Crocodilia
Taxonomy and Evolution
Crocodilia is an order of mostly large, predatory, semiaquatic reptiles, known as crocodilians. They first appeared 95 million years ago in the Late Cretaceous period and are the closest living relatives of birds, as the two groups are the only known survivors of the Archosauria.
The order Crocodilia includes the true crocodiles (family Crocodylidae), the alligators and caimans (family Alligatoridae), and the gharial and false gharial (family Gavialidae). Despite their prehistoric look, crocodiles are among the more biologically complex reptiles. Unlike other reptiles, a crocodile has a cerebral cortex, a four-chambered heart, and the functional equivalent of a diaphragm, by incorporating muscles used for aquatic locomotion into respiration.
Anatomy and Morphology
Crocodilians are more robust and built than other reptiles. They are squat and massive, with flat bodies and thick, short legs. The tail, which accounts for half of the animal's total length, is muscular and flat-sided, adapted for quick, agile movement in water; it propels the reptile when swimming. The hide is thick and plated with the osteoderms, or bony deposits which make the skin rugged and provide the crocodile with an armor-like skin surface.
Behavior and Ecology
Crocodilians are largely carnivorous. They have a slow metabolism, so they can survive a long time without food. Despite their appearance of being slow, crocodiles are top predators in their environment, and various species have been observed attacking and killing other predators such as sharks and big cats.
Crocodilians are also known for their sophisticated behavior. They can exhibit complex social behavior and strong family bonds. For example, crocodile mothers will carry their young in their mouths and will ferociously guard their nests.
Conservation Status
Many species of crocodiles are at the risk of extinction, some being classified as critically endangered by the IUCN. Human activity has caused a decline in many crocodile populations, through habitat destruction, pollution, and hunting.