Jefferson Ground Sloth

Jefferson Ground Sloth

In the Yukon, at the Beringia Center, we learned about the sloth bones found in Kentucky.

The first North American prehistoric sloth was discovered in 1799 in a cave in West Virginia. It would be an exaggeration to say that Megalonyx jeffersonii was responsible for the Lewis and Clark expedition, but the animal was one motivation. President Jefferson hoped Lewis and Clark might find the animal the bones came from—or at least more bones like the ones found. Megalonyx—the “mega” was certainly appropriate; the animal weighed about a ton. “Lonyx” means claw. When Lewis and Clark didn’t find any such bones, Jefferson sent Meriwether Lewis on another expedition closer to home on the same quest, and thus he became known as the father of American archeology.

The giant sloths apparently migrated from Asia through the Beringia area in the Yukon and on down toward South America, leaving evidence of several giant sloth species on the way.  The distance between Beringia and South American must have been eons!

For more detailed information, sketches, and photos of the bones, see the San Diego Natural History Museum site,, as well as the Beringia site, The former states the bones were discovered in 1799, the latter tells us Thomas Jefferson’s lecture at the American Philosophical Society, with a description of the sloth, was in 1797. Wikipedia dates the lecture as August 1796. No matter what the year, that lecture was the beginning of vertebrate paleontology as a study.

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