The Earliest Known Fisher (mustelidae), a New Speciesfrom the Rattlesnake Formation of Oregon

Fishers are elusive carnivorans, with few occurrences in the fossil record. The origin and early evolution of fishers is unclear, but they likely originated in Asia. A new record of Pekania from the Rattlesnake Formation of Oregon represents the earliest known occurrence of a fisher, more than 5 million years earlier than other records in North America. This specimen has an unambiguous derived trait shared with other members of the genus, an external median rootlet on the upper carnassial. The age of this new find is inferred to be between 7.05 and 7.3 Ma, through radiometric and magnetostratigraphic dating. This age is supported by the presence of specimens of a shrew, Sorex edwardsi, and a rhinoceros, cf. Teleoceras, found at the same locality, as well as a rabbit, Hypolagus cf. vetus, and a tapir nearby, all of which are well known from early Hemphillian deposits. This find indicates that fishers were in both North America and Asia in the late Miocene, around the time of their divergence from other members of the clade as estimated from genetic data. Although it is over 7 million years old, this species shows remarkable similarity to extant P. pennanti, highlighting the highly conservative nature of gulonine mustelids. The Rattlesnake specimen is more robust than other fisher species, possibly representing something close to the ancestry of all fishers.