated. Early archosauromorph growth strategies appear to be more diverse than previously suggested based on new data on the osteohistology of Aenigmastropheus.
Highlights
IntroductionCrown group diapsids, are highly taxonomically and morphologically diverse in extant ecosystems, with around 9,400 lepidosaur (snakes, lizards and rhynchocephalians) and 10,000 archosaur (birds and crocodilians) species, including cursorial, semi-aquatic, marine, fossorial and volant forms [1,2]
Saurians, or crown group diapsids, are highly taxonomically and morphologically diverse in extant ecosystems, with around 9,400 lepidosaur and 10,000 archosaur species, including cursorial, semi-aquatic, marine, fossorial and volant forms [1,2]
The new taxon Aenigmastropheus parringtoni was recovered as a basal archosauromorph, being nested within Protorosauria as the sister-taxon of Protorosaurus speneri from the Late Permian of Europe
Summary
Crown group diapsids, are highly taxonomically and morphologically diverse in extant ecosystems, with around 9,400 lepidosaur (snakes, lizards and rhynchocephalians) and 10,000 archosaur (birds and crocodilians) species, including cursorial, semi-aquatic, marine, fossorial and volant forms [1,2]. The stem-groups of Lepidosauria (non-lepidosaurian Lepidosauromorpha) and Archosauria (non-archosaurian Archosauromorpha) include several morphologically disparate saurian lineages that were mostly restricted in time to the Triassic. These lineages formed important components of Triassic continental assemblages, and include kuehneosaurids, rhynchosaurs, proterosuchids, erythrosuchids, euparkeriids, doswelliids and proterochampsids [3,4,5,6,7,8]. The best source of information on the early history of Sauria comes from the numerous fossils of the well-known basal archosauromorph Protorosaurus speneri from the Late Permian of Germany and England [19,20,21]. New information on the Permian saurian record may yield fresh insights into survivorship of this clade across the Permian-Triassic mass extinction and the dynamics of the dramatic saurian radiation in post-extinction ecosystems
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
