RECENT DISCOVERIES OF SMALL VERTEBRATE FOSSILS FROM MCKAY RESERVOIR

McKay Reservoir is a late Miocene (6.7-5.9 Ma, Hemphillian North American Land Mammal Age) site in Umatilla County, Oregon known for its remarkable preservation of small mammals. McKay Reservoir has been the focus of several classic paleoecological studies due to its preservation of small animals in addition to the larger taxa common at other sites in the region. Along with dentition, abundant postcrania of small mammals are well preserved at this site, most likely due to wave erosion of soft sediments along the shore of the reservoir. Despite its historical importance, our work at McKay Reservoir during the summer of 2017 marked the first systematic collection at the site since 1980. Our visit occurred during July, at which point water levels had dropped sufficiently to expose ~100 horizontal meters of fossil-bearing sediments. Rodentia and Lagomorpha were the most abundant small mammals. Among lagomorphs, leporid cheek teeth and tibiae were particularly common. A diverse rodent fauna included the castorids Dipoides and Castor, the cricetid Prosomys, and Sciuridae. Though previous researchers had identified the McKay sciurids as members of the genus Spermophilus, the dentition and postcrania we uncovered indicate that the sciurid material from the site can be assigned to the genus Otospermophilus. Notable among the sciurid material is a mostly complete, well-preserved skeleton of Otospermophilus mckayensis that provides important insight into the morphology and paleoecology of Miocene ground squirrels. Bats, eulipotyphlans, and musteloid carnivores were the other small mammals previously reported from the site; of these three taxa, we uncovered only musteloids. Small non-mammalian vertebrate material includes a single bird cervical vertebra, a large sample of turtle costals and peripherals, and a single fish vertebra. The diversity of small vertebrates at this site reflects the unusual taphonomy of McKay Reservoir and provides a unique opportunity to explore the paleoecology of a well-preserved Miocene ecosystem, both of which will be the focus of ongoing research.