Footprints are among the most common kind of dinosaur fossils. Sometimes scientists find a single, lonely footprint. Sometimes they come across a chaotic jumble of tracks resembling a dance floor, sort of a dinosaur discotheque. But identifying which dinosaur left which track has been notoriously difficult.
Researchers have now developed a method harnessing artificial intelligence to assist in pinpointing the type of dinosaur responsible for the tracks, based on eight different traits of a given footprint.
"This is important because it provides an objective way to classify and compare tracks, reducing reliance on subjective human interpretation," said physicist Gregor Hartmann of the Helmholtz-Zentrum Berlin research center in Germany, lead author of the research published in the scientific journal Proceedings of the National Academy of Sciences.
"Matching track to trackmaker is a huge challenge, and paleontologists have been arguing about this for generations," University of Edinburgh paleontologist and study senior author Steve Brusatte said.
Dinosaurs left behind numerous kinds of fossilized remains, including bones, teeth and claws, impressions of their skin, feces and vomit, undigested remains in their stomach, eggshells and the remnants of nests. But footprints often are more abundant and can tell scientists a lot, including the type of environment a dinosaur inhabited and, when other tracks are present, the types of animals that shared an ecosystem.
The new method was honed with an analysis by the algorithm of 1,974 footprint silhouettes spanning 150 million years of dinosaur history, with the AI discerning eight features that explained variance in the shapes of these tracks.
These features included: overall load and shape, reflecting the foot's ground contact area; the position of loading; the spread of the toes; how the toes attach to the foot; heel position; the load from the heel; the relative emphasis of toes versus heel; and shape discrepancy between left and right sides of the track.
Many of the footprints previously had been identified as a specific kind of dinosaur with confidence by experts. After the algorithm identified the differentiation traits, the experts charted how those corresponded to the various kinds of dinosaurs believed to have made the tracks in order to guide identification of future tracks.
"The problem is that identifying who made a fossilized footprint is inherently uncertain," Hartmann 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 moisture and type of the substrate (ground surface), how the footprint was buried by sediment, and how it was altered by erosion over millions of years. As a result, the same dinosaur can leave very different-looking tracks," Hartmann added.
Dinosaur footprints also come in various sizes.
"The size variation can be quite extreme - from little meat-eating dinosaur footprints about the size of chicken tracks in the barnyard to long-necked sauropod dinosaur footprints that are the size of a bathtub," Brusatte said.
Brusatte said he could think of only one instance in which a paleontologist found a dinosaur skeleton at the end of a trackway made by the animal.
"Which means that if we find footprints, we need to play detective and identify which dinosaur made them. And to do that, we do the same thing as the prince in Cinderella when he matched Cinderella's foot to the slipper: we try to find a dinosaur foot that fits in the footprint," Brusatte said.
One intriguing conclusion made by the algorithm involved images it examined of seven small, three-toed footprints about 210 million years old from South Africa. It validated a prior assessment by scientists that these closely resemble those of birds, even though they are 60 million years older than the earliest-known avian fossils. Birds evolved from small bipedal feathered dinosaurs.
"This, of course, doesn't prove they were made by birds," Brusatte said of the footprints, which he said perhaps were made by previously unknown dinosaurs ancestral to birds or by dinosaurs unrelated to birds that merely had bird-like feet.
"So we have to take this seriously and find an explanation for it," Brusatte said.
