Scientists have confirmed the discovery of what is thought to be the world's first ever two-headed Bull shark (Carcharhinus leucas).
A study, led by Michigan State University, confirmed the specimen found in the Gulf of Mexico in April 2011 was a single shark with two heads, rather than conjoined twins.
The shark was discovered by a fisherman when he opened the uterus of an adult shark. The two-headed baby would have died shortly afterwards and it's thought would have had little if any chance of surviving in the wild.
Although there have been cases of sharks born with two heads in other species, such as Blue and Tope sharks, this is the first record in a Bull shark, said Michael Wagner, MSU assistant professor of fisheries and wildlife, who confirmed the discovery with colleagues at the Florida Keys Community College.
"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 difficulty of finding such oddities is due, in part, to creatures with abnormalities dying shortly after birth.
Wagner explained that cases of two-headed lizards and snakes were more common because they were often bred in captivity, so records of such anomalies could be made more easily.
MRI scans on the shark revealed that it has two distinct heads, hearts and stomachs with the rest of the body joining together in the back half of the animal to form a single tail.
Wagner noted in his research that some may try to attribute the deformed shark to exposure to pollutants, given the timing of the shark’s discovery with the Deepwater Horizon oil spill.
"Making that leap is unwarranted," he said. "We simply have no evidence to support that cause or any other."
The study was published in the Journal of Fish Biology.
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