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3mo ago

Landmark Study Chronicles 35-Million-Year Evolution and Extinction of Sloths

New research links climate shifts, habitat changes, and human activity to sloth size evolution and extinction patterns.

Ancient sloths lived in trees, on mountains, in deserts, boreal forests and open savannahs. These differences in habitat are primarily what drove the wide difference in size between sloth species.
Dallas Krentzel

Overview

  • A study published in *Science* used ancient DNA, fossil analysis, and climate data to map sloth evolution over 35 million years.
  • Researchers found that arboreal sloths remained small due to branch weight limits, while ground-dwelling species evolved into massive forms like the 8,000-pound Megatherium.
  • Climate cycles, such as Miocene warming and Pleistocene cooling, drove sloth size changes, with warming favoring smaller species and cooling promoting gigantism.
  • Some ground sloths developed unique adaptations, including osteoderms for defense and semi-aquatic traits for coastal environments.
  • Human arrival in the Americas 15,000 years ago coincided with the extinction of large ground sloths, while Caribbean tree sloths persisted until about 4,500 years ago.