Shark tail fins, also called the caudal fins, are unique among all fishes. If you look at the top half of the fin, it is noticeably longer than the bottom half. This asymmetrical profile was common in many ancient fishes, but sharks are the only group to maintain the shape over a period of 350 million years.
Scientists still debate the function of this unique shape, and it may serve a different purpose from shark species to shark species when combined with other physical characteristics. However, some research suggests the shape allows for easy, horizontal cruising.
In this illustration, four sharks from the IndoPacific region are placed side by side for comparison. The tiger shark hovers above, the two forks of its caudal fin noticeably similar in size. Considered the least picky of shark species when it comes to prey, the tiger shark will eat practically anything it can sink its teeth into, like birds, dolphins, jellyfish, crabs and even garbage. Research comparing the differences between young tiger sharks and mature sharks suggest the more symmetrical shape may help during long migrations made by adults.
Immediately below is the thresher shark. The thresher shark’s tail serves more than a tool for locomotion. The shark uses its elongated tail to whip unsuspecting prey, a unique behavior that stuns the fish before it is consumed. The fastest strikes reach close to 50 mph, creating strong shock waves that cause gas to diffuse out of the water in bubbles.
The two bottom dwelling sharks, the zebra shark (right) and the smaller epaulette shark (left), have markedly different caudal fin lengths from their open-ocean relatives, presumably to enable them to hug the sea floor and swim unencumbered. The caudal fin of the zebra shark is almost as long as its body.