The extinct ground sloth probably ate meat with its vegetables

A new study by researchers at the American Museum of Natural History suggests that Mylodon– a land sloth who lived in South America until about 10,000 to 12,000 years ago – was not a strict vegetarian like all of his living relatives. Based on a chemical analysis of the amino acids (fundamental biological compounds that are the building blocks of proteins) stored in the sloth’s hair, the researchers found evidence that this gigantic extinct sloth was an omnivore, sometimes eating meat. or other animal proteins in addition to vegetable proteins. question. The study, published today in the journal Scientific reports, contradicts previous assumptions in the field.

“Whether these are sporadic scavengers or opportunistic consumers of animal protein cannot be determined from our research, but we now have strong evidence contradicting the long-held presumption that all sloths were obligate herbivores.” , said lead author Julia Tejada, a museum researcher. associate and postdoctoral researcher at the University of Montpellier, France. Tejada started work on this study as a doctoral student. student in the Museum’s Richard Gilder Graduate School collaborative program with Columbia University.

Even though the six living sloth species are all relatively small, arboreal, plant-eaters, confined to the rainforests of Central and South America, there are hundreds of species of fossil sloths, some as large as an elephant, roamed ancient landscapes from Alaska to the southern tip of South America. Mylodon darwinii, also known as “Darwin’s Earth Sloth,” is believed to have weighed between 2,200 and 4,400 pounds and was nearly 10 feet long. Based on dental characteristics, the biomechanics of the jaw, preserved excreta of some very recent fossil species, and the fact that all living sloths feed exclusively on plants, Mylodon and its extinct parents have long been presumed to be herbivores as well. But these factors could not directly reveal whether an animal might have ingested food that requires little or no preparation and is fully digested, as happens with straying carcasses or other types of meat consumption.

To get a more complete picture, the new study uses an innovative approach based on nitrogen isotopes locked into specific amino acids in animal body parts, known as “compound-specific isotopic analysis. ‘amino acids”. Found in varying proportions in the food consumed by an animal, stable nitrogen isotopes are also retained in their body tissues, including hair and other keratinous tissue such as fingernails, as well as in collagen such as that found in teeth or bones. By first analyzing the nitrogen values ​​of amino acids in a wide range of modern herbivores and omnivores to determine a clear signal of consumption of a mixture of plant and animal foods, the fossils can then be measured for determine the food they ate. This gives paleontologists a single window directly into the diets of animals, allowing them to determine their “trophic level” – whether they are plant-eating herbivores, mixed-feed omnivores, carnivorous carnivores or carnivores. specialized consumers of marine animals.

“Previous methods relied only on aggregate nitrogen analyzes and complex formulas that have many untested or weakly substantiated assumptions. Our analytical approach and results show that many previous conclusions on tropical levels are poorly supported at best. , or clearly false and misleading at worst, said study co-author John Flynn, Frick curator of fossil mammals in the museum’s paleontology division.

The researchers used samples from seven living and extinct sloths and anteaters (which are closely related to sloths), as well as a wide range of modern omnivores, from the scientific collections of the museum’s mammalogy and paleontology departments. and the Yale Peabody Museum. While the other sloth extinct from the study, the North American ground sloth Nothrotheriops shastensis, was determined to be an exclusive herbivore, the data clearly indicated Mylodon as omnivorous.

Previous research speculated that there were more herbivores than the plants available in ancient South American ecosystems could support, suggesting that some of these herbivores may have found other food sources. This new study provides compelling evidence to support this previously untested idea.

“These results, providing the first direct evidence of an omnivore in an ancient sloth species, require a reassessment of the entire ecological structure of ancient South American mammal communities, as sloths have been a major component of these ecosystems over the past 34 million years, ”Tejada said. noted.

Other authors of this study include Ross MacPhee, of the American Museum of Natural History; Tamsin O’Connell of the University of Cambridge; Thure Cerling of the University of Utah; Lizette Bermudez and Carmen Capuñay from Huachipa Zoo in Lima, Peru; and Natalie Wallsgrove and Brian Popp from the University of Hawaii at Manoa.