Hapalops

Sloths in this genus had a long, robust body with more than 19 thoracic vertebrae, a short skull, and long limbs with large, curved claws. They were small sloths, measuring about 1 metre (3.3 ft) in length. On the ground, they probably walked on the knuckles of the forelimbs, like a gorilla. Hapalops had very few teeth with no incisors; the mandible included only four pairs of teeth.[3]

In the Santa Cruz, Hapalops fed on vegetation in intertropical wooded savannahs. It shared its environment with both herbivorous and predatory marsupials, sheep-sized glyptodonts, armadillos, anteaters, toxodonts, typotheres, and litopterns, as well as modern reptiles such as iguanas and birds such as rheas, geese, and hawks. Giant phorusrachid "terror birds" lived in the region and may have been the top predators.[4] Like most extinct sloths it is categorized as a ground sloth, but it is believed that the smaller size of Hapalops allowed it to engage in some climbing behaviors.[5]

The genus is classified within the Megatheroidea, which includes the megalonychid and the nothrotherid sloths. While it is generally represented as an outgroup to Nothrotheriidae and a genus of uncertain relationships, it shows most of the character states that diagnose Nothrotheriidae and may be a close relative. At least 26 species in this genus have been named from the same Santa Cruz formation, a biological impossibility largely based on assigning new species names to fossil fragments. The genus awaits revision.[6]