Rare Two-Headed Shark Embryo Discovered In Spain

Researchers in Spain have discovered a two-headed shark embryo while conducting a cardiovascular study.

“The embryo had two heads fused behind the gills. Each head had a mouth, two eyes, a brain, a notochord and five gill openings on each side,” the researchers said in their study, published in the Journal of Fish Biology. The shark in question was an Atlantic sharptail catshark (Galeus atlanticus). This little known species resides in the Northeast Atlantic, Mediterranean and off West Africa and can be found between 1,000-2,300 feet below the surface and is listed as “Near-threatened” on the IUCN redlist.

The condition of having two heads is called dicephaly and, while rare, it can occur in many different groups of vertebrates, including humans. Dicephaly has been observed in a number of sharks as well, but until now only in species that are viviparous or ovoviviparous — those that either bear live young or lay eggs that develop and hatch inside the mother.

This specimen is unique because it is the first recorded finding of dicephaly in an oviparous, or true egg-laying, species of shark.

The researchers, led by Valentín Sans-Coma of the University of Malaga, believe genetics, rather than environmental factors, led to the shark’s dicephalic condition. Axial bifurcation, —when an embryo fails to split into two separate individuals — is a common cause for two-headed animals. The research team hopes to learn more about the shark’s genetics through further analysis of the embryonic tissue.

Dicephalic animals can survive until birth, but few live long after. It can be difficult for them to catch food, especially for sharks whose streamlined shape isn’t nearly as effective with two heads. Besides the risk of starvation, complications often arise from inadequate function of joined integral organs.

Despite its high fatality rate sharks needn’t add dicephaly to their list of impending threats — we can instead continue to focus conservation efforts on halting shark finning. This specimen was the only one out of the 797 embryos examined by the team to have this condition. If that study sample is any indication only 0.13 percent of Atlantic sawtail sharks exhibit dicephaly.