Two theropod track assemblages from the Jurassic of Chongqing, China, and the Jurassic Stratigraphy of Sichuan Basin

Four Jurassic dinosaur tracksites have been reported from Chongqing Municipality. These include the Lower Jurassic Dazu site in the Zhenzhuchong Formation, which yields the oldest sauropod trackway known from China. Two of the remaining three sites (Nan'an, and Jinji sites), variously regarded as Middle and Upper Jurassic, are here described in detail for the first time and regarded as Upper Jurassic, both from the Shangshaximiao Formation. The fourth site (Chengyu), so far not accessible to the present authors, is not described. The Nan'an site, and type locality of Chongqingpus nananensis, has yielded a large sample of theropod tracks from the heart of Chongqing Municipality, at a site that has been lost in the urban development. Fortunately the sample is preserved at Chongqing Museum of Natural History and has been studied independently on two occasions to produce the results presented here. C. nananensis is a medium-sized track (mean track length ~29 cm) that may best be accommodated in ichngenus Kayentapus, and may in some cases preserve ill-defined hallux traces. Associated tracks are attributed to cf. Anomoepus. Other smaller ichnospecies from other localities outside Chongqing municipality, and from older middle Middle Jurassic formations, were previously assigned to ichnogenus Grallator. The Jinji site has yielded a single long theropod trackway of a robust form tentatively labeled cf. Therangospodus. This Jinji trackway also provides intermittent evidence of a hallux. Although theropod tracks are becoming increasingly well-known in the Jurassic sections of Chongqing Municipality, the Sichuan Basin and the broader region, determining their precise age and assigning them to valid ichnotaxa remain challenging. This is because Jurassic theropod tracks,