The earlier types of Dogs have been placed in different genera. Cynodictis is an Eocene form from European strata. The skull is decidedly Civet-like, with a short snout. The fore- and hind-feet were five-toed, with well-developed pollex and hallux. The dentition was that of modern Dogs, the molars being two in the upper and three in the lower jaw. The general aspect of the creature and the form of the skeleton was much like that of the Viverrine genus Paradoxurus, of which, as well as of the Dogs, Cynodictis might have been an ancestor.
Simocyon of the Upper Miocene serves as the type of a separate sub-family of Dogs, Simocyoninae. The skull is short, broad, and high; the shortening of the skull affecting the jaws has reduced the teeth greatly; the first three premolars are very small, fall out soon, and are thus often deficient. There are only two molars in each jaw. This type is of course nowhere near the ancestral Dog. It is a much-specialised branch of an early type. Cephalogale is less specialised; there are the usual four premolars. Enhydrocyon is an intermediate form; it has lost one premolar in each jaw.
Amphicyon, forming the type of another sub-family, Amphicyoninae, though usually placed among the Dogs, presents us with
many Bear-like features in its organisation. The feet, for instance, were plantigrade and five-toed. The ulna and the radius are specially compared with the same bones in the Bear tribe. The skull on the other hand is as distinctly Dog-like in form. The molars are large, broad, and crushing, and Bear-like. The largest known species, A. giganteus, is of about the size of the Brown Bear. Amphicyon is a Miocene genus. Eocene and allied to it is Pseudamphicyon. This genus has, like Amphicyon, the complete dentition of forty-four teeth. In the Amphicyoninae generally the feet are five-toed, the humerus has an entepicondylar foramen and the femur a third trochanter. The upper molars are large.
The closely allied and American genus Daphaenus has also plantigrade feet, and has in its structure many reminiscences of the Creodonts. So, too, has the Eocene Uintacyon.
Cynodesmus is closely allied to Cynodictis. It has ancient features combined with quite modern ones. The skull is described as being Creodont-like, but the dentition is that of the microdont modern Dogs. In accordance with its age the cerebral convolutions of this Dog are much simpler than in existing Dogs, and the hemispheres do not cover the cerebellum so much.
The Bear-like Carnivora or Arctoidea.—That division of the Carnivora which is typically represented by the Bears embraces three recent families, which are united by a number of characters. These Carnivora are always plantigrade or nearly so. They have nearly always five toes. The claws are not retractile, or at most semi-retractile as in the Panda. In the skull the tympanic bulla is often depressed, and is not so globular and obvious as in the Cats. Its cavity is not divided by a septum. The paroccipital processes are not applied to it. The carnassial tooth is less emphasised in this group than in the Cats.
These characters, however, have to be used with caution, as they are hardly universally applicable. A fairly typical Arctoid bulla is seen in such a form as Cercoleptes. The bulla itself is a little more swollen than in Ursus, but it is flattened off in the same way towards the bony meatus. The paroccipital processes, slightly developed, are at a distance of ¼-inch from the posterior margin of the bulla. In the Raccoon the bullae are much more swollen, and the paroccipital processes are closer to them. In the Marbled Polecat, Putorius sarmaticus, the bullae are fairly
swollen, and there is but little flattening towards the meatus: the paroccipital processes, though slight, are in contact with the bullae basally, though their free tips are turned away from them. Finally, in Ictonyx the bullae are much swollen; there is but little flattening towards the meatus, and the paroccipital processes, themselves much swollen, are pressed closely against the bullae. The Mustelidae, therefore, in this as in other characters, approach the Aeluroids.
