A new Early Permian reptile and its significance in early diapsid evolution

Abstract

The initial stages of evolution of Diapsida (the large clade that includes not only snakes, lizards, crocodiles and birds, but also dinosaurs and numerous other extinct taxa) is clouded by an exceedingly poor Palaeozoic fossil record. Previous studies had indicated a 38 Myr gap between the first appearance of the oldest diapsid clade (Araeoscelidia), ca 304 million years ago (Ma), and that of its sister group in the Middle Permian (ca 266 Ma). Two new reptile skulls from the Richards Spur locality, Lower Permian of Oklahoma, represent a new diapsid reptile: Orovenator mayorum n. gen. et sp. A phylogenetic analysis identifies O. mayorum as the oldest and most basal member of the araeoscelidian sister group. As Richards Spur has recently been dated to 289 Ma, the new diapsid neatly spans the above gap by appearing 15 Myr after the origin of Diapsida. The presence of O. mayorum at Richards Spur, which records a diverse upland fauna, suggests that initial stages in the evolution of non-araeoscelidian diapsids may have been tied to upland environments. This hypothesis is consonant with the overall scant record for nonaraeoscelidian diapsids during the Permian Period, when the well-known terrestrial vertebrate communities are preserved almost exclusively in lowland deltaic, flood plain and lacustrine sedimentary rocks.

The conservation status of the world’s reptiles

“…Reptiles 1 and their immediate diapsid ancestors have had a long and complex evolutionary history, having first appeared on the planet in the late Palaeozoic Era, more than 250 million years ago (based on molecular phylogeny estimates and early fossil records: e.g., Hedges and Poling, 1999;Reisz et al, 2011;van Tuinen and Hadly, 2004). High rates of cladogenesis in the Triassic and Jurassic periods (Vidal and Hedges, 2009) produced a diverse group of animals adapted to almost every temperate, tropical and desert environment, and to terrestrial, freshwater and marine habitats.…”

The palatal dentition of tetrapods and its functional significance

“…Paleothyris , Carroll, ; Petrolacosaurus , Reisz, ; Orovenator , Reisz et al. ), but ectopterygoid teeth were rare (e.g. Araeoscelis , Vaughn, ; Fig.…”

First evidence of centralia in Ichthyopterygia reiterating bias from paedomorphic characters on marine reptile phylogenetic reconstruction

“…These paedomorphic 'loss features' probably have a high risk of being homoplastic and may not satisfy the underlying assumption of homology for characters used in cladistics analyses (Carroll and Dong, 1991). For example, it is known that when the phylogeny of multiple clades of marine reptiles is cladistically analyzed, the absence of pedal centralia supports the monophyly of these groups (Reisz et al, 2011), whereas the feature may turn out to be homoplastic if the fossil record of transitional forms is complete. Also, a combined analysis of molecular and morphological data in salamanders demonstrated that paedomorphic features led to a phylogeny that was incongruent with the molecular signal yet robustly supported by parsimony and Bayesian methods (Wiens et al, 2005).…”

“…The centralia are characters used in phylogenetic analyses of basal diapsids (M€ uller, 2004;Reisz et al, 2011), so their lack in marine reptiles is a potential impediment to the understanding of their phylogenetic relationships. Loss of manual centralia occurred convergently in mosasaurs and thalattosaurs, most likely as a result of aquatic adaptation (Caldwell, 1996;M€ uller, 2005).…”