Oreodont Partial Skull | Merycoidodon | South Dakota

Merycoidodon sp.
Oligocene (33 - 30 MYO)
Brule Formation
White River Badlands
South Dakota

Specimen approx. size: 5.5" x 3.3" x 2"

This specimen exhibits crack repair, but very minimal fill restoration. The teeth are natural and unaltered.

Merycoidodon is an extinct genus of herbivorous artiodactyl (even-toed ungulate) belonging to the family Merycoidodontidae, commonly known as oreodonts. These animals were endemic to North America and lived from the Late Eocene through the Miocene, roughly 40 to 16 million years ago.

Morphology

Merycoidodon had a stocky, pig-like body measuring approximately 1–1.5 meters (3–5 feet) in length. It had short limbs, each ending in four-toed hooves, a long tail, and a relatively large head. Despite its superficial resemblance to pigs, it was more closely related to camels.

The skull was robust with a complete set of teeth, including large canines and complex selenodont molars, ideal for processing vegetation. This dentition suggests a generalist herbivorous diet, probably including leaves, fruits, and possibly tougher vegetation.

One notable feature is the presence of auditory bullae that were inflated, which may suggest acute hearing—an adaptation that may have aided in predator avoidance.

Postcranial Skeleton

The limb morphology indicates that Merycoidodon was not a fast runner but capable of steady movement across a variety of terrains. Its strong, weight-bearing limbs and overall skeletal robustness suggest a terrestrial lifestyle, likely in open woodlands or savanna-like environments.

Paleoecology

Fossils of Merycoidodon are widespread across North America, with notable finds in South Dakota, Nebraska, Wyoming, and Colorado—especially in the White River Formation. Their abundance in fossil beds suggests that they were a dominant herbivore in Oligocene ecosystems.

They likely lived in herds, as suggested by large fossil assemblages, which may have offered protection from predators like entelodonts and nimravids.

Taphonomy and Fossil Record

Merycoidodon is one of the most commonly found mammals in Oligocene deposits of North America. Its fossilized remains often include articulated skeletons, indicating rapid burial, possibly in river floodplains or volcanic ash beds. Their abundance and preservation make them key biostratigraphic markers in Oligocene sediments.