Giant Ground Sloths

Shasta Ground Sloth

illustration of a giant ground sloth
The Shasta ground sloth is one of the two species of giant ground sloth found from Tule Springs Fossil Beds National Monument.

NPS illustration by Benji Paysnoe.

Scientific Name

Nothrotheriops shastensis


The Shasta ground sloth was a large ground dwelling sloth, but one of the smallest ground sloths to live in North America during the late Pleistocene. It was approximately 9 feet long and weighed up to 550 pounds. The front feet bore large claws for grabbing branches and helping defend itself from large predators. It had a long, slender skull with a narrow mouth that might have supported a long prehensile tongue.

The first fossils of the Shasta Ground Sloth were described in 1905.


The ancestors to Nothrotheriops evolved initially in South America and then crossed the Isthmus of Panama to North America roughly 2.6 million years ago. The intermittent movement of different types of animals between North and South America throughout the Pliocene and Pleistocene epochs is known as the “Great American Biotic Interchange.” This phenomenon brought today’s opossums, porcupines, and armadillos to North America and today’s foxes, lamine camels (llamas), and small cats to South America. Nothrotheriops was not closely related to two- nor three-toed tree sloths that are alive today in Central and South America

Distribution and Habitat

The Shasta Ground Sloth is known from central Mexico through most of the American Southwest. Partial mummified ground sloths have been found in desert caves in Arizona and New Mexico, including a cave in Grand Canyon National Park that was full of Shasta Ground Sloth dung.
The Shasta ground sloth inhabited dry, open juniper woodlands, seasonal wetlands, and open woodlands.


The Shasta ground sloth was an herbivore. From fossil dung, paleontologists were able to determine that they ate Joshua tree fruits, desert globemallow, cacti, and yucca, along with other desert plants.


The Shasta Ground Sloth was a slow-moving herbivore like living tree sloths; however, it did not climb trees and spent much of its life on the ground. It has been speculated that it had the ability to rear up on its hind legs to forage and defend itself against predators. It probably lived solitarily, only getting together for seasonal mating.

Tule Springs Shasta Ground Sloth

Fossils of the Shasta Ground Sloth are rare at Tule Springs Fossil Beds but the species is known from a partial cranium and a few teeth.

Large Clawed Ground Sloth

illustration of a giant ground sloth
Megalonyx is one of the two species of giant ground sloth found from Tule Springs Fossil Beds National Monument.

NPS illustration by Benji Paysnoe.

Scientific name

Megalonyx sp.


The large clawed sloth, or Megalonyx, was a large ground dwelling sloth which grew to about 10 feet long and weighed roughly 2,200 pounds. Compared to the Shasta Ground Sloth, Megalonyx and had a more blocky-shaped head with an additional set of peg-like incisors in the upper and lower jaws. Like the Shasta Ground Sloth, its front feet bore large claws for grabbing branches and defense.

The first Megalonyx fossils were described by President Thomas Jefferson in 1797, which he thought originally belonged to a giant lion. Sometimes this sloth is referred to as “Jefferson’s ground sloth.”


Prior to the formation of the Isthmus of Panama, relatives in the same family of sloths as Megalonyx were able to distribute between South America and islands in the Caribbean. Megalonyx shares a common ancestor that evolved in South America with its closest living relative, the three-toed sloth. At some point, one lineage adapted to climbing and spending most of its life in trees, while the other lived primarily on the ground.

Distribution and Habitat

Megalonyx has been found in Central America and up into Alaska and the Canadian Yukon. It is really well known in most states east of the Rocky Mountains but does occur on the west coast of the United States. It was also found at a fossil site in the Rocky Mountains 8, 874 feet above sea level.

Based on its distribution, it has been suggested that Megalonyx was able to occupy a variety of habitats but may have preferred woodlands and forests including spruce dominated, and mixed conifer-hardwood habitats.


The large clawed sloth was an herbivore, most likely a browser, feeding off of trees and low-lying shrubs.


Like other ground sloths, the large clawed sloth was slow-moving and most likely lived solitarily. An adult sloth with two associated juveniles of different ages were found at a unique site in Iowa, suggesting that adults cared for multiple generations of offspring. Like other ground sloths, Megalonyx probably used its large body size and claws to deter predators.

Tule Springs Megalonyx

Sloths are rare at Tule Springs Fossil Beds, but Megalonyx is the rarest. It is only known from a few foot bones and a single tooth.

Part of a series of articles titled Prehistoric Life of Tule Springs.

Previous: Ancient Horse

Next: Dire Wolf

Tule Springs Fossil Beds National Monument

Last updated: October 12, 2021