A fisherman working off the Florida Keys recently caught a bull shark, then opened it up to find that it contained two live fetuses, including one highly unusual one with two heads.
The fishermen gave it to scientists, who wrote about it in an article published in the Journal of Fish Biology this week.
A study carried out by experts at Michigan State University confirmed the shark was a single shark with two heads, rather than conjoined twins.
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.
“In and of itself, this single natural history observation does not tells us anything Earth-shattering about the health of the world’s oceans or populations of bull sharks,” Wagner told Ocean Views via e-mail today.
Wagner and his colleagues confirmed the discovery with magnetic resonance imaging.
Using magnetic resonance imagery, the scientists discovered that the shark had two distinct heads, hearts and stomachs, with the rest of the shark merged together with the organs shared.
“This is certainly one of those interesting and rarely detected phenomena,” said Michael Wagner, the university’s assistant professor of fisheries and wildlife.
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.
The shark had little chance of surviving after birth regardless of its mother being caught, according to Michael Wagner.
He said: “You’ll see many more cases of two-headed lizards and snakes. That’s because those organisms are often bred in captivity, and the breeders are more likely to observe the anomalies.”
The two-headed bull shark displays a process technically called “axial bifurcation,” in which the embryo doesn’t finish splitting into two separate individuals (twins). This mutation has been seen in other animals, including humans.
Studying such rare organisms may help us better understand developmental processes, Wagner added.
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.”
Two-headed sharks are not hugely common, though previous specimens identified include a two-headed top shark from 1934 and a two-headed blue shark found two years ago.
It could be caused by a genetic mutation, or by environmental factors – though Wagner is keen to rule out blaming the BP Deepwater Horizon oil spill, saying “we simply have no evidence to support that cause or any other”.
He 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.”