THE EARLY PLIOCENE (BLANCAN) ALWAYS WELCOME INN OPHIOMYS AND THE MIGRATION OF OPHIOMYS INTO THE PACIFIC NORTHWEST

Ophiomys fossils collected at the ~4.8-4.3 m.y.-old Always Welcome Inn fossil site in Baker City, Oregon, as of December 2008 include 2 lower jaws (including one with a first and second molar and one with a first molar), 22 individual molars, and several incisors. Including the teeth in the jaws, 7 lower first molars, 5 lower second molars, 1 lower third molar, 6 upper first molars, 5 upper second molars, and 1 upper third molar have been found. Measurements of the lengths of the occlusal surfaces of the lower first molars found at the Always Welcome Inn fall into the same range as those of Ophiomys taylori from the ~3.7-3.1 m.y.-old Hagerman fauna of Idaho, but this may reflect a high percentage of juveniles or the small number of specimens. The mean width of the lower first molars is closest in size to Ophiomys cf. mcknighti from the ~3.9 m.y.-old Blufftop fauna of Washington. Cladistic analysis suggests that the Always Welcome Inn vole is closely related to Ophiomys mcknighti from the ~4.3 m.y.-old White Bluffs fauna of Washington and more distantly related to “Mimomys” sawrockensis from the ~4.8 m.y.-old Upper Alturas fauna of California. These results suggest that Ophiomys migrated up the Sacramento River at ~ 4.8 Ma, traveled along the shores of the Glenns Ferry lake during the Pliocene stage of Lake Idaho to the Always Welcome Inn area between ~4.8-4.3 Ma and then crossed the drainage divide and migrated through the Grande Ronde Valley and down the Grande Ronde River into the Columbia River system at ~4.3 Ma.