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

English: Pseudhipparion gratum (Leidy, 1869) - small 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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Small Three-toed Horse Pseudhipparion

Not much bigger than a large dog, Pseudhipparion was the smallest of the Ashfall horses. It was also the most abundant: remains of more than 50 individuals, from newborns to old adults, have been excavated here. Well-developed side-hooves probably helped the animal gain traction on soft ground and in making quick turns. The teeth are typical of a grazer (grass-eater) but have peculiarities which prove that this little horse is not closely related to other three-toed horses, but was on its own evolutionary path. Pseudhipparion originated about 14 million years ago and became extinct 10 million years ago, generally becoming smaller in body size throughout this time range, differing from most horse lineages in this respect. The Ashfall species Pseudhipparion gratum is of average size.

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)

Pseudhipparion was 2.5 feet (0.75 meters) tall at the shoulder.

[The name Pseudhipparion] means "misleadingly similar to Hipparion", the Old World three-toed horse.

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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