The Characteristics of Alligators and Crocodiles

Investigating the Traits of Order Crocodilia

Sep 16, 2009

Crocodilians are "living fossils" in the sense that they are the only remaining reptiles of the same lineage from which the dinosaurs and birds descended.

Remarkably, modern crocodilians (of the same lineage that first appeared in the late Cretaceous period 170 million years ago) differ only slightly in their structure from their early Mesozoic ancestors. To stand on the edge of a swamp and watch alligators slowly swimming through the mist of early morning is to truly stare down the corridors of time.

The Body Plan of Crocodilians

All crocodilians have a massive elongated skull with powerful jaw muscles perfect for a wide opening and very quick, forceful closure. Their teeth, like those of mammals, sit in bony sockets, an arrangement called thecodont that was common among both archosaurs (ancient reptiles that gave rise to dinosaurs and crocodilians) and the earliest birds. Unlike mammals, crocodilians replace their teeth throughout life, though not in extreme old-age.

The nostrils are at the tip of the snout, so the animal can breathe while mostly submerged. Air passageways of the head lead to the rear of the mouth and throat, and a flap of tissue near the back of the tongue forms a watertight seal that allows breathing without inhaling water when the mouth is filled with water or food (or both).

A hard complete secondary palate of bone in the roof of the mouth separates the nasal and mouth passageways and seals them off from one another. This adaptation evolved in the archosaurs and is found today only in crocodilians and mammals.

All crocodilians are also equipped with powerful legs and a muscular elongated tail used for swimming, defense, and prey capture.

Modern crocodilians consist of 21 species organized into three families: Gavialidae – gavials, Alligatoridae – alligators and caimans, and Crocodylidae – crocodiles.

Family Gavialidae

Gavials (or gharials) are found only on the northern Indian subcontinent where most live in the calmer areas of deep fast-flowing rivers. They only leave the water to bask or reproduce and nest.

Gavials have very elongated snouts armed with many razor-sharp teeth, an adaptation to a fish diet in adults. In males the tip of the snout is enlarged. Known as a ghara (after the Indian word for “pot”), this bulbous growth is used to generate a resonant hum during vocalization, act as a visual lure for females, and produce bubbles which have been associated with the mating rituals of the group.

Gavials lack the mechanical strength of the robust skull and jaw of other crocodilians and cannot prey upon large creatures. Being adapted primarily to eating small fish, adult gavials slash the water back and forth with their rapier-like snout and seize the fish with their needle-like teeth. Young gavials eat insects and frogs.

Family Alligatoridae

True alligators are native to only two countries: the United States and China and are now restricted to just two species, Alligator mississippiensis of the southern United States, and the small Alligator sinensis in the Yangtze River, People’s Republic of China.

The average American alligator has a length of 4 m (13 feet) and a weight of 360 kg (800 pounds).

Alligators are opportunistic feeders, eating almost anything they can catch. When young they eat fish, insects, snails, and crustaceans. As they grow, they take progressively larger prey, including large fish, turtles and other reptiles, and various mammals and birds.

In Central and South America, the alligator family is represented by five species of the genus Caiman. The Spectacled Caiman (C. crocodilus) has the widest distribution, from southern Mexico to the northern half of Argentina, and grows to a modest size of about 2.2 m (slightly over 7 feet).

Family Crocodylidae

Despite their prehistoric appearance, crocodiles are morphologically advanced compared to other reptiles in that they possess a four-chambered heart, a diaphragm, and a cerebral cortex like birds and mammals.

True crocodiles live throughout the tropical regions of Asia, Africa, Australia, and the Americas. Crocodiles tend to congregate in freshwater habitats like rivers, lakes, marshes and swamps, and sometimes brackish water environments. The saltwater crocodile, the largest of all the crocodilians, is known to venture far out to sea.

Like alligators, crocodiles are ambush hunters, waiting for prey to come close then grabbing the hapless victim with a lightning fast lunge and snap of the most powerful jaws in the animal world. Crocodiles will eat anything they can latch their powerful jaws onto including fish, birds, mammals (including humans), and even other crocodiles. While accurate accounts are often difficult to obtain, it is believed that these animals kill hundreds of people each year in Southeast Asia, Africa, and Australia.

Members of order Crocodilia have taken everything time and nature has thrown at them for 170 million years and while they have dwindled to only 21 living species, they have prevailed. However, crocodilians face an uncertain future in a world dominated by the wants and greed of humans.

The copyright of the article The Characteristics of Alligators and Crocodiles in Alligators/Crocodiles is owned by Dennis Holley. Permission to republish The Characteristics of Alligators and Crocodiles in print or online must be granted by the author in writing.