Between 25 and 4 million years ago, aquatic sloths nearly the size of elephants lived in what is now known as Chile and Peru. These sloths were skilled swimmers who sustained themselves on vegetation on the seafloor of the ocean, according to a report from researchers at Sorbonne University in Paris.

Believe It or Not!, the ancient mammals had extra dense bones that allowed them to sink more easily and graze on the bottom of the sea similar to manatees!

Sinking Sloths

The study, published in the journal Proceedings of the Royal Society B, found that these giant aquatic sloths gradually made the transition from earth to sea. Study co-author Eli Amson told Live Science, “It was really important for us to show that of course the compactness that was found is really over the top and clearly shows the aquatic adaption, because such high levels of compaction are only found in aquatic animals.”

The density of the sloths’ shin bones and ribs increased 20 percent over a period of around 3 million years. This is moderately fast when it comes to geologic time, according to the researchers, who examined fossil remains of the sloth’s transition from land to aquatic creatures. The reason as to why the sloths started foraging for food in the water is likely because it was hard to find in Peru, which had desert-like conditions.

The Bone-afide Secret

Modern-day sloths are the size of monkeys and reside in trees. However, they still have somewhat dense bones in comparison to other mammals. As a result, scientists think this bone density may serve a purpose on land and thus helped their ancestors transition to an aquatic lifestyle. It’s unclear how the dense bones were/are a benefit on land.

Aquatic sloths have been extinct for approximately 4 million years. They survived until the Isthmus of Panama closed and the Caribbean Sea no longer led into the Pacific Ocean. South American waters became colder, which destroyed the sea grass that the sloths consumed. This, and the possibility that the sloths couldn’t stand the cold water, likely led to their demise.

Aquatic sloth skeleton

Credit: FunkMonk Via Wikimedia Commons (CC BY-SA 3.0).

Research on the five species of sloths is ongoing in order to learn more about their evolution.

Magnificent Mammals

There is an interesting fact about sloths that makes even more sense given these research results: They are great swimmers and can hold their breath for about 40 minutes underwater, according to Travel & Leisure. Their hind legs are weak, but once they hit the water, their long arms help them swim around quite easily.

Other facts you may not know:

  • Sloths relieve themselves only once a week and do so in the same spot every time.
  • Sloths move so slowly that fungi grow on their fur.
  • Sloths can rotate their heads nearly 270 degrees in the same direction.
  • Sloth “nails” are actually four-inch-long finger bones covered in keratin that help them hold onto trees.
  • Sloths typically live alone and have a lifespan of 20-30 years in the wild.

In addition, Thomas Jefferson loved studying fossils, and his research in 1804 led to the discovery of an extinct sloth species, according to the Smithsonian. He is credited as the discoverer of the Megalonyx genus.

Can’t Get Enough Sloths?

This spring, visitors to Ripley’s Aquarium of Myrtle Beach in South Carolina will be able to come face-to-face with the adorable creatures at the brand-new Ripley’s Sloth Valley habitat!

Ripley's Sloth Valley

Think you’re already an expert on all things sloth? Visit the Ripley’s Aquarium of Myrtle Beach website to test your knowledge and be entered to win four early-access tickets to Sloth Valley!

By Noelle Talmon, contributor for


Discover hundreds of strange and unusual artifacts and get hands-on with unbelievable interactives when you visit a Ripley’s Odditorium!