Giant Sloths

10,000 years ago humans had reached the very southern tip of South America, where in present day Chilean Patagonia they shared a cavern with the giant sloth whose bones Charles Darwin discovered in the 1830's. The word is still not in as to which of the creatures portrayed here is the giant sloth.

Seven thousand years later the giant sloth and most other large animal species in the Americas were extinct, but the first beginnings of complex human societies were taking shape, around 3000 BCE.

Many of the large mammals (e.g., the mammoth, the saber-tooth tiger) that inhabited the Americas, some even after the end of the last ice age, became extinct, in an episode known as the late Pleistocene die off. Significant climatic change is most often cited as the reason but some anthropologists argue that the entrance of humans, first on to the North American plains east of the Canadian Rockies, then southward, could have had a dramatic impact, out of all proportions to their numbers, on the big animals at the top of the food chain.

The giant ground sloth was one of the enormous creatures that thrived during the ice ages. Looking a little bit like an oversized hamster it probably fed on leaves found on the lower branches of trees or bushes.

The largest of these ground sloths was Megatherium which grew to the size of a modern elephant.

Like other giant creatures that disappeared at the end of the Pleistocene period (about 10,000 years ago), Megatherium, and its smaller sloth cousin, Mylodon, are extinct.

Only the small tree sloth survives today.

UF Researchers Fibd Oldest Bones of New Giant Ground Sloth Species

June 20, 2000 - University of Florida news

-Bones of a newly discovered ground sloth that is the oldest of its kind ever found in North America have been uncovered by a University of Florida research team.

Weighing more than five tons and able to reach as high as 17 feet, the 2.2 million-year-old prehistoric creature was larger than today's African bull elephants, said UF paleontologist David Webb.

"This is a great, wonderful animal unlike anything in existence whose huge size is almost reminiscent of the dinosaurs," Webb said.

Eremotherium eomigrans, as named in a recent academic journal article, was the earliest of the giant sloths known as megatheres to have migrated from South America north across the Panamanian Land Bridge, Webb said. Before the Ice Age, these slothful plant-eaters lumbered across the Florida peninsula like herds of elephants, using their fearsome claws to strip leaves from branches and entwine them in their long tongues, he said.

Unlike other large-bodied ground sloths, the new species had an extra claw, representing a surprisingly primitive stage of evolution, Webb said. While all other giant sloths had four fingers with only two or three claws, this one had five fingers, four of them with large claws, the biggest being nearly a foot long, he said.

"The existence of such sloths would have been expected at a much earlier time, and in South America, not Florida," he said.

This evolutionary pattern of a reduction in the number of fingers and claws over time continued into the present with its modern-day descendant, the much smaller three-toed sloth, which lives in the tropical forests of Central and South America, he said.

A university geology student found the ground sloth bones in 1986 during a class field trip at the Haile limestone quarry west of Gainesville. Over the years, a dozen other ground sloths were found, some completely articulated skeletons, and were brought to UF's Florida Museum of Natural History.

In 1989, Webb invited two of the world's leading specialists on such animals to examine the bones. Castor Cartelle, a zoologist from the University of Belo Horizonte in Brazil, and Gerardo De Iuliis, a zoologist from the University of Toronto in Canada, studied the bones for a decade before concluding this was a new, huge find. The findings were published as a 20-page paper in the December issue of the Zoological Journal of the Linnean Society of London.

The fossil deposit was unusual in that it was found in what was a quiet pond, which allowed for excellent preservation, Webb said. Most fossil collections in Florida are found in small sinkholes or in stream deposits, where the bones are stirred up, he said.

"To get every bone in a hand perfectly articulated in a stream deposit would be very rare," he said. "Because bones are usually scattered, you would probably never know for sure how many claws an animal had, as we were able to determine with this ground sloth."

The bones of one of the largest, most complete individuals will be assembled at the Natural History Exhibit Hall in Livingston, Mont. Matt Smith, a professional fossil preparator, was in Gainesville last week to collect the bones and will mount the skeleton. He said visitors to nearby Yellowstone National Park can stop and see him work through a picture window. The skeleton is to be posed in an upright position, as if stripping branches from a tree, and the finished product will be returned to the UF museum in 18 months for display in UF's Powell Hall.

"This animal is incredible," Smith said. "It's as interesting to me as the dinosaurs I've been working on."

Giant ground sloths also fascinated President Thomas Jefferson, an amateur palentologist who brought their bones to the White House. "My favorite piece of history is when he instructed Meriwether Lewis, of the Lewis and Clark expedition, to keep an eye out for ground sloths," Webb said. "He was hoping they would find some living in the Western range."