A new study reveals how plesiosaurs swam underwater
Plesiosaurs, who lived around 210 million years ago, adapted to living underwater in an unusual way: their front and hind legs evolved to become four uniform, wing-like flippers over time. Dr. Anna Krahl examined how they utilized them to travel through the water in her thesis, which was supervised at Ruhr-Universität Bochum and the University of Bonn.
She was able to demonstrate that twisting the flippers was crucial for forward motion in part by using the finite element approach, which is often employed in engineering. Using bones, muscle models, and reconstructions of the muscles, she was able to recreate the movement sequence. Her findings were recently published in the journal PeerJ.
Plesiosaurs are distinguished by their often exceedingly long necks and tiny heads; the elasmosaurs even have the longest necks of any vertebrates. On the other hand, there were also enormous predatory types with short necks and enormous skulls. The neck is linked to a teardrop-shaped, hydrodynamically well-suited body with a markedly shortened in all plesiosaurs.
Researchers have puzzled for 120 years how plesiosaurs swam
The second feature that makes plesiosaurs so unusual is their four uniform wing-like flippers.
“Having the front legs transformed into wing-like flippers is relatively common in evolution, for instance in sea turtles. Never again, however, did the hind legs evolve into an almost identical-looking airfoil-like wing,” explains Anna Krahl, whose doctoral thesis was supervised by Professor P. Martin Sander (Bonn) and Professor Ulrich Witzel (Bochum).
Sea turtles and penguins, for example, have webbed feet. For more than 120 years, researchers in vertebrate paleontology have puzzled over how plesiosaurs might have swum with these four wings. Did they row like freshwater turtles or ducks? Did they fly underwater like sea turtles and penguins? Or did they combine underwater flight and rowing like modern-day sea lions or the pig-nosed turtle? It is also unclear whether the front and rear flippers were flapped in unison, in opposition, or out of phase.
Anna Krahl has been studying the body structure of plesiosaurs for several years. She examined the bones of the shoulder and pelvic girdle, the front and hind flippers, and the shoulder joint surfaces of the plesiosaur Cryptoclidus eurymerus from the Middle How Did the Monstrous Plesiosaurs Swim?