Land and Marine Carnivores: Carnivora
The order Carnivora (kar-NIH-vuh-ruh) refers to a group of mammals whose evolutionary ancestors were carnivores, or meat-eaters. Over several millions of years, these ancestors had adapted to the rise of bigger and more powerful herbivores, their main prey, by developing carnassials (kar-NAH-see-uls), bladelike teeth that slice through flesh. Powerful jaws that move up and down were especially useful for stabbing and holding prey and the incisors for biting off pieces of food.
Although the 264 species in the order Carnivora come from the same ancestors, not all species eat only meat. Therefore, while the carnassials are very pronounced in species that eat large prey (cats, for example), those that are not purely carnivorous have less developed carnassials (bears). Some, like the aardwolf that feeds on termites, and the giant panda that eat mainly bamboo, have no carnassials at all.
Carnivores come in a wide range of sizes. The smallest carnivore, the least weasel, weighs about 1.76 ounces (50 grams). In contrast, the southern elephant seal, the largest carnivore, weighs about 5,300 pounds (2,400 kilograms). Some carnivores are terrestrial (land-dwelling) mammals, including the familiar dogs, cats, bears, raccoons, hyenas, mongooses, and skunks. Land carnivores either walk on the soles and heels of their feet (plantigrade) or on their toes (digitigrade). A combination of strong bones in the feet and bendable wrists allow these mammals to climb, run, jump, and overcome their prey. An undeveloped collarbone allows for increased movements of the arms when pursuing prey. The long baculum (penis bone) enables prolonged mating and is especially important in species in which mating brings on ovulation (the formation and release of eggs from the ovary). Anal glands release substances used as scent marks for various types of communication.
Other carnivores are marine (sea-dwelling) mammals, including eared seals, true seals, and walruses. Marine mammals, also called pinnipeds (fin-footed mammals), have a torpedo-shaped body that allows for easy movement through water. The thick layer of blubber, or fat under their skin, not only provides insulation but also contributes to streamlining (smoothing out) their bodies.