Crocodiles, Alligators, Caimans, and Gharials: Crocodylia
CROCODILES, ALLIGATORS, CAIMANS, AND GHARIALS: Crocodylia
The order Crocodylia, also known as the crocodilians, includes 23 species of the most feared and most fascinating animals on the planet. They include 14 species of crocodiles and false gharials in the family Crocodylidae; eight species of alligators and caimans in the family Alligatoridae; and one species of gharial (GUR-ee-ul) in the family Gavialidae.
The crocodilians look somewhat like large lizards, but with thick and scaly skin, exceptionally strong tails, and large teeth-filled jaws. The scales on the upper surface, including the back and top of the tail, are large and rectangular in shape and have bony plates, called osteoderms (OSS-tee-oh-durms), just under the surface. Rows of these scales, which often have knobs or ridges, run from the rear of the head to the tail. On the legs and the sides of the body, the scales are smaller. Belly scales, which may also contain osteoderms, are large and smooth. Crocodilian tails are usually about as long as or a bit longer than the body, and in some species, like the Nile crocodile, the tails have a tall ridge of scales down the center.
The jaws contain large teeth, many of which show outside the mouth even when it is closed. People often describe the "grin" of a crocodilian. Of course, the animals are not actually smiling, but a slight upturn in the back of the jaw line of most species makes them look as if they are. Most, but not all, crocodilians have wide jaws. The Indian gharial is one species without a wide jaw. Instead, it has a very long and exceptionally thin pair of jaws filled with razor-sharp teeth. The false gharial, which looks much like an Indian gharial, has jaws that are only slightly wider and shorter than those of the Indian gharial.
The crocodilian body comes in shades of brown or gray, sometimes with a greenish or reddish tint. The upper surface is typically much darker than the belly, which is usually white to yellow. Bellies of dwarf caimans and dwarf crocodiles, however, are almost black. Many species have patterns of dark brown to black bands or blotches on the back and tail, and often these are most noticeable in youngsters.
The crocodilians are medium- to large-sized species. Cuvier's dwarf caiman is the smallest, with male adults reaching 5 feet (1.5 meters) long and females growing to 4 feet (1.2 meters) long. The largest species include the Indian gharial and the saltwater crocodile. Males of each species commonly grow to 16 feet (4.9 meters) and sometimes, although very rarely, reach 20 feet (6.1 meters). As with other crocodilians, the females are smaller overall than the males.
Most members of the family Alligatoridae live in Central America, Mexico, the southeastern United States, and South America. One species, the Chinese alligator, makes its home in eastern China. The Indian gharial, the lone species in the family Gavialidae, lives in scattered places within India, Nepal, and Pakistan and rarely Bangladesh and Bhutan. The crocodiles and false gharials in the family Crocodylidae live over the largest area of the three families. At least one species lives in Africa, Asia, Australia, North America, and South America.
Most crocodilians live in tropical or subtropical regions. The American alligator, which can be found in the United States as far north as North Carolina, and the Chinese alligator live in the coolest climates of all the crocodilians and sometimes have to survive freezing temperatures. These two species spend the coldest parts of the year in underground burrows, in deep water, or lying in shallow water with just the nose poking above the sometimes ice-covered water surface.
Alligators, caimans, and gharials need freshwater habitat, but crocodiles and false gharials can survive in freshwater or saltwater. Crocodiles usually stay out of the open oceans, however, and instead make their homes in saltwater marshes or creeks.
None of the crocodilians stray very far from the water. The gharials are perhaps most tied to the water. They spend their entire lives either in or within a few feet of the water.
Crocodilians are meat-eaters, or carnivores (KAR-nih-voars), and most are not picky about their prey. Youngsters usually eat insects, spiders, and other invertebrates (in-VER-teh-brehts), or animals without backbones, as well fishes and other small vertebrates (VER-teh-brehts), which are animals with backbones. As they grow older, they begin taking larger and larger prey. The typical adult crocodilian eats everything from clams to frogs, and birds to mammals. Some, such as the Indian gharial, have jaws that are well-suited to catching fish, and they stick to a mainly fish diet. At the end of its thin jaw, the gharial has a number of very sharp teeth that jut out almost sideways in a pincushion fashion. To catch a fish, the gharial lies still, waits for a fish to come close, and then swishes its jaw sideways to skewer the fish on its teeth. With a flick of its head, the gharial tosses the fish off its teeth and down its throat.
A FOSSIL GIANT
About 110 million years ago, a massive beast roamed the waters of Earth. The head of this creature, an ancient relative of modern-day crocodilians, was 5 feet (1.5 meters) long, and its body grew to a whopping 39 feet (12 meters). A team of scientists found the remains of five of the animals, named Sarcosuchus imperator or "emperor of the flesh-eating crocodiles," in 2000. From the fossil skulls, they determined that its diet consisted of large animals, which it hunted by ambush.
Other crocodiles also use the sit-and-wait style of hunting, which is known as ambush hunting. Alligators and caimans also often stalk (stawk) their prey by swimming up ever so slowly, and then chomping on the surprised animal. Many crocodilians kill especially large prey by clamping on the animal and dragging it underwater to drown. They then bite off pieces to swallow. Sometimes, crocodilians work together when eating. Nile crocodiles, for example, will take turns holding onto a large prey animal while others wrap their jaws around part of the body and twist around to tear off pieces of flesh. For smaller prey, however, a crocodilian will simply swallow it whole. Crocodilian stomachs can digest almost anything, except items like hair, nails or claws, and turtle shells. Just as a cat coughs up hairballs, the crocodilian coughs up balls of this undigested material and spits them out.
BEHAVIOR AND REPRODUCTION
Crocodilians are often night hunters and rest or sunbathe during the day. Unlike mammals that use their own energy to keep their bodies warm, crocodilians and other reptiles get their heat from their environment. One of the best ways to warm up is by sunbathing, also known as basking. Crocodilians may bask on dry land or along or just below the surface of the water. Some crocodilians, like gharials, are very careful when they bask on shore and will quickly retreat to the water if they feel the least bit nervous. Others, such as some large American alligators, will continue to bask even if approached quite closely. At a moment's notice, however, this peaceful-looking reptile can spring into action with a swipe of its powerful tail or a snap of its dangerous jaws. Most crocodilians are also quite fast and are actually able to outrun a person over a short distance.
Crocodilians move in several ways. All are excellent swimmers, usually gliding through the water by simply swaying the tail from side to side. Their tails are even strong enough to shoot their bodies several feet straight up and out of the water. On land, they often walk slowly, dragging the belly and tail on the ground. If they want, however, most can do a "high walk," in which they lift up the body to walk much as a lizard does.
A SENSITIVE SIDE
Scientists in 2002 discovered that crocodilians use tiny dots on the skin of their faces to feel even the slightest of ripples in the water. These dots, called pressure receptors, can even feel the ripple made by a single raindrop. This ability helps to make them exceptional night hunters. They can feel even small waves made by prey animals as they move through the water.
Many species live together in groups and get along well for most of the year. During breeding season, however, the males get into arguments, wrestling matches, and sometimes more violent fights. They may bellow back and forth, push one another with their snouts, or bite each other. In some species, males try to attract the females by bellowing, or by rippling their back muscles so that water ripples over their scales. After mating, which occurs in the water, the females of all species lay their eggs out of the water. Some scrape leaves and often mud into a pile and lay their eggs in the pile, and others dig a hole as their nest. Depending on the species, a female may lay fewer than a dozen or many dozen eggs. As in some other reptiles, the temperature of the nest may control the sex of the young. In crocodilians, for example, a nest that is between 87.8 to 89.6°F (31 to 32°C) during a critical time not long before hatching produces mainly males, while an especially high or particularly low temperature during this period produces mainly females. The mother typically remains close by as the eggs develop, often chasing off raccoons or other animals that would dig up her nest and eat her eggs if given the chance.
When the eggs hatch, the mother helps her babies out of the nest and often to the water. Despite her toothy jaws, the mother can safely carry her babies either one or several at a time in her mouth. The young usually stay with their mother, and occasionally both parents, for a while. In most species, the young remain with the family for a few weeks or months, but in the American alligator, they may stay together for as long as two years. During this time, the female may provide protection to her young, may call to them when she finds food, or in some species, may actually chew a prey animal a bit, which helps her young tear off pieces to eat.
CROCODILIANS AND PEOPLE
Crocodilians, which are sometimes hunted for their meat or skin, are perhaps best known as human killers. Death by this reptile, however, is very rare among people who act carefully and responsibly when they are in crocodilian habitat. As people move closer and closer to their habitat, crocodilians may make their presence known by plopping into a swimming pool or eating a family pet.
According to the World Conservation Union (IUCN), almost one-third of the 23 crocodilian species are either Critically Endangered or Endangered. Critically Endangered species are those that face an extremely high risk of extinction in the wild, while Endangered species face a very high risk. The other 16 species are currently doing quite well, thanks to numerous recovery efforts and anti-hunting regulations that have saved them from the brink of extinction.
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