Dinosaur tracks in N China suggest one of slowest meat-eaters

This undated file photo provided by Xing Lida, an associate professor at China University of Geosciences (Beijing), shows a set of three-toed theropod dinosaur fossil tracks discovered in Xuanhua, north China's Hebei Province. (Xinhua)

BEIJING, May 6 (Xinhua) -- Scientists have uncovered fossil tracks in north China, left at least 134 million years ago by what they believe to be one of the slowest meat-eating dinosaurs ever recorded.

Made by a three-toed theropod dinosaur that moved at a pace of 0.28 meters per second (about 1 km per hour), these tracks suggest the creature either stopped intermittently or took an extremely slow walk, a stark contrast to the faster running speeds commonly associated with its kind.

The discovery, published on Wednesday in the Paleontological Journal, stems from two track sites at Xuanhua in the city of Zhangjiakou in Hebei Province. They are located at the Tuchengzi Formation dated to between 154 and 134 million years ago. An international team of researchers from China, Brazil and Australia analyzed 16 larger footprints (23.2-26.7 cm long) and 11 smaller ones (10.1-14.6 cm long).

One particular track consists of five footprints with stride lengths of 32 cm to 46 cm, roughly the step length of a toddler. The estimated speed of 1 km/h is likely one of the most unhurried theropod tracks known globally, according to the study.

"Such short strides and wide tracks indicate the track maker may have been pausing frequently or moving extremely slowly," said lead researcher Xing Lida, an associate professor at China University of Geosciences (Beijing). Xing speculated that the dinosaur could have been scanning the ground for small invertebrates or vertebrates, or checking the path ahead for safety. For comparison, other tracks at the same sites yielded estimated speeds of 9.18 km/h to 14.11 km/h, which is a trotting pace.

The study, in addition, highlighted a "microbial mat" layer on the track surface. These microbial mats acted as a natural preservative film, preserving the footprints for over 100 million years.

The research team also recorded eight footprints of sauropods, which are giant four-legged plant-eating dinosaurs. In 2020, local geological surveyors discovered a vast exposed surface at Xuanhua, covering approximately 30,000 square meters and preserving more than 5,000 dinosaur footprints, including sauropod tracks and medium-sized theropod tracks. The two new sites reported in this study together paint a more complete picture of the ancient dinosaur community.

"Dinosaur tracks are not simply fossilized footprints," Xing added. "They capture living moments, such as behavior and interaction with the environment, and offer information that dinosaur bones alone cannot provide."

Dinosaur tracks were once considered rare discoveries in China. In recent years, however, new dinosaur fossils and footprints have been constantly uncovered in Hebei. Scientists have previously named two track types after locations in this province: Changpeipus and Lockleypus.

In late 1999, Chinese and Japanese scientists jointly announced the discovery of 75 dinosaur track fossils in Luanping County, dated to over 130 million years ago. In 2013, a team found numerous theropod footprints at a site in Zhangjiakou, dating back 140 to 150 million years, while in 2019, a chicken-sized theropod fossil was unearthed in Fengning County and weeks later, nearly 300 Late Jurassic footprints were found in Chengde Mountain Resort, an imperial garden and temple complex in Hebei.

The new study stands out because it unveiled a very slow meat-eater.

"These tracks are precious because most have not been heavily eroded," said Li Jianjun, a dinosaur researcher at the National Natural History Museum of China, who was not directly involved in the study.

Li said conditions for footprint preservation are extremely demanding: sediment must be neither too dry nor too wet, and once tracks are made, they must dry and harden before being rapidly buried.

Thanks to abundant footprints, rare slow-speed tracks and the microbial mats in preservation, scientists can know more about dinosaur diversity, behavior and burial processes in Earth's history, the study noted.