72-million-year-old ‘blue dragon’ unearthed in Japan
Scientists in Japan have unearthed the near-complete remains of an ancient great white shark-sized sea monster that likely terrorised the ancient oceans it used to inhabit. The prehistoric predator, which the researchers have named ‘blue dragon’, has an unusual body plan that sets it apart from its extinct relatives and is unlike any living creature. The exceptional fossils, which are around 72 million years old, were discovered along the Aridagawa River in Wakayama Prefecture on Honshu island. They belong to a never-before-seen species of mosasaur, a group of air-breathing aquatic reptiles that were apex marine predators during the Cretaceous period, 145 to 66 million years ago. The “astounding” remains are the most complete mosasaur fossils ever uncovered in Japan and the northwest Pacific.
In a recent study, researchers named the new mosasaur Megapterygius wakayamaensis.
The new genus Megapterygius translates to ‘large-winged’ after the creature’s unusually large rear flippers, and the species name wakayamaensis recognises the prefecture where it was found. The team nicknamed the creature the Wakayama soryu – a soryu is a blue-coloured aquatic dragon from Japanese mythology. Mosasaurs share a similar body plan and there is very little variation among species. But M. wakayamaensis is something of an outlier, which has surprised scientists. “I thought I knew them [mosasaurs] quite well by now,” said Takuya Konishi, a vertebrate palaeontologist at the University of Cincinnati. “Immediately, [I knew] it was something I had never seen before.”
Like other mosasaurs, M. wakayamaensis had a dolphin-like torso with four paddle-like flippers, an alligator-shaped snout and a long tail. But it also had a dorsal fin like a shark or dolphin, which is not seen in any other mosasaur species. However, what confused researchers the most was the size of the new mosasaur’s rear flippers, which were even longer than their front flippers. Not only is this a first among mosasaurs, but it is also extremely uncommon among all living and extinct aquatic species.
Almost all swimming animals have their largest flippers towards the front of their bodies, which helps them steer through the water. Having larger flippers at the rear of the body would be like driving a car by steering the rear wheels instead of the front ones, which would make it much harder to turn quickly. “We lack any modern analogue that has this kind of body morphology, from fish to penguins to sea turtles,” Konishi said. “None has four large flippers they use in conjunction with a tail fin.” The researchers suspect that instead of using the rear flippers to turn, M. wakayamaensis angled them upward or downward to quickly dive down or ascend through the water column, which may have helped make them adept hunters. The dorsal fin could have made it easier for the creature to turn, which may have counteracted the extra drag from the rear flippers. “It opens a whole can of worms that challenges our understanding of how mosasaurs swim.”