Dinosaur Tracks: Mystery Of Northern China Sauropod Footprints Solved

Unusual dinosaur tracks found at the Gansu Province in northern China appear to have been made by four-legged sauropods, but there's a catch: The tracks show two of the feet left behind. How is this possible?

Sauropods were massive long-necked, plant-eating dinosaurs that included the Brontosaurus and Titanosaurus. Since the prehistoric creatures were far too big to walk on their hind legs, previous theories have suggested that the dinosaurs may have been swimming through the area, with their bodies remaining buoyant in the deep water while they paddled along with their front arms or legs. However, this has been disputed by many.

In the latest study, researchers from China University of Geosciences in Beijing and paleontologists from the University of Bristol confirm the animals that left behind the strange tracks were in fact walking.

"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 hand prints," lead author Lida Xing, of the China University of Geosciences, said 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."

The tracks, dating from the Lower Cretaceous, over 120 million years ago, are circular with a clear set of four or five claw marks at the front. Researchers say the prints are identical to those of medium-sized sauropods.

While the tracks are very well-preserved, there is evidence the animals were walking on soft sand. This means as they walked across the land they sank a little due to their weight. They would have had to dig their claws deeper into the sediment to gain leverage. Weight distribution for saurpods occured at the rear of their bodies, meaning their hind-feet pressed deeper into soft sand. The front feet, however, did not apply enough pressure to leave a lasting impression in the sediment.

"This is not to say that sauropods did not swim. We are simply suggesting that a closer study of the details of fossil footprints and the sediments can suggest a rather less romantic idea," co-author Mike Benton, a professor in the University of Bristol's School of Earth Sciences department, added in the release. "The loss of hand prints is down to sedimentology, not dinosaur behavior."

Their findings were recently published in the journal Scientific Reports.

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