NEW LARGE MAMMALS FROM MCKAY RESERVOIR (MCKAY FORMATION, HEMPHILLIAN, OREGON)

McKay Reservoir, located near Pendleton, Oregon, is paleoecologically significant, as it contains a well-preserved diversity of vertebrates dating to the Hemphillian North American Land Mammal Age. It is especially remarkable for its small vertebrate fauna such as rodents, bats, turtles, and lagomorphs, but also for its larger mammal fossils like camelids, rhinocerotids, canids, and felids. Though it represents a late stage of the transition from forests to widespread grasslands, McKay Reservoir can help answer prominent questions related to morphological, paleoecological, and biogeographic changes across this transition. Despite the importance of the site, few revisions to its faunal list have been published since the original 1956 description. We expand on this original description by describing taxa not previously known from McKay Reservoir on the basis of specimens collected during field work in 2017 and 2021 and through reidentification of previously collected fossils. Most notable is a lower dentary identifiable as the borophagine canid Borophagus secundus, the first occurrence of this species from the Pacific Northwest, representing an expansion of its range. Also identified at the site were a several camelid phalanges and cheek teeth attributable to Megatylopus, an extinct giant camelid, and Pleiolama, a camelid closely related to modern llamas. Finally, we identified jaw fragments from two extinct equid genera not previously known from McKay Reservoir, Cormohipparion and Pseudhipparion. In addition to these fossils, we continue to attempt identifications of other enigmatic specimens found at McKay Reservoir. To aid our identifications, to contribute to the knowledge of this important site, and to aid in education and outreach efforts, we use photogrammetry as a means of creating a digital repository of significant fossils found at McKay.