First two-headed bull shark is confirmed in study

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Two-headed bull shark fetus.
Photo courtesy of Patrick Rice, Shark Defense/Florida Keys Community College

A fisherman in the Florida Keys made a surprising—and incredible—discovery upon landing a bull shark on April 7, 2011. In the shark was a live bull shark fetus that featured two heads.

The fisherman saved the specimen and turned it over to scientists for study. That study in the Journal of Fish Biology finally came out Monday and confirmed it was a single shark with two heads rather than conjoined twins.

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Radiograph of two-headed shark.
Photo credit courtesy of Michael Wagner

Other species of sharks, such as blue sharks and tope sharks, have been born with two heads, but this is a first for the bull shark, according to Michael Wagner, Michigan State assistant professor of fisheries and wildlife who confirmed the discovery with others at the Florida Keys Community College.

“This is certainly one of those interesting and rarely detected phenomena,” Wagner told Phys.org. “It’s good that we have this documented as part of the world’s natural history, but we’d certainly have to find many more before we could draw any conclusions about what caused this.”

What happened was that the embryo began splitting into twins but did not do so completely, leaving the shark to develop with two heads.

The two-headed shark had little chance to survive in the wild since a predator needs to move fast to catch other fast-moving fish and that would be nearly impossible with this mutation, Wagner told OurAmazingPlanet.

Two heads are better than one? Definitely not the case with sharks.

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Two-headed bull shark fetus. Photo courtesy of Journal of Fish Biology / C. M. Wagner et al