A grallatorid track site from the Lower Cretaceous Hekou Group, Gansu Province, China

A variety of avemetatarsalian and non-archosaurian reptile tracks have been discovered in the lower Cretaceous Hekou Group in western China, where they occur alongside a herbivorous dinosaur skeletal fauna. A new track assemblage has recently been identified in the upper Hekou Group in Matan Natural Village, Jingyuan County, situated to the east of the primary track assemblage. The track-bearing bed is composed of sandstone-dominated, gypsum-included mottled clastic deposits, which indicate an arid braided river environment. All of the tracks in this site are classified as Cretaceous ichnospecies of Grallator, G. ssatoi, which are distributed in northern China. Additionally, the specimens exhibit members exceeding the original definition of Grallator (<= 15 cm). These well-preserved tracks not only demonstrate the widespread distribution of this ichnospecies in the Lower Cretaceous of China, but also provide insight into the relationship between the metatarsophalangeal pad traces of G. ssatoi and preservation. The sliding traces among them can indicate the ability of trackmakers to maintain balance while walking. Furthermore, the closely associated parallel trackways suggest that the trackmakers may have exhibited gregarious behaviour, and that such aggregation during marching may have been related to their self-preserving strategy.