A Florida fisherman got a surprise when he caught a bull shark recently - and found a live two-headed foetus inside the animal.
The fisherman released the other shark offspring, which were able to swim away, but kept the specimen and passed it on to scientists who described it in a study published today by the Journal of Fish Biology.
According to discovery.com, Michael Wagner, co-author of the paper and assistant professor at Michigan State University department of fisheries and wildlife, said it is one of only six examples of a two-headed shark ever recorded, and the first time this has been seen in a bull shark.
He told The Register: "They're hardy little critters. But despite this, the two-headed specimen probably would have died after birth. It was near-to-term, but should have been a lot larger – the body looks to have invested so much energy in growing a separate head that the rest of the body was foreshortened."
Wagner added that the specimen was technically called "axial bifurcation," and that the deformity is a result of the embryo beginning to split into two separate organisms, or twins, but doing so incompletely after the mid-spine formed into one unit.
According to planetsave.com, the MRI scan (pictured) confirmed the animal was truly dicephalic (two-headed) showing that the shark has two distinct brains, and, additionally, two complete hearts and stomachs, with the remainder of the body joined together to form a single tail.
Wagner said: "This is certainly one of those interesting and rarely detected phenomena. 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."
Wagner added that it was important to study examples like this shark to get clues as to how this type of abnormality comes about and its implications for biology.
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