Department of Pathology and Anatomical Sciences, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, Buffalo, NY 14214, USA firstname.lastname@example.org.
Department of Vertebrate Paleontology, Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, CA 90007, USA.
Division of Paleontology, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024, USA.
Centro de Geociencias, Universidad Nacional Autónoma de México, Boulevard Juriquilla 3001, Juriquilla, Querétaro 76230, Mexico.
The North American fossil otter Enhydritherium terraenovae is thought to be partially convergent in ecological niche with the living sea otter Enhydra lutris, both having low-crowned crushing teeth and a close association with marine environments. Fossil records of Enhydritherium are found in mostly marginal marine deposits in California and Florida; despite presence of very rich records of fossil terrestrial mammals in contemporaneous localities inland, no Enhydritherium fossils are hitherto known in interior North America. Here we report the first occurrence of Enhydritherium outside of Florida and California, in a land-locked terrestrial mammal fauna of the upper Miocene deposits of Juchipila Basin, Zacatecas State, Mexico. This new occurrence of Enhydritherium is at least 200 km from the modern Pacific coastline, and nearly 600 km from the Gulf of Mexico. Besides providing further evidence that Enhydritherium was not dependent on coastal marine environments as originally interpreted, this discovery leads us to propose a new east-to-west dispersal route between the Florida and California Enhydritherium populations through central Mexico. The proximity of the fossil locality to nearby populations of modern neotropical ottersLontra longicaudis suggests that trans-Mexican freshwater corridors for vertebrate species in riparian habitats may have persisted for a prolonged period of time, pre-dating the Great American Biotic Interchange.