The first limbed vertebrates and all of their descendents are members of the vertebrate group Tetrapoda. Tetrapods are vertebrate
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Humerus Radius Ulna Distal elements
The fossil record provides clues to stages of transformation of the fish fin to the tetrapod limb during the Devonian Period.
animals with four toe-bearing legs. The group also includes two-legged and legless members that are descended from tetrapods.
The first tetrapods descended from fish. The move onto land was not as simple as evolving legs and just leaving the water. Terrestrial habitats were fraught with unique challenges for vertebrates. These pioneers faced many of the same challenges to living on land that plants and arthropods had overcome earlier. These challenges included the adequacy of the creatures' weight-bearing anatomy, the loss of body moisture to the air, the problem of breathing out of the water, sensory adaptation, and reproduction. This section describes the multitude of adaptations that led from fins to feet and to the ability of vertebrates to conquer the land.
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