A new analysis of fossil dinosaur tracks from northern China, which appear to have been made by four-legged sauropods yet contain prints from only two of the creatures’ feet, were likely left behind by animals that were walking, not swimming.
Writing in the latest edition of the journal Scientific Reports, experts from the China University of Geosciences in Beijing and the University of Bristol explained that the tracks, which are more than 120 million years old and date back to the Lower Cretaceous period, are roughly circular in shape and possess a clear set of four or five claw marks at the front.
These footprints are perfect matches for the feet of medium-sized sauropods, including massive long-necked herbivores such as the Brontosaurus and the Titanosaurus, the study authors said in a statement. Yet previous studies concluded that these dinosaurs, which were far too big to walk on their hind legs, could have been swimming. The new paper disputes those findings.
“Nobody would say these huge dinosaurs could stagger along on their hind legs alone – they would fall over,” explained lead author Lida Xing. “However, we can prove they were walking because the prints are the same as in more usual tracks consisting of all four feet.”
Credit: Lida Xing
A matter of sedimentology, not dinosaur behavior
What is unique about this case, Xing said, is that only the hind feet were preserved. However, because we do not see the hand prints does not mean that they weren’t there. If these sauropods had been swimming, the researchers said, the hind legs would have been hanging free and some of the footprints would appear as “scratch marks, as the foot scrabbled backwards.”
The newly discovered tracks are well preserved, but also appear to indicate that the dinosaur had been travelling on soft sand. Because of their weight, their claws dug deeper into the surface and allowed them to secure a foothold in the sediment. Since the majority of the dinosaurs’ girth was towards the rear of the animals, the hind-feet pressed deeper than the front ones, resulting in only the back legs leaving a lasting impression on the sandy terrain.
However, as co-author Professor Mike Benton from the University of Bristol’s School of Earth Sciences explained, this does not indicate that sauropods were unable to swim. Instead, he said, the evidence suggests that “a closer study of the details of fossil footprints and the sediments can suggest a rather less romantic idea,” and the absence of hand prints was due to “sedimentology, not dinosaur behavior.”
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Feature Image: This is an artist’s impression of sauropod dinosaurs on the Isle of Skye. (Credit: Jon Hoad)
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