Half fish, Half tetrapod
Tiktaalik is not always considered a true tetrapod, due to its shared characteristics of a tetrapod and a fish, and has been called a “fishapod.” The organism itself looked half-fish, half-tetrapod; it had a big fin on the posterior half of its body, four legs, and a flattened head resembling a reptile's. It had gills, scales, and fins like fish, along with robust rib bones and a neck like a tetrapod's. The front fins of Tikaalik were also half-fin, half-leg. The fossils of Tiktaalik show functional wrists, elbows, and shoulders, but it still had the rays of a fish fin (Daeschler et al., 2006). More evidence shows that Tiktaalik had both lungs and gills. Its ribs were imbricated, helping to support the needs of lungs. Earlier ancestors of Tiktaalik were able to breathe at the water's surface, showing that these older fish had lungs as well. These unique and innovative features made Tiktaalik a very adaptable organism as it began the transition of tetrapods onto land.
