Most crocodilians live entirely in fresh water, but two species have ventured offshore onto tropical islands and reefs. Juvenile crocodiles stay in the vicinity of rivers, mangroves or fresh water swamps, but occasionally an adult is encountered on a coastal tropical reef, especially in northern Australia and parts of the Caribbean. They are unmistakable when seen, but usually their presence in an area remains undetected due to their excellent eyesight and hearing. At the first sign of danger a crocodile will quietly submerge and wait motionless on the bottom for the disturbance to pass. Unless, of course, it is hungry.

• Four limbs with webbed back feet and a muscular, vertically compressed, paddle shaped tail.
• Scaly skin over your entire body.
• To have hatchlings that look just like their parents (direct development).
• Nostrils that can be closed (valved), and sit on a raised mound on the tip of the long snout.
• Teeth that are visible even when the mouth is closed.
• Salt glands on the tongue to excrete excess salt.

Estuarine crocodile, Gator and Mud Gecko

All crocodiles have an instantly recognisable lizard-like body shape, with four legs and a toothy smile. This smile is because the large teeth at the front of the lower jaw fit into notches at the side of the upper jaw, and are visible even when the mouth is closed. The muscular tail is vertically flattened, and like a paddle, provides more surface area for rapid swimming, while the four webbed toes on the back feet are used only for slow, precise movement under water. On land all four feet are used and the body is held high off the ground while walking, in a comical, swaying motion. The thick scales on the back overlay bony plates inside for added strength. The eyes are set high on the head, and, together with the valved nostrils, are often the only visible evidence that a giant prehistoric reptile lies beneath the water.

Saltwater and American crocodiles live in either freshwater, estuarine or sea water. The saltwater crocodile occurs across South East Asia to New Guinea, the Solomon Islands and tropical Australian waters, and the American crocodile is found from Florida in the USA, south through the Caribbean islands and along the Central American coast to Ecuador and Colombia. All crocodiles are restricted to warm waters, and unlike alligators, will not survive in areas where water temperatures drop much below 25oC. Only adults are likely to be found at sea or living on reefs, as juveniles prefer estuaries or rivers.

All crocodiles are unashamed carnivores. Hatchlings will eat crabs, mud skippers, frogs, small fish and even insects caught in or out of the water. As they grow larger they include prey such as water birds, mammals, turtles and larger fish in their diet. They hunt by slowly approaching an unsuspecting animal, and when they get within reach they make a powerful and lightning fast side-ways snap with the open jaws. If the captured prey is large or struggling, the crocodile will roll over and over rapidly while holding tight with its jaws. This has the effect of ripping and smashing up the prey, thus killing it and breaking it into pieces for easy swallowing. The struggling prey may also be held underwater until it drowns. The teeth are conical and sharp tipped, but without a cutting edge. Feeding will occur either by day or night, as crocodiles have excellent night vision.

Small crocodiles are eaten by predatory birds, some large lizards and snakes, fish and other crocodiles. As they grow the tables are turned, and many of these predators in turn become the crocodiles food. By the time they reach maturity they have outgrown all their predators except other, larger crocodiles and man. As large male crocodiles are highly territorial they will sometimes kill and eat smaller trespassing males and small adults in their territory

Crocodile eggs have a calcareous "chicken-egg" like shell, and up to 80 are laid in the central chamber of a carefully constructed nests that is guarded by the mother. The saltwater crocodile scrapes up a large mound of grass, other plant material and soil, and deposits the eggs inside, while the American crocodile is more likely to bury her eggs in a hole on an open, sandy beach. The mother will stay close and guard the nest, and on hearing the hatchlings' squawk from inside, will open it and carry them down to the water. Hatchlings hunt and feed for themselves, but usually under the watchful eye of their mother who stays nearby for weeks or even months. The sex of the hatchling is determined by the incubation temperature, and very warm and cool incubation temperatures produce females, while intermediate temperatures of about 32OC produce mainly males.

Crocodiles grow large and regard humans as just another tasty food item. In areas where they are still common, people do not swim or bath in open water. However, in most of their former habitat they are rarely seen today as their numbers have been severely diminished by skin hunters. Only in areas of Australia's Northern Territory where they have had legal protection since the 1970s are saltwater crocodile numbers now approaching what they probably were before the 1950s. American crocodiles are endangered in all of their former geographic range. An increasing threat to the survival of these species in some areas is gill netting for fish in estuarine and inshore waters. Many crocodiles become snared and tangled, and subsequently drown in these nets. Notes: In many tropical countries crocodiles are farmed for their excellent skins. The skins are processed and the leather is used for high quality and expensive shoes, handbags and other luxury items, while the meat is in great demand for human consumption. Eggs may be removed from wild nests and hatched in incubators (crocodile ranching - as in the Australian Northern Territory), or alternatively they may be collected from nests constructed by farmed adult crocodiles. If the eggs are hatched in an incubator the crocodile farmer will usually prefer male hatchlings as these grow faster than females. Conveniently for crocodile farmers, the sex of the hatchling is determined by the incubation temperature (see above).