The five three-toed fossil footprints, found in Gansu province, measure between 1 cm (0.39 in) and 3 cm (1.18 in) across and are thought to belong to one of the smallest dinosaurs ever discovered, a tiny genus of bipedal land dinosaur called Minisauripus.
“We estimate that the body length [of the dinosaurs] “It's about 25 cm (9.84 inches), but the tail should be at least half the length,” said Xing Lida, a paleontologist and associate professor at the China University of Geosciences.
By comparison, the house sparrow typically measures around 17 cm (6.69 in) in body length, the pigeon is around 35 cm (13.8 in) from head to tail, and the domestic chicken typically measures between 40–60 cm (15.7–23.6 in) in length.
Similar tracks dating back to the Early Cretaceous period, which lasted from 145.5 to 100.5 million years ago, were first discovered in the Sichuan Basin in southwest China, as well as in eastern Shandong Province and South Korea.
The discovery of the latest tracks, found in the newly designated Linxia UNESCO Global Geopark, expands the known range of Minisauripus, making it one of the richest fossil-bearing regions in China.
The tracks were discovered last August by staff at the park's dinosaur museum after constant rainfall caused tiny marks to appear on the weathered surface of the rock.
The latest discovery could help researchers gain deeper insight into the evolution of birds, said Xing, who was part of a team that studied earlier tracks found in southwest China.
“The miniaturization of dinosaurs was a key factor in their evolution into birds, and it was a very important evolutionary event,” he said.
Ripple marks on rocks in Gansu suggest that the dinosaurs that made the tracks may have been active near water. Waterfowl tracks were also found near the tracks, consistent with similar finds in other regions, Xing said.
Studying the tracks could also help shed light on dinosaur behavior, including how they interacted with their environment, Xing said.
In a paper published in 2016, Xing and colleagues estimated that the body length of an adult Minisauripus could have ranged from 12 cm (4.72 in) to 71 cm (28 in).
According to the paper, Minisauripus is the smallest genus of carnivorous theropod known to science that is not part of the Avialae, the only group of dinosaurs with living representatives in the form of modern birds.
The researchers acknowledged in their paper that there is a possibility that the tiny tracks belonged to a juvenile of a slightly larger species.