Researchers have found fossil evidence of an ancient giant land sloth that lived in the proto-Amazonian swamps. The fossil shows tibial bites from the Miocene caiman Purussaurus, a large crocodile species of the period. In their article, published in the journal Biology Letters, scientists describe the fossil and what they have learned about it.
The fossil was found in rocks of the Pebas Formation (near the Napo River) in the Peruvian Amazon as early as 2004 but has not yet been fully explored. Scientists discovered that it belonged to a giant ground sloth about 13 million years ago. Previous research has shown that at the time the area where the fossil was discovered was a wetland system. Giant sloths roamed the edges of the water, eating the grasses that grew there. Previous research has also shown that there are at least seven crocodile species in the region, although some of them were quite small. The size and shape of the bite marks excluded all but the Purusaurs.
The researchers note that at the time of the fossil record, this area had not yet been captured by mammals, since almost all predators that lived on land were marsupials. The Purusaurus, the largest crocodile species, lived in the water and was the largest species ever to exist, growing up to 6 meters in length and with a bite force that scientists believe was twice as strong as that of a Tyrannosaurus.
Scientists speculate that the Purusaurus jumped out of the water and grabbed the sloth by the hind leg. After that, he dragged the sloth into the water and held it there until he drowned. Researchers found evidence from 46 tooth marks on the fossil that the sloth repeatedly bit the Purusaurus when it attacked it. Purusaurus left behind shallow scratches, as well as holes – traces of penetration into the tibia. There was also no evidence of bone regeneration in the sloth, suggesting that it did not survive the attack.