Ground sloths were large relatives of the modern two-toed and three-toed sloths. They evolved in South America around 35 million years ago, and migrated into North America, starting around 8 million years ago, with the last species arriving during the Pleistocene. All four species became extinct approximately 10,000 years ago. The reason for their extinction is not currently known.

Description

Ground sloths were roughly 20 feet long and weighed about 3 to 4 tons. The smallest species -- Shasta Ground Sloth -- was about 9 feet long and weighed up to 550 pounds (about the size of a modern black bear). They had very large claws, even though they were herbivores. The shape of their hip bones indicates that they could stand up on their hind legs, allowing them to reach high up into trees for the best leaves and twigs. It is likely that they walked on the sides of their hind feet and backs of their forefeet.

Distribution and Habitat

Fossil remains of the Shasta Ground Sloth have been found in Southern California (including the Rancho La Brea Tar Pits in Los Angeles) and Sonora, Mexico. The animal was especially adapted to life in arid regions.

Jefferson's and Harlan's Ground Sloths are the only two species found in the Midwestern United States.

Diet

The flat grinding teeth of the Harlan's Ground Sloth suggest a diet of grasses, but they may have also fed on leaves, tree roots, and twigs.

Shasta Ground Sloth was most likely a browser. Fossilized dung shows that it fed on many species of plants such as yuccas, agaves, Joshua trees, globe mallows, mesquite and cacti.

Jefferson's Ground Sloth probably specialized in eating leaves and twigs from trees of moist habitats (such as willows).

Fossil History

The first report of a fossilized ground sloth in North America came from Thomas Jefferson. The fossils that were subsequently named for him were found in a cave in West Virginia in 1799.

Numerous fossil remains of Harlan's Ground Sloths have been found at the Rancho La Brea Tar Pits in Los Angeles.

Several complete ground sloth skeletons have been found within caves. Some of those skeletons have been found complete with hair, skin and tendons still attached. Fossilized dung has also been excavated from many caves, allowing scientists to gain information about the diet of these giant animals.

Scientific Classification

phylum Chordata
subphylum Vertebrata
class Mammalia
order Edentata?
family Megatheriidae
genera & species
Eremotherium laurillardi Laurillard's ground sloth
Megalonyx jeffersonii Jefferson's ground sloth
Nothrotheriops shastensis Shasta ground sloth
Paramylodon harlani Harlan's ground sloth

Questions or comments about this page?

George C. Page Museum (at the La Brea Tar Pits). www.tarpits.org/education/guide/flora/sloth.html
San Diego Natural History Museum. www.sdnhm.org/exhibits/mystery/fg_giantsloth.html

The Robinson Library
Science.--Geology.--Paleontology.

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