Some characteristics of crocodilians: This is the smallest order of reptilians; it contains only 23 species in three families: Alligatoridae (Alligators, caimans, and dwarf caimans), Crocodylidae (crocodiles and dwarf crocodiles), and Gavialidae (true and false gharials or gavials). Most crocodilians occur in the tropics, only a few extend to temperate regions. These reptiles are adapted to a semi-aquatic life. For example, they have prominent nostrils that allows them to be submerged in the water with only the nostrils in the surface. They also have powerful blade-like tails that they use to swim, and they have a transparent protective third eyelid. On land, they can lift their bodies high off the ground for walking and running. Crocodilians have some features that liken them more to mammals than to other reptiles: their heart has four chambers, they have a structure similar to the diaphragm of mammals, and they have a bony secondary palate.

Some characteristics of Alligatoridae: In alligatorids the teeth cannot be seen when the mouth is closed because teeth in the lower jaw fit into pits in the upper jaw (in crocodylids the fourth tooth in the lower jaw is visible when the mouth is closed). The largest is Caiman niger (over 6m) and the smallest Paleosuchus (less than 1.7m). There are 7 species in 3 genera. All genera are restricted to Central and South America, except for Alligator, which occurs in the southeastern US and one species (A. sinensis) in the lower Yangtze River of eastern China.

Some additional links on crocodilians:

• Crocodilian Communication

Literature: Harshman, J., C.J. Huddleston, J.P. Bollback, T.J. Parsons and M.J. Braun. 2003. True and False Gharials: A Nuclear Gene Phylogeny of Crocodylia. Systematic Biology 52(3):386-402.

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