Land and Marine Carnivores: Carnivora
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.
Carnivores are found throughout the world. Some, however, are not naturally occurring but have been introduced to some areas.
Carnivores are found both on land and sea. Although most terrestrial carnivores live on land, the polar bear spends most of its time on sea ice, while the palm civet is arboreal (a tree-dweller). The sea otter lives exclusively in the water, as opposed to other marine carnivores who forage in the sea and breed on land.
The term carnivore literally means meat-eater, but not all species in the order Carnivora live on a strict diet of meat. Among the true carnivores are cats. Although lions in the Kalahari Desert have been known to eat melons, they only do so for the moisture content, not for sustenance. Some mustelids (weasels, martens, and otters) are also pure carnivores. The rest of the mustelids (skunks, badgers, and tayras) are omnivores, supplementing their meat diet with fruits, roots, and seeds. The bears are generally omnivores, although most prefer a larger proportion of plant food, including fruits, grasses, and roots. The exceptions in the bear family are the giant panda that lives exclusively on bamboo and the polar bear that consumes mainly ringed seals.
Procyonids (raccoon family) are omnivores, with several food specialists. Ringtails prefer meat, red pandas eat mainly bamboo leaves, and kinkajous and olingos live off fruits. The civets and genets (viverrids) eat a mixture of animals and fruits, although palm civets are primarily frugivores (fruit-eaters). The mongoose family, while generally favoring insects, also lives on a mixed diet of rodents, worms, reptiles, and plant matter. Canids (dogs) are also omnivores, eating all sizes of mammals, as well as insects, berries, carrion (dead and decaying flesh), and garbage.
The smallest carnivore family consists of three hyena species and the aardwolf. While the aardwolf eats termites almost exclusively, hyenas have a varied diet, ranging from large antelopes and reptiles to wildebeest feces and human garbage. Hyenas are often described as scavengers who feed off the leftover kills of other animals. However, they often hunt their own prey. In fact, lions have been known to scavenge hyena kills.
The marine carnivores eat various marine mammals, including fish, crustaceans (shrimps, crabs, and lobsters), mollusks (clams, mussels, squid, and octopus), and penguins. Some marine carnivores have specialized diets. The crab-eater seal feeds almost exclusively on krill (a small shrimplike animal), while the walrus feeds almost entirely on mollusks.
BEHAVIOR AND REPRODUCTION
Many carnivores are solitary creatures, except for mating pairs and mother-offspring groups. The majority are not antisocial, as they share overlapping territories and congregate at abundant food sources. Some belong to social groups, in which strict rules are observed. For example, carnivores "talk" to one another through scent marking, or the depositing of anal secretions, urine, and feces. They also use a variety of vocalizations. Some use body postures to show dominance or submission.
The typical mating system among carnivores is polygyny (puh-LIH-juh-nee) in which a male has two or more partners. Some, like canids, are monogamous (muh-NAH-guh-mus), with a male and a female mating with just with each other. Pinnipeds usually breed on land. Males arrive on land to stake out a territory. Females arrive later to give birth to the previous year's pup before mating. The father departs for the sea soon after mating, leaving the mother to raise the pup. When the pup is able to survive on its own, mother and pup leave land for the water, going their separate ways.
CARNIVORES AND PEOPLE
The relationship between carnivores and humans is complex. Humans have domesticated the wolf and wild cats and made them house pets. In addition, humans have trained dogs to perform certain tasks. Collies help herd sheep, German shepherds serve as seeing-eye dogs, beagles sniff for drugs at airports, and bloodhounds help locate missing people.
Humans and carnivores have historically had conflicting interests. Thousands of years ago, early humans and carnivores competed for food. Today, carnivores in the wild continue to prey on domesticated animals, even attacking and killing some humans. Humans who feel threatened by carnivores resort to poisoning, trapping, and shooting, leading to the extinction of certain species. Some carnivores are also hunted for their fur, meat, and body parts, resulting in declining populations.
Certain government agencies and private organizations around the world have established programs to try to save the threatened species. Millions of dollars and plenty of human effort have been devoted to the conservation and protection of endangered species.
The World Conservation Union (IUCN) promotes the conservation of species, assesses their conservation status worldwide, and publishes an annual list of threatened species. The 2003 IUCN Red List of Threatened Species lists 125 carnivores as threatened. Five are listed as Extinct, no longer living: the Falkland Island wolf, the Caribbean monk seal, the sea mink, the Barbados raccoon, and the Japanese sea lion. The black-footed ferret is classified as Extinct in the Wild. The five Critically Endangered species, facing an extremely high risk of extinction, are the red wolf, the Ethiopian wolf, the Iberian lynx, the Mediterranean monk seal, and the Malabar civet.
IT'S ALL IN THE TEETH
The feature that differentiates the order Carnivora from other orders is a set of scissor-like carnassial teeth, specifically the upper last premolar and the lower first molar on both sides of the jaw. These are shearing teeth that slice animal flesh and crush bones. Each carnassial has ridges that grip meat, much like a fork that holds a piece of steak in place, so it does not slide around.
The Endangered list of carnivores, facing a very high risk of extinction, consists of thirty-one species, made up of one dog, one eared seal, one true seal, two bears, four cats, four mongooses, four viverrids, seven mustelids, and seven procyonids. Of these species, three are classified as endangered species in the United States. These are the sea otter, the northern sea lion, and the Hawaiian monk seal.
FOR MORE INFORMATION
Attenborough, David. The Life of Mammals. Princeton, NJ: Princeton University Press, 2002.
Ewer, R. F. The Carnivores. Ithaca, NY: Comstock Publishing Associates, 1998.
Kruuk, Hans. Hunter and Hunted: Relationships between Carnivores and People. Cambridge, U.K.: Cambridge University Press, 2002.
McLoughlin, John C. "The Rise of the Carnivores" and "The World of Mammalian Carnivores." The Canine Clan. New York: The Viking Press, 1983.
Wade, Nicholas, ed. The Science Times Book of Mammals. New York: The Lyons Press, 1999.
Whitaker, John O. Jr., and William J. Hamilton Jr. Mammals of the Eastern United States, 3rd ed. Ithaca, NY: Comstock Publishing Associates, 1998.
Tedford, Richard H. "Key to the Carnivores." Natural History (April 1994): 74–77.
American Society of Mammalogists. Why Species Become Threatened or Endangered: A Mammalogist's Perspective. http://www.mammal-society.org/committees/commconslandmammals/whyendangered.pdf (accessed on June 23, 2004).
World Conservation Union. The IUCN Red List Collection. http://www.iucn.org/redlistcollection/english/index.html (accessed on June 23, 2004).