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From the Horse's Mouth

By Sean Henahan, Access Excellence

horse doctorGainesville, FL (2/4/98)- A bit of scientific detective work with some 5 million year-old horse teeth provides new information on the climate and ecology of prehistoric Florida while calling into question current concepts of horse evolution.

Paleontologists at the University of Florida combined two scientific techniques in a new way to analyze fossilized horse teeth that had been found in mine shafts. Dr. Bruce MacFadden and colleagues were able to cross-reference data obtained from radioisotope carbon dating of the teeth with analyses of scratches and pits found in the teeth.The combined data suggest that the horses ate a combination of foods from a savannah-like grassland interspersed with lush forests and marshy wetlands.

Photo: University of Florida paleontologist Bruce MacFadden measures fossil horse teeth.

MacFadden and his team ground up small parts of the horses' tooth enamel and chemically analyzed them via mass spectrometry. This yields data on the kind and proportions of carbon in the teeth. Soft vegetation and grasses have different spectrometric signatures.

"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. 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," said MacFadden.

MacFadden's research involved six species of extinct horse known as the Bone Valley Horses. Evolutionary studies indicate that horse living 55 million years ago had short-crowned teeth, suggesting a diet of leafy and soft plants. But 20 million years ago things began to change dramatically, and an explosion of new horse species arose, many with high-crowned teeth better adapted for grazing on abrasive plants, particularly grasses. The Bone Valley Horses all had high-crowned teeth. But studies of pits and scratches on the teeth suggest a diet of soft leafy materials and hard scratchy grasses, either alone or in combination.

"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.

"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."

The research appears in the Feb. 5, 1999 issue of the of the journal Science.

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