Temnospondyls and early amphibians

After the Devonian, tetrapods spread into the wet forests and swamps of the Carboniferous. Pederpes from Scotland, about 348 million years old and described by Jenny Clack in 2002, has feet that point forward, an early sign of walking on land. At East Kirkton in Scotland, excavated by Stan Wood from 1985, limestone about 335 million years old yielded Balanerpeton, a small early temnospondyl, and many other early land vertebrates, so the animals were already diverse.¹²

Temnospondyls became the dominant amphibian group for more than 100 million years. They had wide, flat skulls, short legs and moist skin, and laid jelly-coated eggs in water. Eryops, from the Permian of Texas, was about 2 metres long and a strong land predator, and later forms grew still larger. Modern frogs, salamanders and caecilians are called lissamphibians. Whether they descend from temnospondyls, from another group called lepospondyls or from both is an open question. The key limit of all these animals is their eggs, which dry out on land, a problem solved only when the amniotic egg appeared.³