11 Of Ancient Earth’s Most Unbelievable Prehistoric Animals

Published December 2, 2021

Megatherium: The Giant (And Probably Extinct) Ground Sloth

Megatherium Prehistoric Animal

Natural History Museum, LondonThe fossils of the ancient animal known as megatherium show its immense size.

Today’s sloths are small. But the ancient animals that preceded them, called Megatherium americanum, were veritable giants.

Standing nearly 12 feet tall and weighing upwards of four tons, M. americanum once roamed the jungles of South America. Unlike today’s sloths, which live in trees, M. americanum walked the earth. Fossils found in Argentina, Uruguay, and Bolivia suggest that the beast lived between 400,000 and 8,000 years ago.

Though it likely walked on four legs, M. americanum could stretch up to its full height to snatch hard-to-reach leaves. The creature had fearsome claws, but chemical analyses of its teeth suggest that the M. americanum largely stuck to eating leaves and plants.

Like modern-day sloths, however, the M. americanum took its time. It moved slowly, possibly slower than anything else alive at the time. But its size offered plenty of protection, as these prehistoric animals outweighed possible predators like the saber-tooth tiger.


Wikimedia CommonsA rendering of the megatherium.

So if the M. americanum could find plenty to eat, and didn’t have to worry much about predators, then why did these prehistoric animals go extinct?

Scientists are unsure. It could have been a climate event, or disease, or possibly the arrival of humans, seeing as some M. americanum bones seem to bear marks consistent with hunting.

Then again, it’s possible that the M. americanum never went extinct at all. Some believe that the creature merely retreated deeper into the jungle once humans arrived on the scene.

People living in the Amazon rainforest have indeed shared stories of a beast they call mapinguari. Said to be a slow-moving, sloth-like beast that stands on its hind legs, the mapinguari does sound suspiciously like the M. americanum.

However, legend also states that the mapinguari has a giant mouth on its stomach capable of devouring anything that crosses its path. But scientists have found no evidence of such an orifice among the M. americanum — at least, not yet.

Kaleena Fraga
A staff writer for All That's Interesting, Kaleena Fraga has also had her work featured in The Washington Post and Gastro Obscura, and she published a book on the Seattle food scene for the Eat Like A Local series. She graduated from Oberlin College, where she earned a dual degree in American History and French.
Leah Silverman
A former associate editor for All That's Interesting, Leah Silverman holds a Master's in Fine Arts from Columbia University's Creative Writing Program and her work has appeared in Catapult, Town & Country, Women's Health, and Publishers Weekly.