FIRST REPORT OF THE HYPER-GIANT CRETACEOUS CROCODYLIAN DEINOSUCHUS FROM UTAH

The giant crocodile Deinosuchus has been reported from Campanian strata of Montana, Wyoming, New Mexico, Texas, Mexico, Mississippi, Alabama, Georgia, North Carolina, and New Jersey. We report here for the first time, the finding of a partial skull (right maxilla, premaxilla, and palatine), isolated osteoderms, and teeth referable to this taxon, in the Upper Campanian (ca. 75 mya) Kaiparowits Formation, inside Grand Staircase-Escalante National Monument, south-central Utah. This is the first record of the genus between the San Juan Basin of New Mexico and central Wyoming, and it represents the only known cranial skeletal material from west of Texas. The maxilla, an isolated find recovered from a fluvial channel deposit in the lower portion of the Kaiparowits' informal middle mudstone member, is missing its teeth, but otherwise exhibits excellent preservation. It measures 66 cm long by 20 cm wide, with dental alveoli measuring up to 5.4 cm diameter. In all regards, but particularly in the shape of the anterior maxilla and alveoli spacing and arrangement, the Utah specimen is nearly identical to recently collected specimens from the Aguja Formation of Texas. Extrapolating the Utah specimen into a complete animal indicates an individual measuring in excess of 10 m. Previous finds of fragmentary remains belonging to a giant species of goniopholid measuring in excess of 7 meters in length indicate that Deinosuchus was not the only giant crocodylian taxon in the Kaiparowits ecosystem; perhaps the only example of such a co-occurrence known from the Late Cretaceous of North America. In fact, the Kaiparowits Formation has yielded the most diverse Campanian crocodylian fauna in North America; at least six genera. We speculate this remarkable diversity, now including Deinosuchus, resulted from the region's unique paleogeographic setting at, or near, a significant Campanian faunal and floral ecotone.