News Paleontology

Sloths once came in a dizzying array of sizes. Here’s why

Fossil and DNA analysis reveals how habitat drove change — until humans showed up

An artist's conception of three different sloth species, including a modern tree-dwelling sloth, the extinct giant ground sloth and an intermediate semi-arboreal sloth.

Depending on whether they were more terrestrial or arboreal, sloths’ body sizes became larger or smaller. This artist’s representation shows the modern pale-throated sloth, Bradypus tridactylus, at bottom. At left is the extinct semi-arboreal Hapalops elongatus; in the background is the extinct giant ground sloth, Megatherium americanum.