This Ancient And Ginormous Sloth Had an Unexpected Supplement in Its Diet

According to new research, a giant ground sloth lived in the last ice age and was not strictly vegetarian, but enjoyed eating meat.
Mylodon darwinii, along with many other megafauna, went extinct 10,000-12,000 years ago. Scientists had assumed it only ate plants. However, chemical signatures found in M. darwinii's hair suggest otherwise. They are compared to other extinct and still living sloth species and anteaters.

Julia Tejada, a paleontologist at the University of Montpellier in France, says these results are "the first direct evidence of omnivory within an ancient sloth species." These sloths have been a significant part of South American ecosystems for the past 34 millions years, along with other xenarthrans like armadillos and anteaters.

Since all six species are sloths, it has been long believed that M. darwinii, named after Charles Darwin, who found its remains in Argentina in 1832, was also a plant-loving herbivore. M. darwinii's jaw, teeth, large foregut, and dung indicate that it was not an active predator.

This new research changes all that. It suggests M. darwinii might have been a meat-curious, scrap-collecting scavenger, or an opportunistic, omnivore, eating meat and other animal proteins if they were available.

Tejada says that it is impossible to determine whether they were sporadic or opportunistic users of animal protein from our research. "But, we now have strong evidence disproving the long-held belief that all sloths are obligate herbivores."

Some researchers speculated in the past that ancient South American ecosystems had more herbivores then could be supported by available plants. This idea is still untested. However, the new study gives some insight into what other heavy animals such as Mylodon were eating in order to supplement their diets.

Scientists are now rethinking the position of M. darwinii in the food chain and reevaluating ecological structure of ancient mammalian societies that lived in South America millions years ago, long before the megafauna disappeared.

Tejada and his colleagues studied hair strands taken from two sloth fossils and five modern zoo fed xenarthrans. They also examined hairs taken from eight wild omnivores, including the screaming-hairy armadillo, and the black-capped squirrel monkey.

Julia Tejada, Paleontologist, with a three-toed Sloth (Bradypus variegatus), in Peru. (Carmen Capuay).

Darwin's ground slotshs, like other megafauna were huge. M. darwinii was one of hundreds of fossil sloths who once roamed the icecapped Americas. It measured almost 3 meters (10 feet) from head to toe and weighed between 1,000 and 2,000 kilograms (2.200 to 4.400 pounds).

These gentle giants lived close to the coast and had blond fur, skin with bony deposits called Osteoderms. It's these tissues that keep chemical markers alive and make them available for analysis today.

Tejada and his colleagues were looking for stable nitrogen isotopes within the hair of the sloths. These chemical variants can be found in different foods, such as plant matter or protein. These isotopes slowly become part of the protein building blocks (aka amino acids) and are preserved in animals' tissues, including their hairs.

To determine if omnivores eat a mixture of plants and animal proteins, Tejada and his colleagues first tested amino-acid nitrogen levels from modern herbivores. Then they analyzed fossils.

M. darwinii skins and dung are on display at American Museum of Natural History. (AMNH/D. Finnin

The study revealed that Nothrotheriops shastensis was the extinct ground sloth, and was probably an obligate herbivore. However, M. darwinii's data suggests that he was not and likely consumed a diet similar the modern-day American Pine Martten, a type weasel only found in the northern regions of North America.

The researchers wrote in their paper that Mylodon's feeding habits were more like an omnivore. It eats plant material, but may also include animal products in its diet.

These results and the fact that M. darwinii lived in icy Americas, suggest that the research team believes the giant sloth supplemented his diet with energy-rich meat as a way of increasing its metabolism and keeping it cool.

It is amazing how much large, plant-munching herbivores can have an impact on the structure of a ecosystem's vegetation, soil moisture, carbon cycle, and other factors. Knowing that at least one extinct species of sloth ate more than plants may change our understanding of what types of vegetation dominated the landscapes of ancient times could help us to understand the nature of those vegetations.

The research team concluded that this would be true if Mylodon and other fossil sloth species had more varied feeding habits than previously thought.

Scientific Reports published the study. The UK's Natural History Museum has a 3D model that shows the first M. darwinii specimen Charles Darwin found.