Discovered off the coast of the Netherlands, the specimen is the first of its kind ever found.
A newly born two-headed porpoise was documented and studied by a group of Dutch fishermen and a team of researchers from several Dutch institutions. The researchers describe how the fishermen caught the porpoise, photographed it, and then threw it back into the sea in their work published in Deinsea—Online Journal of the Natural History Museum Rotterdam.
Fishermen pulled in the mysterious porpoise off the coast of the Netherlands
Reports of conjoined twins in cetaceans (a family that includes whales, porpoises, and dolphins) are uncommon, owing to the fact that they occur in the open sea—it is also likely that most would die shortly after birth, as the fishermen discovered. In this example, it appears that the porpoise was born unable to swim.
The fishermen were aware that the porpoise was a rare find, but due to rules prohibiting them from keeping captured mammals, they were forced to return it to the sea—but not before taking multiple photographs and sending them to the Deinsea team.
The researchers discovered indicators that it had been born recently when they examined the images taken by the fishermen: the dorsal fins were limp and the umbilical opening was still open, and the tail had not hardened, indicating that it could not swim. Furthermore, both of the heads still had rostrum hair, which normally fades shortly after birth in healthy porpoises. The research team also claims that the porpoise was male and had two fully formed heads. It had individual pectoral fins as well, but only one body. They believe the porpoise was symmetrically conjoined, which occurs when two embryos fuse to form one. In other cases, a single embryo does not divide, preventing the formation of distinct twins.
Despite the fact that there have been nine other incidents of known conjoined sightings in cetaceans, this is the first time a porpoise has been seen. Twins, whether conjoined or not, are thought to be uncommon in porpoises because porpoise calves in gestation are too huge. The formation of conjoined twins generally kills the mother, although it is unknown whether this was the case for the one discovered in the North Sea.