American Cheetah
From Devonshire
The American cheetahs (genus Miracinonyx) were at least two species of feline, morphologically similar to the modern cheetah, but which probably evolved their adaptations for swift running independently. Living from three million to ten or twenty thousand years ago in North America, these cats are known only from fragments of skeletons. They are not of the genus Acinonyx, to which the modern cheetah and its closest ancestors belong, and may be more closely related to species of Puma.
Two species have been identified: Miracinonyx inexpectatus and M. trumani. Sometimes a third species, M. studeri, is added to the list, but it is more often listed as a junior synonym of M. trumani. Both species are similar to the modern cheetah, with faces shortened and nasal cavities expanded for increased oxygen capacity, and legs proportioned for swift running. However, these similarities are not inherited from a common ancestor, but parallel evolution.
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Taxonomy and evolution
Research into the American cheetah has been contradictory. It was originally believed to be an early cougar representative, before being reclassified in the 1970s as a close relative of the cheetah. This suggested that ancestors of the cheetah diverged from the Puma lineage in the Americas and migrated back to the Old World, a claim repeated as recently as Johnson et al. (2006). Other research by Barnett, however, examining mitochondrial DNA and re-analyzing morphology, has suggested reversing the reclassification: the American cheetah developed cheetah-like characteristics through convergent evolution, but it is most closely related to Puma and not to the modern cheetah of Africa and Asia. The supposed American origin of the modern cheetah is thus equivocal; however, it is believed to have evolved from cougar-like ancestors, whether in the Old or New World.
The cougar and M. trumani are believed to have split from a cougar-like ancestor around three million years ago;<ref name=Barnett/> where M. inexpectatus fits in is unclear, although it likely is a more primitive version of M. trumani.
Miracinonyx trumani
M. trumani was the most similar to true cheetahs in morphology. Living on the prairies and plains of western America, it was likely a predator of hoofed plains animals such as the Pronghorn. In fact, predation by Miracinonyx is thought to be the reason that pronghorns evolved to run so swiftly, its 60 mph top speed being much more than needed to outrun living American predators such as cougars and gray wolves.
The similarity between M. trumani and the cheetah is an example of parallel evolution. As grasslands became more common in both Africa and North America, the separate cat species from both continents evolved to catch the new fleet-footed herbivores. The claws of M. trumani had even become only partially retractable, to be used for better grip at high speeds, just as true cheetahs have fully un-retractable claws.
Miracinonyx inexpectatus
M. inexpectatus was more similar to the cougar, its proportions between that of the cougar and M. trumani. It had fully retractable claws, and although it was likely faster than the cougar due to its slim build, it is also thought to have been more adept at climbing than M. trumani.
References
See Wikipedia: http://en.wikipedia.org/wiki/American_Cheetah#References
