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

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

How Do We Know This?

Because direct observation of a fossil animal's behavior isn't possible, paleontologists use comparison and contrast with living animals for guidance. Tracks can sometimes reveal further clues to behavior. At a fossil site, the mix of plant and animal species gives clues to the ecosystem of that time and place.


  • Descriptions of giant ground sloths in the past emphasized their relationship to tree sloths, with slow plodding travel on all fours but more recently with new discoveries and analyses, more movements and behaviors are believed possible, including tree-climbing, swimming, burrowing. (McDonald & DeIuliis 2008)
    • Small dwarf ground sloths in the West Indies may have been arboreal. (Steadman et al 2005)
    • Some sloths in the extinct family Nothrotheriidae might have been unspecialized swimmers, perhaps like capybara (Vizcaíno et al 1999)
    • Several South American ground sloth fossils were studied for the possible functioning of the limbs (Vizcaíno et al 2008)
      • Researchers using trackways and biomechanical calculations said Megatherium americanum and some mylodontid sloths could walk upright (were bipedal).
      • If ground sloths were bipedal, then arms were free for other tasks such as digging and/or defense.
      • Farina and Blanco (1996) suggested Megatherium arms and claws weren't used for digging, but instead were capable of fast, aggressive action perhaps in defense.
      • By contrast with Megatherium, two mylodontid sloths analyzed seemed to be very well suited for powerful digging and they may have produced burrows seen in Pleistocene sediments exposed along sea cliffs in Argentina. (Vizcaíno et al 2001)

Interspecies Interactions

  • Paramylodon harlani are often found with mammoths in North America, sharing a common habitat; not known how they avoided competition for plant resources. (McDonald & Pelikan 2005)
  • Researchers who examined a typical Late Pleistocene fauna from Virginia did not find much difference in the plant diets of all the large herbivores, including ground sloths; how these animals avoided competition was a puzzle. (France et al 2007)
    • Niche compaction and collapse may be reflected in these results, leading to eventual extinction or local extinction (extirpation) of many of the animals.

Page Citations

Fariña and Blanco (1996)
France et al. (2007)
McDonald & DeIuliis (2008)
McDonald & Pelikan (2005)
Vizcaíno et al. (2001)
Vizcaíno et al. (2008)

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