Fishermen off the coast of the Netherlands accidentally made history when they discovered the world's first example of a conjoined twin harbor porpoises.

A Two-Headed Porpoise

While conjoined twins are rare among humans, it is almost unheard of among cetaceans, a group of animals which includes whales, dolphins and porpoises. In fact, this recent discovery is only the 10th such case of conjoined twins to be found among cetaceans, which means that researchers have little data to go on regarding such phenomenon.

"The anatomy of cetaceans is strikingly different from terrestrial mammals with adaptations for living in the sea as a mammal," said Erwin Kompanje who helped author the paper on this discovery.

Of course, this doesn't mean that there aren't more examples out there, but the oceans are simply so large that scientists don't have many opportunities to study conjoining among sealife.

Unfortunately, the researchers were not able to directly study this animal either — which was likely dead at the time of its discovery — since the fishermen returned it to the sea because they thought it would be illegal to keep it. However, they did take several pictures which allowed the researchers to learn something about the porpoise, such as its gender and age.

What We Know About The Two-Headed Porpoise

Thanks to the fishermen's photos, scientists were able to determine that the male twins died shortly after birth as the specimen's tail had not stiffened, which is necessary if the creature is to swim.

Twins — conjoined or otherwise — are rare among cetaceans since there just isn't enough room in the womb to support more than one fetus. In fact, this study represents the second known case of any twins occurring among this particular species of porpoise. Despite the lack of the animal's body, the researchers who worked on this study believes that this find represents a chance to expand their understanding of this little-known phenomenon.

Conjoined Twins

In terms of conjoined twins, there are two ways in which they can develop. Either two separate embryonic discs will fuse in the womb, or the zygote fails to split during the development process. Among humans, conjoined twins are sometimes able to be separated though it is a difficult process.

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