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Giant sloth tooth discovered in a Belize sinkhole. Credit: University of Illinois at Urbana-Champaign.

27,000-year-old tooth reveals hidden insights into the lives of Giant Sloths

Giant sloth tooth discovered in a Belize sinkhole. Credit: University of Illinois at Urbana-Champaign.

Giant sloth tooth discovered in a Belize sinkhole. Credit: the University of Illinois at Urbana-Champaign.

Modern paleontology allows scientists to not only tell what an extinct creature looked like but also how it lived. The exciting discovery of the remains of a giant ground sloth that lived in Belize more than 27,000 years ago is a prime example of this. By studying the extinct sloth’s fossilized tooth, researchers were able to piece together the last year of the animal’s life, revealing new insights into the lifestyle and environment of megafauna we still know little about.

Far from being slow

Tucked between the Caribbean Sea and the eastern coast of Central America, Belize is a small country richly covered in rainforest and home to great biodiversity. For instance, Belize houses the second largest barrier reef in the world. However, during the sloth’s lifetime, Belize looked totally different.

Instead of a dense jungle, Belize used to be barren and dry. This was during the Last Glacial Maximum when massive amounts of water were trapped by icy masses and sea levels were at their lowest.

This means that our sloth — which stood up to 4 meters (13 feet) tall — and other of its contemporary creatures had to subsist on little water. The need for water is what probably led the sloth to a sinkhole from which it never managed to emerge alive. It was found by divers 27,000 years later, who recovered a humerus, a femur, and part of its tooth.

Illustration of giant sloth skeleton alongside human for scale. Credit: the University of Illinois at Urbana-Champaign.

Illustration of giant sloth skeleton alongside human for scale. Credit: the University of Illinois at Urbana-Champaign.

Stanley Ambrose and colleagues at the University of Illinois at Urbana-Champaign faced numerous challenges analyzing the sloth’s 4-inch-long tooth. Unlike other megafaunas, such as mammoths, giant sloth teeth do not have enamel — the hard mineralized surface of teeth that traps information about what a creature ate.

Most of the tooth was also fossilized, meaning much of the original tissue was replaced by minerals. But the researchers worked with what they could. Using a technique called cathodoluminescence microscopy, Ambrose and colleagues isolated the surviving tissue from the minerals. They ended up with 20 samples of orthodentin, the main tissue that teeth are made of, which together represented about one year of growth.

“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,” Ambrose said in a statement.

The tissue showed that the sloth endured a nine-month dry season, with just a three-month rainy season to lighten the load. Judging from what it ate, the sloth lived in a savanna rather than a forest.

The fossilized humerus of the giant sloth. Credit: Lisa Lucero.

The fossilized humerus of the giant sloth. Credit: Lisa Lucero.

The findings show that giant sloths were far from being slow. Instead, they were highly adaptable creatures that lived through periods of great seasonal variability.

“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

An artist’s illustration of an ancient encounter between human hunters and a giant ground sloth. Credit: Alex McClelland/Bournemouth University.

The giant sloth’s resilience in the face of challenging environmental conditions explains why they were so widespread and survived for so long. Climate change is one of the factors that some scholars have pinned to the giant sloth’s demise, which occurred 12,000-13,000 years ago. But the new findings suggest that the creature was highly adaptable. Human hunting now sounds like a more plausible scenario for the giant sloth’s extinction.

The findings were reported in the journal Science Advances.

An artist's illustration of an ancient encounter between human hunters and a giant ground sloth. Credit: Alex McClelland/Bournemouth University.

Fossilized footprints show human hunters stalked giant sloths more than 11,000 years ago

An 11,000-year-old trackway still carries signs of an incredible encounter between human hunters and a mythological-like creature — the now-extinct giant ground sloth. This is the first evidence showing modern humans and giant sloths interacted directly. However, this was no friendly encounter.

An artist's illustration of an ancient encounter between human hunters and a giant ground sloth. Credit: Alex McClelland/Bournemouth University.

An artist’s illustration of an ancient encounter between human hunters and a giant ground sloth. Credit: Alex McClelland/Bournemouth University.

David Bustos, of the National Park Service, had long suspected he’d be able to find fossilized footprints of ancient humans in New Mexico’s White Sands National Monument Park. The dry climate the area has had over the ages provides excellent opportunities for such fossils to be preserved in pristine conditions. Bustos and colleagues struck gold in April 2017, when they found giant sloth tracks — and inside these tracks, they found human footprints. Quite literally, the humans were following the footsteps of the sloth, which they most likely were looking to hunt for food.

Today, the six living species of sloths are usually found dangling from tree branches, or going viral on YouTube. But sloths used to be a lot more diverse—and a lot bigger. The largest giant sloth, called Megatherium, weighed several tons, reached 20 feet in length, and—when reared up on its hind legs—stood over 12 feet tall. That’s about the size of an elephant. However, the White Sands tracks were made by a much smaller ground sloth, either Nothrotheriops or Paramylodon. 

Giant sloth footprints are easy to spot: they’re almost two feet long (30 cm) and a foot wide, shaped like kidneys, and show deep claw marks. In total, the researchers found 251 giant sloth tracks in White Sands from between 15,000 and 10,000 years ago.

The impressions left in the mud, which later become fossilized, suggest that the animal was 7-8 feet tall (up to 2.4 m) when standing on its rear legs. But even so, it would have been a formidable match for any pack of human hunters, with its tight muscles and Wolverine-like claws. According to Bustos who analyzed the fossilized foot, paw and claw marks left at the site, there was actually a standoff between the giant sloth, which reared up on its hind legs, and the humans who were hunting it.

“Human interactions with sloths are probably better interpreted in the context of stalking and/or hunting,” the researchers wrote in the study published in the journal Science Advances. “Sloths would have been formidable prey. Their strong arms and sharp claws gave them a lethal reach and clear advantage in close-quarter encounters.”

Human footprint inside a sloth track. This composite track is part of a trackway in which the human appears to have stalked the sloth. Credit: Matthew Bennett, Bournemouth University.

Human footprint inside a sloth track. This composite track is part of a trackway in which the human appears to have stalked the sloth. Credit: Matthew Bennett, Bournemouth University.

It’s not clear who won but chances have it that the humans, who were only equipped with stone weapons, likely didn’t make the kill. During those times, Bustos says that most human hunts ended in failure. Of course, the standoff might have never happened — instead, the humans might have followed the sloth trail an hour or so later after they were made. Without any butchered bones or artifacts, it’s quite anyone’s guess what happened here.

“The thing that is special about these prints and sets them apart from any other fossil trackways in the world is that this discovery records the interaction between humans and Ice age giant megafauna,” Bustos said. “White Sands National Monument has the largest concentration of human and Ice-age giant megafauna prints in the Americas.”

Beyond the breathtaking story it tells, the ancient trackway reveals how humans and giant ground sloths interacted at the end of the last ice age. The furry giants went extinct around this time, along with other iconic beasts, such as the mammoth and the North American horse. We know that the unforgiving climate made life very challenging for many of these ice age species but more and more evidence suggests humans took an active role in pursuing them. It’s likely that the sad fate of these species was sealed by a lethal combination of climate change and human hunting.

“At the end of the ice age, many of these animals became extinct,” Bennett said. “Were human hunters the cause of this extinction? The footprints at White Sands help us answer this question, by showing how ancient hunters stalked and attacked these fearsome animals.”

Ecosystems still feel the pain of ancient extinctions

The more researchers study ecosystems, the more we learn that an ecosystem behaves, in many ways, just like a living organism: thousands of years after human hunters wiped out big land animals like giant ground sloths, the ecosystems they lived in are still suffering from the effects, much like a body suffers from past trauma.

The giant sloth, imagined in happier days. Image: Jaime Chirinos/SPL

The giant sloth, imagined in happier days. Image: Jaime Chirinos/SPL

Humans wiping out species (directly through hunting or indirectly through habitat destruction) is not really a new thing. Early human hunters have posed a stress on environments for thousands if not tens of thousands of years, because they were so successful and the prey didn’t have enough time to adapt.

Most ecosystems rely on big animals to supply them with nutrients (read: dung fertilizing).

“If you remove the big animals from an ecosystem, you pretty much stop nutrients moving,” says Chris Doughty of the University of Oxford.

In order to understand the impact of this extinction, Doughty and his colleagues studied the distribution of phosphorous – a nutrient that plants need to grow; he analyzed the Amazon basin in South America, an area which was once the home of fantastically large animals, such as elephant-like gomphotheres and giant ground sloths.

Unfortunately for these spectacular animals though, some 12.500 years ago, humans moved to South America, and shortly after this, these animals went extinct due to extensive hunting and climate change. Today, the Amazon basin is home to a huge biodiversity, but there are no more truly big animals – and their extinction still has a massive effect on the distribution of phosphorous throughout the basin.

Using the relationship between animal size and phosphorous distribution, Doughty estimated how much phosphorus South America’s larger extinct animals would have transported 15,000 years ago. His model concluded that megafauna would have spread nutrients 50 times faster than today’s fauna. This happens because big animals carry more food around in their bellies and they also travel more searching for food. It’s just like blood vessels in the body:

When you get rid of big animals, it’s like severing the nutrient arteries.”, says Doughty. He thinks the same thing happened in North America, Europe and Australia, where most big animals have also been wiped out. “The idea that herbivores redistribute nutrients is not new, but the scale of this thinking is much, much bigger,” says Tim Baker at the University of Leeds in the UK.

If his model is correct, than it’s quite safe to assume that the Amazon is still recovering from this drastic event which severely altered the circuit of nutrients. With large herbivores gone from the area, it’s up to the humans to take their role – but we’re doing the complete opposite of what they’re doing.

amazon basin

“These megafauna would disperse nutrients, whereas humans concentrate them,” says Doughty. We spread fertiliser on small plots of productive farmland, and keep large animals like cows fenced rather than letting them roam freely. “There are probably more nutrients because of people, but they are very poorly distributed.”