Crocodilia

Crocodilia is an order of large, predominantly semi-aquatic reptiles that includes alligators, caimans, true crocodiles, and gharials. They inhabit tropical and subtropical regions of Africa, the Americas, Asia, and parts of Oceania. Crocodilians are among the oldest living reptiles and share ancestry with birds and other archosaurs.

Anatomy and physiology: They have elongated bodies, powerful tails, and long snouts. Their skin is thick and armored with bony scutes. Eyes and nostrils are placed on top of the head, enabling them to see and breathe while mostly submerged. They are ectothermic and possess a four-chambered heart, which allows some separation of oxygenated and deoxygenated blood. A palatal valve prevents water from entering the throat when submerged.

Taxonomy and diversity: Crocodilia comprises three living families: Alligatoridae (alligators and caimans), Crocodylidae (true crocodiles), and Gavialidae (gharial). Notable species include the American alligator, the Nile and saltwater crocodiles, and the gharial. The group contains roughly 23 to 29 species, depending on classification.

Habitat and diet: They favor rivers, lakes, swamps, and estuaries in warm regions; the saltwater crocodile can tolerate brackish and seawater. They are apex or near-apex predators, feeding on fish, reptiles, birds, and mammals. They employ ambush tactics and can breathe at the surface between hunts.

Reproduction and life history: Crocodilians lay eggs in nests, often built from vegetation or soil; temperature influences sex determination. Females guard nests and transport hatchlings to water. Juveniles receive protection from parents for a period after hatching.

Conservation: Numerous species are threatened by habitat loss, hunting, pollution, and human conflict. Some populations are stable or increasing, while others, including gharials and several caiman populations, remain at high risk.