MEGATHERIIDIE, a family of extinct mammals of the order Edentata, named by prof. Owen, and containing several genera. Pictet gave it the name gravigrades, placing it between the sloths and the armadilloes. There are nine or inore genera, 1 megatherimn, 2 cmlodon, 3 lestodon, 4 rnegalonyx, 5 mylodon; 6 scelidotherium, 7 splie rodon, 8 tnegalocnus, 9 myomorphus. See MEGATREnium, ante.
MEGATRE'RIlIM (Gr. great beak), a gigantic extinct quadrt' 'Tied of the order Eden tata, nearly allied to the sloth, found in the superficial stratum of the South American pampas. In structure, it is very near its modern representative, except that the whole skeleton is modified to suit the requirements of an immense heavy-boned and heavy bodied animal, some 18 ft. in length and 8 ft. in height. The appellation tardigide. which Cuvier applied to the sloth, cannot be given to the megatherium; its limbsiR-ere comparatively short and very strong, and the feet adapted for walking on the ground, approaching in this respect nearer to the allied ant-eaters, but with this peculiaritY, that the first toe of each of the hind feet was furnished with a large and powerful claw, which was probably used as a digger to loosen roots front the soil, and enable the crea ture the 'more easily to overturn the trees on the foliage of which it browsed. The
enormous development of the bones of the pelvis, the hind legs, and the tail, gave the animal great power w-ben, seated on its hind legs and tail, as on a tripod, it raised its fore legs against the trunk, and applied its force against a tree tha-t had already been weak ened by having its roots dug up. The structure of the lower jaw seems to indicate that the megatherium was furnished with a huge prehensile tongue like that of the giraffe, with which it stripped the foliage from the trees.
The remains of several allied genera of huge edentata are associated with the mega therium in the' pampas deposits. They form the family- megatheriidm of Owen, -which includes mylodon, megalonyx, sceledotherium, etc., genera which are separated from megatherium chiefly from peculiarities in the dentition.
The modern sloth is a native of South America, and the fossil remains of these immense creatures, which represented it in the newer tertiaries, have been found only in this continent, the past and present distribution of the family being the same.