Going Ashore Becoming a Land Animal

About 370 million years ago, a new variety of vertebrates, descended from the lobe-finned fishes, began a cautious migration from the life-sustaining waters of their ancestors, out of the ooze, and onto the rocks and swampy stretches of shoreline that made up the first habitable land. Thus was marked a monumental event in the history of life—a transition that led to the first amphibians and to all vertebrate lineages to follow: reptiles, birds, and mammals, including humans.

If the sea was so inviting, and the land was so bare of the necessities of life, one may question why vertebrates ventured onto the land in the first place. The reasons why animals made this monumental move to dry land have been a matter of much scientific speculation. Recently discovered fossil clues to some of the rarest of all fossils—the remains of the earliest land vertebrates—have begun to lead to some consensus among paleontologists who study the evolution of the earliest land creatures. One startling realization made by scientists is that the development of legs and lungs did not occur to enable them to walk out of the water. The development of legs and lungs allowed these creatures to better adapt to their shallow water habitats. This chapter traces the evolutionary adaptations that allowed vertebrates to migrate to a terrestrial habitat and introduces the first vertebrate representatives to make the transition.

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