ORDER Crocodylia: crocodilians. Long body covered with epidermal horny scales and bony plates. Vertebrae concave at the fore end. Elongated snout, powerful jaws and sharp teeth. Oviparous. Heart with four chambers (three in the rest of reptiles). Semi-aquatic life. Ectotherms (cold-blooded). Anus is a longitudinal fissure. Found mainly in the tropics. America, Africa, South Asia and Australasia. 3 families and 23 species.

FAMILY Alligatoridae: caimans, alligators and yacare. The lower jaw teeth fit into cavities in the upper jaw (invisible with jaws shut). Ventral scales lack sensorial pits. America, Asia. 4 genera, 8 species.
FAMILY Crocodylidae: crocodiles. At least one tooth in the lower jaw is always visible. Ventral scales with sensorial pits (a spot in the center of each scale). Narrow snout. Widely distributed throughout tropical regions. 2 genera, 13 species.
FAMILY Gavialidae: gharials. Snout very narrow, adapted to a piscivorous diet. Asia. 2 genera, 2 species.