December 27, 2012
Starvation Was Not An Issue For Late Pleistocene Saber-tooth Cats And American Lions
April Flowers for redOrbit.com - Your Universe Online
A new study, led by Vanderbilt University, reveals that American lions and saber-toothed cats that roamed the North American continent in the last Pleistocene were living well off the fat of the land. The results of this study, published in PLOS ONE, were gathered from microscopic wear patterns on the teeth of these great cats recovered from the La Brea Tar Pits in southern California.
The study, contrary to prior analysis, did not find any indications that the giant carnivores were having trouble finding prey in the period just before their extinction 12,000 years ago. Contradicting previous dental studies, these new results present a problem for the most popular explanations for the Megafaunal — or Quaternary — extinction when the great cats, mammoths and other large mammals 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. "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."
UCLA researcher Blaire Van Valkenburgh published a paper in 1993 on tooth breakage in late Pleistocene large carnivores. She analyzed teeth from American lions, saber-tooth cats, dire wolves and coyotes found in La Brea. Van Valkenburgh found that they had approximately three times the number of broken teeth of contemporary predators, concluding, "...these findings suggest that these species utilized carcasses more fully and likely competed more intensely for food than present-day large carnivores."
The Vanderbilt researchers used a new technique, called dental microwear texture analysis (DMTA), developed by Peter Ungar of the University of Arkansas. DMTA uses a confocal microscope, which produces a 3D image of the tooth's surface. This image is then analyzed for microscopic wear patterns. Eating red meat creates small parallel scratches, while chewing bones adds larger, deeper pits to the teeth. Dental wear analysis in the past relied on researchers identifying and counting these different features. DMTA, on the other hand, relies on automated software, making it more accurate because it reduces the possibility of observer bias.
The team, which also included scientists from East Tennessee State University, applied DMTA to the fossil teeth of 15 American lions — Panthera atrox — and 15 saber-tooth cats — Smilodon fatalis. All of the cats were recovered from the La Brea tar pits in Los Angeles.
The DMTA analysis revealed that the wear pattern of the American lion teeth most closely resembles those of the modern-day cheetah, which actively avoid bones when it feeds. The wear pattern of the saber-tooth cats teeth resemble that of the present-day African lion, which indulges in some bone crunching when it eats. Previous microwear analysis, using a different technique, concluded that saber-tooth cats largely avoided bone.
The research team examined the pattern changes over time by selecting specimens from tar pits of different ages. They ranged from approximately 35,000 to 11,500 years ago. The scientists did not find any evidence that the two carnivores increased their consumption of carcasses during this period. In fact, their analysis suggested that the proportion of carcasses both kinds of cats consumed actually declined towards the end. Although the team acknowledges the high rate of tooth breakages in the prior study, they find it is more likely the result of breakage from taking down prey, not 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 which regularly chew and crack the bones of their kills, such as hyenas, are as likely to break the rear teeth they use for chewing as their front canines. Species which avoid bones during feeding, however, like the cheetah, are twice as likely to break canines than rear teeth, suggesting that they are more likely to break canines while pulling down prey.
According to the study, previous examinations of the jaws of American lions and saber-tooth cats from this period found three times more broken canines. They interpret this as additional evidence to support their conclusion that most of the excess tooth breakages comes from capture, not feeding.
The team also argues that the large size of the carnivores and their prey helps to explain the high number of broken teeth. Saber-tooth cats were similar in size to the present-day African lion, and the American lion was about 25 percent larger. Their prey included mammoths, four-ton giant ground sloths and 3,500-pound bison.
Because large teeth break more easily than small teeth, the researchers argue that larger carnivores are likely to break more canine teeth when attempting to capture such large prey, citing a study that modeled the strength of canine teeth. The model showed that the canines from a predator the size of a fox can support more than seven times its weight before breaking. The canines of a lion-sized predator, however, can only support about four times its weight. The curved teeth of the saber-tooth cat present a greater challenge, only being able to support about twice the animal's 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 cannot 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."