The fossil fish that shows the transition from fish to tetrapods is Tiktaalik. This Late Devonian animal combined fish traits, including scales, gills, and fins, with tetrapod-like features such as a mobile neck, ribs, lungs, and sturdy fin bones.
Tiktaalik lived about 375 million years ago in shallow waterways. Its fossils were discovered in 2004 on Ellesmere Island in Nunavut, Canada, and formally described in 2006. The internal bones of its front fins included structures comparable to a humerus, forearm bones, and a wrist, suggesting that it could support part of its body in shallow water or on the substrate.
Tiktaalik is often called a “missing link,” but that phrase can mislead. Scientists do not generally claim it was the direct ancestor of all tetrapods. Instead, it is a transitional fossil that illuminates the sequence of anatomical changes between lobe-finned fishes and early four-limbed vertebrates. Acanthostega and Ichthyostega were later, more tetrapod-like animals, while coelacanths are living relatives of the broader lobe-finned fish group.