An X-ray video of a modern bird is helping scientists unravel the secrets to a dinosaur's tracks from the Jurassic period, shedding light on how dinosaurs walked when they still roamed the Earth millions of years ago.
The over 250-million-year-old tracks of the Corvipes lacertoideus, a dinosaur that was about the size of a chicken, had strange features that scientists suspect to be marks that the dinosaur left when it withdrew its feet from the sediment.
With some help from a guineafowl, a relative of chickens, poppy seeds and an X-ray machine, researchers set out to investigate this and came up with a detailed three-dimensional model on how the tracks were made. The researchers said that a bird was chosen for the study because they are known to be the direct descendants of the now-extinct dinosaurs.
For their study published in the journal PNAS on Dec. 8, Peter Falkingham from the Royal Veterinary College in London and Stephen Gatesy from the Brown University's Department of Ecology and Evolutionary Biology, used X-rays to videotape the bird as it walked through a soft bed of poppy seeds just as the Corvipes walked through soft dirt many years ago.
The video revealed that the bird's feet sank about 1.9 inches into the poppy seeds, which is nearly equal to the length of its feet. The researchers observed that an indistinct impression remained when the bird traversed dry and granular surface but about 0.4 inches below the surface, the impression of the guineafowl's feet was persevered in remarkable detail.
The researchers said that the preservation can be attributed to the seeds balancing against one another below the surface and not collapsing just as they do at the surface. The impression did not not faithfully reproduce the bird's foot anatomy, but the x-ray video nonetheless revealed how the bird's feet move.
"Foot movement differed significantly from walking on solid ground; the longest toe penetrated to a depth of ∼5 cm, reaching an angle of 30° below horizontal before slipping backward on withdrawal," the researchers wrote.
The distinct impressions were likewise mimicked in the tracks of the Corvipes, allowing the researchers to see how the mysterious ridges in the ancient tracks formed.
"In this dry, sand-like material, very clear tracks are preserved below the surface, but these reflect foot entry and exit rather than static anatomy," Gatesy said. "Relating track features to formation dynamics helps explain the origin of track diversity in the fossil record and aids reconstruction of dinosaur locomotion."
