File:Cormohipparion occidentale (sturdy three-toed horse) foot bones (Ash Hollow Formation, Miocene, 11.83 Ma; Ashfall Fossil Beds, Nebraska, USA).jpg

English: Cormohipparion occidentale (Leidy, 1856) - sturdy three-toed horse foot bones from the Miocene of Nebraska, USA.

This fossil horse foot was excavated from a volcanic ash deposit at Nebraska's Ashfall Fossil Beds. The ash was derived from the Bruneau-Jarbidge Volcanic Field in southwestern Idaho's Snake River Plain. The wind-blown ash buried a vertebrate-rich biota at what was originally a Miocene waterhole.

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From exhibit info.:

EVOLUTION IN ACTION - HORSE FEET -

Was Darwin right? Today's horses have a single toe (hoof) on each foot. Scientists of Darwin's day predicted that ancestral horses with more toes would someday be found as fossils.

Ashfall proved them right! As you can see in these front feet of horse skeletons from the ash bed, most kinds had 3 toes but one has a single hoof.

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Sturdy Three-toed Horse Cormohipparion

Nebraska-born paleontologist Morris Skinner collected and studied fossil horses for more than 50 years. One of his greatest discoveries was a series of well-preserved skulls of Nebraska horses apparently ancestral to the "Hipparion" horses of Europe and Asia. Other paleontologists had been forced to rely mostly on teeth in researching horse evolution but Skinner pointed out important details of the skull - especially the position and shape of depressions in front of the eye socket. Announcing this discovery in 1977, Skinner and a younger colleague Bruce MacFadden named Cormohipparion. The first complete skeletons of this animal have been found here at Ashfall. These show that the foot bones of Cormohipparion were shorter than those of Neohipparion, a horse with very similar teeth.

Remains of this animal have been found: X In the "RECOVERY" layer (sandstone above the ash) X In the "DISASTER" layer (volcanic ash bed) X In the "WATERHOLE" layer (sandstone below the ash)

Cormohipparion was about 3.5 feet (1.1 meters) at the shoulder.

The Ashfall species, Cormohipparion occidentale, has one of the most complicated enamel patterns on the grinding teeth of any North American horse species. This would help grind grass into small, digestible fragments.

A deep pocket in the skull far forward of the eye is characteristic of this horse.

Cormo means "stem" and Hipparion is the name of the 3-toed grazing horse of the Old World.

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Classification: Animalia, Chordata, Vertebrata, Mammalia, Perissodactyla, Equidae

Stratigraphy: Cap Rock Member, Ash Hollow Formation, Ogallala Group, Miocene, 11.83 Ma

Locality: Ashfall Fossil Beds State Historical Park, northeastern Nebraska, USA

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Info. at:

en.wikipedia.org/wiki/Ashfall_Fossil_Beds