Musteline (Mustelidae) fossil remains from the Early Pliocene Gray Fossil Site of Tennessee: the first pre-Pleistocene record of weasels in the Eastern United States

The Mustelinae (weasels, stoats, minks, and ferrets) are a subfamily of small, elongate-bodied mustelid carnivorans (Carnivora: Mustelidae) that originated during the Late Miocene. Mustelines are the most abundant group of carnivorans in the world today and are commonly found at Pleistocene-aged sites across their range; however, their lack of a more complete fossil record has left many questions regarding the evolution of early mustelines unanswered. Here we report a new occurrence of a musteline from the Early Pliocene age (4.9 – 4.5 Ma) Gray Fossil Site in northeastern Tennessee. Morphology of the P4 and M1 are consistent with the dental characteristics of Mustelinae, and thus this find represents the first reported pre-Pleistocene occurrence of a musteline in the eastern United States. Morphology of the specimens is distinct from the well-known Miocene ischyrictine mustelid Plionictis, but falls within the range of variation observed within the extant genera Mustela and Neovison. Linear measurements also fall within the size ranges of those genera. Distinguishing Mustela from Neovison based on morphological characters alone is very difficult and recent phylogenetic studies differentiating the two have been based exclusively on genetic evidence. Further study will hopefully allow us to place a confident identification on the musteline from Gray. The small, hypercarnivore niche of mustelines is one that was previously not recognized among fauna at the Gray Fossil Site, and improves our understanding of the site’s paleoecology