Jefferson Ground Sloth

Megalonyx jeffersonii

  • Length: 8-10 ft long
  • Weight: 2,200 pounds – (Similar to an Ox) (4x larger than a grizzly bear)
  • Closest Living Relative: Three-toed sloth
  • Status: Extinct 10,000 years ago likely due to changing habitats
Special features of the Sloth include thick fur, blunt snout, and long claws. This slot is around the size of an ox, built strong and stocky. These sloths walked on flat feet, different from other sloths that walk on the sides of their feet. 
The Jefferson Ground Sloth is a herbivore (an animal that eats plants). A large jaw provided room to develop incredibly strong chewing muscles that allowed the Jefferson Ground Sloth to feast on leaves, twigs, and possibly nuts. Large claws were used to strip leaves off of branches. The Sloth had flat feet and a well developed tail that allowed the large animal to stand on its hind legs and reach high branches for a filling meal. The peg-like teeth of the Jefferson’s ground sloth were soft and easily ground down by heavy use, but their teeth grew throughout their entire life, allowing it to keep grinding away at plants for its whole life. 
Given that fossils of adults and juveniles have been found close together, paleobotanists expect that adults cared for their young. 
Distribution and Habitat
Sloths originated in South America, and made their way into North America over millions of years. The Jefferson Ground Sloth first made its appearance in North America around 150,000 years ago. The Jefferson Ground Sloth has been found all over North America, from the East Coast to the West Coast, and as far north as the Yukon. This is the most dispersed range of any sloth. The fossils found at Ziegler reservoir were the first Jefferson’s Ground Sloth fossils found in Colorado. The Jefferson Ground Sloth lived in woodlands and forests, similar to the forests in Colorado today. There is evidence they lived in Spruce dominated, mixed conifer forests, but it is expected this is only one example of the many specific habitats the slots inhabited. The specimens found at Zeigler Reservoir were the highest elevation occurrence of the Ground Sloth to-date.

Fun Facts

  • The Jefferson Ground Sloth is named after Thomas Jefferson, who classified the fossils of the Ground Sloth found in a cave in West Virginia...
    Originally, Jefferson thought the bones belonged to a large cat, but later realized the animal was more closely related to South American tree sloths. He ended up presenting scientific papers on the Sloth and the study of the sloth represents the beginning of vertebrate paleontology. The Sloth was the subject of the first two scientific papers ever published in the US on fossils.
  • Megalonyx is Greek for “Large Claw”