Surprisingly, he occasionally feasted on a piece of tender meat.

The six present-day sloth species are all relatively small, vegetarian and especially very lazy arboreal inhabitants that can be found in the tropical forests of Central and South America. But long ago, bizarre specimens roamed too – some as big as elephants! – through the ancient landscapes of Alaska to the southern tip of South America. Mylodon darwinii was one such. And in a new study researchers reveal a special fact about this giant species.

Mylodon darwinii

Mylodon is an extinct genus of ground sloths. “And it was gigantic,” researcher Julia Tejada describes in conversation with Scientias.nl. “He weighed about 2000 kilograms and was three meters tall. The specimens we analyzed in our study lived in Chilean Patagonia about 14,000 years ago. Mylodon had long hair, thick skin, and large, powerful claws. An interesting feature of Mylodon and other sloths of the same family is the presence of tiny bones embedded in their skin (called osteoderms) that gave them extra protection.”

Skin and poop of the extinct giant ground sloth Mylodon darwinii. Image: AMNH/D. Finnin

In the new study, researchers delved into this bizarre sloth’s diet. Based on dental features, jaws, preserved feces, and the fact that all living sloths eat only plants, it is believed that the giant Mylodon was also an avid herbivore. But what exactly was on his menu?

Study

To get a complete picture, the researchers decided to analyze amino acids (fundamental, biological compounds that are the building blocks of proteins). Certain nitrogen isotopes are locked up in specific amino acids. And from that you can determine exactly what someone has eaten. In addition, such isotopes are preserved in body tissues, including hair and fingernails. This means that even after an animal has already become extinct, you can figure out exactly what it had on its menu. “It does not matter where an animal lives (forest, tundra, desert, etc.) or what it eats (leaves, grasses, fruits, etc.); if an animal is a herbivore, their amino acids will betray that,” Tejada said. The researchers studied samples from seven living and extinct species of sloths and anteaters (which are closely related to sloths) and managed to figure out the diet for each of them.

Not a strict vegetarian

The researchers make the surprising discovery that Mylodon – unlike living relatives and the other extinct ground sloth Nothrotheriops shastensis studied in the study – was not a strict vegetarian. Mylodon was a real glutton who, in addition to juicy, green leaves, also liked the occasional piece of meat. “This is very surprising,” Tejada says. Until recently, sloths were considered purely herbivorous animals. But after studying sloths (both living and fossil specimens) in recent years, I am increasingly convinced that we know almost nothing about the ecology and physiology of these creatures. We have underestimated the ecological versatility of sloths. And our results are proof of that.”

“We underestimated the ecological versatility of sloths”

American marten

The question is, of course, what Mylodon ate; did he actually go hunting for his snack? Or was he simply simply eating what he encountered? “Mylodon was just an opportunistic omnivore, eating meat or other animal protein when available,” Tejada said when asked. “He may have been a scavenger, but he certainly wasn’t a hunter. Our data (and the series of anatomical studies to which the sloth has been subjected) suggest that it was not a predator.” We can only speculate on which specific species the giant sloth was targeting, though Tejada does have an idea. For example, she suspects that Mylodon’s diet was roughly comparable to that of today’s American marten. “This is an animal that eats plants, seeds and fruits, as well as occasionally small vertebrates,” she says.

food web

The researchers have now found strong evidence that contradicts the long-standing assumption that all sloths were exclusively herbivores. It is very important that this has now been clarified, according to Tejada. “Sloths have been an important part of South American ecosystems for the past 34 million years,” she explains. “Understanding the food webs at the time allows us to also gain insight into how stable ecosystems are and how nutrients are transferred.” In addition, prior to this study, some scientists speculated that there may be too few plants available in ancient America to feed all existing herbivores. This means that some herbivores may have been forced to try different foods after all. Although that hypothesis has not yet been tested, the current study shows that certain animals such as Mylodon apparently supplemented their diet with something ‘meaty’ every now and then.

All in all, in their study, the researchers have found a good way to unravel the diet of long-dead animals. The researchers hope that other scientists will follow their example. “The implications of our study go beyond demonstrating the diet of an ancient species,” Tejada points out. “More generally, the study shows how powerful the technique of stable isotopes on specific amino acids is. We therefore hope that our research will prompt others to conduct several studies on the diet of extinct species.”