Two-headed shark found growing in a lab in Spain, potentially helping solve mystery of ‘dicephaly’

The discovery is thought to be the first time that a shark that gives birth to live young has been seen to exhibit dicephaly, or being two-headed

Scientists have found perhaps the first ever two-headed shark embryo of its kind, growing in a lab.

The shark appears to mark the first time that the trait has ever been spotted in a shark that lays eggs. Two-headed sharks have been spotted before - but only in species that give birth to live young.

The new find could help shed light on the mystery of dicephaly – the phenomenon when animals are born with two heads. Scientists suspect that two-headed sharks are the result of genetics, rather than pollution, as in the case of The Simpson’s three-eyed fish.

It isn’t clear why animals with such characteristics are so rare – whether are truly very unusual or they simply don’t survive when they are born.

The shark embryo, which belonged to the rare and threatened species Galeus atlanticus, had just one body. But it had two heads – and each head had “a mouth, two eyes, a brain, a notochord and five gill openings on each side”, according to the scientists, and the two heads came together just behind the gils.

Most of the shark’s organs were fused, too. But not all of them were.

“There were two hearts, two oesophaguses, two stomachs, two livers, but a single intestine with a spiral valve,” the team write.

The shark was one of 797 embryos originally intended to be used in studies of the cardiovascular system. Since there was one of them out of that huge number, the defect presented in around 0.13 per cent of the animals in the study.

Scientists have found sharks with two heads before, but they are incredibly rare and have only ever belonged to species that give birth to live young. In all, only seven two-headed sharks like the one that has been found have ever been reported.

Other specimens have been reported in the past that are described as diprosopus rather than dicephalous, having two faces rather than two heads. Only one specimen has ever been found that truly shows those characteristics, though others have been found that are more similar to that than having two heads.

The researchers report their findings in a paper published in the Journal of Fish Biology.