If you were a big, slow, plant-eating dinosaur, the guys that made these tracks were the last thing you'd want to see. And, chances are, if you did see them, they would be the last thing you'd see.
The gang members are theropods, or flesh-eating, dinosaurs called Dromaeopodus shandongensis. Dixie State College's director of paleontology, Jerry D. Harris, is among six authors of a new paper that casts light on these ferocious predators.
Harris and co-authors examined data about parallel trackways of Dromaeopodus found in Shandong Province, China. The rocks where they were found are between 115 million and 120 million years old, Harris said. The estimate is based on known ages of some other fossils found in the same formations.
Predatory dinosaurs on land were almost always three-toed. "But each of the (Shandong) tracks has only two toes on it," he said.
Besides these, each track has a "nubbin" of another toe. What does that mean? That the raptors held one of their toes off the ground. It would have carried a sharp, curved knife of a claw, and by holding it off the rocks and mud the dinosaur kept that weapon sharp.
The only dinosaurs with that kind of claw are, "in Jurassic Park terminology, raptors," Harris said.
"No tracks of this kind of dinosaurs have been definitively found before," Harris said. A few scattered tracks were not clear enough to be "definitive," and the argument could be made that three toes didn't show up because the tracks were not preserved well enough to show all three.
But the tracks found at Shandong in 2005 by Rihui Li and Mingwei Liu were well preserved. Rihui is from the Qindao Institute of Marine Geology in China while Mingwei is with China's Fourth Geological and Mineral Resources Survey of Shandong.
The tracks showed the movements of at least six theropods who were walking together.
"They're all moving parallel" to each other, Harris said. They walked at the same time, as indicated by the sort of sediment.
"The odds of these tracks being made by different individuals that just happen to be moving in the same direction, without their tracks stepping on one another, are small," Harris said.
The most likely explanation is that the group walked together.
"It's hard to say whether they were hunting," he said. In the past, a big vegetarian dinosaur fossil was discovered in the Midwest, along with "lots and lots of teeth shed by the meat-eating dinosaurs. ... There's too many teeth to be produced by one animal."
That would seem to show pack hunting behavior. But the evidence was not definitive because it was possible that the herbivore's bones and the theropod teeth happened to be washed into the same deposit by a river.
The new trackways show that the raptors were walking together in a group.
"Groups that do that usually have relatively sophisticated behavior, and they're relatively intelligent," Harris said. "By moving together in groups, it's entirely possible that they hunted in groups."Co-authors of the paper, which was published in the European journal Naturwissenschaften, are Harris, a professor at Dixie State College, St. George; Rihui Li, of the Qindao Institute of Marine Geology, China; Martin G. Lockley of the Dinosaur Museum at the University of Colorado, Denver; Peter Makovicky of the Field Museum in Chicago; Mark Norell of the American Museum of Natural History, New York City; and Masaki Matsukawa of Gakugei University, Tokyo.