Last month, a group of Dutch fishermen discovered a double-headed harbour porpoise (Phocoena phocoena). The unusual little fellow was definitely DOA, and fearing that keeping it would get them in trouble, the fishermen took a few photos of the beast and threw it back in the ocean. What the crew didn't realise was they'd found the first case of dicephalic parapagus — or partial twinning — in harbour porpoises.
Image: Henk Tanis
Now, researchers from the University of Rotterdam have examined the photos and are trying to learn more about the unusual creature. While the harbour porpoise is one of the most common cetaceans in the northwest European continental shelf waters, this condition is highly unusual. The team believes the twins did not survive long after they were born, since their dorsal fin was not yet erected. The small hairs on their upper rostrums (that beak-looking dolphins have) had also not fallen off, indicating they died pretty quickly.
— SOSDolfijn (@SOSDolfijn) June 6, 2017
"This case concerns the second known case of twinning, the first case of conjoined twins in Phocoena phocoena, the fourth known case of parapagus dicephalus in a cetacean species and the tenth known case of conjoined twinning in a cetacean species," the researchers wrote. Their work has been published in Deinsea.
Not much is known about what causes conjoined twinning in cetaceans. In humans, conjoined twins are identical twins that are physically attached to each other. In healthy identical twins, an embryo splits into two after fertilisation, but in conjoined twins, this process abruptly stops before the separation is complete.
Hopefully, this unusual case will provide some answers to the questions researchers have about partial twinning in cetaceans. RIP baby porpoises, we hardly knew ye.