A Newly Discovered Phlaocyon-like Dog (Borophaginae) from the Orellan of Nebraska and its Implications for early Oligocene Dog Diversification
WELSH, Ed; Badlands National Park, Interior, SD. MOORE, Jason; University of New Mexico, Albuquerque, NM.
The conventional understanding of canid diversity proximal to the Eocene-Oligocene Transition (~33.7 Ma) is that Hesperocyon is the dominant canid through the White River sequence. There is interpreted to be a gradual diversification of other rare canid taxa through the early Oligocene followed by a major taxonomic and ecological diversification during the Whitneyan-Arikareean Transition (~30 Ma). Here we report the discovery of a new specimen of borophagine canid recovered from the uppermost Orella Member of the Brule Formation (~32.85 Ma) at Toadstool Geologic Park, Sioux County, Nebraska. The specimen consists of a highly diagnostic second lower molar, possessing a metaconid and protoconid of equal height, a basined talonid, and a small protostylid. The presence of a protostylid in Oligocene canids is unique to derived members of the borophagine tribe Phlaocyonini (Phlaocyon and Cynarctoides). No specimen within this clade has been previously confirmed from the Brule Formation or units of equivalent age anywhere in North America, with the possible exception of one questionable occurrence of Cynarctoides from the Whitneyan of South Dakota. Basal Borophaginae are known from Whitneyan assemblages throughout the Midwest, but only one taxon, Otarocyon macdonaldi (known from only two specimens), has ever been recovered from older, Orellan assemblages. All previously documented phlaocyonine taxa make their first appearances in the Arikareean. Based on the placement of Phlaocyonini in previous phylogenetic studies the newly discovered Toadstool Geologic Park specimen suggests that the previously suggested Arikareean diversification of canids actually occurred at least two million years earlier, in the late Orellan.