FOSSIL EDENTATA. Remains of fossil eden tates have been found rarely in the Tertiaries of Europe and Africa. The centre of greatest de velopment seems to have been South America, during ancient times as well as at present, though some imperfectly known forms, more nearly like the normal mammals in dentition, having incisor teeth on both jaws and the nor mal premolar and molar teeth, have been dis covered in the Eocene deposits of North America. The paleontologic evidence does not support the hypothesis that the edentates repre sent primitive forms of mammals, but it does show that they have been derived by regressive evolution front higher normal eutherian types, and that they constitute a degenerate series of mammals, the exact origin of which is, however, unknown. See DEGENERATION AS A FACTOR IN EVOLUTION; and EXTINCTION OF SPECIES.
No fossil form of the sloths (family Brady podida') or ant-eaters (Myrinecophagida) have been found, but an extinct family (Megathe riithe) presents characters intermediate between these two modern groups. They were mostly mammals of gigantic size, such as Megatherintu, Mylodon (qq.v.). Seelidotheri UM, and Mega lonyx, the remains of which are found commonly in the Pleistocene deposits of South America. and
occasionally in the Pleistocene cave deposits of North America, as far north as Kentucky. The armored edentates, such as the armadillos and glyptodonts, arc connected with the megathe riums through Meg,alonyx. which has ossified plates imbedded in its skin. These isolated plates became united into transverse rows in the armadillos and into a solid earapace in the glyptodonts. The gigantic glyptodon (q.v.) and the allied Thedieurus. from the beds if Argentina, have the body inclosed in a solid massive carapace made of polygonal bony plates that are firmly soldered together in the adult animals. but loosely joined in the young individ uals. The tail also is covered by heavy plates. The total length of the skeleton varies from twelve to twenty feet. Armadillos with mov able transverse rows of dermal plates are found fossil in the Tertiary deposits of Patagonia, and the ea•liest forms show no close points of rela tionship with the glyptodonts. The genera are Chlamydotherium. Dasypus. Eutatus. and Proi;u talus, of which the first mentioned attained the bulk of a rhinoceros. Compare GvxonoNTA.