American cheetah

The American cheetah, Miracinonyx, is an extinct genus of at least two feline species morphologically similar to the modern cheetah which were endemic to North America during the Pleistocene epoch (2.6 Ma—12,000 years ago). These cats are known only from fragments of skeletons.

The two species commonly identified are 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 may not be inherited from a common ancestor, but result from either parallel or convergent evolution. These were larger than a modern cheetah and similar in size to a modern northern cougar. Body mass was typically around 70 kg with a head-and-body length of 170 cm, tail length of around 92 cm and a shoulder height of 85 cm. Large specimens could have weighed more than 95 kg.

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; 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, their 60 mph top speed being much more than needed to outrun extant American predators such as cougars and gray wolves.

Miracinonyx inexpectatus
M. inexpectatus was more similar to the cougar than was M. trumani, its proportions between that of the cougar and M. trumani. It had fully retractable claws, and with its lighter build, the Miracinonyx inexpectatus was likely faster than the cougar. Due to the retractable claws, it is also possible that it was more adept at climbing than M. trumani.