The phenomenon of conjoined twins is well-known among humans and other animals. There are often news reports of life-saving surgeries undertaken to separate and save conjoined children. And oddity museums like Ripley’s usually contain pictures or models of conjoined animals like two-headed calves. A recent discovered instance of this condition is even more rare and less well-understood than its occurrence among land mammals.
In May 2017, some Dutch fishermen who were working in the North Sea caught something rather unexpected. When they pulled in their nets, they found that they had snared a set of conjoined newborn twin harbor porpoises. The twin sea mammals had two heads and shared one body, but they were already dead when they were pulled from the sea.
Unfortunately, the fishermen threw the rare specimen back into the sea because they were afraid it would be illegal to keep it. They did at least manage to take some photos of the porpoises before discarding them, though, to prove the truth of what they saw.
This was a loss for science, since there have only been nine other documented cases of conjoined twins in the cetacean species, which consists of porpoises, dolphins, and whales. This was also the first ever recorded case of conjoined twinning in this particular species of porpoise. Even cases of normal twins in these animals are extremely rare, since the wombs of their mothers are typically not large enough to support twins.
Some researchers have expressed dismay at the loss of such an interesting specimen, though they have been able to gather some information from the photos. In one picture, an umbilical opening can clearly be seen, which is evidence that the animals died shortly after birth and were not killed due to being caught in fishing nets. The mammals’ dorsal fins had also not risen yet, meaning they had just been born when they died. In addition, they still had tiny hairs on their faces which are typically lost shortly after birth.
It would have been nearly impossible for any cetacean conjoined in this way to have survived long after birth. The mammals have to be able to swim as soon as they are born in order to live. Due to the abnormalities that would have been present in their shared spinal column, these porpoises probably would not have been able to swim at all and would have quickly drowned. Their single, shared heart also probably could not pump blood adequately enough to keep them alive.