Scientists have confirmed the discovery of the first ever case of a two-headed bull shark foetus.
A fisherman found the 20cm-long foetus in a bull shark caught near Florida in April 2011, and passed it on to the marine science department at Florida Keys Community College.
The finding has been described in a study led by Michigan State University and published in Journal of Fish Biology today.
There have only been about six published reports of two-headed sharks ever recorded, however this is the first example of a two-headed bull shark, Michael Wagner, MSU assistant professor of fisheries and wildlife said.
The shark has what is called "dicephalia" and is not a case of conjoined twin sharks, rather it is a shark with two developed heads.
"This is certainly one of those interesting and rarely detected phenomena," 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."
The fisherman found the two-headed shark alive when he opened the uterus of the adult shark, however it died shortly later. The shark would have had little chance of survival in the wild, Wagner said.
"You'll see many more cases of two-headed lizards and snakes," he said. "That's because those organisms are often bred in captivity, and the breeders are more likely to observe the anomalies."
Wagner and his colleagues confirmed the discovery with magnetic resonance imaging.
Without damaging the unique specimen, the MRIs revealed two distinct heads, hearts and stomachs with the remainder of the body joining together in back half of the animal to form a single tail.
Wagner noted in the study that some may want to attribute the deformed shark to exposure to pollutants, however cautioned against leaping to this conclusion.
"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," Wagner said. "Making that leap is unwarranted. We simply have no evidence to support that cause or any other."