72-Million-Year-Old Fossil of Ancient “Sea Dragon” Discovered in Japan

The “Wakayama soryu” was a mosasaur the size of a great white shark, with a dorsal fin and long flippers. (Photo: TAKUMI)

It's hard to imagine what life was like when dinosaurs roamed the planet. However, by studying fossils, we are able to gain a better understanding of the kind of ancient creatures that used to exist. Although numerous species have been uncovered, there are still new discoveries being made all the time, such as a recent finding in Japan. Researchers uncovered 72-million-year-old fossils of a previously unknown species of mosasaur, which was a type of “sea dragon” native to the Pacific Ocean.

The fossils were unearthed near the Aridagawa River in Wakayama Prefecture in 2006. “In this case, it was nearly the entire specimen, which was astounding,” said University of Cincinnati Associate Professor Takuya Konishi. The skeletal remains make it the most complete mosasaur ever found in Japan or the northwestern Pacific. However, it is also unlike other mosasaur fossils found. The Japanese species has longer rear flippers than front ones, which measure longer than its head. “I thought I knew them quite well by now,” Konishi continued. “Immediately it was something I had never seen before.”

Mosasaurs lived during the era of the T-Rex and other well-known dinosaurs. However, while its contemporaries dominated land, the mosasaur hunted underwater. The new species, which measures about the same size as a modern great white shark, was placed in the subfamily Mosasaurinae and named Megapterygius wakayamaensis. Scientists believe the size of its rear flippers helped it propel through the water; however, this method of swimming is unusual for sea creatures, both ancient and modern. “We lack any modern analog that has this kind of body morphology—from fish to penguins to sea turtles,” Konishi explained. “None has four large flippers they use in conjunction with a tail fin. It opens a whole can of worms that challenges our understanding of how mosasaurs swim.”

Hopefully, in time, more fossils will be found that shed light on the diversity of this ancient underwater predator.