Wilderness Underfoot: Jefferson's ground sloth

StoryImage( ‘/Images/Story//Auto-img-11599949368343.jpg’, ‘Image provided’, ‘Jefferson's ground slothMegalonyz jeffersonii stood about 10 feet tall and weighed up to 3 tons. Fossils of this creature can be found throughout the Midwest and across North America.’);

The fossil bones of the ground sloth are imbedded into American history thanks to the scientist/statesman who first described them: Thomas Jefferson.

Newly elected as vice president of the United States in 1797, Thomas Jefferson had also recently been elected president of the American Philosophical Society. Always a busy politician, Jefferson was also deeply devoted to science and exploration. He’d received bones that had been discovered in a cave in West Virginia by miners who were digging for saltpeter. The bones included parts of the hand, arm and claws of a creature he first believed to be a giant cat. He named the animal Megalonyx, meaning “large claw.”

Prior to a presentation about the bones before the Philosophical Society, however, Jefferson read a magazine article describing Megatherium, a fossil sloth found in Paraguay, which was related to the living tree sloths of South America. Noting the similarities between his fossils and those of Megatherium, he considered his creature was not a cat at all, but a giant sloth. Later research by other scientists confirmed that Jefferson had indeed described a new species of prehistoric sloth, and they dubbed it Megalonyx jeffersonii in his honor. Jefferson’s description of Megalonyx may have been the first paleontology article ever published in North America.

Jefferson went on to build a private collection of fossils, including prehistoric bison, horses, mammoths, mastodons and the giant shark, Megalodon. His collection is housed today by the Academy of Natural Sciences of Philadelphia.

Jefferson’s ground sloth, a huge beast with exceptionally large claws, was a plant eater. This herbivore is one of the oddest creatures to come out of the Ice Age. Large and slow moving, its hips appear to have been built so it could stand up like a human and reach leaves high up in the trees. Its teeth were small and peg-like, just right for tearing leaves and twigs. The large tail helped it balance when upright. It may have relied on its size to keep wolves and large cats at bay.

Only two prehistoric ground sloths have been discovered in North America: Jefferson’s and another named Harlan’s Ground Sloth (Paramylodon harlani).

Ground sloths evolved from smaller tree sloths that first emerged in South America 30 million years ago, during the Age of Mammals (Tertiary Period). The bulky ground sloths became extinct as the Ice Age ended, about 10,000 years ago, possibly because of hunting by humans as they spread across the North American continent. New discoveries of fossils in Cuba and Hispaniola indicate some giant sloths survived on these West Indian islands until 4,400 years ago—outlasting the other sloths, perhaps because humans had not yet moved into the islands.

From the Oct. 4-10, 2006, issue

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