Extremely Rare Two-Headed Porpoise Discovered in North Sea

A Dutch fishing crew on the North Sea was shocked by what they discovered in their trawl net late last month. It wasn’t some kind of a sea monster, but a newborn harbor porpoise with two heads.

The crew snapped a few photos of the deceased porpoise before tossing it back into the sea, fearing it would be illegal to keep it.

The photos circulated around the Netherlands, eventually making their way to Erwin Kompanje, curator of mammals at the National History Museum in Rotterdam. Kompanje would have loved to have been able to examine the porpoise itself, but he and two other researchers were still able to publish a study based only on the photos.

Since the male porpoise had two completely formed heads and a fully formed body with two pectoral fins, the researchers believe it was a case of symmetrically conjoined twins.

“Descriptions of conjoined twins in whales and dolphins are extremely rare,” Kompanje wrote in the study. He was aware of only nine other published cases, and this was the first documented case of conjoined harbor porpoise twins. There are about 700,000 of these cetaceans in the world. Half of them live in the North Sea.

Symmetrical conjoined twins may result “when two separate embryos fuse together or a zygote only partially splits,” National Geographic reports. But the true cause remains an enigma, according to Kompanje. (He and the researchers don’t mention radioactive ocean water as a possible reason, although Dr. Joseph Rachlin, director of Lehman College’s Laboratory for Marine and Estuarine Research, told National Geographic in 2011 that radiation can create “bizarre mutations” in the offspring of ocean animals.)

Tragically, the conjoined twin porpoises likely died soon after being born, as they still had an umbilical opening. They would not have been able to swim since the tail had not yet stiffened and the dorsal fins weren’t erect.

How Rare Are Conjoined Twins in Wild Mammals?

Conjoined twins can occur in humans, domesticated mammals, birds, reptiles, amphibians and fish, Kompanje’s study notes, but are extremely rare in porpoises, whales and other wild mammals. The exact number is unknown, sadly, because conjoined twins are very likely to die before or after birth.

According to the study, almost all known cases of symmetrical conjoined twins in wild mammals “concern embryos and fetuses found during the dissection of dead pregnant females.”

In 1970, for example, what was insensitively referred to as a “double monster” – an embryo with one head and two bodies – was discovered in the womb of a dead dolphin caught by Japanese hunters. Thirty years later, a decomposing bottlenose dolphin calf with two beaks was found in the Mediterranean Sea.

Even twins that aren’t conjoined are a rarity in these cetaceans. “There’s no room in the womb of the mother for harboring more than one baby,” Kompanje told the Washington Post. Only one case of harbor porpoise twins has ever been documented.

Researchers hope the North Sea fishing crew’s unusual catch will result in a better understanding of conjoined twins in sea mammals. ‘Adding any extra case to the known nine specimens brings more knowledge on this aspect,” Kompanje said.

Photo credit: Ecomare

86 comments

Melania Padilla
Melania Padilla3 days ago

There is so much we don't know, how amazing nature is! Poor baby, he/she did not have any chance to live I guess :(

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Jennifer H
Jennifer H26 days ago

"A Dutch fishing crew on the North Sea was shocked by what they discovered in their trawl net late last month." Damn trawlers.

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Peggy B
Peggy B1 months ago

Noted

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Carl R
Carl R1 months ago

Thanks!!!!

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Angela K
Angela K1 months ago

noted

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Carl R
Carl R1 months ago

Thanks!!!!

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heather g
heather g1 months ago

Life must have been a challenge....

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De D
De D1 months ago

Incredible

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Carl R
Carl R1 months ago

Thank you Care2!!!!!

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Carl R
Carl R1 months ago

Thank you Care2!!!!!

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