Their current relatives only mill leaves – but apparently not all representatives of the extinct giant sloths were also strict vegetarians: Mylodon was an omnivore, according to characteristic compounds in the mummified fur remnants of these Ice Age inhabitants of South America. Presumably, in addition to their vegetarian diet, the animals also liked to mess with carrion, the scientists explain. In another representative of the giant sloth, however, they only found indications of a plant-based diet.
Today there are only six species of sloth that leisurely maneuver through the branches of the tropical forests of Central and South America, eating leaves. However, until about 10,000 years ago, these tree dwellers still had gigantic relatives, some of them gigantic: Numerous species of giant sloths trudged through the landscapes from Alaska to the tip of South America, as is known from extensive fossil finds, due to tooth features, the biomechanics of the jaws and the fact that they are If all of today’s sloths feed exclusively on plants, it was previously assumed that the gigantic representatives of this group of animals were also pure vegetarians.
So far, this has also seemed to be confirmed by study results in the case of the comparatively well-studied giant sloth Mylodon darwinii, which may have lived in South America up to 10,000 years ago: When investigating the fossilized feces of these animals weighing up to two tons, researchers only found remains of vegetable food. But how the researchers working with Julia Tejada from the University of Montpellier explain that traces of carnal food could have remained undetected during these analyzes, as they are digested with almost no residue. So it seemed possible that some giant sloths might have consumed meat on occasion after all. Were at least some of them omnivores after all – similar to bears?
On the trail of the diet in fossil hair
The researchers investigated this question in the case of Mylodon and another giant sloth species – Nothrotheriops shastensis, a rather smaller species from North America. The reason for choosing these two species was a peculiarity: in contrast to other representatives of the giant sloth, mummified fur parts were also found. This made it possible to use an examination method based on the detection of certain nitrogen isotopes that are bound in the amino acids of animal body tissues. They occur in different proportions in the food consumed by an animal and are therefore also found in body structures such as hair. By analyzing the isotope patterns, conclusions can be drawn about the diet of an animal, the researchers explain. Specifically, the signatures can be used to determine whether it is a herbivore, omnivore or pure carnivore.
In order to gain comparative information, the researchers first recorded the nitrogen isotope profiles in hair samples from modern sloths, known to be vegetarian, as well as from a wide range of modern omnivores from scientific collections. As they report, the results initially showed that the relative isotope values of the amino acids glutamate and phenylalanine clearly reflect the respective diets. The scientists were then able to compare the patterns with those they found when examining the fossil hair samples from the two giant sloths.
Occasionally carrion
It turned out that the isotope profile of the hair of Nothrotheriops shastensis matched that of today’s sloths – it was apparently also a pure vegetarian. But the results for Mylodon differed significantly from this finding: the profile matched that of the omnivores from the comparison group. Apparently, these representatives of the giant sloths consumed animal proteins in addition to a vegetable diet. It seems unlikely that they were active predators, but they probably devoured carrion on occasion, the scientists explain. “At least we are now delivering results that contradict the long-standing assumption that all sloths were obligatory herbivores,” says Tejada.
The extent to which this diet was widespread among the many different species of giant sloth remains unclear, but a certain flexibility in the food sources of these animals now seems plausible. The results also shed new light on their role in the ancient ecosystems, say the scientists: “The first direct evidence of omnivorousness in an extinct species of sloth requires a reassessment of the entire ecological structure of ancient mammalian communities in South America. Because the sloths have been an important component of these ecosystems there over the past 34 million years, ”says Tejada in conclusion.
Source: American Museum of Natural History, specialist article: Scientific Reports, doi: 10.1038 / s41598-021-97996-9