Scientists have reconstructed the way plesiosaurs swim

(ORDO NEWS) — Plesiosaurs, unusual marine reptiles of the Mesozoic era, had a unique swimming style not found in modern animals: with the help of four flippers, they literally flew under water and perfectly maneuvered. Now scientists, using real and computer models, have managed to reconstruct the way they swim.

Plesiosaurs (Plesiosauria) existed on Earth for almost 150 million years, appearing and disappearing at about the same time as the dinosaurs. These amazing sea lizards inhabited the entire World Ocean: their fossils are now found on all continents, including Antarctica.

There were both long-necked plesiosaurs with a small head that hunted fish and squid, and short-necked pliosaurs with huge heads – other marine reptiles often became their victims.

From other marine reptiles – ichthyosaurs , mosasaurs , marine crocodiles and turtles – plesiosaurs differed primarily in the way they swim: they moved in the water with the help of all four limbs, transformed into long flippers. Ichthyosaurs and mosasaurs, for example, used their limbs only for steering and balancing, while sea turtles mostly paddled with their front flippers, just like penguins.

Scientists have been arguing about the specific way plesiosaurs swim for almost 120 years, since the very moment these animals were discovered: no other marine reptiles had four identical pterygoid flippers, and it was necessary to understand how plesiosaurs could use them.

To finally put an end to this dispute, Anna Krahl ( Anna Krahl ) from the University of Tübingen and her colleagues studied in detail the bones of the shoulder and pelvic girdle, the front and rear flippers, as well as the surfaces of the shoulder joints of the plesiosaur Cryptoclidus eurymerus , who lived 160 million years ago in European seas.

First, it turned out that plesiosaurs could not row with flippers in the way, for example, sea lions do: the joints of their flippers were not mobile enough to provide a back and forth stroke. Most likely, these animals mainly moved their flippers up and down, like a flying bird, while resembling the movements of a penguin’s flippers.

Scientists have reconstructed the way plesiosaurs swim 2
Model from bone casts of the hind flipper of a plesiosaur (a) and its drawing (b): white threads (a) and yellow lines (b) indicate the main muscles

This begs the question: how could plesiosaurs rotate their flippers to generate lift without rotating their shoulder and hip around their longitudinal axis?

They probably used rotation in the transverse axis for this, like a sea turtle: when swimming, it does not turn the entire fin as a whole, but only the ends of the fingers, while the shoulder and wrist remain almost motionless.

Reconstruction of the muscles of the plesiosaur, based on data on the structure of its bones and the structure of the muscles of modern reptiles, showed that this movement was quite accessible to him.

In addition to real models, scientists used computer models based on computed tomography of the animal’s humerus and femur.

Using the finite element method , the functional loads on the bones were calculated (in general, they confirmed the assumption that the plesiosaur rotated its flippers in the transverse direction in motion) and the efforts of individual muscles when moving up and down (it turned out that when moving with the flippers down, the plesiosaur created more effort than when moving the fins up, resembling in this respect exactly the sea turtle, and not the penguin).

Thus, these ancient reptiles did not paddle like seals or fly underwater like penguins, but rather glided like sea turtles. Perhaps their swimming method was less agile than sea lions, but more agile than turtles, making plesiosaurs one of the most successful marine reptiles in history.

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