This Month in Science

Giant Ground Sloth: Eremotherium eomigrans

In December 1991, a young skateboarder (who happened to be an amateur geologist) went in search of a good spot to skateboard. In his quest, he found shell-encrusted dirt from the dig of a nearby drainage pond on Randall Parkway. He recognized that particular type of dirt can be rich in fossils and started looking around. It wasn’t long before he found some very large and very old bones. The Smithsonian was contacted, and their scientists collected a number of the discovered bones, including teeth, claws, and vertebrae, to take back to Washington for testing. A former Cape Fear Museum staffer, John Timmerman, also participated in the excavation.

The fossils were eventually identified as belonging to Eremotherium eomigrans, a species of giant ground sloth. Prior to this discovery, the furthest north a giant ground sloth skeleton had been found was South Carolina. Most fossils of this species have been found in Florida, suggesting that region to be their primary habitat. The sloth’s manus, or hand, was important in identifying the species as E. eomigrans. These fossils had five fully-formed, distinct claws, unlike their close relatives Eremotherium llaurilardi which, like the smaller tree sloths of today, had only three digits, and Eremotherium mirabile, which had three full claws and reduced, vestigial fourth and fifth digits.

E. eomigrans roamed the Americas during the early to middle Pleistocene Epoch, between 600,000 to 2.6 million years ago. While they primarily lived in South America, this species of sloth was the first of its kind to migrate from South America to North America. In fact, migrans is the Latin word for migrant. To call these ground sloths “giant” is no understatement. The claws alone from an E. eomigrans could be up to a foot long. E. eomigrans could weigh up to 3 tons and grow up to 18 feet in length from head to tail. Researchers believe that males and females likely differed in size, but they have not determined which sex was larger and which was smaller.

Researchers use the shape of the teeth to provide information about the diets of prehistoric animals. E. eomigrans had v-shaped teeth with the bottom and top teeth fitting together, good for smashing leaves and other vegetation. These teeth indicate that giant ground sloths were vegetarians. It is likely that they walked around on all fours, but they could use their tail as a stabilizing third “leg” when rearing up on their hind legs to reach vegetation in the trees. This and other species of giant ground sloth went extinct around 10,000 years ago. While the exact cause is unknown, the arrival of humans to the continent and a possible ice age likely contributed to the mass extinction.

The fossils from the Randall Parkway excavation were returned from the Smithsonian to the North Carolina Museum of Natural Sciences in Raleigh. The bones came from two separate animals and both were more than 50 percent complete, a rare find in paleontology. The Museum of Natural Sciences had the resources and capability to reconstruct a skeleton from the fossils. While the majority of the original fossils remain in the care of the state museum in Raleigh, a full replica of the giant ground sloth skeleton was cast from the bones and can be seen right here at Cape Fear Museum, along with a few of the original fossils on loan from the state museum. Come in and check it out!