They resemble the Condylarthra, another very generalised group, in having an ent-epicondylar foramen.
They occurred throughout the Tertiary period in both Europe and North America, and have also been found in India. One of the best known genera is Hyaenodon.
Suborder (2). Carnivora vera or Fissipedia.
The skeleton is mainly adapted for a terrestrial mode of life, and the hind limbs have the normal mammalian position. In almost every case the number of incisors is 3/3. Each jaw always has one specially modified carnassial or sectorial tooth which bites like a scissors blade against a corresponding tooth in the other jaw. In front of it the teeth are always more or less pointed, while behind it they are more or less broadened and tuberculated. In the manus the first digit, and in the pes the first and fifth digits are never longer than the rest, and the digits of both limbs are almost invariably clawed. Some forms are plantigrade, some digitigrade, some subplantigrade. The group includes all the ordinary terrestrial Carnivora, and is divided into three sections:—
Æluroidea[135], including the cats, civets, hyaenas, and allied forms.
Cynoidea, including the dog tribe.
Arctoidea, including the bears, raccoons, weasels, and allied forms.
Suborder (3). Pinnipedia[136].
In this suborder the limbs are greatly modified and adapted for a more or less purely aquatic life, the proximal and middle segments of the limbs are shortened, while the distal segment, especially in the leg, is much elongated and expanded. There are always five well-developed digits to each limb, and in the pes the first and fifth digits are generally larger than the others. The digits generally bear straight nails instead of claws, but even nails are sometimes absent. There is no carnassial tooth, and the teeth in other ways differ considerably from those of Carnivora vera. The incisors are always fewer than 3/3; while the cheek teeth generally consist of four premolars and one molar, all of very uniform character, being compressed with conical crowns, and never more than two roots.
The suborder includes three families—Otariidae (Eared Seals), Trichechidae (Walrus), and Phocidae (Seals).