This chapter traced the evolutionary adaptations that allowed vertebrates to migrate to a terrestrial habitat and introduced the first vertebrates to make the transition.

1. The first limbed vertebrates and all of their descendents are members of the vertebrate group Tetrapoda—animals with four toe-bearing legs.

2. Tetrapods overcame several anatomical and physiological challenges to living out of the water by evolving adaptations to improve their weight-bearing anatomy, their water retention, their respiration, their senses, and their reproductive strategies.

3. The limbs of tetrapods were an adaptation of vertebrates that still lived in the water; these limbs presumably provided a means for animals living in shallow water to move through swampy ecosystems and also enable them to lay in wait and ambush prey.

4. Limbs of waterborne animals had the additional advantage of allowing them to lift their heads out of the water to breathe air, a critical step in the move toward living on land.

5. Tetrapods eventually left the water to occupy a largely untapped habitat that they could easily dominate.

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