Standing over 2 meters (6.5 feet) tall with forelegs tipped with claws, giant sloths were formidable adversaries for our prehistoric ancestors. Yet scientific consensus has held that the animal was over-hunted into extinction by humans around 11,000 years ago.

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Now researchers have uncovered fossilized evidence showing how ancient humans would have pursued and taken down a giant sloth. The team of American and British scientists published their findings on Wednesday in the journal Science Advances.

Evasion, stalking and hunting

In the article, the researchers present fossilized footprints of both sloth and man that had been found in the salt flats of White Sands National Monument in the southwest American state of New Mexico. The "extremely rare" traces reveal that humans walked in the exact footprints of the giant sloth before confronting it and, perhaps, hurling spears at it to try and hit a vulnerable area like the heart or neck.

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"The sloth trackways show evidence of evasion and defensive behavior," the scientists wrote. "Behavioral inferences from these trackways indicate prey selection and suggest that humans were harassing, stalking, and/or hunting the now-extinct giant ground sloth."

Matthew Bennett, one of the article's co-authors and a professor at Britain's Bournemouth University, explained what information could be inferred from the fossilized footprints:

He compared the tracks to reading a story and said humans would work together as a group to try and kill the giant animal.

"While it was being distracted and turning, somebody else would come across and try and deliver the killer blow. It's an interesting story and it's all written in the footprints," he told Reuters news agency.

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The researchers examined more than 100 sloth and human tracks. In addition to the footprints that show the humans following the sloth to launch the final fatal attack, the scientists said more human tracks located at a distance revealed that a separate team worked to misdirect and distract the sloth.

A key piece of evidence for the researchers was the presence of "failing circles," which indicate that the sloth rose up on its hind legs to try and fend off its attackers. When no human tracks are evident, the sloth walked in a straight line, but where human tracks can be found, the sloth's prints show sudden changes in direction and evasion.

"The anatomy of sloths was not made for speed but for strength," co-author Sally Reynolds, also of Bournemouth University, said to EFE news agency.

A human footprint inside a giant sloth's shows just how big the prehistoric creatures were

3-D models of fossils

The fossils in New Mexico were found around 10 years ago and were able to be preserved thanks to new 3-D modeling techniques that create an ultraprecise computer rendering. The date of their creation remains unclear.

The researchers believe their find could help shed light on other relationships between early man and now-extinct ancient animals.

"This geological archive has the potential to revolutionize understanding of the behavioral ecology and interaction of humans and megafauna," the researchers wrote in their study.

"During a time of climate change, predation (successful or not) may have contributed to the sloth's extinction in North America," they added.

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Slow down for International Sloth Day Hang tight Sloths move incredibly slowly - less than three meters (9.8 feet) per minute. Their primary form of defense from predators is to remain unseen in the trees. Two-toed sloths can live up to 29 years in the wild, while their three-toed cousins can live upwards of 30 years.

Slow down for International Sloth Day Big snoozers Researchers previously believed the lethargic mammal slept for almost 16 hours a day. However, a 2008 study conducted by the Max Planck Institute for Ornithology in Starnberg, Germany found that sloths actually sleep for less than 10 hours a day - not much longer than a human.

Slow down for International Sloth Day Slow digestion The Sloth Sanctuary in Costa Rica found that sloths can take up to 30 days to fully digest food - the longest rate recorded for any mammal. They also leave the safety of their trees once a week to defecate and urinate on the ground.

Slow down for International Sloth Day Head turners Unlike most mammals, who have seven cervical vertebrae, the three-toed sloth has nine - granting them the ability to rotate their heads up to 270 degrees.

Slow down for International Sloth Day Stay close to mom Sloth babies will cling to their mothers for one year, learning what to eat and how to find it. Afterwards, adolescent sloths acclimate to independent, solitary lives, only meeting other sloths in order to mate.

Slow down for International Sloth Day Furry habitat Sloth fur often appears green as it is covered in algae and fungi - which helps camouflage them in the trees. Recent studies have also shown that some fungi found in sloth fur could help fight certain against certain cancers and bacteria.

Slow down for International Sloth Day Swimming sloths They may move slowly in trees, but some types of sloths are actually very adept swimmers. Using a type of doggy-paddle stroke, sloths can move up to three times faster in the water than they do on land. Author: Rebecca Staudenmaier



cmb/sms (Reuters, EFE)