Biggest of the big cats:
Until a larger contender is discovered this is the honor we must grant to Panthera leo atrox, the American lion, sometimes known as the American cave lion. This truly enormous cat is estimated to have been at least twenty five percent larger than any living lion, weighing in at as much as 1100 pounds and standing perhaps 4 and one half feet tall at the shoulder with a length of up to 13 feet in the case of the largest specimens.
There is some speculation as to whether the American lion is most closely related to the modern African lion, to the tiger, to the jaguar or to some other as yet unidentified pantherine. This question arises from the shape of recovered fossil skulls, which seem to be morphologically closer to those of modern tigers. Genetic research on available DNA seems to suggest a closer relationship to the jaguar. This matter remains one of controversy, as some authorities consider the American and African lions to be subspecies of the same species, Panthera leo atrox, and Panthera leo leo respectively.
In any event, we are fortunate to be able to view a living specimen very close to the size and appearance of the American lion in the modern lion-tiger hybrid, the liger. The liger, which does not exist in nature, gives some idea of the formidable aspect of its extinct relative.
Range and timeline:
The American lion occupied the western part of the American continent, from the Yukon to northern Peru. No remains have been found from the eastern portions of the Americas.
Its timeline is neatly contained by the Pleistocene epoch, spanning a period from 1.8 million years ago and going extinct about 10,000 years ago. Their disappearance correlates with the mass extinction of most North American mega fauna that took place at the end of the Pleistocene.
Most fossil remains of Panthera leo atrox come from the Yukon and from the tar pits at Rancho la Brea, indicating a widely diverse environment. It is thought that in colder climates the lions would often utilize caves for shelter, bringing in grasses and leaves to soften their sleeping quarters.
Their prey probably included most of the major herbivores of the day, camels, north American horses, bison, deer and antelope but almost certainly not the giant sloth, megatherium unless a sick , injured or juvenile specimen could be overpowered.
It is likely that American lions and early Native Americans hunted one another from time to time.
Extinction and possible cloning:
Whether the changing climatic conditions that took place 10,000 years ago or the demise of the larger herbivores the lions fed upon, or unsuccessful confrontations with humans ultimately caused the extinction of the American lion will probably remain a topic of discussion. Most likely it was a combination of all three factors.
Interestingly enough, if sufficient intact DNA is recovered either from a mummified specimen from the frozen north, or from a particularly well preserved individual from the tar pits, the American lion is a prime candidate for revival by cloning, with any of the modern big cats acting as surrogate. What to do with this apex predator once we have one is an entirely different subject.