The American lion (Panthera atrox (), with the species name meaning "savage" or "cruel", also called the North American lion) is an extinct pantherine cat native to North America during the Late Pleistocene from around 129,000 to 13,100 years ago. Genetic evidence suggests that its closest living relative is the lion (Panthera leo), with the American lion representing an offshoot from the lineage of the largely Eurasian cave lion (Panthera spelaea), from which it is suggested to have split around 165,000 years ago. Its fossils have been found across North America, from Canada to Mexico. It was about 25% larger than the modern lion, making it one of the largest known felids to ever exist, and a dominant apex predator in North American ecosystems, alongside the sabertooth cats Smilodon and Homotherium. It has been suggested, like modern lions, they were social animals, although this is not known for sure. Unlike modern lions, American lions may have been a diurnal predator.
The American lion became extinct as part of the end-Pleistocene extinction event along with most other large animals across the Americas. The extinctions followed human arrival in the Americas. Proposed factors in its extinction include climatic change reducing viable habitat, as well as human hunting of herbivore prey causing a trophic cascade.
History and taxonomy Initial discovery and North American fossils
The first specimen now assigned to Panthera atrox was collected in the 1830s by William Henry Huntington, Esq., who announced his discovery to the American Philosophical Society on April 1, 1836 and placed it with other fossils from Huntington's collection in the Academy of Natural Sciences in Philadelphia. The specimen had been collected in ravines in Natchez, Mississippi that were dated to the Pleistocene; the specimen consisted only of a partial left mandible with three molars and a partial canine. The fossils did not get a proper description until 1853 when Joseph Leidy named the fragmentary specimen (ANSP 12546) Felis atrox ("savage cat"). Leidy named another species in 1873, Felis imperialis, based on a mandible fragment from Pleistocene gravels in Livermore Valley, California. F. imperialis however is considered a junior synonym of Panthera atrox. A replica of the jaw of the first American lion specimen to be discovered can be seen in the hand of a statue of famous paleontologist Joseph Leidy, currently standing outside the Academy of Natural Sciences in Philadelphia.
Few additional discoveries came until 1907, when the American Museum of Natural History and College, Alaska collected several Panthera atrox skulls in a locality originally found in 1803 by gold miners in Kotzebue, Alaska.Simpson, G. G. (1941). Large Pleistocene felines of North America. American Museum novitates; no. 1136. The skulls were referred to a new subspecies of Felis (Panthera) atrox in 1930, Felis atrox "alaskensis". Despite this, the species did not get a proper description and is now seen as a nomen nudum synonymous with Panthera atrox. Further south in Rancho La Brea, California, a large felid skull was excavated and later described in 1909 by John C. Merriam, who referred it to a new subspecies of Felis atrox, Felis atrox bebbi.Merriam, J. C., & Stock, C. (1932). The Felidae of Rancho La Brea (No. 422, p. 92). Carnegie Institution of Washington. The subspecies is synonymous with Panthera atrox.
Throughout the early to mid 1900s, dozens of fossils of Panthera atrox were excavated at La Brea, including many postcranial elements and associated skeletons. The fossils were described by Merriam & Stock in detail in 1932, who synonymized many previously named taxa with Felis atrox. At least 80 individuals are known from La Brea Tar Pits and the fossils define the subspecies, giving a comprehensive view of the taxon. It was not until 1941 that George Simpson moved Felis atrox to Panthera, believing that it was a subspecies of jaguar. Simpson also referred several fossils from central Mexico, even as far south as Chiapas, as well as Nebraska and other regions of the western US, to P. atrox. 1971 witnessed the description of fragmentary remains from Alberta, Canada that extended P. atroxs range north. In 2009, an entrapment site at Natural Trap Cave, Wyoming was briefly described and is the second most productive Panthera atrox-bearing fossil site. It most importantly contains well-preserved mitochondrial DNA of many partial skeletons.
Panthera onca mesembrina and possible South American material In the 1890s in the "Cueva del Milodón" in southern Chile, fossil collector Rodolfo Hauthal collected a fragmentary postcranial skeleton of a large felid that he sent to Santiago Roth. Roth described them as a new genus and species of felid, "Iemish listai" in 1899. However, the name is considered a nomen nudum. In 1904, Roth reassessed the phylogenetic affinities of "Iemish" and named it Felis listai and referred several cranial and fragmentary postcranial elements to the taxon. Notably, several mandibles, a partial skull, and pieces of skin were some of the specimens referred. In 1934, Felis onca mesembrina was named by Angel Cabrera based on that partial skull from "Cueva del Milodón" and the other material from the site was referred to it. The skull (MLP 10-90) was lost, and was only illustrated by Cabrera.
Further material, including feces and mandibles, was referred to as F. onca mesembrina from Tierra del Fuego, Argentina and other southern sites in Chile.
In 2016, the subspecies was referred to Panthera onca in a genetic study, which supported its identity as a subspecies of jaguar. Later in 2017, one study suggested that P. onca mesembrina represents a junior synonym of Panthera atrox based on morphological similarities, though other researchers disagreed with this identification.
Evolution The American lion was initially considered a distinct species of Pantherinae, and designated as Panthera atrox, which means "cruel" or "fearsome panther" in Latin. Some paleontologists accepted this view, but others considered it to be a type of lion closely related to the modern lion (Panthera leo) and its extinct relative, the Eurasian cave lion (Panthera leo spelaea or P. spelaea). It was later assigned as a subspecies of P. leo (P. leo atrox) rather than as a separate species. Most recently, both spelaea and atrox have been treated as full species.
Cladistic studies using morphological characteristics have been unable to resolve the phylogenetic position of the American lion. One study considered the American lion, along with the cave lion, to be most closely related to the tiger (Panthera tigris), citing a comparison of the skull; the braincase, in particular, appears to be especially similar to the braincase of a tiger. Another study suggested that the American lion and the Eurasian cave lion were successive offshoots of a lineage leading to a clade which includes modern leopards and lions. A more recent study comparing the skull and jaw of the American lion with other pantherines concluded that it was not a lion but a distinct species. It was proposed that it arose from pantherines that migrated to North America during the mid-Pleistocene and gave rise to American lions and jaguars (Panthera onca). Another study grouped the American lion with P. leo and P. tigris, and ascribed morphological similarities to P. onca to convergent evolution, rather than phylogenetic affinity.
However, genetic studies indicate that the living lion is the closest living relative of P. atrox and P. spelaea. Lion-like pantherines first appeared in the Tanzanian Olduvai Gorge about . These felids then dispersed into Eurasia from East Africa around the end of the Early Pleistocene and the beginning of the Middle Pleistocene, giving rise to Panthera (spealea) fossilis. The oldest widely accepted fossils of P. fossilis in Europe date to around 700,000-600,000 years ago, such as that from Pakefield in England, with possible older fossils from Western Siberia and Spain dating to around 1 Mya of the late Early Pleistocene.
Mitochondrial genomic analysis suggests that Eurasian cave lions and modern lions split off around 1.85 Ma. On the other hand, nuclear DNA analysis found that modern lions and Eurasian cave lions suggests that the lineage of the cave lion and American lion diverged from that of the modern lion around 500,000,
Mitochondrial DNA sequence data from fossil remains suggests that the American lion (P. atrox) represents a sister lineage to Late Pleistocene populations of the Eurasian cave lion (P. spelaea), and likely arose when an early cave lion population became isolated south of the North American continental ice sheet. While initial studies suggested that the divergence between American and Eurasian cave lions took place around 340,000 years ago, later studies suggested that the split took place considerably later, around 165,000 years ago, consistent with the earliest appearance of cave lions in eastern Beringia (now Alaska) during the Illinoian (190-130,000 years ago).
Cladogram after Tseng et al. (2014):
Description
Size The American lion is estimated to have measured from the tip of the nose to the base of the tail and stood at the shoulder. Panthera atrox was sexually dimorphic, DeSantis et al. (2012) estimated that male American lions weighed between in males, with females weighing between . Wheeler and Jefferson (2009) study found American lions were more sexually dimorphic than modern lions in terms of size: American lion males being 1.4 times larger than females, compared to modern male lions being 1.26 times larger. The study estimates that average males could've weighed , with the largest male within the sample weighing . While females averaged , with the largest female weighing . Sorkin (2008) estimated that the American lion may have weighed up to . Christiansen and Harris (2009) showed an average weight of for males and for the largest specimen analyzed.
Anatomy About 80 American lion individuals have been recovered from the La Brea Tar Pits in Los Angeles, so their morphology is well known. Their features strongly resemble those of modern lions, but they were considerably larger, similar to Panthera spelaea and the Pleistocene Natodomeri lion of eastern Africa. Panthera atrox had limb bones more robust than those of an African lion, and comparable in robustness to the bones of a brown bear; also its limbs were 10% longer than extant African lion in relation to skull length. Regressions found both P. spealea and P. atrox having more robust limbs than the large machairodont Nimravides. The robustness of the humeri was likely the result being part of lineages of felids that possessed humeri significantly more robust than similar sized felids. Analysis of the cranial endocast suggests that the brain was similar to those of other patherine big cats, though the brain was less flexed in shape. The encephalization quotient (relative size of the brain compared to the body) is higher than the living lion, with the brain being the among largest in absolute size of any cat.
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