Legend has it that in the early 13th century a mermaid washed ashore in Hakata Bay on the Japanese island of Kyushu. Blessed by a shaman and declared a good omen, the piscine harbinger of prosperity was buried at the underwater palace of the dragon god. Some 800 years later, those unearthed "mermaid" bones are on display at Ryuguji Temple in Fukuoka.

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Now, you might be wondering why we're dabbling in ancient folklore about legendary aquatic creatures. After all, science writers have had their work cut out debunking mermaid malarkey for years, thanks to a certain (fake!) documentary duo*. But there's actually an interesting story behind the partial skeleton at Ryuguji  – and it's one that a bit of palaeontological knowhow can help us unpack. 

As is the case with many tales of mermaids, this one initially leads us to a chubby, flesh-toned marine mammal. Like their close kin the manatees, dugongs belong to the order Sirenia, whose members have long inspired mermaid myths across the globe. The gentle giants are the perfect mermaid doppelgängers – and, indeed, many anecdotes suggest early sailors mistook them for the mythological creatures.

The bones at Ryuguji are often attributed to a dugong – but this particular sea-cow "origin story" didn't hold up when we checked in with the experts. "These bones are definitely not dugong," says Dr Daryl Domning of Howard University, who specialises in Sirenian palaeontology. 

At the right angle, it's not hard to see why dugongs inspired mermaid myths. Image: Jurriaan Persyn/Flickr

To the untrained eye, one pile of bones can look just like another, but for an expert, skeletal remains hold clues about the creatures they once belonged to. Dugong skeletons, for example, are solid: the bones are heavy, thick (pachyostotic) and dense (sclerotic), and contain little to no marrow. 

But if we're not dealing with a dugong, then what? It's also been suggested that the Ryuguji mermaid could have been a finless porpoise (genus Neophocaena). The Indo-Pacific finless porpoise (Neophocaena phocaenoides) does turn up in these waters, and all seven cetaceans in this group lack a dorsal fin – an anatomical quirk that many have stood out to the inhabitants of 13th-century Japan. Contrary to some reports, however, the porpoise proposition doesn't fit the bill either. In fact, Domning explains that these bones don't belong to any marine mammal. 

"They pertain to some artiodactyl," he notes. That group of land mammals includes hoofed creatures like deer, cows and pigs. But which one? Without diving into comparative anatomy, narrowing that ID down any further is tricky. But several researchers suspect a bovine culprit.

Unlike the princess of Disney fame, traditional Japanese mermaids ("Ningyo") were often portrayed with fierce teeth and horns. Image: Toriyama Sekien/Wikimedia Commons

Shinjiro Sadamatsu of Japan's The Asahi Shimbun daily newspaper reports that the description provided in the temple's main hall leaves some room for interpretation about the bones as well. It states that the remains are believed to be "from a mermaid excavated near the premises", but also notes that "all of [the bones] are considered to be from some mammals".

Could it be that the remains belong to more than one animal? That's definitely a possibility. But whatever they might be, there's no doubt they played an important cultural role for local inhabitants – and nothing suggests the intention was ever to deliberately mislead. If there's one thing we know about encounters with animals in any state of decay, it's that they can quickly lead to a case of mistaken identity – whether it's today or 800 years ago. (Just last year, a bit of maceration meant that dead whales were misidentified as "polar bears" in Scotland, for example.)

Interestingly, some elements of this fish tale do hold up. When translated to English, the name of the bones' original burial site means "dragon palace", which sounds just about as fantastical as it gets. But if we return to the Japanese, the picture begins to clear up. In Japanese folklore, "Ryūgū-jō" is the underwater palace of Ryūjin, the dragon god of the sea. But Ryūgū was also the alternative name once used for "Ukimido temple", which has since become Ryuguji. 

Long-ago visitors to Ryūgū-Ukimido were given water in which the "mermaid bones" had been soaked, allegedly to protect them from disease. It was thought that sipping or rubbing on the sirenian solution would cure a number of ailments, and while that practice has stopped, legend of the bones' supposed mystical powers persisted through the centuries. To this day, a stone monument stands near the beach where the mystery creature was laid to rest ... though we now know it was probably more "moo cow" than sea cow.

* "Mermaids: The Body Found" and "Mermaids: The New Evidence" were fake documentaries – for some essential debunkery, head on over to Southern Fried Science.


Top header image: Klaus Stiefel/Flickr