There are 23 species of crocodilians, in three families — crocodiles (13 species), alligators (two species) and caimans (six species) and gharials (two species) — living in 100 tropical and sub-tropical countries. All reside within 4000 kilometers of the equator.
Crocodiles have been around for 240 million years, appearing 25 million years before the first dinosaurs and 100 million years before the first birds and mammals. Crocodiles that lived 230 millions years ago were up to 40 feet long. "Our primate ancestors were ratty little things that went around stealing eggs," Dr. Perran Ross, a crocodile specialist and professor of wildlife ecology and conservation at the University of Florida, told the New York Times. "Ancestral crocodiles had basically the same body plan we see today, apparently because it works."