Pleistocene diet: tough on teeth.

For a predator, dinner is always catch as catch can. But the saber-toothed cats and other large carnivores living in America at the end of the last ice age had a particularly difficult time finding enough food, according to a study of teeth preserved in the tar pits of Los Angeles' Rancho La Brea. The preponderance of jaws with broken teeth suggests that carnivores back then had to crunch on bones or pick them clean in order to get their fill.

Blaire Van Valkenburgh and Fritz Hertel of the University of California, Los Angeles, analyzed specimens dating from the late Pleistocene epoch, 36,000 to 10,000 years ago, when Earth was emerging from the latest ice age. The most plentiful fossilized teeth at Rancho La Brea belong to coyotes and three species of extinct animals: the American lion, the saber-toothed cat, and the dire wolf.

Compared with modern carnivores, the animals that died at Rancho La Brea had a far higher frequency of broken teeth. The tar pit animals fractured between 5 and 11 percent of their teeth, whereas existing predators break only 0.5 to 2.7 percent, the researchers report in the July 23 SciENCE.

The researchers also found a high proportion of broken teeth among ice age remains of dire wolves in Mexico and Peru, suggesting that this pattern occurred elsewhere, not just at Rancho La Brea.

Among modern carnivores, those that eat bone, such as the hyena, run the greatest risk of fracturing their teeth. Van Valkenburgh and Hertel therefore propose that carnivores from Rancho La Brea broke many teeth because they ate or gnawed on bones more often than their modern counterparts do. These early carnivores may have been forced to consume as much of their kill as possible because prey was scarce or because predators faced stiff competition.

The teeth story from the tar pits could reflect how the ecosystem of North America was changing in response to a wave of extinctions that wiped out most of the larger mammals on the continent between 13,000 and 10,000 years ago. This was the time when mastodons and mammoths disappeared, as did camels, many species of horses, and super-size elk. With their prey vanishing, predators may have had to alter their feeding practices, the researchers suggest.

Paleontologist Russell Graham of the Illinois State Museum in Springfield praises the study, saying, "It's a novel way of trying to figure out what the feeding strategy of these animals was. A lot of previous studies have looked at this in a subjective way, but Van Valkenburgh has found a way to quantify this and test it."

The new findings could rekindle the debate concerning the causes of the late Pleistocene extinctions. Paleontologists have traditionally explained the die-offs as the result of climate change at the end of the ice age. But some argue that human hunters, arriving from Asia, sped across the virgin continent, wiping out the big herbivores (SN: 3/27/93, p. 197).

If future teeth studies show that carnivores altered their habits long before humans came to North America, that would bolster the climate change hypothesis, Graham says.