Mesohippus
Name:
Mesohippus
(Middle horse).
Phonetic: Mee-so-hip-pus.
Named By: Othniel Charles Marsh - 1875.
Synonyms: Anchitherium celer, Mesohippus
celer, Mesohippus hypostylus, Mesohippus latidens, Mesohippus
portentus, Mesohippus praecocidens, Mesohippus trigonostylus,
Mesohippus viejensis, Miohippus celer, Pediohippus portentus,
Pediohippus trigonostylus.
Classification: Chordata, Mammalia,
Perissodactyla, Equidae, Anchitheriinae.
Species: M. bairdi, M. barbouri,
M. braquistylus, M. equiceps, M. hypostylus, M.
intermedius, M. latidens, M. longiceps, M. metulophus,
M. montanensis, M. obliquidens, M. proteulophus, M.
westoni.
Diet: Herbivore.
Size: 60 centimetres (6 hands) high at the
shoulder.
Known locations: Canada & USA.
Time period: Bartonian of the Eocene through to
Rupelian of the Oligocene.
Fossil representation: Multiple specimens.
‘Middle
horse’ may seem an uninteresting name for a prehistoric horse, but
Mesohippus is actually one of the most important.
The middle horse
name is actually a reference to the position of Mesohippus
in
relation to earlier forms like Hyracotherium
and larger and later forms
like we know today. Aside from having longer legs, Mesohippus
only
had three toes in contact with the ground rather than the four seen in
Hyracotherium. The centre toe was the main weight
bearing appendage
and overall the construction of the foot and larger size reveals that
Mesohippus would be the faster horse.
By
having longer legs, Mesohippus could cover a
greater amount of ground
during foraging while expending a reduced amount of energy in doing
so. However this adaptation may have also been pushed by the
emergence of predators such as Hyaenodon
and nimravids (false
sabre-toothed cats) that would have been too powerful for Mesohippus
to fight. As such the best chance that Mesohippus
had of staying
alive was to quite literally run for its life and try to outpace and
outlast its attacker. Unfortunately for Mesohippus
this was not
always a successful strategy, with fossils revealing that Mesohippus
was a prey animal for the aforementioned Hyaenodon.
Despites its
position lower down on the food chain however, Mesohippus
was the
evolutionary success story as its progeny would go on to become larger
and faster running horses, while both predators like Hyaenodon
and
the nimravids would eventually disappear from the planet without any
surviving descendants.
Mesohippus
was similar to another primitive horse named Anchitherium.
In fact
one species of Anchitherium, A. celer
has been found to be a
synonym to Mesohippus bairdi.
1 - Hyracotherium, 2 - Mesohippus, 3 - Merychippus, 4 - Pliohippus, 5 - Hipparion.
Further reading
- New Oligocene horses. - Bulletin of the American Museum of Natural
History 20(13):167-179. - H. F. Osborn - 1904.
- Fossil horses of the Oligocene of the Cypress Hills, Assiniboia. -
Transactions of the Royal Society of Canada, series 2 11(4):43-52. - L.
M. Lambe - 1905.
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