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It is theorized that "walking" among tetrapods originated underwater with air-breathing fish that could "walk" underwater, giving rise to the plethora of land-dwelling life that walk on four or two limbs.[24] While terrestrial tetrapods are theorised to have a single origin, arthropods and their relatives are thought to have independently evolved walking several times, specifically in insects, myriapods, chelicerates, tardigrades, onychophorans, and crustaceans.[25] Judging from footprints discovered on a former shore in Kenya, it is thought possible that ancestors of modern humans were walking in ways very similar to the present activity as many as 1.5 million years ago.[26][27] |
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