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|American Lion - Panthera (leo) atrox|
|Tweet Topic Started: Mar 4 2012, 04:14 PM (6,878 Views)|
|Taipan||Mar 4 2012, 04:14 PM Post #1|
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.
|Taipan||Apr 30 2012, 09:46 PM Post #2|
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)
|Taipan||Apr 30 2012, 09:46 PM Post #3|
The "American Lion" is not a lion (?)
Posted on May 8, 2010 | 0 Comments
By Hans-Dieter Sues
Among the great mammalian predators from the Pleistocene Epoch (1.8 million to 10,000 years ago) of North America, an enormous cat stands out. Only the giant bear Arctodus simus (discussed in a previous blog) exceeded it in size. No, I am not talking about the famous saber-toothed cat, Smilodon fatalis.
Renowned American naturalist Joseph Leidy first described a large extinct cat (which he named Felis atrox, "cruel cat") in 1853 based on an incomplete lower jaw with teeth from Mississippi. Since then, bones of this predator have been recovered from Pleistocene deposits across the United States and in Canada.
The best fossils of what now is known as Panthera atrox have been found in the La Brea "tar pits," which today are located in the Miracle Mile district of Los Angeles.
At La Brea, crude oil has slowly been seeping to the surface through deep fissures in the ground for the last 40,000 years or so. The light fraction of this oil evaporates, leaving deposits of thick, sticky asphalt (usually incorrectly referred to as "tar"). Water often collected on and covered the asphalt, luring thirsty animals to their doom. Over countless millennia, many animals and plants have been preserved in these deposits.
Many of the species found as fossils at La Brea still live in the Los Angeles region. However, the big mammals--including saber-toothed cat, dire wolf, mammoths, mastodon, ground sloths, long-horned bison, and camels--vanished about 11,000 years ago.
Some 90 percent of the large mammal fossils collected from La Brea belong to carnivores. Most of the bird remains also belong to forms that are predators and (or) scavengers --eagles, an extinct group of enormous birds known as teratorns, vultures, and condors. Presumably the plight of mired animals attracted predators, which then joined their intended quarry in the deadly embrace of the asphalt. In addition, some carnivores may have inadvertently become trapped while pursuing their prey across the sticky ground.
The relationships of Panthera atrox, often called the American lion, to other big cats have long been contentious.
John C. Merriam, a renowned paleontologist from the University of California at Berkeley, and his students first started scientific investigation of the La Brea fossils in 1901. In 1932, together with his former student, Chester Stock, Merriam published a classic monograph on the extinct cats, including Panthera atrox, from La Brea.
The two researchers noted many similarities between Panthera atrox and present-day lions and tigers (Panthera tigris). However, they concluded that overall the skull of the extinct cat was most like that of the jaguar (Panthera onca). Some later authors accepted this view, but other experts considered Panthera atrox most closely related to the African lion (Panthera leo) and its extinct Eurasian relative, the cave lion (Panthera spelaea). A few paleontologists even went so far as to assign the extinct American cat to Panthera leo rather than to a separate species.
A new study by the Danish zoologist Per Christiansen and the American paleontologist John Harris has recently clarified the relationships of Panthera atrox to other big cats (Pantherinae). The two researchers employed a variety of methods for statistical and shape analysis to compare large samples of skulls of present-day and extinct pantherine cats.
Side view of a complete skull of Panthera atrox from La Brea, now housed in the collections of the University of California Museum of Paleontology. The length of this skull (measured from the tip of the snout to the back of the base of the skull) is 40.6 cm (16 in.). The illustration was scanned and digitally modified from the classic monograph by Merriam and Stock (1932) on the extinct cats of La Brea and represents a fine example of traditional scientific illustration.
Their analyses confirmed that the skull of Panthera atrox shares similarities with those of lions but also revealed many differences. The lower jaw of the extinct cat was more similar to those of the jaguar and tiger but also had features not found in any of the present-day big cats.
In a comprehensive analysis of 23 skull dimensions, Panthera atrox emerged as quite distinct from lion, tiger, and jaguar. A separate study of the evolutionary history of pantherine cats by Christiansen placed the "American lion" closest to the jaguar (Panthera onca).
The work by Christiansen and Harris makes a compelling case that Panthera atrox was, in fact, a kind of giant jaguar rather than a lion. There exists no evidence now that true lions ever immigrated to the Americas.
Panthera atrox was one of the largest true cats of all time, reaching an estimated weight of at least 351 kg (772 pounds). It apparently lived in open habitats and presumably could tackle even prey as large as a bison. Although present-day jaguars prefer forest settings the largest individuals are usually found in less forested habitats.
Writing this blog I am inspired by the cats sharing their lives with my family and me. They are beautiful (if much less menacing) examples of one of the most successful groups of predators in the history of mammals.
Hans-Dieter (Hans) Sues is a vertebrate paleontologist based in Washington, D.C. He is interested in the evolutionary history and paleobiology of vertebrates, especially dinosaurs and their relatives, and the history of ecosystems through time.
|Taipan||Dec 29 2012, 01:01 PM Post #4|
Evidence Contradicts Idea That Starvation Caused Saber-Tooth Cat Extinction
Dec. 26, 2012 — In the period just before they went extinct, the American lions and saber-toothed cats that roamed North America in the late Pleistocene were living well off the fat of the land.
That is the conclusion of the latest study of the microscopic wear patterns on the teeth of these great cats recovered from the La Brea tar pits in southern California. Contrary to previous studies, the analysis did not find any indications that the giant carnivores were having increased trouble finding prey in the period before they went extinct 12,000 years ago.
The results, published on Dec. 26 in the scientific journal PLOS ONE, contradicts previous dental studies and presents a problem for the most popular explanations for the Megafaunal (or Quaternary) extinction when the great cats, mammoths and a number of the largest mammals that existed around the world disappeared.
"The popular theory for the Megafaunal extinction is that either the changing climate at the end of the last Ice Age or human activity -- or some combination of the two -- killed off most of the large mammals," said Larisa DeSantis, assistant professor of earth and environmental sciences at Vanderbilt, who headed the study. "In the case of the great cats, we expect that it would have been increasingly difficult for them to find prey, especially if had to compete with humans. We know that when food becomes scarce, carnivores like the great cats tend to consume more of the carcasses they kill. If they spent more time chomping on bones, it should cause detectable changes in the wear patterns on their teeth."
In 1993, Blaire Van Valkenburgh at UCLA published a paper on tooth breakage in large carnivores in the late Pleistocene. Analyzing teeth of American lions, saber-tooth cats, dire wolves and coyotes from La Brea, she found that they had approximately three times the number of broken teeth of contemporary predators and concluded, ." ..these findings suggest that these species utilized carcasses more fully and likely competed more intensely for food than present-day large carnivores."
The latest study uses a new technique, called dental microwear texture analysis (DMTA), developed by co-author Peter Ungar at the University of Arkansas. It uses a confocal microscope to produce a three-dimensional image of the surface of a tooth. The image is then analyzed for microscopic wear patterns. Chowing down on red meat produces small parallel scratches. Chomping on bones adds larger, deeper pits. Previous methods of dental wear analysis relied on researchers to identify and count these different types of features. DMTA relies on automated software and is considered more accurate because it reduces the possibility of observer bias.
DeSantis and Ungar, with the assistance of Blaine Schubert from East Tennessee State University and Jessica Scott from the University of Arkansas, applied DMTA to the fossil teeth of 15 American lions (Panthera atrox) and 15 saber-tooth cats (Smilodon fatalis) recovered from the La Brea tar pits in Los Angeles.
Their analysis revealed that the wear pattern on the teeth of the American lion most closely resembled those of the present-day cheetah, which actively avoids bones when it feeds. Similarly, the saber-tooth cat's wear pattern most closely resembled those of the present-day African lion, which indulges in some bone crushing when it eats. (This differs from a previous microwear study using a different technique that concluded saber-tooth cats avoided bone to a far greater extent.)
The researchers examined how these patterns changed over time by selecting specimens from tar pits of different ages, ranging from about 35,000 to 11,500 years ago. They did not find any evidence that the two carnivores increased their "utilization" of carcasses throughout this period. If anything, their analysis suggests that the proportion of the carcasses that both kinds of cats consumed actually declined toward the end.
The researchers acknowledge the high rate of tooth breakage reported in the previous study, but they argue that it is more likely the result of increased breakage when taking down prey instead of when feeding.
"Teeth can break from the stress of chewing bone but they can also break when the carnivores take down prey," DeSantis pointed out. Species like hyenas that regularly chew and crack bones of their kills are as likely to break the rear teeth they use for chewing as their front canines. Species like the cheetah, however, which avoid bones during feeding are twice as likely to break canines than rear teeth. This suggests that they are more likely to break canines when pulling down prey.
The researchers report that previous examinations of the jaws of the American lions and saber-tooth cats from this period found that they have more than three times as many broken canines and interpret this as additional evidence that supports their conclusion that most of the excess tooth breakage occurred during capture instead of feeding.
In addition, the researchers argue that the large size of the extinct carnivores and their prey can help explain the large number of broken teeth. The saber-toothed cats were about the size of today's African lion and the American lion was about 25 percent larger. The animals that they preyed upon likely included mammoths, four-ton giant ground sloths and 3,500-pound bison.
Larger teeth break more easily than smaller teeth. So larger carnivores are likely to break more canine teeth when attempting to take down larger prey, the researchers argue. They cite a study that modeled the strength of canine teeth that found the canines of a predator the size of fox can support more than seven times its weight before breaking while a predator the size of lion can only support about four times its weight and the curved teeth of the saber-toothed cats can only support about twice its weight.
"The net result of our study is to raise questions about the reigning hypothesis that "tough times" during the late Pleistocene contributed to the gradual extinction of large carnivores," DeSantis summarized. "While we can not determine the exact cause of their demise, it is unlikely that the extinction of these cats was a result of gradually declining prey (due either to changing climates or human competition) because their teeth tell us that these cats were not desperately consuming entire carcasses, as we had expected, and instead seemed to be living the 'good life' during the late Pleistocene, at least up until the very end."
Sabertoothed cats were not limited by food in California during the late Pleistocene.
Larisa R. G. DeSantis, Blaine W. Schubert, Jessica R. Scott, Peter S. Ungar. Implications of Diet for the Extinction of Saber-Toothed Cats and American Lions. PLoS ONE, 2012; 7 (12): e52453 DOI: 10.1371/journal.pone.0052453
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