How can a guineafowl, two million poppy seeds and an x-ray machine help scientists understand how the dinosuars walked?
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 foot print made on a hard surface because they often involve sinking motions and the action pulling a foot out of a subsurface as oppose to simply stepping.
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 guineafowl specifically was more arbitrary.
"It just happened to be both available and the right size to fit in the x-ray machine," he told the Los Angeles Times.
He used poppy seeds because although they behave like dry sand, they are less dense and it is easier for an x-ray to see through them.
Over the course of the study, the scientists discovered that when the guineafowl walked through the poppy seeds, the tracks at the surface of the poppy seed bed were difficult to interpret as tracks at all. However, two centimeters beneath the surface there was a much clearer imprint of the shape of the animal's foot.
Falkingham said that depth would change if the substrate were different, or if the animal making the track was 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 guineafowl and that created by a dinosaur 200 million years ago. Both tracks displayed rounded features which the model of the guineafowl'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.