A caiman (also cayman as a variant spelling) is an alligatorid belonging to the subfamily Caimaninae, one of two primary lineages within Alligatoridae, the other being alligators.
Caimans inhabit Mexico, Central and South America from marshes and swamps to mangrove rivers and lakes. Caimans have scaly skin and live a fairly nocturnal existence.
They are relatively small-sized crocodilians with an average maximum weight of 6 to 40 kg (13 to 88 lb) depending on species, with the exception of the black caiman (Melanosuchus niger), which can grow more than 4 m (13 ft) in length and weigh up to 500 kg (1,100 lb). The black caiman is the largest caiman species in the world and is found in the slow-moving rivers and lakes that surround the Amazon basin. The smallest species is the Cuvier's dwarf caiman (Paleosuchus palpebrosus), which grows to 1.2 to 1.5 m (3.9 to 4.9 ft) long. There are six different species of caiman found throughout the watery jungle habitats of Central and Southern America. The average length for most of the other caiman species is about 2 to 2.5 m (6.6 to 8.2 ft) long.
Caimans are distinguished from alligators, their closest relatives, by a few defining features: a lack of a bony septum between the nostrils, ventral armor composed of overlapping bony scutes formed from two parts united by a suture, and longer and sharper teeth than alligators, plus caimans tend to be more agile and crocodile-like in their movements. The calcium rivets on caiman scales make their hides stiffer and thus less valuable than those of alligators and crocodiles, both of which have a similar appearance, but are more pliable. Several extinct forms are known, including Purussaurus, a giant Miocene genus that grew to 12 m (39 ft) and the equally large Mourasuchus, which had a wide duck-like snout.