Tiktaalik

Tiktaalik is a genus of extinct lobe-finned fish. As Tiktaalik roseae is the only species classified under the genus, Tiktaalik can be called a monospecific genus. It lived about 375 million years ago, during the Late Devonian Period. Although Tiktaalik generally had the characteristics of a lobe-finned fish, it also shared some traits with tetrapods: it had gills, scales, and fins, but it also had a robust ribcage, primitive lungs, and a mobile neck. Tiktaalik is often referred to as a “transitional fossil” because it also had intermediate features, such as half-fish, half-tetrapod limbs and joints with functional wrist joints and radiating, fish-like fins instead of toes. It also had an ear region that was half-fish, half-tetrapod. While it is not an ancestor to any currently living animal, Tiktaalik is evidence of animals with intermediate forms that bridged the evolutionary gap between fish with fins and animals with arms and legs.