File:Neohipparion affine (slender three-toed horse) in volcanic tuff (Ash Hollow Formation, Miocene, 11.83 Ma; Ashfall Fossil Beds, Nebraska, USA) 4.jpg

English: Neohipparion affine (Leidy, 1869) - slender three-toed horse skeleton in volcanic tuff in the Miocene of Nebraska, USA.

Volcanic tuff is a fine-grained, clastic-textured, extrusive igneous rock - basically a solidified volcanic ash deposit. Volcanic tuff can be well to poorly indurated / lithified. This exposure is at Nebraska's Ashfall Fossil Beds. The ash is 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.

The fossils seen here are part of an adult female skeleton of Neohipparion affine, a long-extinct species. Its common name is the slender three-toed horse.

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From on-site info.:

3-TOED MARE AND COLT SKELETONS

These skeletons have been disturbed (by trampling and scavening?). However, it is clear that the baby was between the adult's legs when it died.

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Slender Three-toed Horse Neohipparion

The long, slender legs of this three-toed horse show that it was a fast runner. The large functional "side hooves" (one on each side of the main hoof) suggest that it was a good dodger as well and perhaps was better at dealing with soft, treacherous ground than the single-toed horses. Like the other four species of horses found in the ash bed, this one has tall-crowned molar teeth capable of grinding tough, silica-rich grss into digestible mush. The species found at Ashfall, Neohipparion affine, is larger than its ancestors found in older fossil beds and smaller than its descendants found in younger deposits.

Single teeth of Neohipparion can be difficult to distinguish from those of Cormohipparion, hence the question marks about its occurrence above and beow the ash bed.

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

Neohipparion was 4 feet (1.2 meters) at the shoulder.

When the first fossils of three-toed horses were found in Europe, they were named Hipparion. When a skeleton of a similar horse was found later in South Dakota, it was named Neohipparion ('neo' means new) because of its occurrence in the New World.

The Greek word for horse is "hippos" and "-arion" means "small" or "diminutive".

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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: Hubbard Rhino Barn, Ashfall Fossil Beds State Historical Park, northeastern Nebraska, USA

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Info. at:

en.wikipedia.org/wiki/Ashfall_Fossil_Beds