200 Million-Year-Old Plesiosaur Reveals Ancient Sea Monster Was Freakishly Strong and Swam With Underwater Wings

Plesiosaurus battling Temnodontosaurus (Oligostinus), front piece from the "Book of the Great Sea-Dragons" by Thomas Hawkins. This drawing shows early, speculative depictions of the plesiosaur family. Public Domain

The remains of an ancient marine reptile that once torpedoed through the ocean with powerful flippers were found in a mud pit in Germany and represent the oldest plesiosaur ever discovered.

Plesiosaurs were mysterious, aquatic animals that swam the prehistoric oceans during the reign of the dinosaurs. With paddle-like limbs and, in most cases, long, snake-like necks, these sharp-toothed beasts resembled the mythical Loch Ness Monster. But unlike Nessie, plesiosaurs were diverse, ancient and real.

Scientists recently described the new specimen, which had flippers that helped propel it through the water like a bird in the sky, in the journal Science Advances. The animal, called Rhaetocosaurus mertensi, outdates all other plesiosaur finds at 201 million years old.

As recently as August of this year, scientists discovered what had been the oldest-known plesiosaur. That specimen was dated to 132 million years ago. However, the new find, Rhaetocosaurus, is significantly older and pushes back the timeline of evolution for plesiosaurs from the Jurassic to the Triassic.

The fossilized remains of Rhaeticosaurus were found in a pit in Germany. Yasuhisa Nakajima

This unique specimen is a "holotype," meaning it is the only one that scientists have to describe the whole species. Luckily, it is a relatively complete specimen, with a spine, tail, ribs, parts of the flippers and parts of the skull. By analyzing the shape and cross sections of the fossilized bones, paleontologists were able to uncover several interesting facts about the animal's body.

For one, they found that the animal grew really big, really fast. They also found that its long neck was actually quite rigid and inflexible. The body, meanwhile, was small and stout when compared to other plesiosaurs, at around 7 feet 7 inches long. However, this individual was a sub-adult, and could have grown longer if it had survived.

Rhaetocosaurus featured strong muscles around its flippers, so that all four of them could propel it forward for speedy underwater pursuits of ancient fish. It used its short tail as a rudder, and may have used its long neck to direct its swims.

"This evolutionary design was very successful, but curiously it did not evolve again after the extinction of the plesiosaurs," paleontologist Martin Sander, one of the authors of the paper, said in a press release. After rhaetocosaurus, diverse plesiosaurs of all sizes evolved all over the world. Their presence in cold oceans indicates that they were warm-blooded creatures.

While plesiosaurs weren't dinosaurs, they lived and evolved at the same time as them. And, despite their success, living in waters all over the world, they all died out after the meteor impact at the end of the Cretaceous.