Prodesmatochoerus is an oreodont. Oreodonts are a group of mammals which existed for over 40 million years. They came in a wide variety of forms, from cat-sized to pig-sized and at the peak of their abundance and diversity in the middle to late Oligocene (27 – 29 million years ago) they may have been the most abundant group of large mammals ever. Yet oreodonts rarely feature in popular paleontology books, and very few people outside of paleontology have ever heard of them. They have no living descendants, and their strange mix of primitive and advanced anatomical characters has made it difficult to place them accurately in the evolutionary tree of mammals. Recent studies suggest that they may be a very early offshoot from the artiodactyl line, before the modern groups diversified. They are only known from North America.

Prodesmatochoerus is perhaps the closest thing to an ‘average’ oreodont. Its body was stoutly built, with a comparatively long body and tail, but short skull, neck, and limbs. The animal’s weight was supported on the toes (rather than the sole of the foot), which had small hooves. The upper canine and lower first premolar were enlarged to form pig-like tusks, and various features of the skull suggest that they may have been capable of opening their mouths wide to show the teeth in a threat display. Some modern ungulates such as hippos, peccaries, and hyraxes use threat displays when interacting with other members of their species and the presence of the feature in oreodonts has led some researchers to suggest that oreodonts may also have lived in social herds.

Oreodonts declined dramatically in diversity during the Miocene and by 10 million years ago, there was only one genus still in existence. The decline and extinction of the oreodonts during the Miocene mirrors that of a number of groups of mammals that were poorly adapted to drier, more open habitats. It is interesting to compare the fortunes of the oreodonts with those of the tapirs, a very similar group of mammals which also declined dramatically in diversity and abundance during the Miocene, but which still survive today as a single genus with four species. As oreodont specialist Bruce Lander says, it is only a twist a fate that today we compare the anatomy of extinct oreodonts with living tapirs to try to determine oreodont lifestyle, rather than the other way around.