Eleven thousand years ago, a New Mexican Nothrotheriops stumbled into a volcanic gas vent and died. Still, we know more about it than any other ground sloth thanks to one amazing find. Rivaling a black bear in size, Nothrotheriops would have been dwarfed by behemoths like Megatherium. Therefore, younger species were less buoyant-and probably more aquatic-than their ancestors had been. Over time, evolution fitted the amphibious sloths with increasingly dense ribs and limb bones. Hooked claws helped them latch onto submerged, seaweed-covered rocks once anchored, a Thalassocnus could consume marine algae. These Peruvian herbivores, which lived 8 to 4 million years ago, dove into the ocean for their supper. You’ve just pictured a member of the Thalassocnus genus. Imagine a sloth that’s trying hard to be a marine iguana. And some marks show that they were filleting the meat off the bone.” 7. “The only thing that is clear,” he said in 2012, “is that there are disarticulation marks: they were separating the limbs from each other they were cutting the joints. The 13,000-year old fossil is riddled with 41 unusual cuts that appear to have been left by manmade tools.Īs archaeologist Haskel Greenfield points out, we’ll likely never know if early Americans killed this animal or merely scavenged its remains. Then, in 2008, incriminating scars were found on the femur of an Ohio Megalonyx. Scientists have long speculated that humans killed and devoured ground sloths-but, for many years, there was no physical evidence to support this idea. What killed off the woolly mammoth, the scimitar cat, and North America’s other ice age mega-mammals? Homo sapiens usually gets a good chunk of the blame. On March 8, 2008, West Virginia recognized the animal as its official state fossil. The future president dubbed this creature Megalonyx, or “great claw.” Though we now know that it was a large, flat-footed sloth, Jefferson originally mistook the animal for an enormous lion or tiger-like carnivore.Ĭurrently, four different species of Megalonyx are recognized the most famous, Megalonyx jeffersonii, was named in Jefferson's honor. Still, Jefferson spoke at length about the big-clawed mystery animal at a 1797 meeting of the American Philosophical Society in Philadelphia. This find wasn’t all that unusual-similar-looking fossils had also emerged in Kentucky and other parts of Virginia. In 1796, Jefferson-a respected armchair naturalist-received some curious bones from western Virginia (modern West Virginia). The Sage of Monticello’s importance to American paleontology cannot be understated. ONE SPECIES IS NAMED AFTER THOMAS JEFFERSON. Whenever a ground sloth did this, its muscular tail would act like another leg, helping to support its considerable body weight. MANY USED THEIR TAILS TO FORM “TRIPODS.”įor these animals, standing up on two limbs required some extra stability. A few modern animals, including armadillos and crocodilians, also have osteoderms of some kind-as did many dinosaurs. Known as “osteoderms,” these little knobs (nickel-sized in Harlan’s ground sloth) were mostly clustered around the back, shoulders, and neck and would have acted like protective chainmail. 3. AT LEAST SOME HAD ARMOR PLATES.īuried in the skin of the mylodontid ground sloths-including the Harlan’s ground sloth, whose range extended from Florida to Washington state-were a series of small bony discs. Because of the shapes of their ankle and/or hind claws, sloths from the megatheriid, mylodontid, and nothrotheriid families had to trudge along by putting weight on the outer sides of their feet. Scientists have divided ground sloths up into four recognized families, and only one-the megalonychids-stood flat on their rear feet like humans do. While they were more than capable of standing up on two legs (more about this later), the animals preferred to get around on four-but individual species differed widely from each other in terms of limb posture. MOST WALKED ON THE SIDES OF THEIR HIND FEET.Īll ground sloths were predominantly quadrupedal. Above the equator, its slightly-smaller cousin, the 6000-pound Eremotherium, managed to spread as far north as New Jersey. The biggest sloth of all time, Megatherium americanum, occupied South America between five million and eleven thousand years ago. Megatherium (above) means “ giant beast”-a fitting name for a creature that weighed several tons, reached 20 feet in length, and-when reared up on its hind legs-stood over 12 feet tall.
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