Researchers have detailed a mosasaur from Japan that was about the size of a great white shark and dominated Pacific waters 72 million years ago. The lengthening of its rear flippers likely enhanced propulsion, working in conjunction with the lengthened fin tail. Unlike other mosasaurs or extinct large marine reptiles, the
University of Cincinnati associate professor Takuya Konishi and international co-authors describe the mosasaur in the Journal of Systematic Palaeontology and place it in a taxonomic context.
This mosasaur was named after Wakayama Prefecture, where it was found. Researchers call it "Wakayama Soryu," which means blue dragon. Konishi said that a dragon is a creature in Japanese folklore.
"In China, dragons make thunder and live in the sky. In Japanese mythology, they become aquatic creatures," he said.
The specimen was discovered in 2006 in Wakayama's Arida River by co-author Akihiro Misaki. Konishi said the specimen is the most complete mosasaur skeleton ever found in Japan or the Pacific Northwest.
"In this case, it was almost a whole specimen, which was shocking. I thought I already knew them well. This was something I had never seen before," said Konishi, who has been studying these ancient marine reptiles. But he said the Japanese specimen had unique characteristics that defied easy classification. Its hind fins are longer than its front fins. These massive fins were even longer than its crocodile-like head, making them unique among mosasaurs.
The apex predator of the prehistoric ocean
Mosasaurs were the apex predators of the prehistoric oceans and lived from about 100 million to 66 million years ago. They were contemporaries with Tyrannosaurus rex and other late Cretaceous dinosaurs that dominated the Earth. When an asteroid struck what is now the Gulf of Mexico, nearly all the dinosaurs became extinct.
The researchers classified the specimen into the mosasaurine subfamily and named it Megapterygiuswakayamaensis in honor of the place where it was found. Megapterygius means "big wing", which is consistent with the mosasaur's huge flippers.
Xiaoxi said that those large paddle-like flippers may be used for exercise. But this way of swimming is very rare not only among mossazoles, but among almost all other animals.
"From fish to penguins to turtles, we lack any modern analogues with this body shape. None of them have four large webbed feet that are used in conjunction with the tail fin," he said.
The researchers speculate that large front fins may have aided in rapid maneuvering, while large rear fins may have provided pitch angle for diving or surfacing. Presumably, like other mosasaurs, its tail also produced powerful and rapid acceleration when preying on fish.
"This opens up a whole new perspective and challenges our understanding of how mosasaurs swam," Konishi said.
Compiled source: ScitechDaily