During the Late Carboniferous, the temnospondyls and anthracosaurs dominated most terrestrial landscapes, especially the damp forests. Small lizard-sized tetrapods were also in existence, creeping in and out of the vegetation in drier areas, in search of insects and worms. They laid eggs that did not have to hatch in water. These were the first amniotes, and they included the ancestors of all subsequent major tetrapod groups (i.e. reptiles, birds and mammals) that were to dominate Earth from Permian times onwards. These early amniotes are generally called reptiles, although the traditional 'Class Reptilia' is paraphyletic as it excludes the birds and mammals, descendants of these early forms.

In this chapter, the early amniotes will be described, and key biological problems of living a life completely divorced from the water will be explored. The radiation of amniote groups in the Late Carboniferous and Permian built up complex ecosystems that were to be destroyed by the huge end-Permian mass extinction. But among these Permian amniotes were the ancestors of the animals that dominated during the better-known ages of the dinosaurs and of the mammals.

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