Crocodiles, alligators

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Aetosauria were herbivorous armored forms. They have a pig-like snout and peg-like teeth. Their shared derived character is the heavy coat of armor covering the back (3). Desmatosuchus from the Chinle and Stegomus from the Newark of New Jersey and Connecticut is a good example.

  • The Crocodylomorpha are by far the most diverse forms and are still with us today. The shared derived character for the group is to have a pair of very elongated carpal bones (the radiale and ulnare [4]). These probably act to add an extra joint to the fore leg increasing its swing. Triassic crocodylomorphs were very graceful, slender forms - more reminiscent of a greyhound than a true crocodile. Some modern crocodiles such as one form from Australia can still move very quickly and can even run in a full gallop [fig]. This was almost certainly true of the Triassic forms. It was not until after the extinction of the phytosaurs at the end of the Triassic that the crocodylomorphs evolved into crocodiles of modern aspect, although fully terrestrial forms persist into the Cretaceous. Some Triassic (and later) forms even evolved into herbivorous forms and forms with very mammal-like teeth.

  • Dwarf West African Crocodile in a highwalk mode of locomotion.

    Erpetosuchus originally from Scotland and recently found in the Newark Supergroup of Connecticut is an example of one of these early, terrestrial crocodylomorphs. On the right, "a" is the skull of Erpetosuchus from Connecticut, and "b" is the skull from Scotland (based on Olsen et al., in prep.). Scale is 5 mm.

  • Reconstruction of a galloping Erpetosuchus.

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