Choristodera

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Choristodera is an order of semi-aquatic diapsid reptiles that ranged from the Middle Jurassic, or possibly Late Triassic, to at least the early Miocene. It was named by Edward Drinker Cope in 1884. Choristoderes have been found in North America, Asia, and Europe, and possibly also North Africa and East Timor. The most common fossils are typically found from the Late Cretaceous to the lower Eocene. Cladists have placed them between basal diapsids and basal archosauromorphs, but the phylogenetic position of Choristodera is still uncertain. It has also been proposed that they represent basal lepidosauromorphs. Most recently, workers have placed Choristodera within Archosauromorpha.

Champsosauridae is the best-known family of the Choristodera and typifies the group. Champsosaurus was first described from Late Cretaceous strata of Montana by Cope in 1876. Champsosaurs resembled modern gharials (gavials) or false gharials. The skull of these animals have a long, thin snout filled with small, sharp conical teeth. This is due to champsosaurs and gharials occupying similar niches: hunting small aquatic prey in rivers and swamps. This is a classic example of convergent evolution. More primitive choristoderes have shorter, broader snouts.