American cheetah

The American cheetah (Miracinonyx) is an extinct genus of at least two feline species, which were endemic to North America during the epoch (2.6 Ma – 12,000 years ago) and morphologically similar to the modern cheetah (Acinonyx jubatus). These cats are only known 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 may instead 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 (150 lb), with a head-and-body length of 170 cm (67 in), tail length of around 92 cm (36 in) and a shoulder height of 85 cm (33 in). Large specimens could have weighed more than 95 kg (209 lb).

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 the 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 2006 by Johnson et al, and in 2015 by Dobrynin et al. However, other research by Barnett and Faurby, through examining and re-analyzing morphology, has suggested reversing the reclassification: the American cheetah developed cheetah-like characteristics through parallel evolution, but it is most closely related to Puma and not to the modern cheetah of Africa and Asia. Moreover, Faurby notes that there have been no Acinonyx fossils found in North America, and no Miracinonyx fossils elsewhere. However, O'Brien et al (2016) posits that the supposed homoplasy between the genera is controversial, as it is asserted that is not necessarily any conclusive anatomical or genetic basis for dismissing a homologous relationship between Acinonyx and Miracinonyx. The veracity of the origin of the modern cheetah is also debated; however, Miracinonyx is believed to have evolved from cougar-like ancestors, regardless of whether in the Old World or the New World.