How can a guinea fowl, 2 million poppy seeds and an X-ray machine help scientists understand how the dinosaurs walked?
It all has to do with the complicated dynamics of footprints. The creation of a footprint is not as straightforward as one might think. It involves an interaction between a foot and a substrate. That substrate might be hard and flat, or it might be porous and shifting, like sand, mud, clay or snow.
Footprints made in these compliant substrates are more likely to be preserved through the ages, but they are also more complex than a footprint made on a hard surface because they often involve sinking motions and the action of pulling a foot out of a subsurface as opposed to simply stepping.
In a study published in the Proceedings of the National Academy of Sciences, scientists used X-ray video of a guinea fowl walking through a trough of poppy seeds to create a detailed 3-D model of how tracks get made. Their hope is that this model will allow researchers to tease out even more of the information embedded in dinosaur footprints and understand how these animals may have moved.
Peter Falkingham, a research fellow at the Royal Veterinary College in London and the lead author of the study, said he turned to birds for this study because they are direct descendants of dinosaurs. That his test subject was a guinea fowl specifically was more arbitrary. "It just happened to be both available and the right size to fit in the X-ray machine," he said.
Over the course of the study, the scientists discovered that when the guinea fowl walked through the poppy seeds, the tracks at the surface of the poppy seed bed were difficult to interpret as tracks at all. However, 2 centimeters beneath the surface there was a much clearer imprint of the shape of the foot.
Falkingham said that depth would change if the substrate were different, or if the animal making the track were different. "We're still working on what depends on scale and what is general principles," he said.
Still, the researchers were able to find similarities between the track created by their guinea fowl and that created by a dinosaur 200 million years ago. Both tracks displayed rounded features which the model of the guinea fowl's footsteps showed is associated not with a strange foot morphology, but with the way the substrate shifted when the animals pulled their feet out. It might be possible that the more we learn about how birds walk, the better we can understand the fossilized footprints of their ancestors.
