Caimans are South American alligators, closely related to crocodiles. There are four species, two of which are rarely seen dwarf caimans. The two common species are black caiman and spectacled caiman. Caimans eat fish and small animals, such as frogs, turtles and snakes. They lay eggs in large nests made of gathered grass and twigs. The sex of the young are determined by the temperature in the nest, rather than by genetics. Females guard the nest and are dangerously aggressive at this time, although they are usually wary of humans.
A Black Caiman (Melanosuchus niger) lies in wait for unsuspecting prey. This species is the largest of the South American crocodilians, and the Amazon's biggest predator.
The caiman is supremely adapted to aquatic life, with eyes and nostrils at the top of the head. Note that the nostrils are sealed, to prevent water entering when the animal is under water.
Black caiman are big enough to take even the largest Amazon land animals. When an animal approaches close to the river bank, the caiman will lunge forward and grab the animal, pulling it under water where it quickly drowns.