The 500 Million Year History of Vertebrates

This early tetrapod still lived mostly in water.

Some vertebrates soon evolved four limbs, making them tetrapods. These animals could move more easily, and some could even leave the water for a short time to escape predators. However, the early tetrapods still needed to spend most of the time in the water to keep their skin moist.

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That's a weird-looking creature! Do all tetrapods look like that?

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Tetrapods are animals that have four limbs. From the picture, I can see that legs are limbs. What else counts as a limb?

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Tetrapods are animals with four limbs. Legs, arms, and wings are all examples of limbs. So humans, birds, and dogs are all examples of tetrapods. Whales are also considered tetrapods, even though they eventually adapted to lose their hind limbs.

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