North Dakota Stratigraphy Mesohippus bairdi ROCK ROCK UNIT COLUMN PERIOD EPOCH AGES MILLIONS OF YEARS AGO Common Name: Holocene Oahe .01 Three-toed horse Coleharbor Pleistocene QUATERNARY Classification: 1.8 Pliocene Unnamed 5 Miocene Class: Mammalia 25 Arikaree Order: Perissodactyla Family: Equidae Brule Oligocene 38 South Heart Chadron Chalky Buttes Three-toed horse skeleton (cast) of Mesohippus bairdi on exhibit Camels Butte Eocene Golden at the North Dakota Cowboy Hall of Fame Museum in Medora. 55 Valley Bear Den Brule Formation. Stark County. Height at shoulder 465 mm. Sentinel Butte Description: TERTIARY Mesohippus was one of the early species of horses that lived in North Dakota during the Oligocene about 30 million years. It surficially resembled the modern horse except it was much smaller, Bullion Paleocene Creek only about 2 feet tall at the shoulder and up to 4 feet long. They were about the size of a greyhound dog. They had slender limbs Slope adapted for trotting and running. Mesohippus also had three toes Cannonball on each foot in contrast to the modern horse that has one. The Ludlow teeth of Mesohippus were also different than today’s horse. Their 65 teeth were low crowned and therefore adapted to browse leaves Hell Creek from bushes and trees. Fox Hills ACEOUS Pierre CRET 84 Niobrara Carlile Carbonate Calcareous Shale Claystone/Shale Siltstone Sandstone Sand & Gravel Mudstone Lignite Glacial Drift Mesohippus in a savanna habitat. Painting by Michael R. Long, courtesy of The Natural History Museum, London. Locations where fossils have been found ND State Fossil Collection Prehistoric Life of ND Map North Dakota Geological Survey Home Page.