BSCI392
11-19-07
The many careers of crocodilians

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Archosauria: (Permian - Recent)

The most recent common ancestor of crocodilians and birds. Archosaurs, ancestrally were medium-sized saurian predators who shared the Late Permian world with the dominant synapsids. After the Permo-Triassic extinction, they proliferated so that, by the middle Triassic, they had replaced synapsids as the dominant land vertebrates, both as predators and as herbivores.

They have a long list of synapomorphies, of which this course will only sample a few. Note that they are biologically very significant.

Here we see two major biological themes: The ability to bite chunks out of food effectively, and an accelerated metabolism.

  • Food processing: In lepidosaurs, we saw an evolutionary trend toward the ability to swallow larger and larger items. Animals that did this had to cope with a surface volume ratio problem: It took much longer to digest food. Thus, we got the proverbial python resting for a week after each meal.

    Crocodylomorph diversity

    The Late Triassic extinction created an ecological vacuum at the upper levels of the terrestrial food-chain. By the Middle Jurassic dinosaurs had occupied the major herbivore and carnivore niches. Crocodylomorphs weren't out of the picture, however. In the Jurassic, we see the adaptive radiation of Metasuchia (Early Jurassic - Recent). These creatures:

    Eusuchia (Cretaceous - Recent): Within Neosuchia is the monophyletic group containing living crocodilians and their closest relatives. Characterized by:

    Fossil eusuchians seem generally to have had similar ecological, locomotor, and thermoregulatory adaptations as living crocodilians, but there are some specialists worth noting:

    Crocodylia (Cretaceous - Recent): For the record, the monophyletic group Crocodylia (note spelling) = "The most recent common ancestor fo living crocodilians and all of its descendants." It includes: