C Orycteropidae. The last family of the living Edentata is that of the Orycteropidae, comprising only the single genus Orycteropus. This genus comprises two or three species, the best known being O. capensis, which is peculiar to South Africa, and is known by the Dutch colonists as the "Aardvark" or Ground-hog. The animal is nocturnal in its habits, and lives upon insects. The body is elongated, and the tail is long, the species attaining a total length of four feet or more. The zygomatic arch is complete. The legs are short, and the feet plantigrade, the anterior pair having four unguiculate toes, the posterior five. The claws are strong and curved, and enable the animal to construct extensive burrows. The skin is very thick, and is thinly covered with bristly hairs; and the tail is hairy. The head is elongated, and the mouth small - devoid of incisor and canine teeth (fig. 375), but furnished with a number of cylindrical molars are flat, and they are composed of dentine traversed by numerous dichotomising pulp-cavities, their cross-section resembling a piece of bamboo cut across. The tongue is long, flat, and slender, and is covered by a sticky saliva, by the aid of which the animal catches insects. The head is long and attenuated, the snout truncated and callous, and the ears large, erect, and pointed. Other species of Orycteropus occur in Senegal and Southern Nubia.
Fig. 375. - Skull of Orycteropus capensis.
The crowns of the molars As regards their distribution in time, the oldest Edentates at present known occur in Europe, in which country no members of the order now exist. These are the Macrotherium and Ancylotherium of the Miocene Tertiary, both apparently allied to the Orycteropidae, with affinities to the Manidae. The Pliocene deposits of North America have yielded to the researches of Professor Marsh two large Edentates of the new genus Moro-therium, and the Miocene deposits of the same country contain remains of another Edentate type (Moropus). It is, however, in the Post-tertiary deposits of the American continent, and especially of South America - the present metropolis of the order - that we find the most abundant and the most remarkable remains of Edentate animals. Here, both in Post-pliocene superficial deposits and in cave-earths of the same age, we meet with the remains of numerous Edentates often of gigantic size, but in the main representing the existing types.
Thus the existing Sloths are represented in the Brazilian bone-caves by a number of extinct genera of Bradypodidae, whilst the Post-pliocene sands and gravels of the open country have yielded the bones of various huge Edentates, resembling the Sloths in most essential respects, but adapted for a terrestrial instead of an arboreal life. Of these great "Ground-sloths" (Gravigrada), the most remarkable are the Megatherium (fig. 376), which attained a length of eighteen feet, with bones as massive as, or more so than, those of the Elephant; and the Mylodon and Megalonyx, both of which extended their range into the United States.
Fig. 376. - Skeleton of Megatherium. Post-tertiary, South America.
In the same way the little banded Armadillos of South America were formerly represented by gigantic species, constituting the genus Glyptodon. The Glyptodons (fig. 377) differed from the living Armadillos in having no bands in their armour, so that they must have been unable to roll themselves up. It is rare at the present day to meet with any Armadillo over two or three feet in length; but the length of the Glyptodon clavipes, from the tip of the snout to the end of the tail, was more than nine feet.
Fig. 377. - Glyptodon clavipes. Pleistocene deposits of South America.
The trunk-armour of Glyptodon is formed of nearly hexagonal bony scutes, forming a massive dome, for the support of which the skeleton is specially modified. Thus the last cervical and first two dorsal vertebrae are anchylosed to form a single bone ("trivertebral bone" of Huxley), which articulates by a movable hinge-joint with the remaining dorsal vertebrae, which are likewise anchylosed to form a kind of "tunnel or arched bridge of bone." The last two lumbar vertebrae are also fused with the sacral and caudal to form a continuous bony mass, whilst the ilia are of enormous size. Numerous extinct forms of genuine Armadillos have also been found in the Brazilian bone-caves, one of them (Chlamydotherium) being as big as a Rhinoceros.
Lastly, the South American Myrmecophagidae are represented in the Brazilian cavern-deposits by the extinct Glossotherium.