High up in the north: the wood frog, Rana sylvatica

As poikilothermic animals, most amphibians live in the warmer parts of the world. But thanks to astonishing special adaptations, some species have made it all the way into the coldest regions beyond the polar circle or into high mountain areas. The wood frog freezes solid in the winter and is alive and well when it thaws again in the spring. That way, it defies the harsh conditions of its home in Alaska, Canada and the Northern contiguous United States. Up to 1/3 of its body fluids can freeze to ice crystals, the rest is protected by a naturally produced cryoprotectant. No North American frog has ventured further north.