New Mexico Geological Society Annual Spring Meeting — Abstracts

Phytosaur specimens represent more than 60% of all fossil tetrapods from Upper Triassic strata in the western United States. However, articulated phytosaur skeletons are very rare. Only three out of 20 newly collected phytosaur skulls from the Bull Canyon Formation of east-central New Mexico are associated with articulated postcranlal bones. Two of these partial skeletons preserve stomach contents. Both skeletons are from the lower Bull Canyon Formation of Barranca Creek. The first skeleton represents Pseudopalatus buceros and includes the skull. lower jaws. most of the pelvic and pectoral girdles. several limb bones, and many ribs and vertebrae. The skeleton is slightly disarticulated and has been scavenged by a large archosaur. Several vertebrae of a small. unidentified ?crocodylotarsan reptile are found within and around the rib cage. These reptile centra average 2.2 mm long and include cervical and dorsal elements. indicating it had a moderately-elongate neck and was probably terrestrial in habit.

The second skeleton represents Pseudopalatus pristinus and includes a skull. lower jaws. and an articulated string of vertebrae with associated scutes. Most of the limbs and girdles were exposed on the surface and destroyed by weathering. Associated with the mid portIon of the vertebral column are four centra of a new long-bodied, small metoposauroid. The putative gastric residues do not represent juveniles phytosaurs and must therefore be true stomach contents or taphonomical associated specimens. The Barranca specimens are both considered true stomach contents because of their location in relation to articulated skeletons and because of the absence of any elements of any other taxa (e. g. not a bone bed). This is only the second report of phytosaurs with preserved stomach contents. I have previously proposed three ecomorphs of phytosaurs based on cranial morphology: type 1 with narrow rostrum (e. g. P. pristinus): type 2 with crested rostrum and (e. g. P. buceros): type 3 with massive rostrum (e. g. "Rutiodon" gregorii). Presumed diets of these ecomorphs are piscivorous (type 1). generalist (type 2) and predatory ( type 3). The Barranca stomach contents broadly agree with this classification if it assumed that piscivorous forms would also take small amphibians.