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Encoded lunch. Paleoecologist Larisa DeSantis drills into the enamel of a fossilized llama tooth to find out what kinds of foods it ate more than a million years ago.

Mary Warrick/Florida Museum of Natural History

Ancient Mammals Not So Finicky

More than 1 million years ago--as an ice age withered--the world warmed, glaciers shrank, and vast forests gave way to sprawling grasslands. The ancient deer, llamas, and peccaries that had spent thousands of years eating tree leaves had to make a decision: stay and eat the grass or move north with the shifting woodlands. Scientists have long thought that the mammals were too fussy to forgo their favorite food, but new research shows that their palates were surprisingly adaptable. The findings may help researchers understand how animals will respond to climate change in the future.

Paleontologists can tell what animals were eating because the isotopic signature of foods is preserved in their teeth. For example, grasses tend to contain more of an isotope of carbon known as carbon-13 than leaves and shrubs do. Paleoecologist Larisa DeSantis of the University of Florida, Gainesville, decided to apply the methodology to ice age mammals experiencing a major climate transition. Her team analyzed the teeth of several ancient animals, including deer, llamas, peccaries, mastodons, and tapirs, that once roamed a relatively cool Florida about 1.9 million years ago. The group also looked at the same type of animals from about 1.3 million years ago, when Florida was much warmer.

The animals' diets changed substantially between the two periods, the team reports this week in PLoS ONE. Most mammals from the warmer period had more carbon-13 in their teeth than did the animals from the colder period, suggesting that they ate new foods. Peccaries and llamas shifted to a mixture of grass and tree foliage, for example, whereas deer ate leaves from less-dense forests. Not everyone changed: The tapir, for one, continued to munch on tree leaves. Overall, the findings suggest that, rather than migrate several hundreds of kilometers to follow their usual foods, most of these ancient mammals stuck it out and adjusted their diet to work with the changing cuisine.

Mark Clementz, a paleontologist at the University of Wyoming in Laramie, says the findings may apply to modern animals: "[It's] a nice model for what we could expect for some of the scenarios for rapid climate change today." Still, Clementz notes that the study looks at only diet, and there are additional factors that affect animals' ability to adapt to climate change, such as temperature and humidity tolerance.