Running Rhino Jaw Fossil – Hyracodon from South Dakota

Swift Runner of the Ancient Plains — Hyracodon Jaw Fossi

Species: Hyracodon Nebrascensis

Age: Oligocene (54 million – 34 million years ago)

Location: Pennington County, South Dakota, USA

Formation: Brule Formation

Size: Approximately 59mm × 33mm × 52mm

Weight: 110 gram

This remarkable fossil specimen is a preserved section of jawbone with teeth from Hyracodon nebrascensis, an unusual prehistoric mammal often called the “Running Rhino.” The fossil shows part of the jaw with several well-preserved molars still intact. These teeth display the complex ridges and grinding surfaces used for processing vegetation, while the surrounding fossilised bone reveals the dense mineralisation typical of mammal fossils preserved for millions of years. Even as a partial jaw, this specimen provides an exceptional look at the feeding anatomy of this fast-moving prehistoric herbivore.

Hyracodon belonged to the extinct family Hyracodontidae, relatives of modern rhinoceroses but with a very different body design. Unlike the heavy, horned rhinos we know today, Hyracodon had a much lighter build with long legs and a body adapted for speed. It lived during the Oligocene Epoch, roughly 34 to 23 million years ago, roaming open plains and woodland environments across North America. These animals likely relied on their speed to escape predators while grazing on leaves and low vegetation. The group eventually disappeared as climates changed and new grazing mammals evolved.

This fossil was discovered in the famous Brule Formation of Pennington County, South Dakota, part of the larger White River fossil region. The Brule Formation is one of the most scientifically important fossil sites in North America, preserving a rich record of Oligocene ecosystems filled with early horses, oreodonts, rhinoceroses, carnivores, and many other mammals. Fossils from this formation have helped paleontologists understand how mammals evolved and adapted to changing environments after the age of dinosaurs.

With its preserved teeth and identifiable jaw structure, this fossil offers a fascinating glimpse into the swift herbivores that once roamed the ancient plains of North America.

Add this authentic Running Rhino jaw fossil to your collection and own a rare relic from the extraordinary mammal ecosystems of the Oligocene world.