Paper No. 229-5
Presentation Time: 2:45 PM
A NEAR MISS, THE IMPORTANCE OF PUBLIC MUSEUM COLLECTIONS, AND A GLOBAL RANGE EXTENSION OF NON-DINOSAUR DINOSAUROMORPHS IN NORTH AMERICA
The relatively recent discoveries and contextualization of silesaurid and lagerpetid dinosauromorphs has led to a revolution in understanding the early evolutionary history of the dinosaurian lineage. Lagerpetids are known from the Americas in Middle and Upper Triassic rocks, especially the Chinle Formation of New Mexico and the Dockum Group of Texas. A new lagerpetid astragalus, MNA V7237, from the Owl Rock Member of the Chinle Formation found on Ward Terrace in the Navajo Nation of Arizona is referred to Dromomeron romeri. Until now, only a single specimen of Dromomeron gregorii was known from the Upper Triassic Chinle Formation of Arizona. Distal ends of reptile femora collected as part of an expansion inventory at Petrified Forest National Park were initially referred to the Lagerpetidae. These would have been the first lagerpetids from the park and resemble less derived lagerpetids such as Lagerpeton, which were hypothesized to be coeval with more derived lagerpetids like Dromomeron in the Late Triassic of North America. However, a last-minute collection visit at different Chinle Formation localities in Bureau of Land Management parcels in Colorado showed that those isolated distal ends of femora actually belong to the Aetosauria. This supports the idea that apomorphy-based identifications remain difficult with isolated specimens and provides yet another instance in which museum collections from public lands provide the necessary data to simultaneously support and overturn hypotheses in paleontology. Despite this, MNA V7237 from the Navajo Nation represents the youngest radioisotopically-dated record of Lagerpetidae, indicating that Dromomeron romeri persisted throughout the entire Norian (Otischalkian into the Apachean) in North America.