Unlike sloths, the megatherium has seven cervical vertebrae; and the spines of all the trunk-vertebrae incline backwards.
Although similar teeth occur in the phosphorite beds of South Carolina, which may have been transported from elsewhere, no undoubted remains of Megatherium are known from North America.
From Megatherium these animals, which rivalled the Indian rhinoceros in bulk, differ in the shape of their cheek-teeth; these (five above and four below) being much smaller, with an ovate section, and a cupped instead of a ridged crown-surface, thus resembling those of the true sloths.
Except, indeed, for its relatively shorter limbs Megatherium americanum rivalled an elephant in bulk, the total length of the skeleton being 18 feet, five of which are taken up by the tail.
From all these Megatherium differs in the form and structure of the teeth.
All the above genera differ from Megatherium in having a foramen on the inner side of the lower end of the humerus.