Oreodonts fill the plains
Sheep-sized artiodactyls unrelated to anything living become the most abundant mammals in North America.
- When
- —
- Duration
- 11 million years
- Known to
- ± 1 million years
- Era
- Oligocene, Cenozoic
Oreodonts are so common in the White River badlands that collectors historically treated them as background noise. They are endemic North American artiodactyls with no close living relatives, filling roles somewhere between pigs, sheep and marmots, with some genera apparently semi-aquatic and others burrowing. Their sheer abundance across millions of years makes them the workhorse fossils for studying population variation, growth and sexual dimorphism in an extinct mammal group.