Today, crocodilians comprise a small group of 23 species of crocodiles, alligators and gavials that live in fresh and salt waters of the tropics (Ross and Garnett, 1989). This limited modern diversity conceals the breadth of their former radiations and their range of adaptations. Croc-odilians arose within a larger clade Crocodylomorpha 220 Myr ago and their first representatives were small bipedal insectivores (see p. 145).Since the Triassic,most crocodilians have been semi-aquatic and some Jurassic forms were highly adapted to marine life. In the Tertiary, other groups became fully terrestrial and, in South

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