Tiktaalik was found in the Arctic, but didn't live there...
Tiktaalik was found in the Canadian Arctic, at approximately 78° North latitude. The climate is extremely harsh for all but a few weeks of each year. During this time, the ground only thaws 6 inches below the surface, making it very difficult for large plants to grow. Consequently, there are no trees or even bushes in the high Arctic. Instead, there is tundra: a landscape of mosses, lichen, and hardy grasses that can cope with the short growing seasons and harsh temperatures.
It follows then, that the animals in the Arctic must be specially adapted to extreme cold and long periods without a lot of food. Average winter temperatures are -28°C (-18.4°F) and since there are no trees, winds can reach speeds of 48-96 km/hr (30-60 mph). With such harsh conditions, it makes sense that there are only a few specially adapted animals living in the Arctic today.
How then is it possible that we're finding tropical species like Tiktaalik in the rocks of the Arctic?
The answer has to do with continental drift. Three hundred and seventy-five million years ago in the Devonian, the world did not look anything like it does today. First of all, the climate was much warmer overall, so the north and south pole were not covered in ice. Secondly, the continents were not arranged in the same way as they are today. The continent Tiktaalik lived on was not located at 78° N. Instead, it was located almost entirely in the southern hemisphere. And the stream Tiktaalik probably lived in was located in the Northern part of that continent, very close to the Equator.
For more paleomaps and continental drift animations, visit Scotese's Paleomap Project