Additional Discussion, Tables, and Figures from Discovery of the fossil otter <i>Enhydritherium terraenovae</i> (Carnivora, Mammalia) in Mexico reconciles a palaeozoogeographic mystery

The North American fossil otter <i>Enhydritherium terraenovae</i> is thought to be partially convergent in ecological niche with the living sea otter <i>Enhydra lutris</i>, both having low-crowned crushing teeth and a close association with marine environments. Fossil records of <i>Enhydritherium</i> 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 <i>Enhydritherium</i> fossils are hitherto known in interior North America. Here we report the first occurrence of <i>Enhydritherium</i> 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 <i>Enhydritherium</i> is at least 200 km from the modern Pacific coastline, and nearly 600 km from the Gulf of Mexico. Besides providing further evidence that <i>Enhydritherium</i> 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 <i>Enhydritherium</i> populations through central Mexico. The proximity of the fossil locality to nearby populations of modern neotropical otters <i>Lontra longicaudis</i> 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.