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Sauropod Dinosaurs that Lived Millions of Years Ago Walked Instead of Swam

First Posted: Feb 18, 2016 11:22 AM EST

Scientists have learned a bit more about sauropods, the dinosaurs that lived millions of years ago. They've shed some light on tracks that appear to have been made by four-legged sauropod dinosaurs, though only two of their feet have left prints behind.

Previous studies of such trackways suggested that the dinosaurs might have been swimming, since they were far too big to walk on their hind legs. Like many animals, dinosaurs could swim; however, the evidence for swimming has been disputed. Now, researchers argue that some feet-only tracks were produced by walking and not swimming animals.

The tracks are from the Lower Cretaceous, which was over 120 million years ago. They're roughly circular with a clear set of four or five claw marks at the front. These prints are matched perfectly by the feet of medium-sized sauropod dinosaurs, massive long-necked, plant-eating dinosaurs such as Brontosaurus and Titanosaurus. But how come the prints of the hind feet only were preserved?

"Nobody would say these huge dinosaurs could stagger along on their hind legs alone-they would fall over. However, we can prove they were walking because the prints are the same as in more usual tracks consisting of all four feet, it's just that here, we don't see the handa prints," said Lida Xing, lead author of the new study, in a news release. "If they had been swimming, with the hind legs dangling down, some of the foot prints would be scratch marks, as the foot scrabbled backwards."

There's evidence that the animals were walking on soft sand. They pressed down because of their weight, and the claws dug deeper so they could gain purchase in the sediment. Most of the animal's weight was towards the rear, and so the hind-feet pressed deeper. The front feet, on the other hand, did not apply enough pressure to make a lasting mark.

"This is not to say that sauropods did not swim," said Mike Benton, one of the researchers. "We are simply suggesting that a closer study of the details of fossil footprints and the sediments can suggest a rather less romantic idea. The loss of hand prints is down to sedimentology, not dinosaur behavior."

The findings are published in the journal Scientific Reports.

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