Sloths are interesting creatures, to say the least. They are one of those species that everyone knows about but no one knows much about. For starters, most of them walk on the sides of their hind legs. They are capable of standing on two legs, but they generally prefer to walk around on all fours. Scientists divide sloths who live primarily on the ground into four subcategories, three of which walk on the outer sides of their hind feet. The other group, the megalonychids, stand on their back feet, with their walk resembling how humans walk.
Thomas Jefferson, the third president of the United States, had an understated importance in paleontology. Jefferson was sent some bones in 1796, and, instead of disregarding them, spoke about them at a meeting of the American Philosophical Society and eventually named the creature from which the bones came Megalonyx. Years later, it was determined that the Megalonyx was actually just a flat-footed sloth. One of the species is now named Magalonyx jeffersonii in Thomas Jefferson’s honor. It is also the official state fossil of West Virginia, where the bones were found.
Today, there are only six living species of sloths, all fairly similar in size. But, if you look back thousands—or possibly millions— of years, it was a very different picture. The Megatherium americanum, which means “giant beast” was the biggest sloth of all time. It was found in South America, and it was the size of an elephant. This creature was up to 20 feet long, and 12 feet tall when standing on its hind legs. Another similar creature was the Eremotherium, which could be found in the United States and weighed in around 6,000 pounds. Many of the larger species of sloths also used their tail, which was extremely muscular, as a third leg, when standing up on their hind legs.
In those days, thousands of years ago, it is believed that sloths were a common food amongst humans. There was no proof of this until a sloth fossil that was found in 2008 showed evidence of cuts made by manmade tools. Rewind a few million years, and sloths were also sea-dwellers. These sloths, from the Thalassocnus genus, dove into the sea for food, which, over time, evolved into newer sloth species having denser ribs and limbs.
For nearly 11,000 years, there have been no indigenous sloth species on North America. Five hundred years after sloths in North America became extinct, indigenous sloths in South America also became extinct.