Tiktaalik is the fossil fish often used to illustrate the transition toward four-limbed vertebrates.
Tiktaalik lived about 375 million years ago during the Devonian Period. Fossils were discovered on Ellesmere Island in the Canadian Arctic and described in 2006. It had fish features such as scales and fins, but also a broad, flattened head, a mobile neck, robust ribs, and fin bones capable of supporting the body in shallow water.
Its paired fins contained bones corresponding in arrangement to the upper arm, forearm, and wrist, although Tiktaalik did not possess true fingers. These traits place it near the evolutionary transition between finned fishes and early tetrapods.
Tiktaalik was not the direct ancestor of every later land vertebrate. It is better understood as a close relative that preserves a combination of traits expected in this major evolutionary transition.