Tiktaalik, extinct walking fish. Some Lungfish evolved into frogs round 375 million years in the past, in the course of the Devonian interval. It was much hotter and drier on Earth throughout that interval - with a lot of the land consisting of one large continent, called Gondwana. Some fish within the drying seas advanced to dwell on land in order to survive. Tiktaalik was certainly one of the first fish with legs and spinal cords and an ancestor to the frog.
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