Merychippus sejunctus
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Merychippus Temporal range: Miocene |
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| Fossils | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Perissodactyla |
| Family: | Equidae |
| Subfamily: | Equinae |
| Genus: | Merychippus |
| Binomial name | |
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Merychippus insignis Leidy, 1856 |
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Merychippus is an extinct proto-horse of the family Equidae that was endemic to North America during the Miocene from 20.43—10.3 Ma living for approximately 10.13 million years.
It had three toes on each foot and is the first horse known to have grazed. Its name means "ruminant horse", but current evidence does not support Merychippus ruminating.
Merychippus was named by Leidy (1856). Numerous authors around the turn of the century put the type species in Protohippus, but this is ignored. Its type is Merychippus insignis. It was assigned to Equidae by Leidy (1856) and Carroll (1988); and to Equinae by MacFadden (1998) and Bravo-Cuevas and Ferrusquía-Villafranca (2006).
Four specimens were examined by M. Mendoza, C. M. Janis, and P. Palmqvist for body mass. The results were:
Merychippus lived in herds. It was about 89 cm (35 in) tall; at the time it was the tallest equine to have existed. The muzzle was longer, the jaw deeper, and the eyes wider apart than any other horse-like animal to date. The brain was also much larger, making it smarter and more agile. Merychippus was the first equine to have the distinctive head of today's horses.
The foot was fully supported by ligaments, and the middle toe developed into a hoof, which did not have a pad on the bottom. In some Merychippus species, the side toes were larger, whereas in others, they had become smaller and only touched the ground when running. Its teeth were like those of Parahippus; the extra crest that was variable in Miohippus was permanent in Merychippus, and the other teeth were beginning to form a series of tall crests with higher crowns.
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