Biologists have documented two-headed animals before, like snakes and lizards — but a finding like this is extremely rare. It's a two-headed bull shark, and it was discovered by a Florida fisherman after cutting open the uterus of an adult shark.

This handsome specimen never had a chance to be born, but it's doubtful it would have survived anyway. It's an example of dicephalia, and it's the first time marine biologists have seen it in a bull shark.

The deformity is also referred to as an axial bifurcation, the result of an embryo failing to split properly into two separate individuals; halfway through the process of forming twins, the embryo stops dividing. As the MRIs show, the sharks have their own hearts and stomachs, with the rest of the body joining together in the back half to form a single tail. The findings were recently published in the Journal of Fish Biology.


Scientists have discovered two-headed sharks before, including blue sharks and tope sharks, but this is the first time it's been seen in a bull shark.

Lead researcher Michael Wagner, assistant professor of fisheries and wildlife at Michigan State University, was reluctant to attribute the dicephalia to pollutants.


"Given the timing of the shark's discovery with the Deepwater Horizon oil spill, I could see how some people may want to jump to conclusions," he said in a statement. "Making that leap is unwarranted. We simply have no evidence to support that cause or any other."

Image: Courtesy of Patrick Rice, Shark Defense/Florida Keys Community College; Michael Wagner, MSU.