Giant ground sloths have often been portrayed as gentle giants of the ice age. Much of their anatomy, from their flat molars to their vat-like guts, seems consistent with a diet centered around the Pleistocene salad bar. But now there is evidence that some giant ground sloths had more cosmopolitan tastes that incorporated flesh.
The crucial clues come from isotopes of nitrogen tied to particular amino acids preserved in the fur of Darwin鈥檚 ground sloth, Mylodon darwinii, an approximately 3-metre-long animal that lived in South America between about 1.8 million and 12,000 years ago. These geochemical signals act as a proxy for diet as nitrogen isotopes from what an animal eats becomes incorporated into the tissues in their bodies, in this case hairs that remained intact for thousands of years.
Different plants and animals have different nitrogen signatures, and palaeontologist at the University of Montpellier, France, and her colleagues found that Darwin鈥檚 ground sloth was an omnivore.
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The results dovetail with what zoologists have come to understand about living sloths. 鈥淭wo-toed sloths are omnivorous, so it鈥檚 not too hard to imagine similar diets in some giant ground sloths,鈥� says , a giant sloth expert at Applied EarthWorks, a cultural resource management company in California.
The key will be finding additional fur samples that allow more species to be examined using the new technique. 鈥淚t would be interesting to see where other sloths would fall on the omnivory to herbivory spectrum,鈥� says Macias, as gross anatomy alone can only go so far in informing an extinct creature鈥檚 diet.
Realising that some giant ground sloths regularly consumed meat alters what paleontologists expect of ancient ecosystems, Tejada鈥檚 team writes. While another fossil sloth in the study named Nothrotheriops shastensis came out as an herbivore in the new analysis, Darwin鈥檚 ground sloth was doing something different. Given that giant sloths were both diverse and common in the Americas during much of the ice age, what they ate shaped their environments.
In fact, palaeontologists have previously noted a seeming lack of meat-eating species in prehistoric South America 鈥� a role that giant sloths may have helped fill.
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