New Mexico Geological Society Annual Spring Meeting — Abstracts

Phytosaurs are superficially crocodile-like archosaurs that are the most common fossil vertebrates in Upper Triassic strata of western North America. The Bull Canyon Formation of east-central New Mexico has yielded a large collection of phytosaurs that are mainly undescribed. Three species and two genera are present. Pseudopalatus pristinus is a slender snouted form that is represented by several skulls and some postcrania. The second species is a crested species of the genus Pseudopalatus. Previously, specimens of this taxon have been placed in the species P. buceros. However, the holotype of this species pertains to the German genus Nicrosaurus. The third species is a massively constructed animal and represents a new genus. Specimens of this species have previously been assigned to Rutiodon gregorii which is a taxon with a more primitive temporal arcade. This taxon is only known from skulls and cervical vertebrae. There are approximately twenty skulls from the Bull Canyon Formation of which three represent the new genus, and the remainder Pseudopalatus.

The two species of Pseudopalatus also occur in the Cooper Member of the Dockum Formation in West Texas, the Petrified Forest Formation in north-central New Mexico and the Painted Desert Member of the Petrified Forest Formation in northeastern Arizona. Diverse evidence from palynology, vertebrate correlations and sequence stratigraphy indicates that these strata are of early-middle Norian in age.

The three species of phytosaurs represent three distinct ecomorphs. Pseudopalatus pristinus has a very narrow snout and a fairly homodont dentition and was obviously mostly piscivorous. One skeleton of this species includes intercentra of the small metoposaur Apachesaurus among its stomach contents. The massive species has a robustly constucted skull with a very heterodont dentition consisting principally of serrated teeth. This taxon was obviously predatory and was capable of killing large tetrapods. The second species of Pseudopalatus shows intermediate conditions in the robustness of the skull and in the form of the dentition. This species was probably a generalist feeder. The stomach contents of one specimen include a small reptile (centra < 2 cm long).

Phytosaur fossils are most commonly associated with specimens of the aetosaur Typothorax and less commonly Desmatosuchus and Paratypothorax. They are rare in localities that are rich in terrestrial reptiles (dinosaurs, rauisuchians, sphenosuchians).