Oreodontidae

Oreodontidae, commonly called oreodonts, is an extinct family of small- to medium-sized, even-toed ungulate mammals that lived in North America during the Cenozoic. They ranged from the Eocene to the Miocene, roughly 42 to 8 million years ago, and are known from abundant fragmentary to well-preserved fossils, especially in the western interior and Great Plains.

Taxonomy and classification: Oreodontidae is treated as an extinct family within Artiodactyla. Their exact systematic position has varied among authors, with oreodonts often referred to as the broader group Merycoidodontidae or Oreodontoidea; some classifications place them within the suborder Tylopoda, while others link them more broadly to ruminants. In all cases, they form a distinct North American lineage of herbivorous artiodactyls.

Anatomy and adaptations: Oreodonts were generally robust, short-legged animals with a pig-like appearance and elongated snouts. They possessed selenodont (crescent-shaped) molars and premolars adapted to processing fibrous vegetation. The dentition and facial morphology varied among genera, and some species bore tusk-like canines.

Ecology and behavior: They occupied a range of habitats—from woodland edges to open plains—and included both grazing and browsing forms. Digestive anatomy indicates efficient fermentation typical of ruminants. The abundance and diversity of oreodonts at many sites suggest they were ecologically successful and often common in Miocene faunas.

Fossil record and extinction: The oreodont lineage persisted for tens of millions of years but gradually declined in the late Miocene, with final occurrences by about 5 million years ago. Climate change, habitat transformation, and competition with other herbivores are cited as factors in their extinction.