The first known case of a two-headed harbour porpoise was documented last month when Dutch fishermen in the North Sea accidentally caught the anomalous creature as bycatch in a beamtrawl net.

Fearing it would be illegal to keep the deceased marine mammal, they threw it back into the ocean, but not before taking photos of their bizarre find and alerting researchers.

While case studies of conjoined twins have been studied in humans, reptiles, and domestic animals, they are rarely seen in wild mammals. In fact, before this find, only nine other instances of two-headed cetaceans of any kind had ever been reliably documented.

A study recently published by the online Journal of the Natural History Museum Rotterdam contextualized the rarity of the find.

"Descriptions of conjoined twins in whales and dolphins are extremely rare," Erwin Kompanje, from the National History Museum Rotterdam, noted in his study. "We were aware of only nine [other] published cases."

(Read about the first two-headed shark embryo found in the western Midetteranean last year.)

Though researchers lamented not being able to physically examine the porpoise, they could glean details from the fisher's photos.

Scientists know definitively the porpoise was both a newborn and a male.

The dorsal fins were not yet erect, the rostrums (or top of its heads) still contained hairs, and it still contained an umbilical opening, indicating the porpoise died shortly after birth. The tale had also not stiffened, a necessary development that porpoises need in order to swim.

On average, porpoises produce one offspring every one to two years, and even cases of twins are extremely rare. Nearly 700,000 porpoises can be found around the world, with 345,000 residing in the North Sea, though never before with two heads (as far as the scientists could determine).

The International Union for the Conservation of Nature states that incidental catch is the biggest threat facing porpoises. As a result, the European Union has adopted measures to monitor the effect nets and trawls have on populations.

Symmetrical conjoined twins, such as this porpoise, are thought to result when two separate embryos fuse together or a zygote only partially splits.</s>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.</s>A pair of conjoined harbour porpoise twins were caught by fishermen off the coast of the Netherlands, reports New Scientist, in the 10th known case of conjoined twins in cetaceans.

This case of a single body and two fully grown heads, also known as partial twinning or parapagus dicephalus, is extremely rare -- only 9 other cases of conjoined twins in cetaceans, the group of animals which includes whales and dolphins, are known. Twins are extremely rare in cetaceans as there is usually not enough room in the body of female for more than one fetus.

Two-headed animals, called bicelphalic or dicephalic, and three-headed animals, or tricephalic, are the forms of polycelphaly, or the condition of having more than one head that exist in the real world, as opposed to mythical creatures like the Hydra. A polycephalic organism may be thought of as two or more beings with a shared body, and are formed by the same process as conjoined twins from monozygotic twin embryos.

Scientists believe the twins probably died shortly after birth because their tail had not stiffened, which is necessary for newborn dolphins to be able to swim. The fishermen who made the discovery unfortunately returned the twins to the ocean because they believed it would be illegal to keep such a specimen.

Although researchers will not be able to study the body of the twins, they can learn from photographs taken by the fishermen. "The anatomy of cetaceans is strikingly different from terrestrial mammals with adaptations for living in the sea as a mammal. Much is unknown," says Erwin Kompanje, a researcher at the Erasmus MC University Medical Center in Rotterdam and one of the authors of the paper describing the find.

He also remarked that although there are only 10 known cases, most instances of conjoined twins in cetaceans are never found because they born and die at sea.</s>In the cold waters of the North Sea, trawlers catch all manner of unintended things.Garbage, often. Porpoises, sometimes, for the shores of the Netherlands are teeming with hundreds of thousands of them.

But on May 30, several nautical miles off the Hook of Holland, a boat hauled up something perhaps never before seen by man. Two feet long . . . and with two heads.

A photo of the thing began to circulate through the Netherlands – eventually to the inbox of Erwin Kompanje, the curator of mammals at the Natural History Museum in Rotterdam, who was astounded.

He recalled his first thought: “Where??”

Where was it, and how soon could he get it into a lab?

Even today, in an age of science, it might appear to many people to be a two-headed sea monster.

Kompanje knew better, though the truth was no less astounding. He was looking at photos of two conjoined harbor porpoises, newborns sharing a single body, a rarity among rarities in all the oceans in the world.

“There are only nine cases known until now” of conjoined twins among cetaceans, said Kompanje, who has studied dolphins, whales and porpoises for 20 years. “Even normal twinning is rare; there’s no room in the womb of the mother for harboring more than one baby.”

And the few specimens that had been found were usually undeveloped fetuses, like the “double monster” – one head and two bodies – found in the womb of a dolphin caught by herders off the coast of Japan in 1970. In 2001, a bottlenose dolphin calf with two beaks was caught in the Mediterranean sea, but it was partially decomposed. And these are among the better-documented cases.

The photos Kompanje found himself staring at in shock showed a specimen that – while obviously dead – looked to be in perfect condition.

The brothers (for he could tell they were male) must have just been born, he reasoned, for the dorsal fin had not yet risen. And tiny hairs lost soon after birth could be seen on the two faces above the fin.

“I think it was born alive,” Kompanje said.

The brothers couldn’t have survived long. They would have either drowned as two brains told one body to swim different ways, or simply succumbed to their single heart’s failure to pump enough blood.

But whatever happened in their short life, they had by pure luck found their way into a fishing net before nature destroyed their body’s value to science.

For a researcher hungry for any morsel of information about man’s aquatic mammalian cousins, it was a one-in-a-billion discovery.

So Kompanje got the boss of the fishing crew on the phone, who was helpful – providing the exact coordinates and details of the catch.

The possibilities expanded in the researcher’s mind. Kompanje had been planning an MRI for the porpoises. A CT scan, 3-D imaging. And then, when the research was completed, the brothers might be preserved forever in a museum.

And just then, on the phone with the trawler boss, he learned the true end of this strange tale.

“They thought it was illegal to collect it,” Kompanje said. “They made four photographs and threw it back into the sea. Back into oblivion.”

In that expanse of square miles of deep water, there was no hope of finding it again.

Kompanje did what he could with what evidence that chance had preserved. The fishermen’s photos from the boat were good enough to co-author a paper with other marine researchers, which was published this month, and said what there was to say about the porpoises.

But Kompanje has no illusions. He does not expect to see anything like it again in his lifetime.</s>A group of fishermen accidentally discovered the world's first two-headed porpoise, but tossed it back into the sea for fear of getting into trouble.

The bizarre animal was picked up by a Dutch trawler near Hoek van Holland, and is the first known case of conjoined twin porpoises.

Fearing it would be illegal to keep the specimen, the fishermen took a few quick photographs of the dead creature and threw it back into the ocean.

Experts at the University of Rotterdam are now poring over those photographs in the hopes of learning more about parapagus dicephalus - partial twinning - in marine life.</s>A two-headed harbour porpoise, believed to be the first one ever seen, was caught by fishermen in the North Sea.

Believing it would be illegal to keep the mammal, the Dutch fishermen threw it back into the sea, but luckily, they took photographs that specialists could examine so they could shed light on the mysterious creature.

“The specimen, however, is lost for science and natural history,” Erwin Kompanje, of the Erasmus MC University Medical Centre in Rotterdam, wrote in his paper.

The bizarre-looking mammal (Phocoena phocoena) was caught dead and scientists say they are certain the conjoined Siamese twins were newborn males.

Experts noted there were hairs on the upper lip, which should have fallen out after it was born, the dorsal fins were erect and it still contained an umbilical cord opening – indicating the creature died very young.

The harbour porpoise is one of the most common cetaceans (marine life which includes whales and dolphins) found in north-west European waters.

While cases of conjoined twins have been studied in humans, reptiles and domestic animals, they are rarely seen in wild animals.

“Descriptions of conjoined twins in whales and dolphins (Cetacea) are extremely rare,” Kompanje said.

“We were aware of only nine published cases and symmetrical conjoined twins, such as this porpoise, are thought to result when two separate embryos fuse together or a zygote only partially splits.”

The harbour porpoise is the smallest and most abundant cetacean in the European waters. Nearly 700,000 porpoises roam the waters around the world, with 345,000 residing in the North Sea.

According to the International Union for the Conservation of Nature, incidental catch is the biggest threat facing porpoises and measures have been taken to monitor nets and trawls to see whether they are causing the numbers to dwindle.

The species produces offspring every one to two years.</s>In the cold waters of the North Sea, trawlers caught 2-feet long animal and with two heads</s>The bizarre animal was picked up by a Dutch trawler near Hoek van Holland, and is the first known case of conjoined twin porpoises.

A group of fishermen accidentally discovered the world’s first two-headed porpoise, but tossed it back into the sea for fear of getting into trouble.

The bizarre animal was picked up by a Dutch trawler near Hoek van Holland, and is the first known case of conjoined twin porpoises.

Fearing it would be illegal to keep the specimen, the fishermen took a few quick photographs of the dead creature and threw it back into the ocean.

Experts at the University of Rotterdam are now poring over those photographs in the hopes of learning more about parapagus dicephalus – partial twinning – in marine life.

They have already confirmed that the porpoises died shortly after birth because the tail had not stiffened, which allows newborn porpoises to swim.

Both heads also had small hairs on the upper lip, which should fall out shortly after the animals are born.

The harbour porpoise is one of the most common cetaceans – a group of marine life which includes whales and dolphins – found in north west European waters.

“The anatomy of cetaceans is strikingly different from terrestrial mammals with adaptations for living in the sea as a mammal. Much is unknown,” Erwin Kompanje, of the Erasmus MC University Medical Center in Rotterdam, told the New Scientist.

“Adding any extra case to the known nine specimens brings more knowledge on this aspect.”

He said it was regrettable that the fisherman decided to throw the creature back into the ocean, as it is unlikely it will ever be seen again.

The two-headed porpoise is the 10th example of a conjoined twin to be found within the cetaceans group.

“There is simply not enough room in the body of the female to give room to more than one fetus.”</s>Two-headed conjoined porpoises were recently hauled up by a fishing boat in the North Sea, not far off the coast of the Netherlands.

The bizarre-looking creatures were already dead, and the fishermen, who feared trouble from the authorities, took photos and then tossed the duo back overboard.

It's not clear exactly why the porpoises died, but the double-headed creatures likely could not swim, said Erwin Kompanje, a researcher at the Natural History Museum and the Erasmus MC University Medical Center in Rotterdam, the Netherlands, who recently wrote up the case in the June 7 issue of the journal Deinsea. Another cause may have been their fused hearts, which may not have worked adequately, Kompanje said. [Porpoise Photos: The World's Most Endangered Mammal]

Conjoined twins are a rarity for humans, but they're also extremely rare for harbor porpoises (Phocoena phocoena), Kompanje said. That's because newborn dolphins and porpoises, which are mammals, need to immediately start swimming on their own or they drown, Kompanje said.

"Normal twins are extremely rare in cetaceans, as there is not enough room in the mother's body to have more than one fetus," Kompanje told Live Science. One case report pegged the incidence of twinning in cetaceans at less than one in 200.

Only one past case of a harbor porpoise bearing twins has ever been reported. Given the rarity of twinning, it stands to reason that conjoined twins are even more of an oddity, Kompanje added. In the past, only nine other cases of conjoined twins have been reported in whales or dolphins, and most of these were described in fetuses pulled from dead pregnant females, according to the study.

Conjoined twins likely form in cetaceans in the same way they do in humans; either two separate embryos fuse after having separated, or a single embryo fails to completely split.

Harbor porpoises are the most abundant cetaceans in the waters off northwest Europe, with at least 345,000 of these creatures frolicking in these northern waters. Each female typically produces one offspring every year or two.

In the current case, the fused porpoises were first pulled up in the netting of a fishing boat on May 30, 2017, near Hoek van Holland, the Netherlands.

The creatures were clearly newborn; they had a floppy dorsal fin, an open umbilical opening and hairs in the rostrum, or beak-like snout — all telltale signs that the creatures were not long outside the womb. The body was about 27 inches (70 centimeters) long and weighed about 13 lbs. (6 kilograms).

However, the specimen had two completely formed heads and one fully formed body with two pectoral fins. This makes it likely that the porpoises were symmetrical conjoined twins (or "Siamese twins"), meaning fusion occurred between two well-developed embryos. The twins had fused side-by-side at the pelvis and abdomen. The lone genital opening revealed that the porpoises were male.

Because the fisherman tossed the porpoises overboard (they thought keeping the body would be illegal), other insights that could have been gleaned from the rare case are lost to science, the researchers said in the study.

If researchers had been able to study the porpoise more thoroughly, they likely would have captured 3D computed tomography (CT) scans, put the porpoises in a magnetic resonance imaging (MRI) machine, conducted CT angiography to study the blood vessels leading to and away from the heart, and 3D-printed a skeleton of the creature, Kompanje said.</s>Two heads are usually better than one. Unless you’re porpoise.

Fishermen last month discovered a double-headed harbor porpoise off the shores of the Netherlands.

Reeled in from the North Sea, the two-foot, 13-pound creature was DOA. The crew, however, feared repercussions for keeping a dead porpoise and threw it back into the water.

“Fortunately, first a series of photographs was taken,” according to a research paper by led by Erwin Kompanje, curator of mammals at the Natural History Museum in Rotterdam. “The specimen, however, is lost for science and natural history.”

At first glance, the cetacean could be mistaken for a mythical two-headed sea monster. But when Kompanje saw the circulating images, he knew this was even stranger than fiction: two newborn porpoises sharing a single body.

“There are only nine cases known until now” of conjoined twins among wild mammals, Kompanje told The Washington Post. “Even normal twinning is rare; there’s no room in the womb of the mother for harboring more than one baby.”

The brothers—an educated guess based on a single genital opening—were most likely born alive, but couldn’t have survived long.

As reported by the Post, the creature probably drowned, as two brains directed one body to swim different ways; or its heart simply gave out trying to pump enough blood to the extra extremities.

The truth will never be known: Without a body, Kompanje cannot conduct any analysis; his hopes of running an MRI or CT scan, administering 3D imaging were dashed when the fishermen tossed the porpoise “back into oblivion,” he told the Post.

After two decades of study, this is the big breakthrough any scientist dreams of. But even with no physical evidence, Kompanje made the best of the situation, co-authoring a paper with another marine researcher.

Still, he understands his one chance was lost when that two-headed mammal hit the water.

“For a cetologist, this is a real horror,” he said.

A small-yet-abundant aquatic mammal, the harbor porpoise (Phocoena phocoena) boasts a global population of at least 700,000; there are some 345,000 in the North Sea alone.
The deceased body of a rare two-headed porpoise is located for the first time in the North Sea by Dutch fishermen.