New Mexico Geological Society Annual Spring Meeting — Abstracts

Phytosaurs are large, semi-aquatic, carnivorous reptiles known from Upper Triassic strata in North America, Brazil, Europe, Turkey, North Africa, Madagascar, India, and Thailand. The Chinle Group of New Mexico yields many phytosaur fossils. A giant skull, mandible, and associated postcranial fossils representing a Rutiodon-grade phytosaur, possibly Leptosuchus, was collected by the New Mexico Museum of Natural History and Science (NMMNH) in 2009 and 2010. NMMNH locality 1176 in the Garita Creek Formation of the Chinle Group, (Santa Fe County) normally yields metoposaurid amphibian (Koskinonodon perfectum) remains in an extensive bone bed designated the Lamy Amphibian quarry. In 2009, one of the authors (WLL), discovered a very large phytosaur mandible straigraphically about 1.2 meters below the amphibian level. That level is now designated NMMNH locality 8276. The mandible and associated postcrainia were subsequently collected and prepared. In 2010, WLL found a nearly complete, but badly crushed skull less than two meters from the mandible. The fossils are from silty mudstone strata representing overbank deposits similar to those of the overlying amphibian bonebed. The mandible as prepared is 1240 mm long. The skull as measured in the field is approximately 1390 mm long from the snout tip to the distal squamosals, which were broken, but apparently in life position, and 630 mm across at the widest point (quadratojugals) and is among the largest phytosaur skulls found to date. The relative sizes of the skull and mandible and their close association indicate that they probably belonged to the same individual. Published data and our observations indicate that other giant phytosaur skulls measure between 1215 mm and 1420 mm long, with incomplete skulls estimated up to 1500 mm. The posterior half of the Lamy skull is badly crushed and consists largely of small, disarticulated pieces but an intact connection of bone between the snout tip and quadrates yields an accurate minimum length. Associated paramedian scutes, NMMNH P-61225 and NMMNH P-61238, show healed bite marks. Some duplication of anatomical elements indicates that more than one phytosaur individual is represented by the fossils from locality 8276.