FAUNAL ANALYSIS OF FIVE NONMARINE MICROVERTEBRATE LOCALITIES, LATE CRETACEOUS, SOUTHERN UTAH

Five, Late Cretaceous nonmarine microvertebrate localities from the eastern margin of the Pausaugunt Plateau were analyzed for faunal content. These localities are in stratigraphic sequence and include Utah Museum of Natural History Vertebrate Paleontology Locality 820 (Straight Cliffs Fm., John Henry Member, Coniacian), UMNH VP 781 (Straight Cliffs Fm., John Henry Member, early Santonian), UMNH VP 799 (Straight Cliffs Fm., John Henry Member, middle Santonian), UMNH VP 83 (lower Wahweap Fm.; Campanian) and UMNH VP 77 (upper Wahweap Fm., Campanian). Fish, including rays, sharks, lepisosteids, amiids, and teleosts were the most common elements at all localities. Dinosaur elements were rare at all localities (<1%). Mammals comprised less than 2% at the Coniacian and Santonian localities but are proportionally high at UMNH VP 83 where they comprised 19% of the vertebrate fauna. UMNH VP 820 is thought to be riverine and near the coastal margin and contains the highest proportion of ray teeth (38%). UMNH VP 781 is in an organic rich mudstone with abundant bivalves and gastropods and may represent a paludal environment and has a high freshwater fish component, but rays and sharks are rare. UMNH VP 799 appears to be a proximal crevasse splay and has a large number of fish teeth and scales (Lepisosteus), and also has the highest proportion of shark teeth (16%) of any of the localities. UMNH VP 83 is a floodplain locality consisting of mudstone which has by far the highest proportion of mammal teeth (19%) and amiid teeth (26%). UMNH VP 77, stratigraphically the highest locality, is in a channel sandstone and although similar to riverine localities lower in section, has a higher proportion of mammals and fewer sharks. In conclusion, the data indicate that local depositional environment is the most important control on the distribution of taxa at nonmarine microvertebrate localities, but proximity to coastline also impacts faunal composition. The data may also suggest that mammals become more common from the Coniacian to Campanian.