Product Code Database
Megalonyx (Greek language, "great-claw") is an extinct genus of of the family Megalonychidae, native to North America. It evolved during the Pliocene Epoch and became extinct at the end of the Late Pleistocene, living from ~5 million to ~13,000 years ago. The type species, M. jeffersonii (also called Jefferson's ground sloth), the youngest and largest known species, measured about in length and weighed up to .
Megalonyx is suggested to have descended from Pliometanastes, a genus of ground sloth that had arrived in North America during the Late Miocene around 9 million years ago, prior to the main phase of the Great American Interchange. Megalonyx had the widest distribution of any North American ground sloth, having a range encompassing most of the contiguous United States, extending as far north as Alaska during warm interglacial periods.
Megalonyx is notable for having been originally described by future U.S. President Thomas Jefferson in 1799 based on remains found in West Virginia; the species M. jeffersonii was described later, named in honor of him.
Megalonyx became extinct as part of the end-Pleistocene extinction event, simultaneously with all other mainland ground sloths and most other large mammals native to the Americas. These extinctions followed the arrival of humans in the Americas, and there is evidence that humans interacted with Megalonyx, including butchering its remains shortly prior to its extinction.
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. In his original draft of the paper, Jefferson thought the animal was a carnivore, one of the large cats, writing “Let us only say then, what we may safely say, that he was more than three times as large as the lion”. In a postscript, composed after learning of Baron Georges Cuvier's description and illustration of the giant ground sloth Megatherium, discovered in Argentina (mistakenly referred to as Paraguay), Jefferson revised his interpretation and compared Megalonyx to Megatherium.
Contrary to Baron Cuvier's view that extinction had played an important role in natural history, an idea that would reach scientific consensus decades later, Jefferson wrote about a "completeness of nature" whose inherent balance did not allow species to go extinct naturally. He asked Lewis and Clark, as they planned their famous expedition in 1804–1806, to keep an eye out for living specimens of Megalonyx, as this would support his case. His idea made no headway and was later shown to be incorrect.Rowland, Steve, "The Fossil Record", Published lecture notes for "The Fossil Record" course at the University of Nevada, Las Vegas, August 2010 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.
His presentation to the American Philosophical Society in 1797 is often credited as the beginning of vertebrate paleontology in North America. In 1799, Caspar Wistar correctly identified the remains as those of a giant ground sloth. In 1822, Desmarest named the species Megatherium jeffersonii in honor of the former statesman and scientist, although he classified it in the genus Megatherium instead. Richard Harlan in 1825 revived the genus Megalonyx with the type species M. jeffersonii, and provided additional taxonomic description . (1997). 9780231110136, Columbia University Press. ISBN 9780231110136 Scientific papers variously give the authority for the genus as Jefferson 1799 (after Jefferson's original naming of the genus), or Harlan 1825. Most authors gave Jefferson as the authority on the genus until a 1942 paper by George Gaylord Simpson, who suggested that the attribution of the authority to Jefferson “is certainly erroneous,”, and suggested that Harlan “may have been the first to use the name in a valid Linnaean form”. A 2024 review paper by Loren E. Babcock found that Simpson's views were mistaken, and clarified that Jefferson was the valid author of the genus, as the description was done in accordance with the rules of taxonomic nomenclature at the time, despite him not assigning a species to it.
Recent research confirms that the sloth bones were discovered in Haynes Cave in Monroe County, West Virginia. For many decades in the twentieth century, the reported origin of Jefferson's "Certain Bones" was Organ Cave in what is now Greenbrier County, West Virginia. This story was popularized in the 1920s by a local man, Andrew Price of Marlinton.Humphreys, Blanche (1928), History of Organ Cave Community (Greenbrier County, West Virginia); Agricultural Extension Division. The story came under scrutiny when in 1993 two fragments of a Megalonyx scapula were found in Haynes Cave in neighboring Monroe County. Smithsonian Paleontology Frederick Grady presented evidence in 1995 confirming Haynes Cave as the original source of Jefferson's fossil.Grady, Fred (1995), "The Search for the Cave from which Thomas Jefferson Described the Bones of the Megalonyx" Abstract, In: "Selected Abstracts from the 1995 National Speleological Society National Convention in Blacksburg, Virginia"; In: Journal of Cave and Karst Studies, April 1997, pg 57.
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 Niter vats. An investigation of property ownership records revealed "Frederic Crower" to be an apparent misspelling of the name Frederic Gromer.
Organ Cave was never owned by Gromer, but Haynes Cave was. Two letters written by Tristram Patton, the subsequent owner of Haynes Cave, indicate that this cave was located in Monroe County near Second Creek. Monroe County had originally been part of Greenbrier County; it became a separate county shortly after the discovery of the bones. In his own letters Patton described the cave and indicated that more fossil bones remained inside.
M. jeffersonii is still the most commonly identified species of Megalonyx. It was designated the state fossil of West Virginia in 2008.
M. leptostomus, named by Cope (1893), lived from the Blancan to the Irvingtonian. This species lived from Florida to Texas, north to Kansas and Nebraska, and west to New Mexico, Nevada, Oregon, and Washington. It is about half the size of M. jeffersonii. It evolved into M. wheatleyi, the direct ancestor of M. jeffersonii. Species gradually got larger, with different species mostly based on size and geologic age.
The earliest representatives of Megalonyx appeared during the Pliocene. M. jeffersonii lived from the late Middle Pleistocene/ late Irvingtonian (250–300,000 years ago) through to the Rancholabrean of the Late Pleistocene (11,000 BP). M. jeffersonii was probably descended from M. wheatleyi. (2025). 9780253342683, Indiana University Press. ISBN 9780253342683 The Megalonyx lineage increased in size with time, with the last species M. jeffersonii being the largest.
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.
|
|
