Diversification Of Jurassiccretaceous Reptiles

The diapsids diversified enormously during the Mesozoic, the dinosaurs, crocodilians and lizards on land, the pterosaurs in the air, and the ichthyosaurs and plesiosaurs in the sea. The great mass extinction at the end of the Cretaceous marked a major switch in tetrapod evolution from diapsid-dominated faunas to mammals.

The evolution ofreptiles in the Mesozoic and Ceno-zoic (Figure 8.39) shows two main phases of expansion, the radiation of the dinosaurs, pterosaurs, crocodilians and the marine reptiles in the Late Triassic and Jurassic, and the radiation of the 'modern' groups (lizards, snakes, turtles, birds) from the Late Cretaceous onwards. Mass extinctions among tetrapods have been postulated in the Late Triassic (see pp. 156-7) and, of upper upper

Fig. 8.37 The ichthyosaurs: (a) skull and (b) skeleton of the Early Jurassic Ichthyosaurus; the body outline is based on skin impressions preserved with some European material. (After Andrews, 1910.)

Fig. 8.37 The ichthyosaurs: (a) skull and (b) skeleton of the Early Jurassic Ichthyosaurus; the body outline is based on skin impressions preserved with some European material. (After Andrews, 1910.)

Fig. 8.38 Adult specimen of the ichthyosaur Stenopterygius,from the Lower Jurassic of Holzmaden, Baden-Württemberg, south-west Germany, pictured with juvenile specimens of the same species. This is one of more than 50 specimens with associated young, and these are interpreted as embryos and juveniles that have just been born. (Courtesy of Rupert Wild; specimen in the Museum für Naturkunde, Stuttgart.)

course, at the end of the Cretaceous. Others, at the end ofthe Jurassic and in the mid-Cretaceous, are probably artefacts of an incomplete fossil record (Fara and Benton, 2000).

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