Case Solved: Why Sloths Are Slothful

Sloths navigate trees just like monkeys do, a new study finds. The only difference is, sloths use their slothfulness to their advantage.

Using X-ray video, researchers from the University of Jena studied the movement of three two-toed sloths named Julius, Evita and Lisa. As the sloths slowly inched along a branch, hanging upside-down, the researchers watched their muscles and joints move.

"To our great surprise, the locomotion of sloths is basically not so different from the locomotion of other mammals, like monkeys for instance," study researcher John Nyakatura, an evolutionary biologist at the University of Jena in Germany, said in a statement. When the sloths move upside-down along a branch, Nyakatura said, "the position of their legs and the bending of their joints matches exactly those of other mammals in the process of walking."

For Subscribers

FOR SUBSCRIBERSCBP leaders cut out of Trump ad buy decision

FOR SUBSCRIBERSAmerican passenger drafted goodbye texts to her family as Flydubai plane plummeted

FOR SUBSCRIBERSCornell rape allegation pushes embattled New York prosecutor into national spotlight

FOR SUBSCRIBERSAbdul El-Sayed tries to woo MAHA voters as Democrats seek inroads with RFK’s supporters

FOR SUBSCRIBERSKratom-like substances are popping up in a typically benign supplement

FOR SUBSCRIBERSGOP super PAC increases its spending for Sen. Jon Husted in tough Ohio race

FOR SUBSCRIBERSRecords reveal tumultuous marriage between slain New York Times executive and wife

FOR SUBSCRIBERSFrom clean energy warrior to ‘wall of shame,’ James Talarico reverses on a fossil fuel money pledge

FOR SUBSCRIBERSCongressional staff planned official trip with luxury stops in Italy and France weeks before election

FOR SUBSCRIBERSA harrowing ordeal aboard an Israel-bound plane

FOR SUBSCRIBERSOpenAI CEO Sam Altman to skip congressional hearing on rogue AI agents

FOR SUBSCRIBERSKey DOJ lawyers departed Trump ‘grand conspiracy’ probe amid pressure to produce, source says

FOR SUBSCRIBERSTrump’s new AI chatbot often links to a site launched under Clinton 26 years ago

FOR SUBSCRIBERSAt MAHA summit, industry CEOs the movement once vilified take the stage

FOR SUBSCRIBERSThis Paralympian has two goals: Win medals and give away $500,000 to her teammates

The research, part of Nyakatura's doctoral thesis, revealed that sloths are lazy for good reason. Their bodies have evolved to have adaptations to save energy, with long arms set on short shoulder blades allowing for a large reach with very little movement. This enables sloths to save energy while making the same movements as other mammals.

For Subscribers

FOR SUBSCRIBERSCBP leaders cut out of Trump ad buy decision

FOR SUBSCRIBERSAmerican passenger drafted goodbye texts to her family as Flydubai plane plummeted

FOR SUBSCRIBERSCornell rape allegation pushes embattled New York prosecutor into national spotlight

FOR SUBSCRIBERSAbdul El-Sayed tries to woo MAHA voters as Democrats seek inroads with RFK’s supporters

FOR SUBSCRIBERSKratom-like substances are popping up in a typically benign supplement

FOR SUBSCRIBERSGOP super PAC increases its spending for Sen. Jon Husted in tough Ohio race

FOR SUBSCRIBERSRecords reveal tumultuous marriage between slain New York Times executive and wife

FOR SUBSCRIBERSFrom clean energy warrior to ‘wall of shame,’ James Talarico reverses on a fossil fuel money pledge

FOR SUBSCRIBERSCongressional staff planned official trip with luxury stops in Italy and France weeks before election

FOR SUBSCRIBERSA harrowing ordeal aboard an Israel-bound plane

FOR SUBSCRIBERSOpenAI CEO Sam Altman to skip congressional hearing on rogue AI agents

FOR SUBSCRIBERSKey DOJ lawyers departed Trump ‘grand conspiracy’ probe amid pressure to produce, source says

FOR SUBSCRIBERSTrump’s new AI chatbot often links to a site launched under Clinton 26 years ago

FOR SUBSCRIBERSAt MAHA summit, industry CEOs the movement once vilified take the stage

FOR SUBSCRIBERSThis Paralympian has two goals: Win medals and give away $500,000 to her teammates

"With their mode of life, sloths are filling an ecological niche," said study researcher Martin Fischer, a professor of systematic zoology and evolutionary biology at the University of Jena. "Sloths lead their lives in energy-saving mode."

You can follow LiveScience  senior writer Stephanie Pappas on Twitter. Follow LiveScience for the latest in science news and discoveries on Twitter @livescience  and on.

• Image Gallery: Evolution's Most Extreme Mammals
• 10 Amazing Things You Didn't Know about Animals
• The World's Freakiest-Looking Animals