| Megalonyx jeffersonii Temporal range: Middle to Late Pleistocene |
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|---|---|
| Reconstructed Megalonyx jeffersonii, Museum of Natural History, University of Iowa. | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Superorder: | Xenarthra |
| Order: | Pilosa |
| Family: | Megalonychidae |
| Subfamily: | Megalonychinae |
| Genus: | †Megalonyx |
| Species: | †Megalonyx jeffersonii Desmarest, 1822 |
Megalonyx jeffersonii, or Jefferson's ground sloth, is an extinct species of giant ground sloth that lived from the Illinoian Stage during the Middle Pleistocene (150,000 years BP) through to the Rancholabrean of the Late Pleistocene (10,000 BC). Its closest living relatives are the two-toed tree sloths of the genus Choloepus.
This species ranged widely in North America. It belongs to the genus Megalonyx, a name proposed by Thomas Jefferson, future president of the United States, in 1797. (Jefferson's surname was appended to the animal as the specific epithet in 1822 by the French zoologist Anselme Gaëtan Desmarest.)
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M. jeffersonii was a large, heavily built animal about 8 to 10 feet (2.5–3 m) long. Its maximum weight may have been as much as 800 pounds (360 kg). This is medium-sized among the giant ground sloths. Like other ground sloths it had a blunt snout, massive jaw, and large peg-like teeth. The hind limbs were plantigrade (flat-footed) and this, along with its stout tail, allowed it to rear up into a semi-erect position to feed on tree leaves. The forelimbs had three highly developed claws that were probably used to strip leaves and tear off branches.
M. jeffersonii was apparently the most wide ranging giant ground sloth. Fossils are known from many Pleistocene sites in the United States, including most of the states east of the Rocky Mountains as well as along the west coast. It was the only ground sloth to range as far north as the present-day Yukon[1] and Alaska.[2]
In the fall of 2010, the first specimen ever found in Colorado was discovered at the Ziegler Reservoir site near Snowmass Village (In the Rocky Mountains at an elevation of 8,874 feet).[3]
In 1796, Colonel John Stuart sent Thomas Jefferson some fossil bones (a femur fragment, ulna, radius, and some foot bones including three large claws) from a cave in Greenbrier County, Virginia (present-day West Virginia). In 1797, Jefferson (who was serving at the time as Vice President) presented a paper on "Certain Bones" to the American Philosophical Society in Philadelphia. He theorized that they were the remains of a lion which he named Megalonyx ("giant claw").[4] Jefferson believed that this lion was still alive (the species was extant), which is of particular importance because the validity of his argument would directly be used in the argument for or against evolution. Jefferson believed in a "completeness of nature" worldview which contrasted the new theory of evolution, where no species have or ever will go extinct naturally. When Lewis and Clark embarked on their expedition (1804–1806), he asked them to keep an eye out for this "Megalonyx", as he insisted this species was still in existence. If the creature was found, he could use this to support his argument against the concept of the extinction of species. His argument, of course, was later not supported by the scientific community and shown to be incorrect.[5]
Jefferson is considered to have initiated the science of vertebrate paleontology in the United States with the reading of this paper. In 1799, Dr. Caspar Wistar correctly identified the remains as belonging to a giant ground sloth. In 1822, Wistar proposed naming it Megalonyx jeffersonii in honor of the former president.[6][7] Desmarest then published it as such.
For many decades, Jefferson's "Certain Bones" had been assumed to have come from Organ Cave in what is now Greenbrier County, West Virginia. This theory originated in the early 20th century when a local man, Andrew Price of Marlinton, decided this and popularized the idea.[8]In 1993, two fragments of a Megalonyx scapula were found in Haynes Cave in neighboring Monroe County. In 1995, Smithsonian paleontologist Frederick Grady proposed[9] that Haynes Cave was the true original source of Jefferson's fossil.
Grady’s reasons had to do with historical land-ownership records. Jefferson reported that the bones had been found by saltpeter workers and gave the cave owner’s name as Frederic Crower, an apparent misspelling (according to Grady) of Frederic Gromer. Correspondence between Jefferson and Colonel Stuart, who sent him the bones, indicates that the cave was about five miles from Stuart’s home and contained saltpeter vats. Grady believes that Organ Cave can be eliminated as the source cave as it was never owned by Gromer. In addition, two letters written by the subsequent owner of the cave—Tristram Patton—indicate that the cave was in Monroe County near Second Creek. (Monroe County, originally part of Greenbrier County, was separated shortly after the discovery of the bones.) In the letters, Patton described the cave and indicated that more bones were there.[10]
M. jeffersonii is still the most commonly identified species of Megalonyx. It was designated the state fossil of West Virginia in 2008.