A Good Narrative about the American Cheetah (Miracinonyx trumani) may be Ruined but maybe not

The close physical similarity between the extinct cheetah (Miracinonyx trumani) of Pleistocene North America, and the still extant cheetah (Acinonyx jubatus) of Africa and Asia caused confusion among paleontologists.  The anatomy of both species shared characteristics of a cat built for great speed.  Paleontologists thought cheetahs originally evolved in North America and later colonized Asia and Africa.  Then, based on a re-evaluation of the fossil evidence and new genetic studies, scientists realized the similarity between the Old World cheetah and the North American cheetah was just a case of convergent evolution that occurs when 2 unrelated species evolve similar traits to help them adapt to similar environments.  The 2 species were not as closely related as formerly thought.  Instead, the North American cheetah evolved from an extinct Asian cougar (Puma pardoides) that crossed the Bering Land Bridge over 6 million years ago.  After Puma pardoides colonized North America, the species diverged into 3 lineages.  One line led to an animal adapted for hunting on the grassy plains–M. trumani.  Another line evolved into the jaguarundi (Puma jagouaroundi), a small cat of tropical brush habitat.  The third line evolved into the modern cougar (Puma concolor), a generalist species well adapted for living in a wide range of environments.  Puma concolor doesn’t occur in the fossil record until ~500,000 years BP, but I believe its evolutionary predecessor was Miracinonyx inexpectus.  Temporally, fossil material of Puma concolor and M. inexpectus doesn’t overlap. The latter was likely the late Pliocene/early Pleistocene version of the cougar.  Miracinonyx studeri, a scientific name used in some studies, is merely a synonym for M. inexpectus.

The American Cheetah looked like its African cousin, but became extinct in North America about 10,000 years ago.

Artist’s depiction of an American cheetah chasing a pronghorn.  Pronghorns can run up to 60 miles per hour.  No extant predator in North America even comes close to this.  An analysis of the anatomy of the extinct American cheetah suggests it was built for this kind of speed with long legs, flexible spine, and large nasal passages for rapid air intake.

Pronghorn antelopes (Antilocapra americana) reach speeds far exceeding any extant predator living in North America.  Scientists hypothesized they evolved this capability to outrun a predator that is now extinct.  They believe M. trumani was that predator.

A few years ago, paleontologists excavated fossil material they identified as M. trumani from several caves within the Grand Canyon.  This high elevation habitat was home to mountain goats (Oreamnos harrington and Oreamnos americanus) not pronghorns.  These scientists proposed the American cheetah, at least at this locality, occupied a niche like that of an alpine snow leopard (Uncia uncia), a big cat that hunts on steep rocky slopes.  It would seem the narrative about the American cheetah and pronghorn might be ruined.  However, Ross Barnett, author of a study referenced below, is not convinced the fossil material found in the Grand Canyon is from American cheetah.  These specimens were identified by comparing them with bones from modern cougars and other American cheetah remains.  M. trumani was somewhat larger than modern cougars, so it was assumed the Grand Canyon material represented American cheetah, not cougar.  Dr. Barnett suggests the material should have been compared with fossil remains of Pleistocene cougars which were on average larger than modern cougar.  The Grand Canyon material may actually be Pleistocene cougar.  Cougars are well adapted for living on steep slopes. So the narrative of the American cheetah and the pronghorn may not be ruined. Incidentally, the cougars that lived in North America were an extinct ectomorph–all modern North American cougars descend from a small population originating from eastern South America.

There’s no fossil evidence M. trumani ever lived east of the Mississippi River.  But M. inexpectus and Puma concolor are a common enough (for a large carnivore) find in fossil sites throughout southeastern North America.

Some now refer to the American cheetah as the “false cheetah.”  I don’t think the adjective “false” should be used to describe an animal, simply because humans were once confused about its evolutionary relationships.

References:

Barnett, Ross; et. al.

“Evolution of the Extinct Sabre-tooths and the American Cheetah-like Cat”

Current Biology 2005

Hodnett, Jean-Paul; et. al.

“Miracinonyx trumani (Carnivore: Felidae) from the Rancholabrean of Grand Canyon, Arizona and its Implications for the Ecology of the American Cheetah”

Programs and Abstracts, Journal of Vertebrate Paleontology 2010

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