Some crocodiles may venture into larger bodies of fresh or salt water, but all must lay their eggs on dry land. Most crocodilians live in the tropics. All crocodilians have a similar body shape, with a head held horizontally in front of the body, four legs which project from the sides, heavy scales which function as armor, and a heavy muscular tail. Their front feet have five separate toes and their rear feet have four partially-webbed toes. The nostrils are crescent-shaped and valvular, and set at the end of the snout, which allows breathing even when the animal is almost entirely submerged.
Male crocodilians are larger than females.
Their skin is covered with non-overlapping scales composed of the protein keratin and often studded with bony plates called scutes. This skin does not provide much insulation, preventing crocodilians from inhabiting cooler climates. No other reptiles move in this way. Most of the time crocodilians cruise slowly through the water, holding their legs against their body to reduce drag. Adults, especially mothers, often guard nests.