An Early Theropod Leaves an Impression on Scientists

If there is one top complaint paleontologists have about restorations of dinosaurs in movies, it is that the filmmakers never get the hands right. Theropods, be they Tyrannosaurus or Velociraptor, are always shown with their "palms" facing downwards—even though this would have been anatomically impossible. Paleontologists have long known that they held their hands so that their palms faced each other, almost as if they were holding a basketball.

A new paper published in PLoS One by a team of scientists from Utah and Colorado confirms what paleontologists have long known from the structure of the bones. About 198 million years ago, a large theropod dinosaur trudged along a muddy stretch of land, leaving well-defined tracks behind it. It also stopped every now and then to crouch down on a small berm near an ancient lake. When it did so, impressions were made of the positions of other parts of its body like its tail, hips, and hands.

The hand impressions showed that this dinosaur held its hands facing each other. This is important because it means that this way of holding the hands, which is also seen in modern birds, appeared relatively early among theropod dinosaurs. It is yet another trait considered "bird-like" that appeared in dinosaurs first.

As is typically the case, the precise identity of the trackmaker cannot be determined. Footprints, like fossils of organisms, are traditionally given their own genus name so that scientists can identify the same types of prints from different locations. The Utah tracks were attributed to a well-known track genus called Eubrontes, although the theropod Dilophosaurus (which is known from the same area, even if it is geologically a little younger than the tracks) seems like a good candidate for the animal that made the marks.

Riley Black | | READ MORE

Riley Black is a freelance science writer specializing in evolution, paleontology and natural history who blogs regularly for Scientific American.