Giant sloths, massive animals that lived in the Americas during the Ice Age, subsisted on an exclusively plant-based diet, according to an isotopic analysis of bones reported in the journal Gondwana Research.

Sloths may well rank among the world’s most peculiar animals: with their backs pointing downward, they hang in trees and move in slow motion from branch to branch with the aid of their sickle-shaped claws.

“The extinct relatives of the sloths lived up to 10,000 years ago, for example the species Megatherium,” said study lead author Professor Hervé Bocherens, from the Senckenberg Center for Human Evolution and Palaeoenvironment at the University of Tübingen in Germany.

“They could reach the size of an elephant and were much too heavy to spend a significant amount of time in the trees. Instead, they lived on the ground, where they excavated large burrows.”

“For many years, their dietary habits were an enigma; the long claws on their hands and feet, in particular, gave rise to various speculations.”

Prof. Bocherens and co-authors completed an isotopic analysis of collagen extracted from the sloth bones.

“Our measurements show that Megatherium lived on an exclusively vegetarian diet,” Prof. Bocherens said.

“In carnivores, the proportion of proteins is significantly higher than in herbivores, which primarily eat food high in carbohydrates. These differences can be documented in the isotopes.”

In order to reinforce their results, the researchers compared their data with more than 200 bones from modern mammals, whose diet is known, as well as with fossil specimens from both carnivores and herbivores.

“Knowledge of the sloths’ feeding habits is important in order to understand their role in past ecosystems,” Prof. Bocherens said.

“Moreover, the results can help us understand the interactions between Megatherium and the first human inhabitants of America — their habitats overlapped for several thousand years, before the giant sloths became extinct.”

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Hervé Bocherens et al. 2017. Isotopic insight on paleodiet of extinct Pleistocene megafaunal Xenarthrans from Argentina. Gondwana Research 48: 7-14; doi: 10.1016/j.gr.2017.04.003