Merychippus represents a milestone in the evolution of horses. Though it retained the primitive character of 3
toes, it looked like a modern horse. Merychippus had a long face. Its long legs allowed it to escape from predators
and migrate long distances to feed. It had high-crowned cheek teeth, making it the first known grazing horse and the ancestor
of all later horse lineages.
Where & When? Fossils of Merychippus are found at many late Miocene
localities throughout the United States. Species in this genus lived from 17 - 11 million years ago
A thought to chew on...
Did the "ruminant horse" ruminate?
The ruminant digestive system is a slow, but highly efficient method of processing vegetation. So far as
we know, no living horse, rhino, or tapir has ever had such a system, so it is unlikely that the
"ruminant horse" ruminated.
Ruminant ungulates, hoofed mammals such as cows, sheep and goats, swallow vegetation that is then processed in one or
more of the "foregut" chambers (so-called because they occur before the "true" stomach [abomasum]). The animal then ejects
the partially digested food back into the mouth to chew again (called "chewing its cud"). This twice-chewed vegetation is
swallowed once more where it is finally processed in the true stomach (abomasum).
Horses are called "hind-gut fermenters" because they have a digestive pouch in the intestine, or caecum, behind the stomach.
Microbes in the caecum break down the vegetation so that energy and nutrients can be obtained by the horse.
Paleontologists almost never find fossilized digestive tracks and so can only make educated guesses about the digestive
physiology of extinct animals.
The strong crests of the teeth of Merychippus reminded Professor Leidy (the scientist who named this genus)
of the teeth of ruminants.
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