Megalonyx

In 1796, Colonel John Stuart sent Thomas Jefferson, shortly before he took office as Vice President of the United States, some fossil bones: a femur fragment, ulna, radius, and foot bones including three large claws. The discoveries were made in a cave in Greenbrier County, Virginia (presently West Virginia). Jefferson examined the bones and presented his observations in the paper "A Memoir on the Discovery of Certain Bones of a Quadruped of the Clawed Kind in the Western Parts of Virginia" to the American Philosophical Society in Philadelphia on March 10, 1797. The paper was published in 1799, in the same volume as an accompanying paper by his colleague Caspar Wistar, who provided detailed anatomical information about the bones, and illustrated them. Together these two papers are considered the first North American publications devoted to paleontology. In the 1799 paper, Jefferson named the then-unknown animal Megalonyx ("great-claw") and compared each recovered bone to the corresponding bone in a lion. However, Jefferson's notion that humans and Megalonyx co-existed in North America has been shown to be correct, as some bones of Megalonyx show marks made by flint tools. Scientific papers variously give the authority for the genus as Jefferson 1799 (after Jefferson's original naming of the genus), or Harlan 1825. The story came under scrutiny when in 1993 two fragments of a Megalonyx scapula were found in Haynes Cave in neighboring Monroe County. Smithsonian paleontologist Frederick Grady presented evidence in 1995 confirming Haynes Cave as the original source of Jefferson's fossil. Jefferson reported that the bones had been found by saltpeter workers. He gave the cave owner's name as Frederic Crower. Correspondence between Jefferson and Colonel Stuart, who sent him the bones, indicates that the cave was located about five miles from Stuart's home and that it contained saltpeter vats. An investigation of property ownership records revealed "Frederic Crower" to be an apparent misspelling of the name Frederic Gromer. Megalonyx is thought to be descended from Pliometanastes, a ground sloth that arrived in North America during the late Miocene, around 9 million years ago. The earliest representatives of Megalonyx appeared during the Pliocene. through to the Rancholabrean of the Late Pleistocene (11,000 BP). M. jeffersonii was probably descended from M. wheatleyi. The Megalonyx lineage increased in size with time, with the last species M. jeffersonii being the largest. == Description ==

Adult M. jeffersonii measured around long, and weighed up to . The teeth of Megalonyx jeffersonii were hypselodont (high crowned). == Paleobiology ==

During excavations at Tarkio Valley in southwest Iowa, an adult (presumably female) Megalonyx jeffersonii was found in direct association with two juveniles of different ages, the oldest suggested to be around 3-4 years old, suggesting that adults cared for young of different generations. == Distribution and habitat ==

Megalonyx jeffersonii ranged over much of North America, with its range spanning nearly the whole contiguous United States and parts of southern Canada, with some remains known as far south as central Mexico. and the Yukon during interglacial intervals. The sloth ranged as far northeast as New York. In 2010, a specimen was discovered at the Ziegler Reservoir site near Snowmass Village, Colorado, in the Rocky Mountains at an elevation of . The habitat of Megalonyx jeffersonii was highly variable, but often associated with spruce-dominated, mixed conifer-hardwood forest. == Extinction ==

Megalonyx jeffersonii became extinct at the end of the Pleistocene, as part of the Quaternary extinction event, in which all other mainland ground sloths and most other large mammals of the Americas became extinct. == See also ==