A preliminary report on two new vertebrate track sites including dinosaurs from the Early Cretaceous Hekou Group, Gansu Province, China

Abstract

Two track sites were discovered in the Hekou Group(Early Cretaceous), Yanguoxia, Yongjing County, Gansu Province, China. More than 108 dinosaur and pterosaur trackways occur on the same gray fine sandstone surface of the two sites. Site 1 (600 ㎡) contains 245 dinosaur, 25 pterosaur, and 4bird tracks. A total of 1,392 dinosaur tracks with one pterosaur track are preserved in the Site 2 (1,000 ㎡). Dinosaur tracks attributable to theropods, sauropods, and ornithopods in occur both sites. One of the theropod trackways in the both site consists of an unusual didactyl footprints, suggestive of a dromaeosaurid theropod such as Deinonychus. Unusual sauropod and ornithopod trackways are also found at both sites, which appear to have been made by swimming sauropods and ornithopods in shallow water. These include unusual ornithopod trackways that have tail-drag marks between left and right footprints. A pterosaur trackway in Site 1 represents the first record of pterosaur footprints in China, which consists of six pairs of manus and pes and one isolated manus impression. This pterosaur trackway is also the first record from the Early Cretaceous in Asia. A comprehensive analysis of the tracksites deduced from overlapping trackway sequences indicates that the sedimentary environment changed gradually from terrestrial into lacustrine condition. The co-occurrence of dinosaur tracks such as theropods, sauropods, and ornithopods with pterosaur and bird tracks shows a unique faunal association in this area in the Early Cretaceous of China.