The Procyonidæ are animals of small and moderate size, largely arboreal in habits and subsisting upon a mixed diet of fruit, eggs, insects and the like; the teeth are adapted to this diet and the sectorials have mostly lost their shearing form and the molars are tuberculated for crushing and grinding. The species generally have long tails, except in the raccoons proper, in which the tail is of medium length, and five-toed, plantigrade feet, with naked soles. Fossil members of this family are very rare in Tertiary formations and its history is therefore but scantily known; in the lower Pliocene have been found fragmentary remains with less specialized teeth, which appear to belong to the direct ancestor of Bassariscus. The upper Miocene genus †Leptarctus was an undoubted member of the family, and, while it would seem not to have been in the direct line of any of the modern forms, it was near to the common ancestry of the American genera, so far as the imperfect specimens enable us to judge.
Fig. 273.—Dentition of Raccoon (Procyon lotor), left side. i. 3, external incisor. c., canine. p. 4, fourth premolar. m. 1, first molar.
By far the most primitive representative of the family yet discovered is the lower Miocene genus †Phlaocyon, which connected the Procyonidæ with the Oligocene genus of dogs, †Cynodictis ([p. 529]). The dentition resembled that of the latter, with several differences, which were all changes toward the Procyonidæ. All the cusps were lower and blunter than in †Cynodictis; the premolars were small, thick and closely crowded together and the upper sectorial, while still trenchant, had a postero-internal cusp, which is found in none of the Canidæ and was a first step toward the tuberculated pattern of the raccoons, and the lower sectorial had a very low cutting blade and large heel; the other molars of both jaws were low, wide and of subquadrate shape. The skull was short and broad, with the face as much shortened and the orbits as far forward as in Procyon, but the brain-case was narrower, less capacious, and the lower jaw had the curved form and much the same character as in the modern genus. The limbs were relatively more slender than in the latter and the five-toed feet were more canine than procyonine in the proportions of the digits.
The discovery of †Phlaocyon by Dr. Matthew was an event of capital importance, as showing the highly probable derivation of the raccoons from †Cynodictis and thus bringing another fissipede family into relationship with the dogs.
4. Ursidæ. Bears
The present distribution of the bear family is all but exclusively northern, as there is but one African species, confined to the northwestern corner of that continent, and one in the Andes of Peru and Ecuador, all the others belonging to Eurasia and North America.
Fig. 274.—Dentition of Black Bear (Ursus americanus). i. 3, external incisor. c., canine. p. 1, first premolar. p. 4, fourth premolar. m. 1, first molar.—Below is a view, on a larger scale, of the grinding surface of the fourth premolar and first molar, upper jaw.
Structurally, the family is very distinct and the dentition is quite peculiar. The incisors and canines resemble those of other Fissipedia; the three anterior premolars are very small, single-rooted and often shed early; the carnassials have lost their trenchant character; and the molars, which are usually longer than wide, are tuberculated, somewhat resembling those of pigs. Almost all the bears live principally upon vegetable food, and even the Polar Bear, which feeds upon fish and seals, will eat grass and berries in the brief Arctic summer; thus, the shearing teeth of the strictly carnivorous types are unnecessary to these animals. The skull is not unlike that of the dogs in shape, but the tympanic bullæ are much flattened and the entrances to them are long, bony tubes, while the cranial foramina are nearly as in the dogs. The body is very heavy and the tail always short. The limbs are short and thick; the humerus has lost the epicondylar foramen in all existing species except the South American Spectacled Bear (Tremarctos ornatus). The plantigrade feet have naked soles (except in the Polar Bear) and each foot has five well-developed and functional digits, armed with very long, sharp and non-retractile claws.