Jeffersons sloth, megalonyx or “giant claw” is an extinct genus of ground sloths of the family megalonychidae.

Aside from there deceivingly large cuddly, and playful looks. These critters were native and unique to north America during the pliocene and pleistocene. However, because of not many remains, we don’t know as much as some of the other late pleistocene vertabrates. Like sabretooth tiger or direwolf, who were probably found in areas better suited to decomposition.

Thomas Jefferson recorded fossil bones from this animal that had been recovered from a mining cave in West Virginia in the late eighteenth century. Originally, Jefferson thought the remains belonged to a giant cat, based on the size of the large claws. Soon he realized however, that the animal was closely related to South American tree sloths. In 1797, he presented the scientific paper about his findings on megalonyx, or ‘large claw’ to the American philosophical society. The subject was the first two scientific articles ever published in the North America on fossils. Marking the continental beginning of vertebrate paleontology.

Biology and physical description:
There size was quite large. Bigger than most grizzlys, and flat nosed bears. 4m or 10 feet high. Up to 1000Kg or 2200lb big. They had a blunt snout and massive jaw. Large peg like teeth. There hind limbs were flat footed. And, a stout tail. Its believed this allowed them a rear up semi errect portion to feed on leaves.
Forelimbs had 3 highly developed claws. They were quite long. Up to 15-20 inches. Used to strip trees and tear off branches. (the deceiving part)
As with other sloths, the teeth had an outer layer of dentine, rather than enamel, and thus were softer than those of other mammals. Soft teeth wear faster than hard teeth, and to compensate for this, their teeth continued to grow throughout their lifetime (MacFadden et al. 2010).
Although very few specimens have been recovered with preserved soft tissue, better preserved species of late pleistocene ground sloths (shasta ground sloth) were found. And, it is thought that Jefferson’s ground sloth was similarly covered with thick hair.
Sloth bones are truly strange inside and out. Inside, they are virtually unique in the animal kingdom in the absence of any marrow cavity within their long bones. Instead of marrow, the bones are filled with a honeycomb network of bony struts and braces called trabecular or cancellous bone. This gave the bones great strength without the cost of extra weight. Whether that was necessary because of sloths’ weight, due to a unusually active life-style or just an accident of evolution is unknown.

Habitat: woodlands and forest:
Jefferson’s ground sloth had the widest range of all North American ground sloths. They have been recovered from over 150 sites across the United States, as well as from northwestern Canada and western Mexico (Hoganson and McDonald 2007; McDonald et al. 2000). Furthermore, they are the only ground sloth that has been recovered from the Yukon and Northwest Territories in Canada.
Two recent studies were able to link directly-dated specimens from the terminal pleistocene with regional paleoenvironmental records, demonstrating that these particular animals were associated with spruce dominated, mixed conifer-hardwood habitats. (Hoganson and McDonald 2007; Schubert et al. 2004).
Scarcity in the Great Plains has been noted and interpreted as reflecting the paucity or absence of forested areas, the species’ preferred habitat, within the region. (Hoganson and McDonald 2007).

Habitat: Caves:
Megalonyx jeffersoni remains have been recovered from late Pleistocene sites, primarily caves, across the Midwest. These sites include West Cave and Brynjulfson Cave #1 in central Missouri, a site in the Galena Lead region of northwestern Illinois, the Hanson Megalonyx from Minneapolis, Minnesota, the Carter site in western Ohio, Gillenwater near Bowling Green, Kentucky, Robinson Cave in northeastern Tennessee, and Cheek Bend Cave and Darks Mill in central Tennessee.
It is likely several types of habitats were utilized by jefferson’s ground sloth over the course of the Pleistocene.

The first wave of megalonychidae came to North America by island-hopping across the Central American Seaway from South America, where ground sloths arose, prior to formation of the Panamanian land bridge. Based on molecular results, its closest living relatives are the three-toed sloths (Bradypus).

It probably lived solitarily, only getting together for seasonal mating.
While most ground sloths walked on the outsides of their hind feet, Jefferson’s ground sloth kept their feet flat while walking. Furthermore, the shape of the hip bone indicates that this animal could also stand on its hind legs, using its stout tail for support.
During excavations at Tarkio Valley in southwest Iowa, an adult Megalonyx was found in direct association with two juveniles of different ages, suggesting that adults cared for young of different generations.

Teeth shape suggest they were a browser who primarily ate leaves, twigs and possibly nuts. (Kurten and Anderson 1980; McDonald 2005). Isotopic results are consistent with this. (Kohn et al. 2005). Analysis of the bone chemistry of indicate the animal had an herbivorous diet, (France et al. 2007), which is in keeping with a previous study conducted for ‘giant claw’ recovered in Alberta, (Bocherens et al. 1994).

Extinction: The youngest widely-accepted radiocarbon dates are from northern Illinois. Obtained from purified bone collagen. A combined age date of 13,800-13,160 years ago.
(Schubert et al. 2004). A slightly older direct date of 13,830-13,560 cal BP was obtained on a toe bone (ungual) in North Dakota (Hoganson and McDonald 2007).

Bipedal Walking:
How and why humans separated themselves from the other primates and began striding confidently on two legs is a question mankind has asked for thousands of years. Many scientists consider it the single characteristic that put us on the evolutionary path to becoming tool-users and uniquely human. So it was with no little surprise that scientists realized 100 years ago that some ground sloths probably could walk upright also. Why do they do it? What advantage is there that all the rest of the mammals have overlooked? Perhaps the answer can be found by considering the theories of why our human ancestors did.
Some scientists credit changing climate, and expanding savannas offering rich new ecological niches to a species that could climb down and out of the trees. Moving more efficiently and safely to open ground. Standing erect may have also been necessary to see predators approaching.
-Other scientists suggest foraging from the ground and being forced to reach up into the trees for food encouraged our ancestors to remain upright to reduce the effort of repeatedly lifting and lowering their torsos; and,
-Some scientists suggest the benefit of being able to hold things in their hands or arms was the force that put us on the bipedal evolutionary path. They also cite tools, food collection and/or infants needing an extended period of maternal care as the motivating force(s).
No one thinks sloths are as efficient striders as humans became. Then again, no one believes primate ancestors dropped out of trees and started walking. What did you think?
Whatever benefits ancestors reaped from upright standing. It started a long time ago, and improved from there. Studying megalonyx may some day produce new insights into our own evolution. Maybe they wanted to have a better view of the moon and solar system. One things for sure, the world is not the same without megalonyx, jeffersons ground sloth or ‘giant claws.’


Bradford, A. (2016, November 5). Facts About the Giant Ground Sloth.

Jefferson, Thomas, “A Memoir on the Discovery of Certain Bones of a Quadruped of the Clawed Kind in the Western Parts of Virginia”, Read before the American Philosophical Society, March 10, 1797.

McDonald, H. G.; Harington, C. R.; De Iuliis, G. (September 2000). “The Ground Sloth Megalonyx from Pleistocene Deposits of the Old Crow Basin, Yukon, Canada” (PDF). Arctic. Calgary, Alberta: Arctic Institute of North America. 53 (3): 213–220. doi:10.14430/arctic852.

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