This ancient and gigantic sloth had an unexpected supplement in its diet

A giant sloth that lived during the last ice age was not nearly as vegetarian as its contemporary tree-dwelling relatives, but enjoyed munching on meat, according to a new study that has found evidence of its diet in fossilized hair samples.

Mylodon darwinii became extinct about 10,000 to 12,000 years ago along with most other megafauna, and scientists had assumed that it only ate plants. But a comparison of chemical signatures in M. darwinii‘s hair for the diet of other extinct and living species of sloths and anteaters now suggests something else.

These results are the “first direct evidence of omnivores in an ancient sloth”, says paleontologist Julia Tejada from the University of Montpellier in France. Along with other xenarthrans, such as anteaters and armadillos, these sloths have been a major part of South American ecosystems for the past 34 million years.

Given that all six species of live sloths are herbivores, it was long thought that M. darwinii -which was named after Charles Darwin, who discovered its remains in Argentina in 1832-was also a plant-loving herbivore. Its teeth, jaw, large front and manure all suggest it M. darwinii was no active predator.

But this new research abolishes that mindset and proposes M. darwinii could have been a meat-curious scavenger who picked up leftovers, or even an opportunistic omnivore, by chopping down meat or other animal protein if available.

“Whether they were sporadic scavengers or opportunistic consumers of animal protein cannot be determined from our research,” says Tejada. “But we now have strong evidence to contradict the long-held presumption that all sloths were obligatory herbivores.”

In the past, some researchers have speculated that the ancient ecosystems of South America had more herbivores than could be supported by the available plants. Although that idea is still untested, this new study provides some clues as to what other feral animals like Mylodon ate to supplement their diet.

The results also prompt researchers to reconsider where M. darwinii sits in the food chain and reevaluates the ecological structure of ancient mammal communities that lived in South America millions of years ago before most megafauna became extinct.

In the study, Tejada and colleagues analyzed hairs plucked from two lazy fossils, five modern zoo-fed xenarthrans and eight wild omnivorous species, including the screaming hairy armadillo and the black-covered squirrel beak.

A double sloth (Bradypus variegatus)
Paleontologist Julia Tejada with a three-toed sloth (Bradypus variegatus) in Peru. (Carmen Capuñay)

Like other megafauna, Darwin’s earthworms were really big creatures. Among hundreds of other fossil sloths that once roamed the ice-covered America, M. darwinii measured nearly 3 meters (10 feet) from top to toe and weighed in at an estimated 1,000 to 2,000 kg (2,200 to 4,400 pounds).

But these gentle giants who lived near coastal areas also had blond fur and skin filled with bony deposits called osteoderms, and it is these types of tissues that preserve chemical markers that are available for analysis today.

Stable nitrogen isotopes in the hair of sloths were the target of Tejada and colleagues, as these chemical variants are found at different levels in foods such as plant material and protein. When animals eat these foods, nitrogen isotopes are slowly incorporated into the building blocks of proteins (aka amino acids) and preserved in an animal’s body tissues, including hair.

Tejada and colleagues first analyzed amino acid nitrogen levels in samples from modern herbivores and omnivores to find a clear signal of eating a mixture of plants and animal protein versus plants alone and then analyzed the two fossils.

M. darwinii fossils exhibitedM. darwinii skin and fertilizer on display at the American Museum of Natural History. (AMNH / D .. Finnin)

While the other extinct ground laziness in the study, Nothrotheriops shastensis, was probably a mandatory herbivore, the data suggest M. darwinii did not and probably ingested a diet similar to today’s American pine mares — a kind of weasel found in the northern parts of North America.

“[Mylodon’s] feeding behavior is better suited to that of an omnivore that consumes plant material, but sometimes also incorporate products of animal origin into its diet, “the researchers write in their paper.

Based on these results, and given the icy conditions in America, when M. darwinii and other megafauna lived, the research team suspects that the giant sloth supplemented its diet with high-energy meat to meet its high energy needs, as a way to increase its metabolism to maintain a constant body temperature under cooler conditions.

Knowing how large herbivorous herbivores greatly affect the vegetation structure, soil moisture and carbon cycle of an ecosystem, and finding that at least one extinct sloth ate more than just plants, could change our understanding of the vegetation types that dominated ancient landscapes back then.

“This would be especially the case if in addition Mylodon, other fossil sloths also had more versatile feeding behaviors than was traditionally thought, “the research group concludes.

The study was published in Scientific reports. You can also see a 3D model of the very first sample of M. darwinii found by Charles Darwin here, with permission from the British Museum of Natural History.

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