Sloth Rescued On The Highway

Sloths are members of the superorder Xenarthra, a group of mammals that appeared approximately 60 million years ago, although at least one source puts the date at which sloths and related animals broke off from other placental mammals at about 100 million years ago. Also included among the Xenarthra are anteaters and armadillos. The earliest xenarthrans were arboreal herbivores with sturdy spines, fused pelvises, stubby teeth and small brains.
The living sloths belong to one of two families, known as the Megalonychidae ("two-toed" sloths) and the Bradypodidae (three-toed sloths). All living sloths have in fact three toes; the "two-toed" sloths, however, have only two fingers. Two-toed sloths are generally faster moving than three-toed sloths. Both types tend to occupy the same forests: in most areas, one species of three-toed sloth and one species of the larger two-toed type will jointly predominate.
However, their adaptations belie the actual relationships of the living sloth genera, which are more distant from each other than their outward similarity suggests. The common ancestor of the two genera apparently lived 35-40 million years ago, making the living forms stunning examples of convergent or parallel evolution. The two-toed sloths of today are far more closely related to one particular group of ground sloths than to the living three-toed sloths. Whether these ground-dwelling Megalonychidae were descended from tree-climbing ancestors or whether the two-toed sloths are really miniature ground sloths converted (or reverted) to arboreal life cannot presently be determined to satisfaction. The latter possibility seems slightly more likely, given the fact that the small ground sloths Acratocnus and Neocnus which were also able to climb are among the closer relatives of the two-toed sloths, and that these together were related to the huge ground sloths Megalonyx and Megalocnus.