The identification of Amahuacatherium peruvium as a late Miocene gomphothere from Amazonian Peru has been challenged, with some authors claiming the specimen is only a western Amazonian example of the widespread, late Pleistocene genus Haplomastodon. Arguments against placing Amahuacatherium in synonymy with Haplomastodon include diagnostic dental characters, the presence in the former of lower tusks in adult individuals, and the upper Miocene age of the deposits from which it came. Amahuacatherium, as originally reported, is the oldest known North American mammal to enter South America in an early phase of the Great American Faunal Interchange. © 2009 E. Schweizerbart'sche Verlagsbuchhandlung.