THE ?STRANGE REPTILES? OF THE TRIASSIC: THE MORPHOLOGY, ECOLOGY, AND TAXONOMIC DIVERSITY OF THE CLADE ALLOKOTOSAURIA ILLUMINATED BY THE DISCOVERY OF AN EARLY DIVERGING MEMBER

NESBITT, S. J.; STOCKER, MICHELLE R.; EZCURRA, M. D.; FRASER, N.C.; HECKERT, A.B.; MARSH, A.; PARKER, W.; MUELLER, B.; PRITCHARD, A.C.

Congreso; SVP anual meeting 2017; 2017

Following the end-Permian mass extinction, archosauromorph reptiles underwent rapidlineage diversification, increases in disparity and body sizes, and expansion into newecological opportunities. However, tracing the early portion of this diversification hasbeen challenging because of taphonomic and biologic factors, including: 1) mostskeletons are incompletely preserved, frequently disarticulated, and preserved with othertaxa; 2) many early archosauromorphs are small (~1 meter in length or less) makingcharacter states determinations difficult; and 3) much of the fossil record is Late Triassic,tens of millions of years after the initial divergences and achieving high disparity.Mediation of some of these challenges is now possible with the recently recognized earlyarchosauromorph clade Allokotosauria. This clade contains disparate, ecologicallydiverse (faunivores and herbivores), and typically larger bodied (1-3 meters in length)archosauromorphs (Azendohsaurus, Trilophosaurus), but to this point, plesiomorphic,early-diverging allokotosaurians have not been identified. Here, we recognize specimensassigned to the enigmatic taxon Malerisaurus from both present-day India and westernTexas as members of Allokotosauria, and more specifically, the Azendohsauridae. Themorphology of the skull of Malerisaurus indicates that it had a long and low snout withrecurved teeth, character states that represent plesiomorphic traits of the clade. Remainsof Malerisaurus have been mistakenly identified as fragments pertaining to a diversity ofTriassic reptiles (e.g., dinosaurs, phytosaurs, Trilophosaurus) and larger, likelyontogenetically older, representatives of the taxon were described as rhynchosaurs (e.g.,Otischalkia). These fossils show that Malerisaurus was a common faunal member of thelate Carnian to mid-Norian faunal assemblages from Upper Triassic strata of thesouthwestern United States. The recognition of Malerisaurus as both an allokotosaur andan azendohsaurid has also helped identify other fragmentary remains of close relativesfrom Triassic deposits across Pangea including India, elsewhere in North America, andAfrica. As such, Allokotosauria had a near Pangean distribution for much of the Middleto Late Triassic. Allokotosauria represents one of the oldest successful clades ofarchosauromorphs that achieved a wide geographic distribution and both taxonomic andecomorphological diversity.