Most of us are familiar with sloths, the bear-like animals that hang from trees, live life in the slow lane, take a month to digest a meal and poop just once a week. Their closest living relatives are anteaters and armadillos, and if that seems like an odd pairing, there’s a reason why. Today, there are only six sloth species, but historically, there were dozens of them, including one with a bottle-nosed snout that ate ants and another that likely resembled the ancestors of modern armadillos.
Most of these extinct sloths also didn’t live in trees, because they were too big. The largest sloths, in the genus Megatherium, were about the size of Asian bull elephants and weighed roughly 8,000 pounds.
“They looked like grizzly bears but five times larger,” said Rachel Narducci, collection manager of vertebrate paleontology at the Florida Museum of Natural History.
Narducci is co-author of a new study published in the journal Science in which scientists analyzed ancient DNA and compared more than 400 fossils from 17 natural history museums to figure out how and why extinct sloths got so big.
Ground sloths varied widely in size, from the truly massive Megatherium — which could rip foliage off the tops of trees with its prehensile tongue and acted as a sort of ecological stand in for giraffes — to the modestly chunky Shasta ground sloth that terrorized cacti in the desert southwest of North America.
Jerald Pinson