Megatherium: The Giant (And Probably Extinct) Ground Sloth
Natural History Museum, LondonThe fossils of the ancient animal known as megatherium show its immense size.
Today’s sloths are relatively 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.
Deinosuchus: The Fearsome Prehistoric Animal Called ‘Terrible Crocodile’
Wikimedia CommonsThe skull of a Deinosuchus rugosus.
When it comes to prehistoric animals that seem like modern-day monsters, it’s hard to beat Deinosuchus. Stretching 33 feet long and with teeth the size of bananas, Deinosuchus inhabited North America during the late Cretaceous period, some 82 to 73 million years ago. Even its name literally translates to “terrible crocodile.”
The giant crocs mostly ate sea turtles and shellfish, but sometimes tangled with T. Rex cousins like Appalachiosaurus montgomeriensis and Albertosaurus — and left the bite marks to prove it.
“Deinosuchus was a giant that must have terrorized dinosaurs that came to the water’s edge to drink,” explained Adam Cossette, a vertebrate paleontologist at the New York Institute of Technology who has studied the beasts.
These fearsome prehistoric animals lived across the present-day United States and Mexico. Fossils have been found in Utah, Montana, Wyoming, New Mexico, New Jersey, Georgia, Alabama, Mississippi, Texas, and North Carolina.
The monster does differ somewhat from modern-day crocodiles, however. In addition to its massive size, it also has a bulb-like snout with two vents. Scientists aren’t sure what Deinosuchus needed the vents for, but they possibly helped cool the animals down.
As with other prehistoric animals on this list, it took scientists a while to understand the full picture of these ancient animals. Deinosuchus fossils were originally classified under the genus Polyptychodon, another marine predator, but in 1904, the zoologist and paleontologist William Jacob Holland studied the available evidence and concluded that Deinosuchus was a monster all its own.
Specimens of Deinosuchus, Cossette noted, were few and far between. But the ones that scientists have found are “HUGE.”
For a long time, Deinosuchus was considered the largest crocodile ever discovered. It’s since been dethroned by Sarcosuchus imperator who, at 40 feet long and 17,600 pounds, could have taken Deinosuchus in a fight.
