Crocodilians (Crocodilia) are a group of reptiles that includes crocodiles, alligators, caimans and the gharial. Crocodilians are semi-aquatic predators that have changed little since the time of the dinosaurs. All species of crocodilians have similar body structures—elongated snout, powerful jaws, muscular tail, large protective scales, streamlined body, and eyes and nostrils that are positioned on top of the head.
Crocodilians have several adaptations that make them well-suited for an aquatic lifestyle. They have an extra transparent eyelid on each eye that can be closed to protect their eye when underwater. They also have a flap of skin at the back of their throat that prevents water from seeping in when they attack prey underwater. They can also close their nostrils and ears in a similar manner to prevent the unwanted influx of water.
Crocodilian males are territorial animals that protect their home range from other male intruders. Males share their territory with several females with whom they mate. Females lay their eggs on land, near water in a nest built out of vegetation and mud or in a hollow in the ground. Females care for the young after they hatch, providing them with protection until they grow large enough to defend themselves. In many species of crocodilians, the female carries her tiny offspring in her mouth.
Crocodilians are carnivores. They feed on live animals such as birds, small mammals and fish. They also feed on carrion. Crocodilians use several methods of attack when pursuing live prey. One approach is that of ambush—the crocodilian lies motionless beneath the water's surface with only their nostrils above the water line. This enables them to remain concealed while they watch for prey that approaches the water's edge. The crocodilian then lunges out of the water, taking their prey by surprise and dragging it from the shoreline into deep water for the kill. Other hunting methods include catching fish using a quick side-snap of the head or catching waterfowl by drifting towards it slowly and then lunging for it when at close range.
Crocodilians first appeared about 84 million years ago during the late Cretaceous. Crocodilians are diapsids, a group of reptiles that possess two holes (or temporal fenestra) on each side of their skull. Other diapsids include dinosaurs, pterosaurs, and the squamates, a group that encompasses modern lizards, snakes and worm lizards.
The key characteristics of crocodilians include:
- elongated, structurally reinforced skull
- wide gape
- powerful jaw muscles
- teeth set in sockets
- complete secondary palate
- adults provide extensive parental care to young
Crocodilians are divided into the following taxonomic groups:
- Gharial (Gavialis gangeticus) - There is one species of gharial alive today. The gharial, also known as the gavial, is easily distinguished from other crocodilians by its very long, narrow jaws. The diet of gharials consists primarily of fish, and their long jaws and plentiful sharp teeth are especially well-suited for catching fish.
- True crocodiles (Crocodyloidea) - There are 14 species of true crocodiles alive today. Members of this group include the American crocodile, freshwater crocodile, Philippine crocodile, Nile crocodile, saltwater crocodile and many others. True crocodiles are efficient predators with a streamlined body, webbed feet, and a powerful tail.
- Alligators and caimans (Alligatoridae) - There are 8 species of alligators and caimens alive today. Members of this group include Chinese alligators, American alligators, spectacled caiman, broad-snouted caimen and several others. Alligators and caiman have wider, shorter heads when compared to true crocodiles.