heterocercal tail In fish, a tail in which the tip of the vertebral column turns upward, extending into the dorsal lobe of the tail fin; the dorsal lobe is often larger than the ventral lobe. The heterocercal tail is present in many fossil fish, in the sharks (Chondrichthyes), and in the more primitive bony fish, e.g. the families Acipenseridae and Polyodontidae. In the later, ray-finned fish (Actinopterygii) the homocercal tail developed, in which the vertebral column stops short of the tail fin, which is supported only by bony rays, giving rise to an apparently symmetrical type. Compare DIPHYCERCAL TAIL.

heterocercal tail In fish, a tail in which the tip of the vertebral column turns upward, extending into the dorsal lobe of the tail fin; the dorsal lobe is often larger than the ventral lobe. The heterocercal tail is present in many fossil fish, in the sharks (Chondrichthyes), and in the more primitive bony fish, e.g. the families Acipenseridae and Polyodontidae.