Scientists in Japan have discovered a never-before-seen species of mosasaur. University of Cincinnati Associate Professor Takuya Konishi and his international co-authors described the creature in the Journal of Systematic Palaeontology. The extinct predator has been dubbed Megapterygius wakayamaensis, though researchers have nicknamed it Wakayama Soryu, which means “blue dragon.”
Mosasaurs were apex predators in prehistoric oceans from about 100 million years ago to 66 million years ago. They had a dolphin-like torso with four paddle-like flippers, an alligator-shaped snout and a long tail. This particular specimen was discovered by study co-author Akihiro Misaki along the Aridagawa River in Wakayama Prefecture on Honshu island in 2006. A team of researchers then spent five years removing the surrounding matrix of sandstone from the fossils, after which they took a cast of the mosasaur in place to record of the orientation of the bones before they were excavated. When all was said and done, it turned out to be the most complete skeleton of a mosasaur ever found in Japan or the northwestern Pacific. However, the most remarkable feature of the sea monster was its unusual body plan. “I thought I knew them quite well by now,” Konishi said in a press release. “Immediately it was something I had never seen before.”
There were a few ways that M. wakayamaensis differed from other similar species. The first was that it had had a dorsal fin like a shark or dolphin. Even more confusing for the researchers was the size of M. Wakayamaensis’ rear flippers. They were not only longer than the front flippers, but even larger than its crocodile-like head. This was the first time this feature had been seen among mosasaurs and also an extremely uncommon trait among any aquatic species, living or extinct.
“We lack any modern analog 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.” This unique structure led researchers to speculate that the front fins might have been used for rapid maneuvering, while the rear fins could have provided pitch to dive or surface.
However, the mystery of how M. wakayamaensis navigated the ocean is far from solved.“It’s a question just how all five of these hydrodynamic surfaces were used. Which were for steering? Which for propulsion?” said Konishi. “It opens a whole can of worms that challenges our understanding of how mosasaurs swim.”
