A fisherman in the Florida Keys discovered a live bull shark fetus with two heads, something that scientists had never seen before in that species.

The discovery took place in April 2011, but it was not made public until now with its publication in the Journal of Fish Biology. Scientists from Michigan State University studied it and confirmed the initial observations.

The fisherman found the fetus when he opened up the uterus of a bull shark he had caught in the waters of the Gulf of Mexico. Upon noticing that the fetus was alive and had two heads, he contacted a scientific team.

MSU's Michael Wagner, the co-author of the study, said in his analysis that the specimen exhibited axial bifurcation, a deformity where the embryo begins to split into two separate organisms but does not complete the process.

"Halfway through the process of forming twins, the embryo stops dividing," he said.

This phenomenon has been observed in other shark species.

Wagner acknowledged that there are those who might link this rarity to the effects of pollution from the 2010 Deepwater Horizon oil spill in the Gulf, but he insisted that there is no evidence that would establish that relationship.

The difficulty in finding rare specimens such as this one is due, in part, to the fact that creatures with genetic anomalies tend to die shortly after being born. 

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