File:Protohippus simus (slender, grass-clipping horse) foot bones (Ash Hollow Formation, Miocene, 11.83 Ma; Ashfall Fossil Beds, Nebraska, USA).jpg

English: Protohippus simus - slender, grass-clipping 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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Slender, Grass-clipping Horse Protohippus

Despite its name, Protohippus was not the first (oldest) member of the horse family, but it does share some skeletal and dental features with modern horses that other 12-million-year-old kinds of horses do not. For example, it has a "smooth face" (i.e., no deep depressions in the skull in front of the eye sockets). Its chewing teeth are also more similar to modern horse teeth than are those of the other four horses found in the ash bed. Its front teeth, however, are more specialized than those of living horses. They are arranged in a straight line, presumably to clip more grass at ground level than other horses which have the nipping teeth arranged in a curve. Like Pliohippus, Protohippus had vestigial, non-functional side toes and probably was a fast runner in flat, open grasslands.

Remains of this animal have been found:

-  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)

Protohippus was about 3 feet (0.9 meters) at the shoulder. Its legs were proportionately as long as the living wild ass of Somalia, a very fleet animal.

Protos means "the very first" and hippos means "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