Michigan State University researchers studying the specimen found in the uterus of an adult bull shark taken in the Gulf of Mexico April 7, 2011, said it was the first record of the phenomenon known as dicephalia ever seen in bull sharks although it has been seen before in other species of shark.
"This is certainly one of those interesting and rarely detected phenomena," MSU fisheries and wildlife Professor Michael Wagner said. "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."
A fisherman found the two-headed specimen when he cut open the adult shark, Wagner said, and it died shortly thereafter.
It would have had little, if any, chance to survive in the wild, he said.
"You'll see many more cases of two-headed lizards and snakes," Wagner said in a university release Monday. "That's because those organisms are often bred in captivity, and the breeders are more likely to observe the anomalies."
An MRI scan revealed two distinct heads, hearts and stomachs with the remainder of the body joining together in the back half of the animal to form a single tail, the researchers said.