Carnivores come in all shapes and sizes, ranging in size from the 1.76 oz (50 g) least weasel (Mustela nivalis) to the 48,000 times heavier, 5,300 lb (2,400 kg) southern elephant seal (Mirounga leonina). Most are so distinctive that even laypeople can easily distinguish the various families, even though the order has considerable diversity. Bears, dogs, hyenas, mongooses, martens and weasels, cats, and even viverrids are readily recognizable, although the marine families and procyonids are more difficult to tell apart.
The pinnipeds have streamlined, oval-shaped bodies with limbs modified as flippers. Terrestrial carnivores either walk on the soles of their feet (plantigrade) or on their toes (digitigrade). The limbs of evolutionarily ancient carnivores underwent a fusion of bones in the feet that probably originally provided a firm basis for flexion at the midcarpal joint. This gave them the flexibility to climb, grapple with prey, or absorb the shock of running and leaping. Another skeletal characteristic is an undeveloped collar-bone or clavicle. The main function of the well-developed clavicle in primates is to allow attachment of muscles to give the necessary flexibility of lateral movement to the limbs. This is not necessary for the back and forth movement of the limbs needed for a long stride for running as is the case for most carnivores. With the exception of the hyenas, carnivores possess an elongated penis bone known as the baculum to prolong copulation. This is probably especially important in species where ovulation is induced by copulation. Modified skin glands often located in the anal region secrete substances as a means of communication and information exchange between members of the same species.
The typical dental formula for carnivores is (I3/3 C1/1 P4/4 M3/3) X 2 = 44, with variation in the number of molars and premolars. The canines are usually large and the car-
nassial shear, the modified fourth upper premolar and the lower first molar, with high cusps and sharp tips, is adapted to cutting and slicing meat. The typical carnivore skull shows a powerful jaw for the capture of prey and tearing up of meat, and the skull often has a sagittal and/or occipital crest to enlarge the area for muscle attachment.
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