Footprints are among the most common types of dinosaur fossils. Sometimes scientists find a single, solitary print. Sometimes they encounter a chaotic jumble of tracks that resembles a dance floor—a kind of "dinosaur disco." But identifying which dinosaur left which track has long been known to be an extremely difficult task.
Researchers have now developed a method that uses artificial intelligence to help more precisely determine the type of dinosaur that made the prints, based on eight different features of a single footprint, Reuters reports.
"This is important because it provides an objective way to classify and compare traces, thereby reducing reliance on subjective human interpretation," said physicist Gregor Hartmann of the Helmholtz-Zentrum Berlin research center in Germany, lead author of the study published in the scientific journal Proceedings of the National Academy of Sciences.
"Matching a track to a track 'maker' is a huge challenge, and one that paleontologists have debated for generations," said University of Edinburgh paleontologist Steve Brusatte, senior author of the study.
Dinosaurs left behind many types of fossilized remains, including bones, teeth, and claws, skin impressions, feces and vomit, undigested remains in the stomach, eggshells, and nest remains. But footprints are often more numerous and can tell scientists a lot, including what kind of environment the dinosaur inhabited, when other tracks exist, and which animals shared the same ecosystem.
The new method was perfected by analyzing an algorithm that processed 1.974 footprint silhouettes, spanning 150 million years of dinosaur history, with artificial intelligence recognizing eight features that explain the differences in the shapes of these tracks.
These features include: total load and shape, which reflects the area of contact of the foot with the ground; load position; toe span; the way the toes connect to the foot; heel position; heel load; relative emphasis of the toes relative to the heel; and the difference in shape between the left and right sides of the footprint, Reuters reports.
Many of the footprints had previously been assigned with high confidence to a particular species of dinosaur thanks to expert assessments. After the algorithm identified the features that set the tracks apart, the experts mapped how those features linked to the different species of dinosaur believed to have made them - to serve as a guide for future identifications.
"The problem is that identifying who made the fossilized footprint is essentially uncertain," Hartman said.
"The shape of a track depends on many factors, beyond the animal itself - including what the dinosaur was doing at the time, such as walking, running, jumping or even swimming, the humidity and type of substrate (ground surface), the way the track was covered by sediment, and how it was altered by erosion over millions of years. This is why the same dinosaur can leave very different tracks," Hartman added.
Dinosaur footprints also occur in various sizes.
"The differences in size can be quite extreme - from small footprints of carnivorous dinosaurs, the size of chicken tracks in a farmyard, to long-necked sauropod footprints that are as big as a bathtub," Brusat said.
Brusat said he could only think of one case in which a paleontologist found a dinosaur skeleton at the end of a trail of footprints made by the animal.
"This means that when we find footprints, we have to play detective and determine which dinosaur made them. And to do that, we do the same thing that the prince in Cinderella did when he compared Cinderella's foot to the shoe: we try to find a dinosaur foot that fits the footprint," Brusat said.
One interesting conclusion the algorithm came to was based on the images it analyzed—seven small, three-fingered footprints, about 210 million years old, from South Africa. The method confirmed scientists' earlier assessment that they strongly resembled bird footprints, even though they are 60 million years older than the earliest known bird fossils. Birds evolved from small, two-legged, feathered dinosaurs.
"Of course, that doesn't prove they were made by birds," Brusat said of the footprints, which he believes may have been left by previously unknown dinosaurs - the ancestors of birds - or dinosaurs that are not related to birds but simply had bird-like feet.
"That's why we have to take this seriously and find an explanation," Brusat said.
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