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American cheetah
The American cheetah (''Miracinonyx'') is an extinct genus of at least two feline species, which were endemic to North America during the Pleistocene epoch (2.6 Ma – 12,000 years ago) and morphologically similar to the modern cheetah.〔(【引用サイトリンク】title=Miracinonyx Adams 1979 (American cheetah) )〕 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 , with a head-and-body length of , tail length of around and a shoulder height of . Large specimens could have weighed more than .
==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 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 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 the ''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 World or the 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 is probably a more primitive version of ''M. trumani''.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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