New Mexico Geological Society Annual Spring Meeting — Abstracts

An incomplete right mandible and two associated osteoderms from the Fossil Forest Member of the Fruitland Formation in the San Juan Basin, New Mexico show characteristic features (very large size; large, raised, confluent mandibular alveoli 3-4; thick and inflated osteoderms with deep pits) that justify their assignment to the giant “terror crocodile” Deinosuchus. These associated elements are the first definitive record of Deinosuchus from New Mexico. Three large, procoelous caudal vertebrae from the same stratigraphic unit may also pertain to Deinosuchus, based on their overall large size and procoelous nature. We consider the genus monospecific, with D. rugosus = D. riograndensis and D. hatcheri. The New Mexican D. rugosus is about 80% the size of the largest reported Deinosuchus from Texas. Thus, based on various size estimates the length of the New Mexican specimen would be between 9 and 10 meters, making Deinosuchus the largest semiaquatic predator present in the Late Cretaceous of New Mexico. Using this length estimate and extrapolating from age/length studies based on other Deinosuchus specimens, the New Mexican Deinosuchus was at least 55 years old. Deinosuchus records from the United States extend from Montana to Texas to New Jersey and are all of Campanian (Judithian-Kirtlandian) age, ~73-80 Ma.