A megaraptor emerges from footprint fossils

Thanks to their reign of terror in Jurassic Park, Velociraptors are infamous prehistoric predators.

The sickle-clawed killing machines familiar to moviegoers, though, are far removed from their scientific counterparts -- and not just because the fictional ones lack feathers. In real life, Velociraptors topped out at the size of a Labrador retriever and were much smaller than the human-size hunters portrayed in the film series.

Still, some raptors did achieve imposing sizes. And a team of paleontologists said it might have identified a new megaraptor based on a set of fossilized footprints found in China. In a paper published this week in the journal iScience, the researchers estimated that the tracks had been left by a dinosaur that would be among the largest raptors known to science.

The raptor's footprints are part of a larger dinosaur trackway discovered in southeastern China in 2020. During the Late Cretaceous period, about 90 million years ago, the area was a muddy river plain home to all manner of dinosaurs, including long-necked sauropods and duck-billed herbivores. As these dino denizens stomped about, they left muddy footprints -- some of which have been preserved for tens of millions of years.

Around 240 dinosaur tracks have been discovered in Longxiang, at the track site, which is roughly the size of a hockey rink. A few of the footprints are oddly shaped, with preserved imprints featuring only two toes.

"When you see dinosaur footprints with only two toes, you can play the Cinderella slipper game and look for feet that match them," said Stephen Brusatte, a paleontologist at the University of Edinburgh who was not involved in the new study. "The only dinosaurs that walked on two toes were 'raptors' like velociraptor and their close relatives."

Raptors left such odd imprints because their inside toes were held off the ground. This prevented the toe's oversize, recurved claw from dragging on the ground and becoming dull.

Several of Longxiang's two-toed tracks appear to have been left by a small, velociraptor-size dinosaur. But the researchers found a set of five tracks that are more than 13 inches long, making them the largest raptor tracks in the fossil record. Based on the size of the tracks, the dinosaur that left them stood roughly 5 feet tall and 15 feet long, putting it in the neighborhood of the largest known raptors, including Utahraptor.

Its distinct footprints inspired the paleontologists to name the new raptor Fujianipus (meaning the "the foot of Fujian") yingliangi. While finding fossilized bones would help researchers further flesh out what the animal looked like, the proportions of its two toes make it likely that Fujianipus was a troodontid, a type of birdlike raptor that inhabited Asia and North America during the Cretaceous period.

Raptors are often depicted as fast-paced predators. But footprints alone can't provide a sense of how fast Fujianipus moved, according to W. Scott Persons, a paleontologist at the College of Charleston in South Carolina and co-author of the new paper.

He thinks the raptor was most likely watching its step as it crossed the muddy riverbed. "When you walk across mud, you would be moving very carefully to avoid slipping," Persons said. "That was probably also the case for our raptor."

Without fossilized leg bones, the researchers cannot estimate Fujianipus' speed. But members of the troodontid group, to which it probably belonged, were "among the leggiest of all raptors," Persons said, suggesting that Fujianipus was probably a swift predator.

Speed would have come in handy during the late Cretaceous, a period when older lineages of predatory dinosaurs were gradually giving way to up-and-coming groups of carnivores like raptors and lanky tyrannosaurs.

"During this time, it seems like these two iconic groups of dinosaurs, the tyrannosaurs and the raptors, were both vying for that midsized predator crown," Brusatte said.

While tyrannosaurs would continue to grow into behemoths like Tyrannosaurus rex, raptors largely stayed small. Giants like Fujianipus and Utahraptor are outliers.

"Raptors experimented with large body sizes but, unlike a lot of other groups of carnivorous dinosaurs, they didn't stick with it," Persons said. "Raptors appear to have been way better at being small- and medium-sized carnivores than they were at being big."