HYRACOIDEA, a group of small hoofed mammals, includ ing the biblical cony. The name cony or coney originally referred to the rabbit but has also come to be used for the related pikas, and for the present quite distinct animals. There is no unambig uous popular term for members of the Hyracoidea. They are usually called hyraxes (or hyraces). "Rock rabbits," also some times used, is objectionable because they are not rabbits and many of them have nothing to do with rocks. In appearance the living hyraxes, with their plump, pointed heads, short necks, relatively short, slender legs, and squat, almost tailless bodies, look much more like rodents than ungulates. Nevertheless their anatomy clearly shows they are related to the hoofed mammals.
Living hyraxes are confined to Africa south and east of the Sahara and extreme southwestern Asia. They may be divided into two groups. One, the genus Procavia, includes the ground living forms, especially characteristic of deserts, hills and moun tains up to about io,000 feet, living in holes and fissures among the rocks. The other group is similar but is best separated as Dendrohyrax. These forms, confined to Africa, are almost entirely tree-dwelling, the only true arboreal hoofed mammals. They live in holes in trees and move readily along the trunks and branches. Both types climb easily, clinging even to almost vertical surfaces by the pads on their feet.
The hyraxes have numerous structural peculiarities which sepa rate them sharply from any other mammals. The normal adult dental formula is II The upper incisors are large, 2 0 4 3 curved in a semicircle longitudinally, and grow continuously throughout life like those of rodents. Canines are absent. The premolars and molars are in pattern surprisingly like those of some of the typical ungulates, especially the rhinoceros. The dorsal and lumbar vertebrae are unusually numerous (up to 3o in Procavia). On both front and hind feet the three middle toes are well-developed. In the forefeet the other two toes are also present, although the first is much reduced ; in the hind feet the first toe is absent, the fifth vestigial. The hoof of the inner (second) toe of the hind foot is claw-like, but on all the other toes the hooves are normal, although small. The wrist-bones are arranged serially, the individual bones generally coming in con tact with only one bone of the opposite row—an arrangement typical of the most primitive extinct ungulates but lost in the more specialized modern forms. The alimentary canal is unique in having a pair of large coeca opening into the large intestine some distance below the usual one at the junction of large and small intestines. There is a gland on the back.
The relationships of the hyraxes are doubtful. There is no question that the numerous resemblances to the rodents are all superficial and that the fundamental characters indicate affinities with the ungulates, but these affinities must be distant so far as any living forms are concerned. In addition to their many very primitive characters, the hyraxes show some special resemblance to primitive or extinct members of several groups, particularly the Proboscidea, Perissodactyla, some Condylarthra (Menisco therium), and the peculiar South American fossil ungulates. This confusing series of resemblances suggests that the group is an ancient and unprogressive offshoot derived from the ungulate stem at a time when the modern groups of ungulates were not well differentiated.