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A new way to study extinct animals' diets

Fossil teeth and other skeletal tissues hold many clues to an extinct animal's diet. But a new study by National Science Foundation-funded researchers challenges a long-held assumption that all plant-eating mammals, from the tiniest shrew to the largest sloth, can be approached the same way. To glean details about the diets of long-extinct animals, paleontologists have historically focused on fossil teeth and jaws: tooth shape, tooth enamel wear and tear and the shape of skull and jaws all offer clues. One relatively recent method of analyzing teeth and other biological tissues hinges on a specific biomarker: stable carbon isotopes. Found in different proportions in various plants, stable carbon isotopes are also preserved in the tissues of the animals that consume vegetation, offering paleontologists a window into the diets and other features of extinct animals' environments. Until now, scientists had assumed that all plant-eating mammals absorbed carbon isotopes from plants, similar to how cows and other large ungulates do today, at a constant proportion of 14 per mil (or 14 parts in a thousand). That constant, called an enrichment value, is widely used in calculations for geochemical analyses of animal skeletal tissues. But a new study challenges that assumption, and shows that enrichment value fluctuates based on body size.

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