Smilodon fatalis

Joined: February 11th, 2012, 7:29 am

February 12th, 2012, 4:51 am #1

Smilodon fatalis

Temporal range: Early Pleistocene to Early Holocene, 2.5–0.01 Ma

Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Suborder: Feliformia
Family: Felidae
Subfamily: †Machairodontinae
Tribe: †Smilodontini
Genus: †Smilodon
Species:Smilodon fatalis Leidy, 1869

Smilodon fatalis ("the deadly knife-tooth") is possibly the best-known of the machairodontine saber-toothed cats.

Fossils of Smilodon were discovered in North America from the second half of the 19th century onwards. In 1869, American paleontologist Joseph Leidy described a maxilla fragment with a molar, which had been discovered in a petroleum bed in Hardin County, Texas. He referred the specimen to the genus Felis (which was then used for most cats, extant as well as extinct) but found it distinct enough to be part of its own subgenus, as F. (Trucifelis) fatalis. The species name means "fate" or "destiny", but it is thought Leidy intended it to mean "fatal". In an 1880 article about extinct American cats, American paleontologist Edward Drinker Cope pointed out that the F. fatalis molar was identical to that of Smilodon, and he proposed the new combination S. fatalis. Most North American finds were scanty until excavations began in the La Brea Tar Pits in Los Angeles, where hundreds of individuals of S. fatalis have been found since 1875. S. fatalis has junior synonyms such as S. mercerii, S. floridanus, and S. californicus. American paleontologist Annalisa Berta considered the holotype of S. fatalis too incomplete to be an adequate type specimen, and the species has at times been proposed to be a junior synonym of S. populator. Swedish paleontologists Björn Kurtén and Lars Werdelin supported the distinctness of the two species in 1990.

Distribution and Habitat
Smilodon lived during the Pleistocene epoch (2.5 mya–10,000 years ago), and was perhaps the most recent of the saber-toothed cats. Smilodon probably lived in a closed habitat such as forest or bush. Fossils of the genus have been found throughout the Americas. In North America, the varied habitat supported other saber-toothed cats in addition to Smilodon, such as Homotherium and Xenosmilus; the habitat here varied from subtropical forests and savannah in the south, to treeless mammoth steppes in the north. Smilodon inhabited the temperate latitudes of North America, where the mosaic vegetation of woods, shrubs, and grasses in the southwest supported large herbivores such as horses, bison, antelope, deer, camels, mammoths, mastodons, and ground sloths. Other large carnivores included Dire Wolves, Short-faced Bear (Arctodus simus) and the American Lion. Due to competition from larger carnivores in North America, S. fatalis was perhaps not able to attain the same size as S. populator. The similar sizes of S. fatalis and the American Lion suggests niche overlap and direct competition between these species, and they appear to have fed on similarly sized prey.

It appeared in North America about 1.6 million years ago and later migrated down the west coast of the continent to Peru. It became extinct around 10,000 years ago.

Physical Characteristics
Smilodon fatalis, 1.6 million-10,000 years ago, replaced Smilodon gracilis in North America and invaded western South America as part of the Great American Interchange. In size it was between Smilodon gracilis and S. populator. This species was about 1 m high at the shoulder and is estimated to have ranged from 160 to 280 kg (350 to 620 lb). Particularly large Smilodon fatalis males may well have reached a body mass of around 350 kg Sometimes two additional species are recognized, Smilodon californicus and Smilodon floridanus, but usually they are considered to be subspecies of Smilodon fatalis.

Although the saber-toothed cat has no close living relatives, paleontologists reconstruct how the saber-toothed cat looked by comparing its bones with those of large cats living today. Very powerful front legs and a short tail indicate that saber-toothed cats used stealth and ambush rather than speed to capture their prey.

Isotopes preserved in the bones of S. fatalis in the La Brea Tar Pits reveal that ruminants like bison (Bison antiquus, which was much larger than the modern American Bison) and camels (Camelops) were most commonly taken by the cats there.

Recent investigations suggest that this saber-toothed cat probably used its long canines to slash through the throat, severing the wind pipe and cutting the jugular. Its teeth were surprisingly delicate and could easily snap off if a prey animal struggled. Its mouth could open up to 120 degrees, whereas its closest living relative, Panthera leo, or lion, can only open its jaws to 65 degrees.

Some fossils show healed injuries or diseases that would have crippled the animal. Some paleontologists see this as evidence that saber-toothed cats were social animals, living and hunting in packs that provided food for old and sick members.
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Joined: February 11th, 2012, 7:29 am

May 4th, 2012, 11:34 am #2

Saber-Toothed Cat Had Wimpy Bite

By Jeanna Bryner, LiveScience Staff Writer
posted: 01 October 2007 05:00 pm ET

The saber-toothed cat just lost some of its swagger. Long considered a most fearsome predator among Ice Age giants, at least one species of saber-tooth bit more like a "pussycat," new research suggests.

About the size of a modern African lion, but much heftier, Smilodon fatalis has captured popular imagination for decades, most recently as "Diego" in the animated film "Ice Age." The cat is often referred to as the saber-toothed tiger, though scientists say this is misleading, as Smilodon and related species are more closely related to lions.

While there are several saber-toothed cats, this Smilodon species is the most well-preserved in the fossil record, showing the animal likely prowled across the grasslands of North America and parts of South America until about 9,000 or 10,000 years ago when saber-tooths became extinct.

For more than a century, scientists have debated how the cat used its knife-like teeth called sabers to take down formidable prey, such as bison, horses and perhaps even mammoths.

A new study, posted online today in the journal Proceedings of the National Academy of Sciences, finds the saber-tooth was more of a kitty cat, with a bite with just one-third the strength of a lion.

"For all its reputation, Smilodon had a wimpy bite," said study team member Stephen Wroe, a paleontologist at the University of New South Wales.

Digital crash tests

Wroe, lead author Colin McHenry of the University of Newcastle and colleagues used fossils to digitally reconstruct the skulls of a Smilodon and a lion (Panthera leo).

"We simulated the forces you might expect if each one was taking large prey," McHenry said. The "computerized crash tests" showed if the prey was still on its feet and struggling, the saber-tooth's skull didn't hold up to the associated forces, while the lion's skull did fine.

McHenry likens these forces to a person chomping down on a raging bull. "Imagine biting onto something like a bull at a rodeo while it's trying to buck you off," McHenry told LiveScience. "Imagine the forces that would go through your skull as it's trying to throw you off. The lion skull actually copes with those [forces] really well, but the saber-cat skull doesn't."

The results show the saber-toothed cat had a less-powerful bite compared with the lion, which the scientists suggest is partially due to Smilodon's relatively small lower jaw (a feature that makes space for the cat's lengthy sabers).

Kill style

In order to avoid a butt-whipping but still come away with a meal, the giant cat must have had a different killing style than lions.

"Smilodon was an awesome beast, and what it lacked in bite force it more than made up for elsewhere," Wroe said.

They suggest Smilodon used its powerful forelimbs and oversized claws to take down a prey and restrain the animal before deploying its devastating canine teeth.

"The saber-cat had an immensely powerful body, perfect for wrestling large prey to the ground, and our models show that it needed to do this before trying a bite," McHenry explained. "Killing was more likely applied to the prey's throat, because it is easier to restrain the prey this way. Once the bite was done, the prey would have died almost instantly."

The result would be an ambush followed by a quick kill, the researchers say. In contrast, lions often hold a bite for many minutes to suffocate their large prey.

With such muscle mass for wrestling large prey, Smilodon was not so agile and therefore couldn't snag quick gazelle and antelope, for instance, as lions can. This limitation could be a reason the giant cats went extinct at the end of the last Ice Age.

"[Smilodon] sacrificed the ability to catch small prey, and when the large prey disappeared at the end of the last Ice Age, it went with them," McHenry said.

Journal Reference:
Colin R. McHenry, et al. Supermodeled sabercat, predatory behavior in Smilodon fatalis revealed by high-resolution 3D computer simulation16010–16015, doi: 10.1073/pnas.0706086104

The American sabercat Smilodon fatalis is among the most charismatic of fossil carnivores. Despite broad agreement that its extraordinary anatomy reflects unique hunting techniques, after >150 years of study, many questions remain concerning its predatory behavior. Were the “sabers” used to take down large prey? Were prey killed with an eviscerating bite to the abdomen? Was its bite powerful or weak compared with that of modern big cats? Here we quantitatively assess the sabercat's biomechanical performance using the most detailed computer reconstructions yet developed for the vertebrate skull. Our results demonstrate that bite force driven by jaw muscles was relatively weak in S. fatalis, one-third that of a lion (Panthera leo) of comparable size, and its skull was poorly optimized to resist the extrinsic loadings generated by struggling prey. Its skull is better optimized for bites on restrained prey where the bite is augmented by force from the cervical musculature. We conclude that prey were brought to ground and restrained before a killing bite, driven in large part by powerful cervical musculature. Because large prey is easier to restrain if its head is secured, the killing bite was most likely directed to the neck. We suggest that the more powerful jaw muscles of P. leo may be required for extended, asphyxiating bites and that the relatively low bite forces in S. fatalis might reflect its ability to kill large prey more quickly, avoiding the need for prolonged bites.
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May 4th, 2012, 11:35 am #3

Here's Wroe describing the Smilidon Fatalis's killing method -

"Although its bite was weak, this is not to imply Smilodon was not was a formidable predator. "Anything but," says Dr Wroe. "Smilodon was an awesome beast -- and what it lacked in bite force it more than made up for elsewhere."

"The sabrecat had an immensely powerful body; perfect for wrestling large prey to the ground, and our models show that it needed to do this before trying a bite, "explains Mr McHenry. "Killing was more likely applied to the prey's throat, because it is easier to restrain the prey this way. Once the bite was done the prey would have died almost instantly."

Dr Wroe describes the lion as a "better all rounder" in the hunting stakes. Smilodon was massively over-engineered for the purposes of taking small prey, but a ruthlessly efficient hunter of big game."

Imaging shows the Smilodon bite had a narrow jaw which restricted its killing behavior. (Credit: Dr. Stephen Wroe)

Saber-toothed Cat Was More Like A pussycat Than A Tiger

Joined: February 11th, 2012, 7:29 am

May 4th, 2012, 11:36 am #4

Sabretooth tigers hunted in packs

By James Morgan
Science reporter, BBC News

Sabretooth "tigers" hunted in packs, sharing the spoils among themselves

Forget their ferocious fangs - sabretooth "tigers" were social animals who lived in family prides, like lions today, according to UK and US experts.

The abundance of S.fatalis fossils in Californian tar seeps suggests they were packs of scavengers, lured in by the distress calls of trapped prey.

Research in Africa found that audio playbacks of prey sounds attract social carnivores, but not solitary hunters.

This suggests S.fatalis was social too, claims the Royal Society journal study.

Jaw dropping

The so-called sabretooth tiger - Smilodon fatalis - is famous for its extremely long canine teeth, which reached up to seven inches and extended below the lower jaw.

But although commonly called "tigers", due to their size, the species is actually part of a different subfamily, and they lived very differently.

While sabretoothed "tigers" were powerful predators, they were social beasts, rather than skulking loners, according to Dr Chris Carbone, a research fellow of the Zoological Society of London.

He said: "The extinct sabretoothed cat, Smilodon fatalis, has been something of an enigma, with almost nothing known of its behaviour.

"This research allowed us... to conclude that this cat was more likely to roam in formidable gangs, than as a secretive solitary animal."

S.fatalis - one of many sabretooth cat species - lived between 1.6 million and 10,000 years ago, in North and South America.

Many Smilodon fossils have been found in the Late Pleistocene era tar seeps at Rancho La Brea, California - apparently lured to their fate by the calls of trapped, dying herbivores.

In fact, the fossils are so numerous, many palaeontologists now believe the cats were pack hunters, who came to scavenge prey and share the spoils.

The cats lived in prides similar to modern day lions, research suggests

Cat calls

In search of further evidence, Dr Carbone and colleagues looked at the behaviour of modern day carnivores, in the Serengeti region of Tanzania and the Kruger National Park, South Africa.

Big cats were lured to sites using audio "playbacks" of prey in distress, or the sounds of lions and hyenas.

The playbacks attracted large numbers of social carnivore species. Lions and spotted hyenas made up 84% of the individuals attending. But solitary carnivores, of all sizes, were rare.

Overall, social carnivores attended the playbacks approximately 60 times more often than would be expected, based on their abundance relative to other carnivore species in the regions.

The researchers compared these to the carnivore species drawn into the tar seeps, apparently by the sounds of prey.

Again, they found that two species appear to dominate. The presumably social dire wolf (51%) and Smilodon fatalis (33%) made up 84% of the carnivores in the tar seeps.

"The striking similarities between the playbacks and the fossil record support the conclusion that Smilodon was social," said Dr Carbone.

Social animals

"[Sabretooths] were dependent on scavenging as a food source and are likely to have evolved more complicated social organisation in order to optimise their caloric intake."

Professor Alan Turner, an expert in carnivore evolution, from Liverpool John Moores University, said: "These findings make sense when you look at the full picture.

"In the tar seeps, you find so many sabretooth fossils. There is almost one predator for every prey.

"The implication is that several carnivores were attracted to each prey animal. Logically, these predators were not all coming from different territories.

"We now have a whole battery of evidence - from the fossil record to modern ecological studies - all suggesting sabretooths were social.

"We can't say the case is closed, but we have some pretty strong indications."

The research, published in The Royal Society's journal Biology Letters, involved scientists from the University of California, Tshwane University of Technology and University of Pretoria.


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May 4th, 2012, 11:39 am #5

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.

Journal Reference:
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.

Sexual dimorphism has long been purported in the American lion Panthera atrox well-known from the asphalt deposits at Rancho La Brea. However, few studies have quantified this dimorphism. Along with the sabertoothed cat, Smilodon fatalis, we examine sexual dimorphism in dentaries from the Rancho La Brea tar pits using extant Panthera leo as a guide. Although growth rate in large carnivores declines after a certain age, it has been demonstrated to continue well beyond adulthood, therefore age must also be incorporated into a measure of sexual dimorphism in large carnivores. Prior studies demonstrated that tooth wear can be an inaccurate measure of age in Rancho La Brean carnivores, as it is affected by both diet and age. This study, instead, uses per cent pulp cavity closure of the lower canine tooth which is solely a measure of relative age, combined with linear measurements of the dentaries to separate the sexes of these two extinct cats. Results show that P. atrox has similar, or slightly greater, levels of sexual dimorphism than P. leo, whereas S. fatalis shows little to no sexual dimorphism. Our results also demonstrate that both Panthera species continue to grow into adulthood, strengthening the case that it is necessary to incorporate a measure of age into studies of sexual dimorphism in large carnivores, living or extinct. ... x/abstract
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May 4th, 2012, 11:40 am #6

Extinct sabertooth cats were social, found strength in numbers, study shows

A reconstructed scene in the Pleistocene of western North America, showing a group of sabertooth cats of the species Smilodon fatalis, with several adults and cubs.

By Stuart Wolpert October 30, 2008 Category: Research

The sabertooth cat (Smilodon fatalis), one of the most iconic extinct mammal species, was likely to be a social animal, living and hunting like lions today, according to new scientific research. The species is famous for its extremely long canine teeth, which reached up to seven inches in length and extended below the lower jaw.

Instead of relying on the bones and teeth of the sabertooths to make their findings, scientists from UCLA and the Zoological Society of London concluded that the sabertooth cat was social by using a novel technique: They compared numbers of present-day carnivores competing for kills in Africa with those of mainly extinct species found in a North American fossil deposit.

The research is published in the current issue of the Royal Society's journal Biology Letters (Oct. 28). Co-authors also included scientists from South Africa's Tshwane University of Technology and University of Pretoria.

Smilodon existed in North and South America between 1.8 million and 10,000 years ago and is one of the most common species preserved at the Rancho La Brea tar pits of Los Angeles, a fossil deposit in which dying herbivores trapped in sticky asphalt attracted numerous dire wolves and sabertooth cats, some of which also died there.

Because most living cats are solitary, controversy has persisted over the social life of Smilodon.

The study reported in Biology Letters took a new approach to the question by comparing data from the La Brea fossil record and data obtained from "playbacks" used in Africa, in which the recorded calls of distressed prey and the sounds of lions and hyenas are used to attract carnivores. This technique has been used by scientists to estimate carnivore densities in eastern and southern Africa.

Results showed that large social species made up a far larger proportion of the animals attracted than one would expect, considering their population size compared to other carnivores. Large social carnivores were, in fact, found to attend approximately 60 times more often than expected on the basis of relative abundance. When these results were compared with the records at the tar pits of California, the scientists found that the proportion of Smilodon records matched the proportion of the large social carnivores in the playbacks.

"It absolutely makes sense that social species will predominate at carcasses, both now and in the past," said Blaire Van Valkenburgh, UCLA professor of ecology and evolutionary biology and senior author on the paper. "Why approach a situation where you are likely to encounter dangerous competitors without having a few friends along?"

The same social advantage, she said, would apply to all scavengers, including early humans, who began consuming more meat about 2 million year ago, some of which they probably scavenged.

Although commonly called the "sabertoothed tiger," the species is actually not closely related to the tiger, which is part of a different subfamily. However, the sabertooth cat was large and muscular, similar in size to a modern-day tiger.

"The extinct sabertooth cat, Smilodon fatalis, has been something of an enigma, with almost nothing known of its behavior," said Chris Carbone, a senior research fellow at the Zoological Society of London and lead author of the paper. "This research allowed us to use the behavior of its present-day relatives to conclude that this extinct cat was more likely to roam in formidable gangs than as a secretive, solitary animal." ... 70874.aspx
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May 4th, 2012, 11:42 am #7

Saber-toothed Cats Wrestled Prey with Powerful Arms

By Charles Q. Choi, LiveScience Contributor
posted: 02 July 2010 04:59 pm ET

The sabertooth cat may have been less aggressive than its feline cousin, the American lion, a new study says.

Saber-toothed cats might be most famous for their oversized fangs, but scientists now find the feisty felines had another exceptional feature — powerful arms stronger than those of any cat alive today.

Commonly known as the "saber-toothed tiger," the extinct cat Smilodon fatalis roamed the Americas until roughly 10,000 years ago, preying on "megafauna" — large animals such as mammoths, bison, camels and mastodons. Their specialization on such giant creatures might have doomed these hunters when their Ice Age prey died off.

The most recognizable features of the saber-toothed cat — giant, dagger-like canines — were also perhaps its most puzzling. The fangs would have been excellent at inflicting deadly slashing bites to its prey's throat, but their size and shape would also have made them highly vulnerable to fracturing compared with modern cats. That led researchers to wonder how the fangs developed in the first place.

Cat teeth

"Cats living today have canines that are round in cross-section, so they can withstand forces in all directions," said researcher Julie Meachen-Samuels, a paleontologist at the National Evolutionary Synthesis Center in Durham, N.C. "If the prey is struggling it doesn't matter which way it's pulling — their teeth are unlikely to break."

In contrast, the long canines of saber-toothed cats were oval in cross-section, or thinner side-to-side, making them relatively fragile. This suggested that saber-toothed cats must have killed prey differently from other cats. In fact, research published in 2007 suggested Smilodon had a wimpy bite.

That's where the powerful arms come in. These predators might have pinned victims down with their heavily muscled forelimbs to protect their teeth from fracturing as they bit struggling prey, Meachen-Samuels said.

Feline wrestling match

In an arm-wrestling match of sorts, the researchers compared saber-tooth arms with those of other cats. To do so, they X-rayed the arm and leg bones of fossils recovered from the La Brea Tar Pits in Los Angeles. They also analyzed the limb bones of 28 cat species living today — ranging in size from the 6-pound (2.7-kilogram) margay to the 600-pound (272-kg) tiger — as well as the extinct American lion, the largest cat with conical teeth that ever lived. These measurements helped the researchers estimate bone length, rigidity and strength for each species.

Species with longer limbs generally had stronger bones. However, while saber-tooth leg bones fell within the normal range, their arm bones were exceptionally thick for their length. Not only that, their arms also had thicker cortical bone — the dense outer layer that makes bones strong and stiff.

"When I looked at Smilodon, I knew they were thicker on the outside than other cats, but I was really shocked at how much thicker they were on the inside as well," Meachen-Samuels told LiveScience.

The thicker cortical bone seen with the saber-toothed cats makes sense if the arms were under greater stress than normally expected for cats their size, Meachen-Samuels explained. Just as lifting weights improves bone density over time, so too may the repeated strain of grappling with prey have resulted in thicker and stronger arm bones in saber-toothed cats.

"As muscles pull on bones, bones respond by getting stronger," Meachen-Samuels said. "Because saber-toothed cats had thicker arm bones, we think they must have used their forelimbs more than other cats did."

The researchers would like to next look at other saber-toothed cats, as well as other saber-toothed predators that once existed. "There aren't a lot of arm bones to X-ray for other saber-toothed predators, but it'd be interesting to see if there were convergent processes with their arms as well," Meachen-Samuels said.

Meachen-Samuels and her colleague Blaire Van Valkenburgh detailed their findings online July 2 in PLoS ONE. ... 00702.html

Journal Reference:
Meachen-Samuels JA, Van Valkenburgh B (2010) Radiographs Reveal Exceptional Forelimb Strength in the Sabertooth Cat, Smilodon fatalis. PLoS ONE 5(7): e11412.


The sabertooth cat, Smilodon fatalis, was an enigmatic predator without a true living analog. Their elongate canine teeth were more vulnerable to fracture than those of modern felids, making it imperative for them to immobilize prey with their forelimbs when making a kill. As a result, their need for heavily muscled forelimbs likely exceeded that of modern felids and thus should be reflected in their skeletons. Previous studies on forelimb bones of S. fatalis found them to be relatively robust but did not quantify their ability to withstand loading.
Methodology/Principal Findings
Using radiographs of the sabertooth cat, Smilodon fatalis, 28 extant felid species, and the larger, extinct American lion Panthera atrox, we measured cross-sectional properties of the humerus and femur to provide the first estimates of limb bone strength in bending and torsion. We found that the humeri of Smilodon were reinforced by cortical thickening to a greater degree than those observed in any living felid, or the much larger P. atrox. The femur of Smilodon also was thickened but not beyond the normal variation found in any other felid measured.
Based on the cross-sectional properties of its humerus, we interpret that Smilodon was a powerful predator that differed from extant felids in its greater ability to subdue prey using the forelimbs. This enhanced forelimb strength was part of an adaptive complex driven by the need to minimize the struggles of prey in order to protect the elongate canines from fracture and position the bite for a quick kill. ... =printable
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May 4th, 2012, 11:43 am #8

How a Smilodon sabretooth cat closed its gaping mouth

By Victoria Gill
Science and nature reporter, BBC News
Page last updated at 12:14 GMT, Friday, 25 February 2011

The sabretoothed cats killed prey with a deep stabbing bite to the throat

The mystery of how prehistoric sabretoothed cats coped with their oversized teeth has been solved in part by a new analysis of the cats' jaws.

To impale prey with these impressive weapons, the famous sabretoothed cats must have opened their mouths wider than any modern big cat, but it was unclear if their jaw muscles were strong enough to do it.

Now the new analysis reveals that the cats' jaw muscles evolved into a specialised pattern, which allowed them to open their mouths so wide.

Details are reported in the Zoological Journal of the Linnean Society.

Weak bite?

Per Christiansen, from Aalborg University in Denmark, led the study. He took a novel approach to studying the extinct predators by creating a complex model of how their jaws moved.

Beautifully preserved skeletons of the most recently extinct sabretoothed cat, Smilodon, have been uncovered in tar pits in the US, offering the researcher plenty of fossilised remains to work with.

These fearsome-looking cats - the biggest of which would have hunted very large prey, including buffaloes, horses and extinct giant ground sloths - had a relatively weak bite force compared to their modern feline relatives, previous studies have revealed.

But this is not surprising, according to Dr Christiansen. He has found the cats must have had remarkable jaw muscles to close their mouths with any force at all.

"Smilodon could open its mouth wider than any modern cat," explained Dr Christiansen, "because if you have big teeth, you have to open your mouth at a very high angle to get anything in your mouth."

Fatal stabs

Smilodon (right) was able to open its mouth wider than any modern cat

Over the years, scientists have debated what the now extinct cats used their enormous teeth for, with some even suggesting the teeth were ornaments that males used to attract mates.

But the consensus is now that the teeth, which measured up to 20cm, delivered final, fatal stabs to already subdued prey.

Bulkier and more muscular than most modern cats, Smilodon would have brought large animals down with its forelimbs.

"They pounced on their prey, wrestled it to the ground and twisted the neck with massive forelimbs," explained Dr Christiansen.

"They then delivered a quick, powerful and deep stabbing bite to the throat or upper neck. But, there were no minute-long massive asphyxiating throat-clamps like those used by modern big cats when they suffocate prey. The sabrecats simply didn't have the jaw muscles for that."

Opening their mouths sufficiently wide to kill and consume their hard-earned meal would have stretched and significantly weakened their jaw muscles.

Dr Christiansen created a model of the cats' jaws, carefully calculating how they must have moved, to work out how Smilodon evolved to compensate for this weakness.

His model revealed how the cats' jaw muscles were aligned to pull its jaws closed, very directly and efficiently.

But Smilodon would also have done something that every cat-owner can see a relic of in their own pet.

"When you put a piece of food on the floor for your cat, you'll see it bobs its head forward as it eats it," he explained.

"And we know that [Smilodon] probably closed its jaws by twisting its head downward and throwing its head forward.

"Its neck was longer than that of modern cats and its neck muscles would have been stronger."

'Killing ecology'

The study also looked back at the earliest and most primitive sabretoothed animals.

"Smilodon was outrageous in terms of its anatomy," said Dr Christiansen.

"It was the most [highly evolved and therefore] different from modern cats, so to understand this animal from a biological sense, you need to study more primitive animals to work out why they have become that way through evolution."

Smilodon would have brought down prey with its powerful forelimbs

He examined hundreds of skulls, drawing an evolutionary map showing why sabretooths evolved such different jaw anatomy from modern cats.

"Killing ecology", he explained, was the driving factor - the evolutionary pressure to kill prey with a deep and efficient stab to the throat.

"The cat species became gradually more and more specialised, culminating with monsters such as Smilodon," said Dr Christiansen.

As sabretooths evolved longer canine teeth, their jaw muscles actually grew smaller, but the fibres became more vertically orientated and thus probably more efficient in closing the jaw.

Dr Christiansen explained: "At the same time, changes in the way the muscle fibres inserted on the lower jaw meant that the animals could stretch their muscles more - the fibres became re-orientated so as to allow a higher gape, necessary for gaping with huge fangs."

But their impressive appearance might well have been key to their demise; the sabre-toothed cats were dependent on large, relatively slow-moving prey.

"They had very powerful but heavy bodies and rather short, extremely powerful legs," said Dr Christiansen, "so they probably weren't very fast, and certainly nowhere near as fast and agile as leopard and tigers." ... 399605.stm

Journal Reference:
CHRISTIANSEN, P. (2011), A dynamic model for the evolution of sabrecat predatory bite mechanics. Zoological Journal of the Linnean Society, 162: 220–242. doi:10.1111/j.1096-3642.2010.00675.x

The ability of sabretoothed felids to achieve sufficiently high bite forces for predation at extreme gape angles has been the subject of decades of debate. Previous studies have indicated that bite forces in derived sabretoothed felids would have been low, but that they were probably augmented by head depressing muscles. However, bite mechanics is a dynamic process, and mechanical properties change with changes in gape angles. In this study, I present the first comprehensive model of bite mechanics, vector angles, and forces about the temporomandibular joint at gape angles from occlusion to maximal inferred gape in sabretoothed felids. Primitive sabrecats (Machairodus, Paramachairodus) appear broadly comparable to extant large felids (Panthera, Puma), but derived sabrecats in the groups Homotherini (Amphimachairodus, Homotherium, Xenosmilus) and Smilodontini (Megantereon, Smilodon) are often substantially different from either of the former. The ability of the mandibular adductors to generate torque changes with gape angle, indicating that previous models fail to capture potentially important differences in bite function. Inferred muscle sizes and the angles of effective torque from individual adductor fibres in derived sabrecats are different from those of primitive sabrecats and extant large felids, but they had evolved a number of compensatory adaptations for maximizing force output at the canine and carnassial, primarily changes in muscle fibre angles and more compact crania. Inferred outforces at the canines and carnassials were comparable amongst all groups at low gape angles, but at extreme gape angles outforces would have been low, supporting previous hypotheses of head flexor contribution during initial stages of the killing bite in sabrecats. Mandibular adduction in extant carnivores is a complicated pattern of differences in twitch tension and electromyographical activity at different gape angles, and inference of maximal isotonic bite forces from reconstructed mandibular adductor sizes in fossils will give estimates primarily suitable for comparative purposes. Potentially, derived sabrecats could have evolved differences from extant felids in adductor histochemistry or pinnation angle of individual fibres. ... x/abstract
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Joined: February 11th, 2012, 7:29 am

December 29th, 2012, 4:01 am #9

Evidence Contradicts Idea That Starvation Caused Saber-Tooth Cat Extinction

Sabertoothed cats were not limited by food in California during the late Pleistocene.

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." ... 222838.htm

Journal Reference:
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

The saber-toothed cat, Smilodon fatalis, and American lion, Panthera atrox, were among the largest terrestrial carnivores that lived during the Pleistocene, going extinct along with other megafauna ∼12,000 years ago. Previous work suggests that times were difficult at La Brea (California) during the late Pleistocene, as nearly all carnivores have greater incidences of tooth breakage (used to infer greater carcass utilization) compared to today. As Dental Microwear Texture Analysis (DMTA) can differentiate between levels of bone consumption in extant carnivores, we use DMTA to clarify the dietary niches of extinct carnivorans from La Brea. Specifically, we test the hypothesis that times were tough at La Brea with carnivorous taxa utilizing more of the carcasses. Our results show no evidence of bone crushing by P. atrox, with DMTA attributes most similar to the extant cheetah, Acinonyx jubatus, which actively avoids bone. In contrast, S. fatalis has DMTA attributes most similar to the African lion Panthera leo, implying that S. fatalis did not avoid bone to the extent previously suggested by SEM microwear data. DMTA characters most indicative of bone consumption (i.e., complexity and textural fill volume) suggest that carcass utilization by the extinct carnivorans was not necessarily more complete during the Pleistocene at La Brea; thus, times may not have been “tougher” than the present. Additionally, minor to no significant differences in DMTA attributes from older (∼30–35 Ka) to younger (∼11.5 Ka) deposits offer little evidence that declining prey resources were a primary cause of extinction for these large cats. ... ne.0052453
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Joined: February 11th, 2012, 7:29 am

July 2nd, 2015, 3:05 am #10

Dagger-like canines of saber-toothed cats took years to grow
New research technique assigns ages to Smilodon fatalis developmental events, shows rapid canine growth but overall delayed dental maturity

Date: July 1, 2015
Source: American Museum of Natural History
The fearsome teeth of the saber-toothed cat Smilodon fatalis fully emerged at a later age than those of modern big cats, but grew at a rate about double that of their living relatives. The findings, for the first time, provide specific ages for developmental dental events in Smilodon. The eruption rate of the cat's permanent upper canines was a speedy six millimeters per month, but the teeth weren't fully developed until three years of age.

This fossilized jaw of an adult Smilodon fatalis shows the fully erupted canine.
Credit: Copyright AMNH/J. Tseng

New research shows that the fearsome teeth of the saber-toothed cat Smilodon fatalis fully emerged at a later age than those of modern big cats, but grew at a rate about double that of their living relatives. The findings, published today in the journal PLOS ONE and based on a new technique that combines isotopic analysis and x-ray imaging, for the first time provide specific ages for developmental events in Smilodon, notably in their teeth. The study estimates that the eruption rate of S. fatalis's permanent upper canines was 6 millimeters per month--double the growth rate of an African lion's teeth. But the extinct cat's dagger-like canines weren't fully developed until about three years of age.

"For predators such as big cats, an important determinant of an individual's full hunting ability is the time required to grow their weapons--their teeth," said Z. Jack Tseng, a National Science Foundation and Frick Postdoctoral Fellow in the American Museum of Natural History's Division of Paleontology and a coauthor on the new paper. "This is especially crucial for understanding sabertoothed predators such as Smilodon."

S. fatalis lived in North and South America until going extinct about 10,000 years ago. About the size of a modern tiger or lion but more solidly built, the cats are famous for their protruding canines, which could grow to be 18 centimeters (about 7 inches) long. Although well-preserved fossils of S. fatalis are available to researchers, very little is known about the absolute ages at which the animals reached key developmental stages.

"Timing of development is critical for many aspects of vertebrate ecology and evolution," said Robert Feranec, curator of Pleistocene vertebrate paleontology at the New York State Museum and the corresponding author on the paper. "Changes in the timing of life-history events can have major effects on an organism's adult features and final appearance. For extinct species, we can usually only determine the relative sequence of developmental events. This technique will permit the determination of absolute developmental age not only for Smilodon, but other extinct species."

Using S. fatalis specimens recovered from the La Brea Tar Pits in Los Angeles, Feranec, Tseng, and colleagues from Clemson University and the Neural Stem Cell Institute combined data from stable oxygen isotope analyses and micro-computed tomography (μCT) to establish the eruption rate for the saber-toothed cat's permanent upper canines. At 6 millimeters per month, the calculated eruption rate is speedy--for comparison, human fingernails grow at about 3.4 millimeters per month.

By using the eruption rate to calibrate a previously published tooth-replacement sequence for the saber-toothed cat, the researchers calculated the timing of various growth events in absolute units (months), as opposed to the relative timing used in all previous research on this animal.

S. fatalis, like many other mammals, had two sets of teeth in its lifetime, and the first stopped erupting when the cub was about one-and-a-half years old. Toward the end of the eruption of the baby teeth, the permanent teeth started to erupt, with about an 11-month period where both sets of saber teeth could be seen inside of a cub's mouth.

As in human babies, the cubs of S. fatalis had loosely fitted pieces of bones in their skulls that fuse over time. The two parietal bones at the back of the cats' skulls were where their main jaw muscles attached, making the bones' fusion a necessity for supporting forces that enable them to eat larger chunks of meat or hunt larger prey. In S. fatalis, parietal bone fusion happened when the cubs were between one and one-and-a-half years old, about eight months earlier than is seen in modern lions. The timing coincides with the full eruption of the baby canines.

"This means that the jaw muscles of these cubs were anatomically ready to be used in hunting early on with their loaner set of sabers," Tseng said.

After about 20 months, the cats shed their baby canines, and the permanent ones continued to grow until the animals were between three to three-and-a-half years old, later than seen in modern large cats like tigers, leopards, and lions, but not as late as might be expected, the researchers said.

"Despite having canine crown heights that were more than twice those of the lion, Smilodon didn't require twice as much time to develop its canines," said Aleksander Wysocki, a graduate student at Clemson University and lead author on the paper.

Based on the results, young cats--less than 4-7 months old--are extremely rare in the vast collections from the La Brea Tar Pits.

"Considering the abundance of predators at Rancho La Brea, younger cubs would have been at risk of being preyed upon themselves if they attempted to feed on the animals trapped within the tar pits," Wysocki said. "The cubs probably remained hidden or at den sites while the adults pursued prey trapped in the tar pits and never made it back out."

The researchers say that the technique they demonstrate in the paper could be applied to a variety of extinct species to better understand the manner and rate by which different animals grew, for example, by looking at the tusks of extinct elephants or marine mammals.

Story Source: American Museum of Natural History. "Dagger-like canines of saber-toothed cats took years to grow: New research technique assigns ages to Smilodon fatalis developmental events, shows rapid canine growth but overall delayed dental maturity." ScienceDaily. (accessed July 1, 2015).

Journal Reference:
Wysocki MA, Feranec RS, Tseng ZJ, Bjornsson CS. Using a Novel Absolute Ontogenetic Age Determination Technique to Calculate the Timing of Tooth Eruption in the Saber-Toothed Cat, Smilodon fatalis. PLoS ONE, 2015 DOI: 10.1371/journal.pone.0129847

Despite the superb fossil record of the saber-toothed cat, Smilodon fatalis, ontogenetic age determination for this and other ancient species remains a challenge. The present study utilizes a new technique, a combination of data from stable oxygen isotope analyses and micro-computed tomography, to establish the eruption rate for the permanent upper canines in Smilodon fatalis. The results imply an eruption rate of 6.0 millimeters per month, which is similar to a previously published average enamel growth rate of the S. fatalis upper canines (5.8 millimeters per month). Utilizing the upper canine growth rate, the upper canine eruption rate, and a previously published tooth replacement sequence, this study calculates absolute ontogenetic age ranges of tooth development and eruption in S. fatalis. The timing of tooth eruption is compared between S. fatalis and several extant conical-toothed felids, such as the African lion (Panthera leo). Results suggest that the permanent dentition of S. fatalis, except for the upper canines, was fully erupted by 14 to 22 months, and that the upper canines finished erupting at about 34 to 41 months. Based on these developmental age calculations, S. fatalis individuals less than 4 to 7 months of age were not typically preserved at Rancho La Brea. On the whole, S. fatalis appears to have had delayed dental development compared to dental development in similar-sized extant felids. This technique for absolute ontogenetic age determination can be replicated in other ancient species, including non-saber-toothed taxa, as long as the timing of growth initiation and growth rate can be determined for a specific feature, such as a tooth, and that growth period overlaps with the development of the other features under investigation.

Fig 1. Smilodon fatalis specimen UCMP 152565 with partially formed permanent upper canine.
(A) Photograph of UCMP 152565. Scale bar represents 1 cm. (B) Image of the 3D model created from the uCT data of UCMP 152565. The model represents the proximal-most portion of the canine. Dark brown color indicates completely mineralized enamel, whereas light brown is unfinished or unmineralized portion of canine. Scale bar represents 1cm. (C) A slice from the uCT data of UCMP 152565. ... ne.0129847
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