American Lion - Classification

Classification

The American lion was initially considered a distinct species of Pantherinae, with the scientific name Panthera atrox ( /ˈpænθərə ˈætrɒks/), which means "cruel" or "fearsome panther" in Latin. Overall, the skull of the extinct cat was most like that of the jaguar (P. onca). Some later authors accepted this view, but other experts considered the American lion most closely related to the African lion (P. leo) and its extinct Eurasian relative, the cave lion (P. leo spelaea or P. spelaea). Later paleontologists assigned the extinct American cat as a subspecies of P. leo (P. leo atrox) rather than as a separate species.

Cladistic studies using morphological characteristics have been unable to resolve the phylogenetic position of the American lion. At least one authority considers the American lion (along with the cave lion), to be more closely related to the tiger, P. tigris, citing a comparison of skull shapes; the braincase, in particular, appears to be especially similar to the braincase of a tiger. It has also been suggested that the American lion and Eurasian cave lion were successive offshoots of a lineage leading to an extant lion-leopard clade. A more recent study that compared the skull, jaw, and teeth of the American lion with other pantherines concluded it was not a lion and was distinct from all extant species. The authors suggested that it may have arisen from pantherines that migrated into North America in the mid-Pleistocene epoch and also gave rise to jaguars.

However, mitochondrial DNA sequence data from remains of the American lion from Wyoming and Alberta show that it is a sister lineage to the cave lion, and likely arose when an early cave lion population became isolated south of the North American continental ice sheet. The most recent common ancestor of the two populations apparently lived about 340,000 (194,000–489,000) years ago. The most recent common ancestor of the atrox lineage is estimated to have lived about 200,000 (118,000–246,000) years ago. The dates imply that genetic isolation from spelaea had begun by the time of the Illinoian glaciation, ~300,000–130,000 years ago (a spelaea population is known to have been present in eastern Beringia by that period, where it persisted until at least 11,925 ± 70 years ago). This separation was maintained during the Sangamon interglacial, ~130,000–110,000 years ago, as well as during later interstadials of the earlier glaciation and those of the following Wisconsinan glaciation, ~110,000–10,000 years ago. It has been suggested that boreal forest may have contributed to the separation during warmer intervals; alternatively, a species barrier may have existed. The study also indicated that the present-day lion is the closest extant relative of atrox and spelaea. (In the same study, Eurasian and Beringian cave lions were found to be genetically indistinguishable.)