Ancient otter tooth found in Mexico suggests mammals migrated across America

An ancient otter tooth recently discovered in Mexico suggests certain mammals migrated across America during the Miocene geologic epoch, roughly 23 million to 5.3 million years ago. The new hypothesized route questions other theories such as migrations above Canada and through Panama, and has implications for a much larger biologic event — the Great American Biotic Interchange, when land bridges were formed and animals dispersed to and from North America and South America.
Paleontology News — ScienceDaily