PAUL D STEWART / SCIENCE PHOTO LIBRARY PAUL D STEWART / SCIENCE PHOTO LIBRARY
Fossil and pentadactyl limb evolution. The five-fingered pentadactyl hand is shared by humans with ancestors going back over 300 million years of evolution. Here, a human hand is shown with the hand of a small predatory Permian reptile called Captorhinus, which is approximately 280 million years old. Scientists take the enduring feature as evolutionary evidence for shared ancestry. It appears the trait may have arisen only once in a shared amphibian ancestor. Captorhinus lived in North America, Europe, India and Africa.
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