27,000-Year-Old Giant Ground Sloth Tooth is Like a Climate Time Capsule
Fossil discoveries are exciting on their own, but sometimes, they carry even more information about the past. Newly uncovered fossils from an extinct giant ground sloth that lived in Belize 27,000 years ago provide a portrait of what the climate was like for the last year that the sloth was alive, according to a new study.
During the sloth’s lifetime, Belize wasn’t the jungle it is today. It was dry and barren. The Last Glacial Maximum had trapped most of Earth’s water in glaciers and polar ice caps. The sea level and water tables were lower, and water was hard to find.
The giant ground sloth, which could reach over 13 feet tall, was desperate for water. It found relief in a deep sinkhole, but it was never able to climb out.
Divers searching for ancient Mayan artifacts in a natural pool in Cara Blanca in 2014 found a humerus, a femur and part of a tooth belonging to the sloth. The area is a system of 25 lakes and cenotes, or natural sinkholes.
The tooth, only partially fossilized, contained enough tissue that could be tested to show what the sloth ate for the last year it was alive. The analysis also revealed the region’s climate and environment during that time.
The findings of the fossil analysis were published Tuesday in the journal Science Advances.
Studying this fossil wasn’t easy. The giant sloth didn’t have enamel on its teeth like humans and even other giant extinct mammals such as mammoths. Scientists usually use enamel as a way to study a creature’s diet. And most of the time, giant sloth teeth are found completely fossilized, which replaces the tissue with minerals.
The tooth revealed that it contained tissue through cathodoluminescence microscopy, which can show how much something has fossilized. The researchers drilled for samples of orthodentin, a type of dense tooth tissue, from the nearly 4-inch-long tooth.
“This allowed us to trace monthly and seasonal changes in the sloth’s diet and climate for the first time, and also to select the best part of the tooth for reliable radiocarbon dating,” Stanley Ambrose said in a statement. He’s a study author and University of Illinois at Urbana-Champaign anthropology professor.
During the last year of its life, the sloth endured a seven-month dry season that was bookended by two short rainy seasons. Rather than a forest, the sloth lived in the open grasslands of a savanna. A variety of plants made up its diet during both seasons.
That diverse diet may be why sloths persisted even as other giant mammals went extinct around them. The sloth was also able to live in areas from southern Brazil to North America’s Gulf and Atlantic coastal regions.
“We were able to see that this huge, social creature was able to adapt rather readily to the dry climate, shifting its subsistence to relying upon what was more available or palatable,” said Jean Larmon, lead study author and graduate student at the University of Illinois, in a statement.
Lisa Lucero, study author and University of Illinois at Urbana-Champaign anthropology professor, said, “This supports the idea that the sloths had a diverse diet. That helps explain why they were so widespread and why they lasted so long. It’s likely because they were highly adaptable.”
But it also reveals what might have led to their downfall.
The findings “add to the evidence that many factors, in addition to a changing climate, contributed to the extinction of megafauna in the Americas,” Lucero added. “One of those potential factors is the arrival of humans on the scene 12,000 to 13,000 years ago.”