Plesiosaurs, stones in their stomachs, and computers

This video is called Juvenile Plesiosaur Animation.

From the Columbus Dispatch in the USA:

GEOLOGY

Computer modeling rejects old theories about plesiosaurs

Tuesday, November 28, 2006

DALE GNIDOVEC

Digging for dinosaurs and other prehistoric animals is wonderful, but some of the most interesting information about them comes not from the ground but from computers.

A good example is a recent paper in the journal Lethaia that reported on some modeling experiments performed on plesiosaurs.

Plesiosaurs were one of the groups of Mesozoic sea reptiles.

While dinosaurs dominated life on land, plesiosaurs were the top predators in the oceans.

Some plesiosaurs had short necks and large skulls and were the “killer whales” of their day.

Others, called elasmosaurs, had small skulls on long necks and were like nothing that lives today.

Many elasmosaur skeletons have been found with masses of gastroliths, or stomach stones, inside. One contained nearly 30 pounds of them.

The rocks are different from those holding the skeletal remains — in some cases the nearest source was 200 miles away — so the animals went to a lot of trouble to obtain the stones.

Modern animals that use gastroliths are herbivores, as were dinosaurs found with the stones.

But plesiosaurs were definitely carnivorous, as shown by their sharp teeth, so what were they doing with gastroliths?

One possibility is that the stones were used for ballast, to help counteract the buoyancy of the lungs.

That would have been useful in an animal that had to swim underwater to catch its food.

The new study discounts that idea. Computer models were made for three species of plesiosaur, using the best estimates for weights, densities and lung volumes.

The models were then submerged electronically and allowed to rise to the surface to a stable position.

The technique was applied to two modern reptiles, the alligator and leatherback sea turtle, to test how such models matched reality.

Both produced simulations that agreed well with how the living animals behave.

What the computer models showed was that, while gastroliths added a bit of stability, they probably weren’t there for ballast.

It would have taken stones weighing 5 percent to 13 percent of the animal’s weight to significantly affect buoyancy. And nothing near that weight has been found in them.

From their earliest representations, plesiosaurs were often pictured with their long necks arched upward like a swan.

Another result of the computer simulations was a rejection of that idea — the animal would have fallen flat on its face.

Dale Gnidovec is curator of the Orton Geological Museum at Ohio State University.

gnidovec@geology.ohio-state.edu