📸 Oreodont paleoart
At the end of the Eocene, 34 million years ago, Earth’s ecosystems began to change. A shift in climate and a decline in tropical zones brought about expansive plains and grasslands, new ecosystems that would be home to never before seen flora and fauna. The Oreodonts, a family of small sheep-like artiodactyl, took full advantage of this change and appeared on the plains and forests of North America, where they thrived in the new world for millions of years. From the swamps of Florida to the grasslands of South Dakota, Oreodont’s rugged teeth allowed them to fill many ecological niches, ballooning or shrinking in size based on whatever their environment called for.
📸 A complete oreodont skeleton
The oreodont, sometimes called the ruminating hog, was a short mammal with a heavy body, a long tail, and a hoof-like set of toes. Their name means “mountain teeth,” a testament to the ridge structures of their molars. These flattened teeth indicate a browser’s diet, the Oreodont searching through grassy prairies and wooded areas for roots, shoots, and other plant matter to grind up.
Based on their shape, it was first believed that these creatures were related to modern-day pigs, but new science suggests this is a case of convergent evolution rather than familial relation. Today, the Oreodont’s closest relative is camels, but even this link is quite distant.
📸 A Merycoidodon culbertsoni skull
Oreodonts achieved a widespread distribution across North America, diverging from the well-represented and anatomically simple Merycoidodon culbertsoni. These Oreodonts grew to be around 4-5 feet long and walked the plains on short, stubby legs. Like other Oreodonts, they had flat molars that tore and ground tough plant matter. These teeth were a vital adaptation to survival in the prehistoric grasslands—without this specialized function the Merycoidodon’s diet would have been impossible. Strangely, the species also had very powerful and long canine teeth alongside their molars, though the use of those teeth is poorly understood.
From this baseline, Oreodonts adapted to their surroundings in a number of unique ways. Species varied from cat-sized desert dwellers, cow-like herd animals, and massive semi-aquatic beasts. Strangest of all was Brachycrus, a unique branch that evolved a specialized trunk to scrounge for food much like the modern tapir. Though they were only distantly related to Cervidae, one could compare the two families by their large amount of specialization and variance between species.
📸 Grasslands like where Oreodont would graze
Oreodonts were so proficient that their classification has been challenging for paleontologists today. Since their discovery, 450 species of Oreodont have been named, though many of these have been reordered and combined. The over-representation owes itself to the family’s abundance in the fossil record. We know Oreodonts were pack animals, based on the close proximity of mass mortalities in fossil beds. This would likely have helped protect them from predators of the time, like the Nimravid, a muscular feline-like hunter.
Merycoidodon culbertsoni is a good example of this survival strategy: the species lasted over 30 million years, a very impressive span given that the average mammalian species typically survive 1-2 million years. What ultimately did in the creatures was a snowball of circumstances—reduced food sources led many Oreodonts to starvation and those that survived lived in weaker herds allowing for over-predation. All of these factors stemmed from one thing: a radical change in climate that made the world unsuitable for the Oreodont.
📸 Oreodont jaw fossils with included teeth
📸 Oreodont fossil tooth and jaw section
Chew, chew, chew, and swallow
This specimen from Mini Museum is a single jaw fragment from a Merycoidodon culbertsoni Oreodont. Within this jaw are the teeth that allowed Oreodonts to spread across North America, munching and grinding on a wide variety of vegetation. These animals had what is called hypsodont dentition, or simply high crowned teeth, which makes them tougher and more resistant to the abrasive browser diet. The added layer of material protects the tooth from this type of plant’s higher levels of silica and fiber as well as inorganic grit like dust and ash.
Through finds like this, paleontologists can speculate on the composition and distribution of the grasslands where Oreodonts fed. Oreodonts are best represented in western North America, particularly in the White River Badlands of South Dakota where thousands of specimens have been found. As Oreodonts lived in massive herds, their presence at a given site indicates that a sufficiently large food source existed there to support them. Wherever an Oreodont’s tooth can be found, an interlinked food source can not be far away.
Bader, Robert S. “Variability and Evolutionary Rate in the Oreodonts.” Evolution, vol. 9, no. 2, 1955, pp. 119–140.
MACFADDEN, BRUCE J, and GARY S MORGAN. “Chapter 15: New Oreodont (Mammalia, Artiodactyla) from the Late Oligocene (Early Arikareean) of Florida.” Bulletin of the American Museum of Natural History 279 (2003): 368–396. Web.
Mihlbachler, Matthew C, and Nikos Solounias. “Coevolution of Tooth Crown Height and Diet in Oreodonts (Merycoidodontidae, Artiodactyla) Examined with Phylogenetically Independent Contrasts.” Journal of mammalian evolution 13.1 (2006): 11–36. Web.
“Oreodont: Ancient Grazer of the Badlands (U.S. National Park Service).” National Parks Service, U.S. Department of the Interior, 10 Nov. 2020
Thorpe, Malcolm Rutherford. “The Geological History of the Oreodonts.” Journal of Mammalogy, vol. 6, no. 2, 1925, pp. 69–82.