A series of one-centimeter-long, 110-million-year-old footprints found in South Korea were left by what may be the tiniest nonbird dinosaur ever discovered. “These were made by several incredibly small raptor dinosaurs,” says Anthony Romilio, a co-author of a study detailing the discovery and a postdoctoral researcher in paleontology at the University of Queensland in Australia. “Prior to our find, there would have been few who would have imagined that some raptors were so small that two or three could have easily fitted in your cupped hand.”

Each footprint resembles the number 11, suggesting that these creatures walked on two toes per foot. The only dinosaurs known to match this style of prints are dromaeosaurs—a family of speedy predators that included Velociraptor mongoliensis, of Jurassic Park fame. These raptors had four toes on each foot; one was diminutive like a cat's dewclaw, and another had a sickle-shaped claw and was held above the ground while a raptor walked. The sparrow-sized dromaeosaurs that left these footprints would have had hips that were only four to five centimeters high. Their tracks, found in the South Korean city of Jinju, were described last November in Scientific Reports by a team led by Kyung Soo Kim of the country's Chinju National University of Education.

The prints look like they were left by an adult dinosaur smaller than any known type other than birds, Romilio says. Still, the possibility remains that a clutch of dinosaur chicks could have made them; similar footprints 10 times bigger—possibly from an adult—have been found at a site 30 kilometers away. Skeletal fossil evidence from the region is needed to pin down which hypothesis is correct, Romilio notes.

“Most people expect dinosaur tracks to be huge, bathtublike depressions, and some dinosaurs did leave some pretty big holes in the ground,” says Anthony Martin, a paleontologist at Emory University who studies trace fossils (such as footprints and burrows) and was not involved in the study. But the new finding “shows us that we also sometimes need to think small.” Even if the footprints were left by hatchlings, he adds, they hint that these juvenile dinosaurs were precocious and able to leave their nest soon after hatching, similar to some modern birds.