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At the end of the Devonian period (), the seas, rivers and lakes were teeming with life but the land was the realm of early plants and devoid of vertebrates though some, such as Ichthyostega, may have sometimes hauled themselves out of the water.
In the early Carboniferous (), the climate became wet and warm.
Extensive swamps developed with mosses, ferns, horsetails and calamites.
Air-breathing arthropods began to evolve and invaded the land where they provided food for the carnivorous amphibians that began to emerge from the waters.
There were no other tetrapods on the land and the amphibians were at the top of the food chain, occupying the ecological position currently held by the crocodile.
Though equipped with limbs and the ability to breathe air, most still had a long tapering body and strong tail.
They were the top land predators, sometimes reaching several meters in length, preying on the large insects of the period and many types of fish in the water.
They still needed to return to water to lay their shell-less eggs, and even modern amphibia have a fully aquatic larval stage with gills like their ancestral fish.
It was the development of the amniotic egg, which prevents the developing embryo from drying out, that enabled the reptiles to reproduce on land and which led to their dominance in the period that followed.

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