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Figure 5. Fish have two types of muscle...Click to Enlarge Image

Both tunas and lamnid sharks, including makos and whites, are top predators and have similar streamlined body shapes. And the similarity between these fishes, it turns out, is more than skin deep. The two groups have developed high-speed swimming techniques that involve efficient movements of only their tail sections, rather than the full-body undulations of most fish. They accomplish this by keeping their red muscle in their torsos and transferring the muscle force to the tail through large, specialized tendons. While the two groups' common ancestor diverged more than 400 million years ago, selection pressures seem to have made both fish hit upon nearly identical movement mechanisms.

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