Metamynodon is a genus of hippo-like rhinoceros that lived in North America ( White River Fauna ) and Eurasia during the early Oligocene to the Miocene, although the questionable inclusion of M. mckinneyi could extend their range to the Middle Eocene . [1] The various species were large, showing a suit of semiaquatic adaptations similar to those of the modern hippopotamus, despite their closer affinities with rhinoceroses.


Metamynodon is a member of the extinct family Amynodontidae , sometimes called "swamp rhinos" as they once were believed to be semi-aquatic. It is split into two the tribes : the semi-aquatic metamynodontini - paramynodon , sellamynodon , megamalamynodon , and metamynodon - and the tapir-like cadurcodontini - procadurcodon , zaisanamynodon , cadurcodon , and cadurcotherium . The Metamynodontini are found across the world, with Paramynodon from Myanmar, Sellamynodon from Romania, and Megalamynodon and Metamynodon from North America. [2] Megalamynodon is probably the ancestor of Metamynodon , although it is possible to have evolved from an Asiatic ancestor. [3]

In 1922, paleontologist Clive Forster-Cooper initially described tooth remains from Balochistan, Pakistan as M. bugtienses before returning 2 years later and reassigning it to the genus Paraceratherium . [4] [2]

Metamynodon bones are common in Early Oligocene Riverbed deposits of Badlands National Park in South Dakota, giving them the nickname "the Metamynodon channels." [5] [3]

In 1981, a large jawbone, 41723-5, from Brewster County , Texas was described as M. mckinneyi , named after one of the discoverers Billy Pat McKinney, and was found in a area dated to 43 mya in the Late Eocene . The jawbone and tusks were more massive than that of M. chadronensis, and it could represent either a transitional phase between Amynodon and M. chadronensis , or simply a migrant to the area.