If you could have wandered across the United States in the area that is now the Great Plains 15,000 years ago, you may have mistaken it for the African Serengeti. Elephants, camels, horses, cheetahs . . . all would be roaming across the vast savannahs of North America. And the most impressive of all would have been the North American Lion.
Fossilized skull of Panthera atrox, the North American Lion, on display at the Smithsonian Museum of Natural History.
By about 15,000 years ago, the last of the Ice Age glaciations was beginning to end. As the Earth warmed and the glaciers retreated, animals known as the "Pleistocene megafauna" began expanding into the grasslands and savannahs that were left behind. Among the megafauna that could be found in North America at the time were the mammoths and mastodons (relatives of the elephants), the American cheetah (actually a relative and not a true cheetah), the short-faced bear (a long-legged version of the grizzly designed for running), antelopes, the dire wolf, the sabertooth cat, the American camel, the Teratorn giant vulture, the nine-foot sabertooth salmon, the six-foot giant tortoise, and the apex predator, the North American Lion.
The American Lion first appears in the fossil record about 1.8 million years ago. Originally a North American animal, the American Lion also spread into South America when the falling sea levels caused by the Ice Age produced a land bridge between the two continents, allowing megafauna to move north and south (a period known as "The Great Interchange"). About one hundred complete skeletons of the American Lion have been found preserved in the La Brea tar pits in California. Other fossils have been found in Canada, Texas, Idaho, Nevada, Nebraska, Wyoming, Mississippi, northern Florida, Mexico, and Peru. These skeletons show that it was about 30 percent larger than today's African Lion, measuring about 10 feet long, 4 feet high at the shoulder, and weighing about 750 pounds--the males were larger than the females. The legs were slightly longer relative to the body size, and the brain was slightly larger.
During this time, other lion species (in the genus Panthera) were found in Africa (where they first appeared about 3.5 million years ago), Europe, and Asia. Cave paintings by Cro-Magnon people in Europe depict lions without manes. Of the large mammal species on earth at the time, only humans had a wider distribution. It is generally accepted that the ancestors of the American Lion crossed into North America from Asia during the periods when the Beringian land bridge was open between Siberia and Alaska. The American Lion ranged from Alaska all the way to Peru, and although it seems to have preferred open grassland and savannah habitat, and is not found in forested areas, it lived in a wide range of habitat, from dry hot savannah to colder tundra.
The fact that males were larger than females indicates that American Lions lived in social groups, with males competing with each other for control of the group. Many of the skulls have broken teeth, which may have resulted from battles over dominance. The number of male and female found next to prey animals in the La Brea tar pits is roughly equal, however, indicating that unlike modern lions, in which the females do all the hunting, the American Lion hunted in male-female pairs or small groups. Modern lions are ambush hunters that carefully stalk their prey and then make a sudden rush. The American Lion, with its longer legs and its more powerful skull and jaws, may have been a better runner, pursuing its prey over longer distances.
Ever since its discovery, it has been debated how closely the American Lion is related to other cat species. Joseph Leidy, the Philadelphia paleontologist who first described the species in 1852, from a jawbone found in Mississippi, considered it to be a distinct species of lion, and named it Felis atrox (later placed in the genus Panthera). Over time, other authorities argued that the American Lion was a subspecies of the African Lion, and named it Panthera leo atrox. In 2010 another study by Danish and American scientists concluded that while the American Lion was its own distinct species, the skull had more traits in common with the jaguar than with lions, and concluded that Panthera atrox should be called the Giant Jaguar instead.
By 11,000 years ago, the American Lion--and all the rest of the large animals in North America--were extinct, an event known as the Pleistocene Megafauna Extinction Event. There has been much debate about the causes of this extinction wave. One school of thought blames the changing climatic conditions which ended the Ice Ages. Another group of scientists has postulated that a meteor impact in North America wiped out the megafauna. Perhaps the most common explanation is the entry of humans from Siberia into North America about 13,000 years ago, who hunted the megafauna to extinction. (American Lion bones have been found in Paleo-Indian trash middens, indicating that the early North Americans were capable of hunting and killing them.) It may be significant that the large North American animals who survived the Megafauna Extinction--bison, moose, caribou, musk oxen, bighorn sheep--all had Asian ancestors who were already adapted to live in the presence of human hunters (one exception was the pronghorn, which had evolved speed to escape American cheetahs, which may have protected them from Paleo-Indian hunters). The North American animals that died out, including the American Lion, were those that had evolved in the absence of human hunters.
On the other hand, critics point out, not all of the animals that died out in the extinction were species that would have been hunted by humans. Even for those that were, it is enormously difficult even for modern hunters with high-powered rifles to hunt a species to extinction--as the species gets less and less common, subsistence hunters switch to other species that are more easily-found, allowing the rare individuals to recover and repopulate. And the lessons learned by those who are deliberately trying to exterminate harmful invasive species demonstrate that it is not at all a simple task to eradicate a group of organisms by killing them. To really wipe out an entire species, seems to require a loss of habitat.
It remains a mystery.