Mythical Sea Monsters and Modern Science

Naturalists and scientists investigated ancient sea monsters for centuries – and they discovered something surprising.

The “great sea serpent” spotted by Hans Egede off the coast of Greenland in 1734. The massive creature dwarfs the ship. Unknown/Public Domain

In July 1734, the Norwegian missionary Hans Egede peered over the side of a ship off the south coast of Greenland. In the icy waters, Egede saw something that shook him to the core.

Egede was no stranger to the North Atlantic. He’d lived in Greenland for over a decade as part of the Hope Colony. With the blessing of the Danish-Norwegian king, Egede had established the colony to search for the lost Norse colonists and convert them to Lutheranism. 

Instead, Egede found only Inuits. Eager to share his religion with the Greenlanders, Egede taught them the Lord’s Prayer––with a modification. Under Egede’s watchful eye, the Inuits learned to say, “Give us this day our daily seal.” After all, Egede reasoned, the Inuits had no word for “bread.”

Yet even the experienced traveler was not ready for what he spotted off the side of his ship in 1734. 

“A sea-monster appeared to us,” Egede wrote, “whose head, when raised, was on level with our main-top.”

The sea monster had distinctive features, which Egede described. “Its snout was long and sharp, and it blew water almost like a whale.” But unlike a whale, “it has large broad paws; its body was covered with scales; its skin was rough and uneven.”

The frightened missionary concluded, “In other respects it was as a serpent, and when it dived, its tail, which was raised in the air, appeared to be a whole ship’s length from its body.”

Had Hans Egede discovered a sea monster?

If so, he was in good company. European sailors and travelers crossing the Atlantic often spotted sea creatures that crossed the line between natural and monstrous. 

Even Europe’s great navigators spotted sea monsters. In 1492, when Christopher Columbus sailed west, he found more than a new hemisphere.

In Jan. 1493, while sailing in the Caribbean, Columbus sighted three mermaids. “They are not as beautiful as they are painted,” Columbus noted in his journal, “since in some ways they have a face like a man.”

The explorer Henry Hudson also caught sight of a mermaid in 1608. Hudson and his crew agreed that the mermaid appeared exactly like a woman with long, dark hair––except she had a tail like a porpoise. 

Explorers like Columbus and Hudson had left behind the well-known waters of the Mediterranean and Europe’s Atlantic coasts. On small ships powered by sails, they voyaged into unknown, uncharted waters. But even a landlubber on his first ocean voyage knew the sea teemed with life. And not all of it was friendly.

Sailors told tales of terrifying sea monsters who could destroy ships. Sea serpents wrapped their coils around hulls and pulled men into the deeps. Leviathans sometimes slept on the surface of the ocean, so large that sailors mistook them for islands. But men who left the safety of their ships to sleep on these islands awoke with the ground rumbling beneath them as the leviathan dived, taking the sailors to their graves. 

Yet for every tall tale about a terrifying sea monster, sailors brought home stories of real sea creatures. Naturalists trying to sort through the stories found it impossible to distinguish fact from fiction. As a result, for centuries sea monsters appeared in natural history books.

In fact, 19th century scientists investigated mythical sea monsters like the Gloucester Sea Serpent, spotted off the coast of Massachusetts in 1817. And investigating sea monsters led to some surprisingly scientific discoveries, like the giant squid.

Science and sea monsters are not polar opposites. Studying sea monsters helped birth modern science. 

Tales of horrific monsters like the prister, seen on Olaus Magnus’s 16th-century Carta Marina, terrified sailors. Wikimedia Commons/Public Domain

Sea Monsters on Maps

The Age of Exploration revealed the limits of European knowledge. Explorers, confident that they could sail west to Asia, instead discovered a new world. And that discovery cast doubt on everything Europeans thought they knew.

What was true? The ancient authorities hadn’t known about the Americans––so what else were they wrong about?

In the early years after making contact with the New World, Europeans puzzled over the shape of the Earth. And they also wondered what kinds of beasts inhabited it.

“HIC SUNT DRACONES,” one 1510 map said. The words––”here be dragons”––marked the east coast of Asia on a globe. The same phrase appeared on a 1504 globe drawn on an ostrich egg. 

Did Europeans really expect to find dragons at the edges of the known world? Or did the phrase simply mark out unknown territory that might be dangerous?

Based on the other monsters that appear on 16th-century maps, the notion of dragons seems almost tame. 

Maps in the Age of Exploration decorated empty spaces with all kinds of creatures. And the ocean, which suddenly grew in size compared to medieval maps, offered a blank canvas for European fears. 

So mapmakers decorated oceans with sea creatures, some frightening and some commonplace. Whales, sea serpents, and sea swine all appeared on maps. And in many maps, sea creatures threatened ships.

Take the Carta Martina, created in the 1530s by Olaus Magnus. A naturalist and historian––who had also been appointed the Catholic archbishop of Sweden after the country converted to Lutheranism––Magnus used his map to catalog the sea.

Where did Magnus hear about whales so large that men tried to camp on their backs, mistaking them for islands? What about the terrifying sea serpent who could destroy a ship? The mapmaker’s sources came from a mix of ancient tales––the 6th-century traveler St. Brendan reportedly landed on a leviathan so large it seemed to be an island––and first-hand accounts.

Sailors who saw sprays of water on the horizon came back with tales about whales. And when mysterious sea creatures washed up on shore, baffled beachgoers linked them with mythical creatures. 

In one image, Magnus showed a sea serpent wrapped around a ship. The map’s key said, “A worm 200 feet long wrapping itself around a big ship and destroying it.”

Olaus Magnus’s Carta Marina showed an enormous sea serpent destroying a ship. Wikimedia Commons/Public Domain

The Carta Marina cataloged all the ways sailors might die in the frigid waters. And many of those deaths were caused by spine-chilling monsters.

Whales might attack ships crossing the sea. Pristers, also called “whirlpools” by sailors, cruelly attacked ships. And when sea creatures fought––as they often did on Magnus’s map––sailors might become collateral damage.

The map served as a compendium of the most terrifying fates sailors might face in the Atlantic. 

After completing his map, Magnus continued to work on sea monsters. Later in his life, Magnus wrote a History of the Northern Peoples. He devoted an entire chapter to sea monsters, replicating images from the Carta Marina and adding detailed text. And in that text, Magnus explained where he heard about the sea serpent.

The tale came from Norwegian fishermen, who “do all agree in this strange story,” Magnus began. “There is a Serpent there which is of a vast magnitude, namely 200 feet long, and more––over 20 feet thick.”

The sea serpent lived in the craggy rocks and caves off Norway. On clear nights, the serpent emerged to eat “calves, lambs, and hogs.” The beast also prayed on smaller sea creatures like octopus, lobsters, and crabs. 

What’s more, the sea serpent attacked men. “This Snake disquiets the Shippers, and he puts up his head on high light a pillar, and catcheth away men, and he devours them.”

Magnus’s description of the beast sounded almost identical to Hans Egede’s sighting in the 18th century. “He hath commonly hair hanging from his neck a cubit long, and sharp scales, and is black, and he hath flaming shining eyes.”

The Norwegian sea serpent was only one of many spotted by eyewitnesses. Magnus described another sea serpent, sighted in 1522. Certain that these creatures had a long history, Magnus riddled the chapter with references to ancient and medieval texts that mentioned marine serpents. 

Magnus did not draw the sea serpent and describe its terrifying size and habits merely to frighten people. He saw his mission as one of scientific inquiry.

Investigating the Sea

Before the Age of Exploration, European maps showed the globe as mostly land with a few strips of water. But 16th-century voyages revealed the massive size of the world’s oceans. As explorers charted new waters, naturalists turned their attention to the creatures of the sea. 

What populated the seemingly endless oceans that stretched across the globe? Even monstrous creatures might have a natural explanation.

Today, some call Conrad Gessner the father of modern zoology. His Historia Animalium of 1558 cataloged every known animal. Gessner, who borrowed heavily from Olaus Magnus’s work when describing sea creatures, included quite a few monsters in his book.

The Swiss naturalist depicted a hippocampus, which he described as a creature with the tail of a fish and a horse’s head. He drew a sea monk and a sea bishop. These squid-like creatures looked like Catholic clergy. 

Gessner also included the “sea devil,” also called the devil fish. In his text, Gessner explained that the drawing was based on “a skeleton and mummies.” The creature had ancient origins. Gessner pointed back to Greek mythology, which described “ichthyocentaurs.” These creatures had a man’s upper body with lobster claws and a fish tail. 

The “sea devil,” a monstrous creature drawn by the naturalist Conrad Gessner. Wikimedia Commons/Public Domain

Gessner did not pull the sea devil out of his imagination. He claimed it was based on actual evidence––both in the form of sea carcasses tossed on the beach and ancient Greek texts.

The connection between 16th-century sea monsters and classical texts was no coincidence. Naturalists believed––based on ancient Greek texts––that every animal that existed on land had a counterpart in the air and in the sea. 

The great Roman naturalist Pliny summed up the argument. “Whatever is produced in any other department of Nature, is to be found in the sea as well.” Pliny pointed to “the grape-fish, the sword-fish, the sawfish, and the cucumber-fish” as examples.

And the relationship went both ways. St. Augustine of Hippo argued that finding a serpent on land proved that there would be an eel in the sea––and that the leviathan in the sea proved there was a behemoth on land.

As a result of this ancient wisdom, naturalists expected to find certain things in the ocean. They interpreted reports from sailors and beach carcasses through that lens. And so they found sea horses, sea cows, sea swine, and sea devils. 

The link between land and sea helped early modern naturalists interpret new creatures through a familiar framework. The mysterious narwhal was merely a sea unicorn. A sea cucumber was the ocean version of the land cucumber. And sea serpents were cousins of snakes. 

The Gloucester Sea Serpent

Did 200-foot sea serpents truly inhabit the depths of the oceans? Or were sea serpents more myth than reality?

After Olaus Magnus drew his sea serpent on the Carta Marina, the creature soon began appearing in other maps and books. When Sebastian Münster created a map of monsters that lived on land and sea in 1544, he devoted most of the space to the sea––and pulled images of sea monsters directly from Magnus’s map. 

In 1558, Conrad Gesner’s encyclopedic volume of animals borrowed from Magnus when it came to sea creatures. The sea serpent appeared again in the 1608 History of Serpents by Edward Topsell. A best-selling book on fish also included the sea serpent.

Is it any surprise that two centuries later, Hans Egede thought he spotted a sea serpent in the same waters Olaus Magnus mapped?

And tales of sea serpents continued to pop up throughout history. In the 1810s, multiple eyewitnesses reported on a sea serpent in a Massachusetts harbor. The creature stretched 100 feet long and had a horse-like head. 

Soon, tales of the Gloucester Sea Serpent spread across the country.

The panic heated up in Oct. 1817 when a snake-like creature washed up on the beach in Gloucester. Although it was only three feet long, the creature must have been linked with the serpent living in the harbor.

Described as a hundred-foot serpent with the head of a horse, the Gloucester Sea Serpent caused waves in early 19th-century America. Wikimedia Commons/Public Domain

The reports––including from members of the military––were so persuasive that the Linnaean Society of New England investigated. 

After a thorough investigation, the Linnaean Society declared the discovery of a new species. Named Scoliophis atlanticus, or “Atlantic Humped Snake,” the creature had visited the harbor to lay eggs, which had clearly begun to hatch. 

For the next two years, beachgoers in Massachusetts reported seeing the creature. Except the Atlantic humped snake never existed––no more than the sea serpent drawn by Olaus Magnus centuries earlier.

And the Gloucester sea serpent wasn’t the only sighting in the 19th century. In 1808, a strange carcass washed ashore in the Orkney Islands at the northernmost reaches of Scotland. A natural history society in Edinburgh investigated the carcass and concluded it was a sea serpent. They named the species Halsydrus, or “sea water snake.”

The monster, which measured 55 feet long, had a natural explanation. Later naturalists realized the creature was a basking shark battered by sea rocks. 

What were the creatures mistakenly identified as sea serpents? Hundreds of sightings over centuries of time could not all be hoaxes. Instead, the sea serpent reports were likely cases of mistaken identity, as naturalists began to argue in the 19th century. 

One 19th-century list of animals mistaken for sea serpents included whales, squid, sharks, eels, and porpoises. 

And a recently discovered species may have driven many of the tales. Not spotted alive until 2001, the oarfish looks very similar to a sea serpent. The long, bony fish, which normally lives in deep waters, grows up to 26 feet long. Giant oarfish that washed ashore helped fuel tales of sea serpents. 

Even the “baby sea serpent” discovered in Gloucester in 1817 had a natural explanation. It was actually a land snake with tumors on its spine. 

The “Atlantic humped snake,” as drawn by the Linnaean Society based on eye-witness reports. Wikimedia Commons/Public Domain

When sailors left the land behind, sometimes their imagination transformed marine creatures into monsters. The “mermaids” spotted by Columbus were actually a common sea creature. Columbus grumbled that the mermaids failed to live up to artist’s renderings becau\se “they have a face like a man.” 

In fact, Columbus was the first European to see a manatee. Since he did not recognize the creature, he likened it to something more familiar: a mermaid.

And the same is likely true for Hans Egede and the sea serpent. The Norwegian saw something massive in the ocean, but rather than a sea monster, he likely sighted a giant squid or basking shark. One theory even posits that Egede saw a marine animal trapped in 18th-century fishing nets, which gave it a monstrous appearance. 

The sea monsters described in the early modern period were not fantastical inventions of Olaus Magnus, Conrad Gessner, or other naturalists. Magnus and his fellow investigators collected evidence from sailors, ancient sources, and eyewitness accounts. 

As the 19th-century naturalist Henry Lee wrote in Sea Fables Explained, “the descriptions by ancient writers of so-called ‘fabulous creatures’ are rather distorted portraits than invented falsehoods.” 

Lee confidently asserted, “there is hardly any of the monsters of old which has not its prototype in Nature at the present day.”

In fact, mythical sea monsters became the subject of modern scientific study. 

Ancient Sea Monsters and Modern Science

The British geologist Charles Lyell visited Boston in Oct. 1845. While in the U.S., Lyell came across an exhibition that would unveil “that colossal and terrible reptile, the sea serpent”––for paying customers. 

Lyell wrote off the exhibition as a hoax. But he didn’t rule out the possibility of massive marine creatures hiding in the sea. In fact, when writing about his visit to the U.S., Lyell included a report from a Canadian geologist about a 100-foot sea snake in the Gulf of St. Lawrence.

Though he’d only heard second-hand accounts of sea serpents, Lyell kept an open mind. “I believed in the sea serpent without having seen it,” he admitted. And Lyell’s belief was rooted in his scientific studies.

Investigating rocks had shown Lyell that mysterious creatures once inhabited the ocean. A fossil collector, Lyell knew that recent discoveries had turned up enormous marine reptiles that no living person had ever seen. 

The Plesiosaur, first identified by amateur paleontologist Mary Anning in the 1820s, was proof that monsters once swam in the oceans. Stretching 50 feet long, with a massive neck and four large flippers, the Plesiosaur looked like it might have appeared on Olaus Magnus’s map.

Mary Anning’s drawing of her Plesiosaur fossil, which set off a wave of debates in the scientific community. If Plesiosaurs existed, were other mythical sea monsters real? Wellcome Images/CC BY 4.0

If the Plesiosaur was real, was it so far-fetched to think sea serpents might be, too?

In the 19th century, naturalists wondered if sea serpents were actually prehistoric creatures. Lyell posited that no animal truly went extinct––they merely hid in the deep sea. In Lyell’s thinking, then, the Plesiosaur and sea serpent might coexist in the oceans.

Investigating sea monsters added to man’s knowledge of science. In 1873, the Canadian naturalist Moses Harvey made that argument while holding a squid arm in his hands. The arm, which fishermen claimed they hacked from a massive beast as it attacked their boat, unlocked new knowledge.

“I was now the possessor of one of the rarest curiosities in the whole animal kingdom,” Harvey wrote. He held “the veritable tentacle of the hitherto mythical devil-fish, about whose existence naturalists had been disputing for centuries. 

As he stared down at the severed tentacle, Harvey declared, “I knew that I held in my hand the key of a great mystery, and that a new chapter would now be added to Natural History.”

Harvey identified the creature as a devil fish. That was the name sailors gave to the monstrous creature that could grasp ships in its sucker-covered arms. Even before sightings of the devil fish became common, sailors found evidence of the creature’s existence. Whale bodies were marked with circular scars. Whale stomachs contained pieces of tentacles.

In the 1850s, scientists realized the devil fish was a real animal––it was a giant squid.

The first photograph of a giant squid, taken in Nov. 1873, revealed arms and tentacles that looked indistinguishable from mythical sea creatures. Wikimedia Commons/Public Domain

Years of investigating the devil fish compiled enough evidence for scientists to link the stories with a real creature. While some sea monsters never existed––the sea serpent was a centuries-long case of mistaken identity––others were real.

Our imagination continues to place terrifying creatures in the water. A recent study looked back at sea monster sightings from 1800 to the 21st century. The researchers discovered a shift in what people claimed to see. 

Before the discovery of Plesiosaurs and other large marine fossils, most sea monsters were described as serpents or eels––like the Gloucester Sea Serpent. After creatures like the Plesiosaur and Ichthyosaur began to appear in newspapers, fossil exhibitions, and books, people imaged sea monsters differently.

Suddenly, more sightings claimed to spot a long-necked creature with fins instead of a serpent. These sightings carry on even today in the form of the Loch Ness monster, a Plesiosaur-like creature. 

Vast bodies of water fuel the imagination. Sailors leaving behind the known world on tiny ships filled the sea with terrifying monsters. Naturalists collected stories and beach refuse, combined them with ancient myths, and concluded that some sea monsters were real.

And, in fact, they were right––not about sea serpents and pristers, but about life in the sea. Tales of sea monsters spurred natural history societies and researchers to investigate marine life more closely. In doing so, they uncovered an entire world under the sea.


For more true stories of the ocean and its history, check out Bruce Wilson’s book The Ocean Blue: A History of Maritime Trade, Naval Warfare, and Exploration.

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