Metamynodon

Extinct aquatic rhino

Metamynodon is an extinct genus of amynodont that lived in North America (White River Fauna) and Asia from the late Eocene until early Oligocene, although the questionable inclusion of M. mckinneyi could extend their range to the Middle Eocene. The various species were large, displaying a suit of semiaquatic adaptations more 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 were once all believed to be semi aquatic. It is split into two tribes: the semi aquatic Metamynodontini–Paramynodon, Sellamynodon, Megalamynodon, 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. Megalamynodon is likely the ancestor of Metamynodon, though it is possible it could have evolved from an Asiatic ancestor. 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.

Metamynodon planifrons, the largest species, was about in length and in weight, and, although it was distantly related to modern rhinos, looked more like a hippo (Hippopotamus amphibius). Its front legs had four toes instead of the three found in modern rhinos. It had a dental formula of
The Early Oligocene Badlands National Park were probably streams coursing through grasslands, gallery woodlands, and savannas. Metamynodon was probably abundant and restricted to the streams; common in the gallery woodlands were the horse Mesohippus and artiodactyl Merycoidodon; and in the savannas there were the lagomorph Palaeolagus, the deer like Leptomeryx and Hypertragulus. During the Whitneyan stage of the NALMA classification, still in the Early Oligocene, Metamynodon becomes more rare.