And now, researchers in Spain studying cardiovascular development in Atlantic sawtail catshark embryos found one that also displayed the phenomenon known as dicephaly. The embryo had two heads, and each of them had a brain, a mouth, two eyes and five gill openings on each side.
Previously, dicephaly had been observed in shark species that are either viviparous (give birth to live young, like mammals) or ovoviviparous (where the eggs develop and hatch inside the mother).