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Extinct Ground Sloths (Paramylodon harlani, Nothrotheriops shastensis, and Megalonyx jeffersoni) Fact Sheet: Summary

Extinct Ground Sloths (Paramylodon harlani, Nothrotheriops shastensis, and Megalonyx jeffersoni)

Archived Content

Disclaimer: Fact sheets on prehistoric (extinct) species contain archived content and are no longer being updated. At the time of publication, these pages summarized the best available science. However, some content may become outdated as scientists report new discoveries.

Extinct Ground Sloths (Paramylodon harlani, Nothrotheriops shastensis, and Megalonyx jeffersoni)

Extinct Ground Sloth 

Image credit: © San Diego Zoo Wildlife Alliance. All rights reserved.

Taxonomy Physical Characteristics

Kingdom: Animalia

Phylum: Chordata

Class: Mammalia

Order: Pilosa (anteaters and sloths)

Family: Mylodontidae (family is extinct)

Genus: Paramylodon                              

Species: Paramylodon harlani

Family: Nothrotheriidae (family is extinct)

Genus: Nothrotheriops

Species: Nothrotheriops shastensis

Family: Megalonychidae (family has extinct and living/extant members)

Genus: Megalonyx (extinct)

Species: Megalonyx jeffersoni




Body Weight
Paramylodon harlani: varied estimates from 1,000 kg (2,205 lb) to 1,089 kg (2,400 lb)
Nothrotheriops shastensis: estimated 250 kg (551 lb)
Megalonyx jeffersoni: estimated near 1,000 kg (2,205 lb)

Body Length
Paramylodon harlani: 3 m (9.8 ft)
Nothrotheriops shastensis: about the size of a black bear
Megalonyx jeffersoni: 3 m (9.8 ft)

Long hairs, especially on flanks and rear limbs.

Distribution & Status Behavior & Ecology

Paramylodon harlani: widely distributed across the U.S., especially in western states
Nothrotheriops shastensis: primarily western U.S. but also in Florida, Texas, Mexico
Megalonyx jeffersoni: wide distribution in over 150 sites in United States, including Alaska, northwestern Canada, Mexico

Paramylodon harlani: preferred areas of open grass or parkland, perhaps near water; not found in dry areas
Nothrotheriops shastensis: areas that were drier during the Pleistocene—open savanna scrub land with trees; deciduous forests
Megalonyx jeffersoni: gallery forests along rivers or lakes

All giant ground sloths are extinct. Causes unknown.

Studies suggest a range of movements, including tree-climbing, swimming, and burrowing.

Interspecies Interactions
Extinct ground sloths shared habitats with other large herbivores. Ex. Paramylodon harlani often found with mammoths in North America

Diets of ground sloths varied. Some exclusively herbivorous, some species also ate meat. See Diet & Feeding for details.

Ground sloths juveniles would have been vulnerable to the large cat predators (Smilodon, Homotherium, Panthera atrox) and perhaps Dire Wolves.

Reproduction & Development Species Highlights

Life stages
May have provided extended parental care. Had few young.

Feature Facts

  • The diversity of sloths in the fossil record is high; over 100 genera are recognized
  • 90% of sloth genera became extinct at the end of the Pleistocene
  • The adaptations and biology of living tree sloths are very different from extinct ground sloths; comparisions should be limited
  • Large powerful claws on the sloths' hands were probably for digging as well as defense.
  • Some ground sloths used caves as habitat
  • Sloths in the mylodontid family had small bony deposits (osteoderms) imbedded in their skin; other animals that have more developed osteoderms include lizards, crocodiles, and pangolins

About This Fact Sheet

© 2009 San Diego Zoo Wildlife Alliance


How to cite: Extinct Ground Sloths (Paramylodon harlani, Nothrotheriops shastensis, and Megalonyx jeffersoni) Fact Sheet. c2009. San Diego (CA): San Diego Zoo Wildlife Alliance; [accessed YYYY Mmm dd]. extinctgroundsloths
(note: replace YYYY Mmm dd with date accessed, e.g., 2015 Sep 10)


Disclaimer: Although San Diego Zoo Wildlife Alliance makes every attempt to provide accurate information, some of the facts provided may become outdated or replaced by new research findings. Questions and comments may be addressed to

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