New Discovery of Running Footprints from the Jehol Biota in Inner Mongolia and Analysis of Behavioral Habits

The maximum locomotor capabilities of theropod dinosaurs and their behavioral strategies during secondary acceleration in running have long been of scholarly interest, yet direct evidence remains scarce. Here we report two new discoveries of running footprints from the Jehol Biota in the Otog region of Inner Mongolia, China, which provide novel insights into both extreme running speed and behavioral adaptations during locomotion. First, a trackway of a mid-sized theropod reveals a running speed of 45 km/h or 41±4.9 km/h, making it the fastest-running theropod trackway documented from the Cretaceous period. This inferred speed aligns well with predictions from most biomechanical models, offering compelling evidence for the locomotor capabilities of mid-sized theropods. Second, another newly identified trackway, consisting of seven medium-sized tridactyl footprints attributed to Asianopodus wangi, exhibits variations in stride length, pace angulation, and footprint morphology. For the first time, this trackway demonstrates that the trackmaker employed two distinct strategies during the running phase: shifting toward the center of the trackway and leaning the body forward, both of which served to increase stride length and improve running speed. Together, these findings not only augment the known dinosaur diversity of the Inner Mongolian Jehol Biota but also provide critical fossil evidence for investigating both extreme running speeds and secondary acceleration behaviors in theropod dinosaurs.