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Researchers offer answers about plesiosaurs

August 31 , 2016


It’s a question that has been discussed for nearly 200 years: How did long-dead plesiosaurs — such as those serving as centerpieces at Sternberg Museum of Natural History — swim in the ocean that covered Kansas millions of years ago?

Researchers from Georgia and England said they have an answer. It mirrors what researchers in Denver already had found a dozen years ago and again in 2010.

Calling the plesiosaur “an anatomical oddity,” the online science journal PLOS announced the dilemma solved. “With a long neck, bulbous body and two pairs of flippers, this marine reptile’s means of locomotion have been a subject of debate since the 1824 discovery of a complete skeleton in England. Did its flippers move like oars or with flight strokes? The bones couldn’t tell the story, and scientists had no modern-day counterpart to observe.”

The study actually was published in December, but was part of an update issued Tuesday by PLOS, the open-access Public Library of Science.

But Sternberg adjunct curator Mike Everhart said the study actually doesn’t offer anything new.

The researchers in the PLOS article, aided by a National Science Foundation grant, used a 3-D, life-sized free-swimming digital model of a plesiosaur to perform thousands of motion simulations under different parameters.

“The team concluded that plesiosaurs swam like penguins or turtles, moving the forelimbs in an underwater flight stroke to achieve forward thrust,” the PLOS announcement states. “The smaller, weaker hind flippers primarily contributed to steering and stability.”

The comparison to turtles actually was made as long ago as 1824 and again in 1874.

That’s also what researchers learned a dozen years ago, Everhart said, using human swimmers wearing paddles duplicating the movement of plesiosaurs, findings that were used in the creation of the 2007 Sea Monsters IMAX movie by National Geographic. Everhart was a consultant to the movie based on his 2005 book, “Oceans of Kansas,” which is also the name of his expansive website. An expanded second edition of his book is in the works and should be published next year.

Everhart notes the paddles on the two Sternberg specimens — the nearly complete Dolichorhynchops osborni collected by Marion Bonner and the Megacephalosaurus eulerti in the lobby — were attached low on the body.

“So, one critical issue is how far the limbs could be raised above horizontal,” he said in an email. “Many exaggerated reconstructions show impossible limb orientations, paddles that would dislocate from the shoulder or hip if raised high.

“Bottom line is that I think the new study is worthwhile because it visually shows the ranges of possible motion. But it doesn’t really have anything new.”

That’s why in 2002, Everhart wrote:

“Because of their unusual body-plan, elasmosaurs were most likely slow moving animals, using their paddles as wings or foils to generate the lift necessary to ‘fly’ through the water. This type of swimming is more efficient than the rowing or paddling (i.e., a duck, Grebe or other diving bird) methods that are sometimes depicted. While modern underwater ‘fliers’ such as penguins use only their front limbs, most researchers now believe that plesiosaurs used a coordinated movement of both pairs of limbs. Others think that the hind limbs did not have either the range of movement or the musculature necessary to effectively generate the lifting forces necessary for this method of swimming. Since the hind limbs are located well behind the center of gravity, they may have been more effectively used for steering. In that case, the rear limbs may have been rudders, paddles and/or stabilizers, especially to control the position of the body and head while remaining relatively motionless in the water during feeding.”



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