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Uncertain coexistence

Marks on a fossil suggest that Paleoindians interacted with a giant ground sloth 12,500 years ago

Artist’s rendering of Eremotherium laurillardi, a giant ground sloth that lived in the Americas until about 12,000 years ago

Rodolfo NogueiraArtist’s rendering of Eremotherium laurillardi, a giant ground sloth that lived in the Americas until about 12,000 years agoRodolfo Nogueira

Paleontologist Mário Dantas was a PhD student in August 2010 when he found two pieces of a fossil that fit together perfectly to form a pointed cone. Under the Northeastern sun, he and his colleagues examined a pile of fossilized prehistoric animal bones on the São José farm in the municipality of Poço Redondo, in Sergipe State. “I thought it was the tooth of a saber-toothed tiger, but I wasn’t sure,” recalls Dantas, who is now a professor at the Multidisciplinary Health Institute of the Federal University of Bahia (UFBA).

Now, after several analyses and more accurate dating, he and his colleagues are convinced that the fossil is the tooth of a giant ground sloth that was manipulated by humans. A Paleoindian who lived in that region likely polished the tooth—originally shaped like a long rectangular rod—into a sharp point, long after the animal died, about 12,500 years ago.

This finding adds to the number of signs—all of them still controversial—that prehistoric peoples in Brazil coexisted with Quaternary megafauna, large animals such as saber-toothed tigers and giant ground sloths. These animals are thought to have lived in the Americas between 2.6 million and 12,000 years ago. Some became extinct when humans began to populate the continent. “In North America there are well-documented sites displaying evidence that man killed or processed the bodies of megafauna animals,” says biologist Alex Hubbe of the University of São Paulo (USP), who recently analyzed possible vestiges of the coexistence of humans and megafauna animals in Brazil. South America has fewer sites, a few in Argentina and others in Brazil. “Here, the evidence is questionable,” he says.

In 2010, Dantas and archeologist Albérico de Queiroz of the Federal University of Sergipe observed something strange in the fossil tooth. “Using magnifying glasses, we found deep parallel marks on the sides and back of the tooth. They were too regular to have occurred randomly, hence indicating that someone had made the marks with the intention of molding the object,” Dantas says. “Had the marks been made by flowing water or trampling animals, they would be shallow and skewed in several directions.”

He also pointed out that the marks had smooth edges, suggesting that they were made before the tooth became fossilized. And he called attention to the fact that the color of the material is the same on the edges and in the grooves, which indicates that the marks are as old as the tooth itself.

Years later, Dantas showed his find to paleontologist Cástor Cartelle of the Pontifical Catholic University of Minas Gerais, a leading expert on Brazilian megafauna. At first, Cartelle supported the idea that the fossil was the tip of a saber-toothed tiger fang. He changed his mind after the publication of Dantas’ article in 2012, after Jorge Ferigolo, a paleontologist at the Zoobotanical Foundation of Rio Grande do Sul, helped the UFBA researcher confirm that the internal structure of the tooth was undoubtedly the only species of Eremotherium laurillardi, a giant ground sloth that lived in the Northeast. “Sloths have square-shaped teeth,” explains paleontologist Mario Cozzuo of the Federal University of Minas Gerais, Dantas’ thesis advisor, who was also slow to be convinced. “It’s clear that a fragment from the tooth was polished and manipulated into a point; the uncertainty was in knowing when that happened.”

If he were to use the most common dating method, Dantas would have to extract 10 grams of collagen from the fossilized bone, which would destroy the tooth. Instead, he chose to use a less aggressive method, available to him only within the past year, that measures the carbon-14 deposited in the mineral apatite and requires a much smaller sample (less than three grams). Through this method, a laboratory in the United States determined that the tooth is likely between 12,742 and 12,562 years old—close to the oldest evidence of human settlements in the state of Sergipe. Archeologists have recently found signs of campfires made 11,000 years ago in Canindé, a municipality near Poço Redondo that is famed for ceramics and stone tools made by Paleoindians.

Hubbe notes that the dating method used by Dantas is not accepted by most researchers because it is less accurate. “The pattern of the marks in bones and teeth also constitutes problematic evidence,” he says. “Natural processes can imitate human activity. With regard to the coloration, Hubbe suggests that the tooth could have been completely stained another color through some natural process that occurred after it was presumably polished and thrown onto the pile. Everything that they [Dantas and his colleagues] are arguing may have occurred,” Hubbe says. “But we need to have a better understanding of the history of formation of the fossiliferous deposit where the tooth was found before we can judge the conclusion to be sound.”

“At the same site we found fragments of ceramics and stone tools, but everything was out of context,” Dantas acknowledges. The Poço Redondo site is what people in Sergipe call a “tank”. These are natural depressions in the terrain that fill with sediments accumulated over thousands of years. They hold a treasure for paleontologists: skeletons of animals that died nearby and were dragged along by rains to these “tanks.” Dantas and his colleagues found fossils from 13 extinct species varying in age from 27,000 to 11,000 years. “But water confuses everything by mixing together fossils and artifacts of different ages,” explains the researcher, who hopes to eventually map the marks on the sloth tooth with an electron microscope and come away with a better reconstruction of how they were made. “That kind of study would put an end to the question.”

Scientific article
DANTAS, M. A. T. et al. Dated evidence of the interaction between humans and megafauna in the late Pleistocene of Sergipe state, Northeastern Brazil. Quaternary International.  V. 352, p. 197-99. Oct. 2014.