‘ Wings’ helped ancient marine reptiles fly through water

When dinosaurs ruled the land, the top predators in the seas of the Mesozoic era were plesiosaurs. There were two main groups.

One group, called pliosaurs, had long skulls and short necks and resembled modern killer whales in overall shape. They acted like them, too — their main prey were other large swimming vertebrates. Some species were more than 30 feet long.

The other group of plesiosaurs, called elasmosaurs, had small heads and long necks. In some cases, the necks were very long: one species had 76 bones in its neck alone. These kinds of plesiosaurs ate smaller prey, such as fish and squid, and some approached 40 feet in length.

Both groups had two sets of flippers, a pair in front and a pair in back. The flippers were long and pointed, much like those of penguins and sea turtles, and probably were used in the same way. Rather than row or paddle through the water, plesiosaurs flew underwater, with the same kind of figure-8 pattern used by birds, from hawks to hummingbirds. Their flippers were actually used like wings.

The wings of elasmosaurs were long and thin, like the wings of a glider, making them very efficient for longdistance travel. The wings of pliosaurs were more short and broad, like the wings of a fighter jet, giving them great maneuverability.

One plesiosaur puzzle was how the wings were used. Did the front and back flippers beat in tandem, or did the strokes alternate? One suggestion was that one set was used for propulsion and the other for steering, but the front and back flippers are so similar that that idea was ruled out.

The problem is that no other marine vertebrate has two sets of wings — not whales, penguins, sea turtles or sea lions — so modern animals aren’t much help for comparison.

A recent bit of research attacked the problem by building models of plesiosaur wings and putting them in a flume, a large tank of moving water. Dye injected into the water showed the effects produced by each beat of the wings and allowed the scientists to calculate the kind of stroke pattern that was most efficient.

The results were fascinating. Each beat of a wing produced vortices, “whirlpools” of water containing energy.

Depending on the pattern of flapping, the back wings could actually gain some of the vortex energy produced by those at the front, thereby increasing the amount of forward thrust they produced by 60 percent and increasing their efficiency by 40 percent. It is sort of like migratory birds flying in a V formation, where the birds in back benefit from the work of the birds in front.

The least efficient pattern was when one set (front or back) went up while the other went down. The most efficient pattern depended on the spacing between the front and back wings (and thus the size of the animal) and the speed it was moving.

The plesiosaurs were around for 180 million years, longer than any other marine reptiles. It looks like their efficient wings gave them a leg up on the competition.