#pliohippus

herd of Pliohippus playing in the snow.

Available HERE

Fossil horses from the Ashfall Fossil Beds in Nebraska, a site whise richness of mammal fossils is attributed to a large Yellowstone eruption. Horse remains are plentiful, with five genera known to be present. They are depicted above in the following order: Pseudohipparion, Neohipparion, Cormohipparion, Protohippus, and Pliohippus. The first three genera are three-toed, while the last two bear single hooves.

Unsolved Paleo Mysteries Month #11 -- Strange Snoots: Equid Edition

Horse evolution is often represented as a simple progression from Eohippus* to modern Equus, but it was actually a lot more complicated than that -- and some ancient horses had some very odd things going with their snouts...

(* For a long time Eohippus was considered synonymous with Hyracotherium, but more recently has been split back off as its own genus again.)

Pliohippus, from the Middle Miocene of North America (~15-12 mya), and several of its other close relatives had especially large, deep recesses in their skulls, usually referred to as “preorbital fossae”.

And the purpose of these holes is still unknown. Although superficially similar depressions are seen in various other perissodactyl groups, they vary in position and structure and probably weren’t all homologous.

Ideas have included resonating chambers, some sort of glands, inflatable sacs, or attachment sites for complex lip musculature.

Meanwhile Hippidion from the Pleistocene of South America (2 million -- 10,000 years ago) had especially long and domed nasal bones. This must have supported an enormous nasal area -- possibly giving it a saiga-like air-conditioning system, a highly sensitive sense of smell, or perhaps even some sort of prehensile proboscis-like snout.

Pliohippus