Miracinonyx
(American Cheetah)
Name:
Miracinonyx
(Amazing cheetah).
Phonetic: Mih-rah-sin-oh-nix.
Named By: Adams - 1979.
Synonyms: Possibly Miracinonyx studeri.
Classification: Chordata, Mammalia, Carnivora,
Felidae.
Species: M. inexpectatus, M. trumani.
Diet: Carnivore.
Size: Roughly 85 centimetres high at the shoulder.
Known locations: North America.
Time period: Throughout the Pleistocene.
Fossil representation: Many specimens are known,
although usually of fragmentary remains.
Often
more popularly known as the American cheetah, Miracinonyx
is actually
thought to have been descended from cougar-like ancestors. It could
be that the striking similarity between Miracinonyx
and the African
cheetah (Acinonyx jubatus) is actually a case of
convergent
evolution. This is where two animals from separate lineages end up
looking the same because they make the same adaptations to cope with
the same environment and lifestyle. However despite being thought to
be evolved from cougar-like ancestors, Miracinonyx
is also regarded
as being more closely related to the Puma. The exact origin for
Miracinonyx is also uncertain with theories being
offered to explain
both an Old and New World (Americas) origin for the genus.
Miracinonyx
like with many other prehistoric animals including Smilodon,
displays
species that are quite morphologically different to one another.
Miracinonyx inexpectatus was built more like a
cougar, although its
overall build was considerably more gracile. This means that M.
inexpectatus was much faster while still retaining some of
the
strength of a cougar. The result is that M. inexpectatus
was the
stronger species, and combined with its fully retractable claws was
probably better at climbing.
Miracinonyx
trumani had an even lighter build than M. inexpectatus,
meaning
that it was the most similar to the modern cheetah. The claws on M.
trumani however were only partly retractable. By being
only partly
retractable the claws could be used to gain more traction on the ground
while running. This combined with the more gracile build meant that M.
trumani was easily the faster of the two species. A third
species,
M. studeri, is sometimes mentioned, however
similarities between
this species and M. trumani has led many people
to treat M. studeri
as a synonym to the latter.
Both
species of Miracinonyx display specialist features
for a high rate of
respiration. These include short faces, with enlarged nasal
cavities that would allow for a much greater volume of air being
breathed in while running. This would reduce the amount of anaerobic
respiration in the muscles which in turn would reduce the build-up of
lactic acid meaning that Miracinonyx could run
faster for longer as it
pursued prey. When you do a large amount of exercise but have to stop
because your muscles are tired it is because of a build-up of lactic
acid caused by your muscles not being oxygenated fast enough.
Despite
these adaptations for speed, Miracinonyx probably
could not maintain
these speeds indefinitely, and was probably more like a sprinter than
a marathon runner with bursts of high speeds over short distances.
Miracinonyx would still have had to rely upon
stealth and cunning to
approach a target, downwind to avoid its scent being detected and low
down amongst long grass to avoid being seen. Only when it was sure it
was close enough to its target would Miracinonyx
launch an attack,
and if observation of big cats in Africa today is anything to go by,
even then it might not always have been successful.
Because
Miracinonyx sacrificed strength for speed it could
not hunt the larger
American megafauna and so had to focus its attention upon smaller and
swifter prey. The development of Miracinonyx
towards speed may have
been to fill an ecological niche as many of the other American
predators such as Smilodon
and the dire
wolf were powerfully built
predators adapted for tackling powerful but slower prey. The prey
animal that is most often associated with Miracinonyx
is the
pronghorn, an animal very similar to antelope that has been often
dubbed the second fastest land animal on Earth with speeds estimated at
up to 80km/h (50mp/h). Again this draws another convergent
similarity between Miracinonyx and the cheetah
which hunts fast animals like gazelle.
Further reading
- The Cheetah: Native American. - Science 14 September 1979: Vol. 205
no. 4411 pp. 1155-1158. - Daniel B. Adams - 1979.
- The Plio-Pleistocene cheetah-like cat Miracinonyx
inexpectatus of
North America - Journal of Vertebrate Paleontology 10(4):434-454. -
Blaire Van Valkenburgh, Frederick Grady & Bj�rn Kurt�n - 1990.
-Evolution of the extinct Sabretooths and the American cheetah-like
cat. - Current Biology 15 (15): R589–R590 - Ross Barnett, Ian Barnes,
Matthew J. Phillips, Larry D. Martin, C. Richard Harington, Jennifer A.
Leonard, Alan Cooper - 2005.
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