Fossil Evidence

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In 2004, scientists digging in the Canadian Arctic unearthed fossils of a half-fish, half-amphibian that all but confirmed paleontologists' theories about how land-dwelling tetrapods–four-limbed animals, including us–evolved from fish. It is a classic example of a transitional form, one that bridges a so-called evolutionary gap between different types of animal. In this slide show, examine five important cases.