Oligocene (Pt 7): Not Quite Camels, Not Quite Pigs

Protoceras

While the ruminants of Oligocene North America would have looked similar to the musk deer of today, some of the other cloven-hoofed mammals inhabiting the continent at the time were more distinctive. Protoceratids no longer survive, but they had already been around for millions of years at the dawn of the Oligocene, and would survive throughout the whole of the following epoch and a little way into the one after that - an impressive record. Despite this, they never seem to have been very common, and the only undoubted Oligocene example is Protoceras, known primarily from Nebraska, Wyoming, and South Dakota.

It remains unclear exactly what protoceratids were, beyond the fact that they were obviously related to other cloven-hoofed animals. Some features suggest that they were closely related to ruminants (as was assumed when they were first discovered in the 19th century) while others indicate a close relationship to camels; it may even be that they are some early branch that doesn't fit well with either. Despite being the animal for which the group is named, Protoceras is not so well known as its later relatives, many of which notable for possessing a third horn on their snouts in addition to those in the place we'd expect to find horns on a goat or antelope. 

Miocene (Pt 12): American Rhinos and Horse-Headed Lopers

Moropus

The warming climate of Early Miocene North America was host to a variety of animals, both familiar and unfamiliar. Even in the former category, some of the creatures would have looked a little odd too modern eyes, but we can still say that a three-toed horse is, at least in general terms, still a horse. One group of animals that would be a little harder to place were the oreodonts (or, more technically, "merycoidodontids"), which were already fairly diverse when the Miocene dawned.

These creatures were unique to the continent and were medium-sized herbivores. They would have looked vaguely like pigs, although without the flattened nose-disc of those animals, and with four functional toes on each foot. As far as we can tell from their teeth, they were mostly browsing animals and were spread quite widely across the continent.