A few years ago, a fisherman working in the Indian Ocean off the west coast of Australia reeled in an unusual catch—a tiny two-headed shark! The man found the pup, or baby shark, inside a pregnant blue shark.
Scientists believe the strange shark likely started out as an embryo—an organism in the earliest stages of development—that split in two. This occurrence normally leads to identical twins. But in this case, the embryo didn’t completely separate. The two sharks’ bodies remained conjoined, or attached. Unfortunately for the shark, two heads are not better than one. According to scientists, it would never have been able to swim properly, making it an easy target for predators.
Only about half a dozen two-headed sharks have ever been reported, and most have been blue sharks, says Valentín Sans-Coma, a biologist at the University of Málaga in Spain. “However, there is no reason to think that any species of shark is more prone to produce conjoined twins than any other,” he adds.
In fact, Sans-Coma recently discovered a conjoined sawtail catshark in his own lab. Not all shark pups grow inside their mom’s womb. Species like sawtail catsharks reproduce by laying eggs. Sans-Coma was raising these animals to study, when he spotted a strange two-headed embryo growing in its translucent egg.
It was the first time this phenomenon had been seen in an egg-laying shark species. How rare is it? Sans-Coma says that there was only one double-headed fish out of nearly 800 embryos he examined.