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.

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