Two-headed shark embryo discovered by Spanish scientists

Spanish scientists involved in raising sharks for medical research stumbled upon on an unsightly surprise hidden in their stash of nearly 800 embryos — a two-headed specimen belonging to the Atlantic sawtail catshark species.

Two-headed shark embryos have been discovered in the wild on a couple of occasions. National Geographic reports that two-headed bull shark and blue shark embryos have previously been found by fishermen in Florida and the Indian Ocean respectively.

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What makes this new discovery unique however is the fact that this is the first two-headed shark embryo belonging to an egg-laying species.

The embryo comprised two distinct heads that merged just below the gills. It had just a single intestine and one pair of kidneys as seen in normal sharks, but two each of the heart, liver and stomach. The inconsistencies weren’t confined to internal organs — the specimen had one pair of pelvic fins like a regular shark, but duplicated dorsal and pectoral fins.

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In their paper, the scientists suggest that there are a number of possible causes for the malformation, including “genetic predisposition, viral infections, metabolic disorders and environmental alterations,” although genetic defects appear to be the most likely cause.

They also point out that the abnormality isn’t confined to sharks, writing that “It is known that, although with a low incidence, two-headed conjoined twins occur in all major groups of vertebrates.”

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The anomalous embryo was spotted because the shark egg capsules have transparent walls.

Lead researcher Valentin Sans-Coma told the National Geographic that it’s impossible to say whether the animal would have survived, but that it’s unlikely that two-headed shark offspring survive very long.