Parahippus
Name:
Parahippus
(Near horse).
Phonetic: Pah-rah-hip-pus.
Named By: Joseph Leidy - 1858.
Synonyms: Hippodon barbouri, Hippodon
vellicans, Merychippus socius, Merychippus vellicans, Nannippus
niobrarensis, Neohipparion niobrarense, Parahippus barbouri,
Parahippus vellicans, Protohippus niobrariensis.
Classification: Chordata, Mammalia,
Perissodactyla, Equidae, Anchitheriinae.
Species: P. cognatus
(type?), P. agrestis, P. atavus, P.
coloradensis, P. leonensis, P. maxsoni, P. nebrascensis,
P. pawniensis, P. pristinus, P. tyleri, P. wyomingensis.
Diet: Herbivore.
Size: About 1 meter tall at the shoulder
(withers).
Known locations: Across the USA. Canada,
Saskatchewan.
Time period: Rupelian of the Oligocene to possibly
the Messinian of the Miocene.
Fossil representation: Multiple individuals.
The
Oligocene and Miocene periods were times of change for the world’s
ecosystems, particularly those of the northern hemisphere. Long
covered by temperate and in places tropical forests, these were now
steadily being replaced by grassy plains. Parahippus
is a horse that
shows a shift towards coping with these changing environments.
Primitive
horse forms still had toes like many other kinds of mammals, but in
time most of these toes became reduced until a single hoof was left,
just like in modern horses. Parahippus still had
three visible toes
to the lower foot, but only one was in contact with the ground. The
other two remaining toes that were still visible were now vestigial,
which means that they were still there, just no longer serving a
practical purpose. The legs in general had also changed with enhanced
musculature that limited side to side movement while increasing forward
stride strength. This is a clear adaptation towards living on an open
plains environment where fast locomotion would not only be possible,
but also preferable to escape from predators that were also becoming
faster runners.
Earlier
and shorter snouted horses were better adapted for browsing foliage,
though changing ecosystems meant a continuing reduction in the amounts
of available plants. The head of Parahippus was
also proportionately
longer than earlier forms so that it could more easily reach lower down
to graze upon grass, a plant type that was becoming increasingly
common. Grazing grass means that the teeth have to do more grinding
and the teeth of Parahippus also had higher tooth
crowns to cope with
this increase in grinding. These were not new features exclusive
to Parahippus as the earlier genus Miohippus
also had higher tooth
crowns. However the size of the tooth crown increase was more uniform
and consistent across all of the teeth of Parahippus,
meaning that
while the adaptation was essentially the same, it had still managed
to become more stabilised. This is a good study for evolution in
action since not only can a change be seen to have taken place, it
can also be seen to become refined.
Further reading
- Notice of Remains of Extinct Vertebrata, from the Valley of the
Niobrara River, Collected during the Exploring Expedition of 1857, by
J. Leidy. - In, Nebraska, under the Command of Lieut. G. K. Warren, U.
S. Top. Eng., by Dr. F. V. Hayden, Geologist to the Expedition.
Proceedings of the Academy of Natural Sciences of Philadelphia
10:15-89. - 1858.
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