UF Researcher, New Techniques Help Reconstruct Ancient Diets

Out of the mouths of long-dead animals come stories of vanished landscapes, ancient weather and the way the creatures lived and died.

With a unique combination of two scientific techniques, University of Florida paleontologist Bruce MacFadden and colleagues analyzed fossilized horse teeth to see what the animals ate, and in doing so reconstructed Florida's environment as it existed 5 million years ago.

MacFadden's article in this week's issue of the journal Science describes how he analyzed ratios of carbon isotopes along with the scratches and pits in the fossilized teeth found in Lakeland phosphate mines. He concluded that the horses ate a combination of foods befitting an ancient Florida of savannah-like grasslands interspersed with lush forests and marshy wetlands inhabited by rhinos, llamas, elephants and other exotic creatures.

"This study is noteworthy because it's the first to be published that looks at the combination of these two techniques to understand ancient diets and the ecology of a particular group of extinct mammals," he said. "These techniques are revolutionizing our ability to understand what prehistoric animals ate. Before now, the only way we could figure that out was by looking at their teeth. Not only that, our research challenges the traditional view that the form and structure of the teeth alone can tell you something about diet."

Modern grazers such as horses and zebras develop elongated (high-crowned) teeth because they eat gritty, abrasive grasses, while browsers such as deer, whose diet consists mainly of soft leafy vegetation, have short teeth, MacFadden said.

But MacFadden's research on six species of prehistoric horses that lived 5 million years ago shows that despite all the horses having elongated teeth, they were a combination of browsers, grazers and mixed feeders. "This is the first time we've been able to use other techniques to challenge this assertion that the height of a tooth is uniquely indicative of diet," he said.

MacFadden believes the reason all these particular species had elongated teeth is that elongated teeth also existed in their ancestors, who were grazers.

The findings support modern ecological theory that animals who live together divide up the food supply in order to minimize competition for the same resources, he said.

"This is a milestone study," said John M. Rensberger, a professor in the department of geological sciences and curator of vertebrate paleontology at the University of Washington's Burke Museum. "The research by MacFadden and colleagues provides impressive quantitative evidence that permits precise statements to be made about a partitioning by these related genera of dietary resources between grass and leaf floras."

Learning about changes in the diets of ancient animals is important because it provides clues about how species interacted at certain points in time, MacFadden said. "If all the animals in a particular area were feeding on the same resources and there was a big extinction, you might suspect something about their diet affected the extinction.

"It also gives a lot of information about ancient environments," he said. "If you have a community of ancient animals that are all found to be grazers, then you can infer that the environment of the local habitat was grassland. If the animals are all browsers, then you can infer that there was more forest or scrub. It can give you a broad perspective over millions of years what animals fed upon and what changes occurred in the plant communities."

For this work, MacFadden ground up small parts of the horses' tooth enamel and chemically analyzed them, using an instrument called a mass spectrometer, to determine the kind and proportions of carbon in the teeth. Because of photosynthesis, the way carbon molecules are incorporated into leaves, fruits and other soft vegetation is different from the way they become a part of grass, with the different carbon makeup showing up in the teeth.

The study, supported by the National Science Foundation, also involved the microscopic analysis of scratches and pits on the teeth to determine whether the horses were browsers or grazers. Because it is abrasive, grass forms scratches on the tooth enamel when chewed, while the compression of leaves form pits on the teeth, he said.

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