2-Headed Shark Fetus: Florida Keys Fisherman finds Rare Specimen

An unsuspecting fisherman came across a rare site: one of a shark's live fetuses had two heads. The fisherman kept the specimen and immediately shared it with scientists who described it in a study published online in the Journal of Fish Biology.

There have only been six published reports where a bull shark has ever had a two-headed shark. The first time this has been seen in a bull shark, said Michael Wagner, a study co-author and researcher at Michigan State University.

Technically called "axial bifurcation," the deformity is a result of the embryo beginning to split into two separate organisms, or twins, but doing so incompletely, Wagner said, according to OurAmazingPlanet. It's a very rare mutation that occurs across different animals, including humans, according to Yahoo News.

"Halfway through the process of forming twins, the embryo stops dividing," he said.

The two-headed fetus likely wouldn't have lived for very long in the wild, he said. "When you're a predator that needs to move fast to catch other fast-moving fish ... that'd be nearly impossible with this mutation," he said.  [See the two-headed shark.]

According to Wagner, the deformed shark may someday help people better understand deformities arise in sharks and other animals.