Rare Two-Headed Porpoise Found In North Sea

Dutch fishermen in the North Sea found the first known case of a two-headed harbor porpoise last month, when it was caught as bycatch in a net. However, fearing that it would be illegal to keep the marine animal, they threw it back to the ocean -- but not before taking photos of the bizarre anomaly.

National Geographic noted that case studies of conjoined twins have been found in reptiles, domestic animals and even humans, but these are rarely seen in the wild. In fact, before the porpoises, there had only been nine other instances of two-headed cataceans (aquatic animals that consisted of dolphins, whales and porpoises) that have been documented by reliable sources.

Erwin Kompanje of the National History Museum Rotterdam noted in a study published in the museum's journal that conjoined twins in whales and dolphins are "extremely rare." In fact, normal twinning in porpoises is rare, as there is no room in the mother's womb for more than one baby. Symmetrical conjoined twins such as the found porpoise are thought to be a result of two separate embryos fusing together or a zygote that only partially split.

Researchers were disappointed for not being able to examine the porpoise, but they could see details from the photos provided. For instance, they definitively concluded that the porpoise was a newborn male. The dorsal fins were not yet erect, and the tops of its heads still have hairs on them. It also still contained an umbilical opening, which is a clear indication that the porpoise died shortly after birth.

They would not have survived long, either. They could have two brains that instructed one body to swim different ways, or their single heart could fail to pump enough blood.

With the porpoise dumped back into the deep waters, there is no hope of ever finding it again. However, Kompanje did what he could do to preserve evidence through the study he co-authored about porpoises. However, he has no illusions. He is not expecting to see another one like it in his lifetime.