MYLODON, an extinct genus of large ground-sloths char acteristic of the Pleistocene of the New World. The animal was of the size of a rhinoceros, with short stout limbs, very large digging claws, five digits on each foot, but the outer ones have no claws, a broad body and massive tail. It walked on the outer edge of the sole, both fore- and hind-foot (compare fore-foot of modern ant-eater). The head was rather long, with wide blunt muzzle, no front teeth, and moderately large prismatic cheek teeth, five above and four below on each side. In cross-section the more anterior teeth are rounded oval, while the posterior ones are progressively larger and more elaborate, the last molar always two- or three-lobed. The skin was probably like that of the allied genus Grypotherium in which, as shown by specimens from a cave off the Straits of Magellan, the skin was studded with bony ossicles and covered with heavy coarse brown hair.
The genus Mylodon (in the wider sense) ranged from Canada to Patagonia, and many complete skeletons have been found in Argentina, California and the central United States. A number of related genera are also found in the Pleistocene of South America. Lestodon has the front pair of teeth enlarged as tusks and a flaring, bell-shaped muzzle. Scelidotherium has a much more elongate skull, narrower body and more reduction and specialization in the toes. These with some other less known genera form the family Mylodontidae, whose ancestry can be traced back to the Miocene in Patagonia although not so well known as the related Megatheriidae. These small Miocene ground sloths come near to being ancestors of the modern tree-sloths as well; they likewise approach the ant-eaters in various particulars and suggest a more remote affinity to the armadillos.
(W. D. M.)