American Lion - Panthera (leo) atrox
Temporal range: Pleistocene
Species: Disputed; P. leo or †P. atrox
Subspecies: Disputed; †P. l. atrox or none
The American lion (Panthera leo atrox or P. atrox) — also known as the North American lion, Naegele’s giant jaguar or American cave lion — is an extinct lion of the family Felidae, endemic to North America during the Pleistocene epoch (0.34 mya to 11,000 years ago), existing for approximately 0.33 million years. It has been shown by genetic analysis to be a sister lineage to the Eurasian cave lion (Panthera leo spelaea or P. spelaea).
The American lion was one of the largest types of cat ever to have existed, slightly larger than the Early Middle Pleistocene primitive cave lion, P. leo fossilis and about twenty-five percent larger than the modern African Lion.
The American lion is an extinct animal which originated in North America and went on to colonize part of South America as part of the Great American Interchange. The head-body length of the American lion is estimated to have been 1.6–2.5 m (5 ft 3 in–8 ft 2 in) and it would have stood 1.2 metres (4 ft) at the shoulder. Thus it was smaller than its contemporary competitor for prey, the giant short-faced bear, which was the largest carnivoran of North America at the time. The American lion was not as heavily built as the saber-toothed cat Smilodon populator, which may have weighed up to 360–470 kilograms (790–1,000 lb). Sorkin (2008) estimated it to weigh roughly 420 kilograms (930 lb), but new estimations show a top weight of 351 kg (774lbs.) for the largest specimen and an average weight for males of 255.65 kg (563lbs.).
Approximately one hundred specimens of American lions have been recovered from the La Brea Tar Pits, in Los Angeles, so their body structure is well known. The features and teeth of the extinct American lion strongly resemble modern lions, but they were considerably larger. The American lion was once believed to be the largest subspecies of lion.
South of Alaska, the American lion first appeared during the Sangamonian Stage (the last interglacial). After that it was widespread in the western Americas from Alaska to Peru. It was absent from most of eastern North America and peninsular Florida, although it may have been present in the Lake Michigan area. Like many other large mammals, it went extinct at the end of the Pleistocene, about 10,000 years ago. By then the American lion was one of the abundant Pleistocene megafauna, a wide variety of very large mammals who lived during the Pleistocene. Remains are most common in the Yukon and from the La Brea Tar Pits.
In some areas of its range, the American lion lived under cold climatic conditions. They probably used caves or fissures for shelter from the cold weather. They may have lined their dens with grass or leaves, as the Siberian tiger does, another great cat that currently lives in the north.
There are fewer American lions in the La Brea tar pits than other predators such as saber-toothed cats (Smilodon fatalis) or dire wolves (Canis dirus), which suggests they may have been smart enough to avoid the hazard. American lions likely preyed on deer, North American horses (now extinct), North American camels, North American tapirs, American bison, mammoths, and other large, herbivorous animals.
This species disappeared about the same time as other species during the Holocene extinction event, which wiped out likely prey of megafauna. Bones of the lion have been found in the trash heaps of Paleolithic American Indians, so human predation may have contributed to their extinction.
A replica of the jaw of the first specimen of American lion discovered can be seen in the hand of a statue of paleontologist Joseph Leidy, which is currently standing outside the Academy of Natural Sciences in Philadelphia.
The American lion was initially considered a distinct species of Pantherinae, with the scientific name Panthera atrox, 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 Eurasion 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 shows 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 about 340 000 years ago. The study also indicated that the 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.
Male sabertoothed cats were pussycats compared to macho lions
November 5, 2009
Close up view of a saber tooth cat head on display at the American Natural History Museum, New York.
Despite their fearsome fangs, male sabertoothed cats may have been less aggressive than many of their feline cousins, says a new study of male-female size differences in extinct big cats.
Commonly called the sabertoothed tiger, Smilodon fatalis was a large predatory cat that roamed North and South America about 1.6 million to 10,000 years ago, when there was also a prehistoric cat called the American lion. A study appearing in the November 5 issue of the Journal of Zoology examined size differences between sexes of these fearsome felines using subtle clues from bones and teeth.
The researchers report that while male American lions were considerably larger than females, male and female sabertoothed cats were indistinguishable in size. The findings suggest that sabertooths may have been less aggressive than their fellow felines, researchers say.
In species where males fight for mates, bigger, heavier males have a better chance of winning fights, fending off their rivals and gaining access to females. After generations of male-male competition, the males of some species evolve to be much larger than their mates.
Most big cats have a form of sexual dimorphism where males are bigger than females, said co-author Julie Meachen-Samuels, a biologist at the National Evolutionary Synthesis Center in Durham, NC. So she and Wendy Binder of Loyola Marymount University in Los Angeles wanted to know if extinct sabertooths and American lions showed the same size patterns as big cats living today.
When it comes to fossils, sorting males from females can be tricky. "It's hard to tell who's a male and who's a female in the fossil record," said Blaire Van Valkenburgh, a biologist at UCLA who has studied these animals extensively but was not an author on the paper. "Unless you're lucky enough to get some DNA, or you're working with an animal where males have horns and females don't."
For species that keep growing into adulthood, simply separating the fossils into two groups by size may not do the trick, either. "It's easy to get a younger, smaller male confused with an older, larger female if you're just dividing them by size," Meachen-Samuels said.
The researchers accounted for continued growth using subtle clues from fossilized teeth. "Teeth fill in over time," said Binder. "In young animals the tooth cavity is basically hollow, but as they get older it fills in with dentin. It won't give you an exact age, but it can give you a relative age in terms of young, middle aged or old," Binder added.
Meachen-Samuels and Binder x-rayed the lower teeth and jaws of 13 American lions and 19 sabertoothed cats recovered from the La Brea Tar Pits in Los Angeles. To account for growth over time, they measured tooth cavity diameter and plotted it against jaw length for each species. Plotted this way, the data for the American lion fell easily into two groups, regardless of age. The researchers concluded that "the little ones were females and the big ones were males," said Van Valkenburgh.
In contrast, sabertoothed cat sizes seemed to be governed solely by age. It would appear that the males were indistinguishable from their mates. "Even by incorporating a measure of age, you can't distinguish males and females," said Meachen-Samuels.
Size differences between the sexes tend to be more impressive in species where male aggression is more intense, and in the extinct American lion, size differences between the sexes were even more dramatic than in lions living today.
The closest living relative of the American lion, "African lions engage in aggressive takeovers where one to several males will take over an entire pride - the males have battles to the death," said Van Valkenburgh.
"Living lions have huge sexual dimorphism," said Meachen-Samuels.
Based on their findings, the researchers think the American lion probably lived in male-dominated groups, where 1-2 males monopolized and mated with multiple females. "My guess would be that the American lion was similar to African lions, where males guard groups of females," said Meachen-Samuels.
"But we don't see that in the sabertoothed cat," Binder said. The size similarity in sabertoothed cats suggests that male sabertooths may have been less aggressive than their larger cousins. "Rather than males having harems of females, the males and females in a group might have been more equal," Binder said.
More information: Meachen-Samuels, J. and W. Binder (2009). "Sexual Dimorphism and Ontogenetic Growth in the American Lion (Panthera atrox) and Sabertoothed Cat (Smilodon fatalis) from Rancho La Brea." Journal of Zoology.
Source: Duke University (news : web)