Scientists Solve a 120-Year-Old Mystery: How Did Monstrous Plesiosaurs Swim?

Artist’s impression of a plesiosaur. Plesiosaurs are characterised by 4 uniform fins.

New examine reveals how plesiosaurs swam underwater

Plesiosaurs, which lived round 210 million years in the past, tailored to life underwater in an uncommon approach: their back and front legs developed into 4 uniform wing-like fins over time. time. Dr. Anna Krahl examined how they used them for water journey in her thesis, which was supervised at Ruhr-Universität Bochum and the College of Bonn.

She was capable of show that fin twisting was essential for ahead movement partly utilizing the finite ingredient method, which is commonly utilized in engineering. Utilizing bones, muscle fashions and muscle reconstructions, she was capable of recreate the sequence of actions. His findings had been not too long ago printed within the journal PeerJ.

Plesiosaurs are members of the Sauropterygia, typically referred to as the paddle lizards, a bunch of saurians which have rehabilitated to stay in water. They developed on the finish

” data-gt-translate-attributes=”[{” attribute=””>Triassic, around 210 million years ago, coexisted with dinosaurs, and died out at the end of the

“This could work by means of twisting the flippers around their long axis,” says Anna Krahl. “Other vertebrates, such as the leatherback turtle, have also been shown to use this movement to generate propulsion through lift.”

Twisting, for example, involves bending the first finger far downward and the last finger far upward. The remaining fingers bridge these extreme positions so that the flipper tip is almost vertical without requiring any real rotation in the shoulder or wrist.

A reconstruction of the muscles of the fore- and hind flippers for Cryptoclidus using reptiles alive today showed that plesiosaurs could actively enable such flipper twisting. In addition to classical models, the researchers also made computer tomographies of the humerus and femur of Cryptoclidus and used them to create virtual 3D models.

“These digital models were the basis for calculating the forces using a method we borrowed from engineering: the finite element method, or FE,” explains Anna Krahl.

All the muscles and their angles of attachment on the humerus and femur were virtually reproduced in an FE computer program that can simulate physiological functional loads, for example on construction components but also on prostheses. Based on muscle force assumptions from a similar study on sea turtles, the team was able to calculate and visualize the loading on each bone.

Twisting of the flippers can be proven indirectly

During a movement cycle, the limb bones are loaded by compression, tension, bending, and torsion. “The FE analyses showed that the humerus and femur in the flippers are functionally loaded mainly by compression and to a much lesser extent by tensile stress,” Anna Krahl explains.

“This means that the plesiosaur built its bones by using as little material as necessary.” This natural state can only be maintained if the muscles that twist the flippers and the muscles that wrap around the bone are included. “We can therefore indirectly prove that plesiosaurs twisted their flippers in order to swim efficiently,” Anna Krahl sums up.

The team was also able to calculate forces for the individual muscles that generated the upstroke and downstroke. For instance, it transpired that the downstroke of both pairs of flippers was more powerful than the upstroke. This is comparable to our sea turtles today and different from today’s penguins, which move forward the same distance with the upstroke as with the downstroke.

“Plesiosaurs adapted to life in water in a very different way than whales, for example,” notes Anna Krahl, who now works at the Eberhard Karls University in Tübingen, Germany. “This unique path of evolution exemplifies the importance of paleontological research because it’s the only way we can appreciate the full range of what evolution can bring about.”

Reference: “Determination of muscle strength and function in plesiosaur limbs: finite element structural analyses of Cryptoclidus eurymerus humerus and femur” by Anna Krahl​, Andreas Lipphaus, P. Martin Sander and Ulrich Witzel, 3 June 2022, PeerJ.
DOI: 10.7717/peerj.13342