What structural feature defines the zebra shark's remarkably long caudal fin?

It is heterocercal, meaning the vertebral column extends into the longer, upper lobe.

The caudal fin, or tail fin, of the zebra shark is one of its most defining structural characteristics, aiding identification even when the body pattern is indistinct. This tail is described as remarkably long, specifically because the upper lobe is so elongated that it nearly equals the length of the rest of the shark's entire body combined. This specific configuration where the vertebral column extends into the longer, upper section of the tail classifies the fin as heterocercal. While heterocercal tails are present in many shark species, the extreme length ratio observed in the zebra shark suggests that its primary mode of propulsion is optimized for slow, deliberate movements along the seafloor rather than sustained high-speed swimming.