The first dinosaurs in China: Dating Late Triassic footprint fossils from the Sichuan Basin

Abstract

Dinosaur footprints from the Upper Triassic Xujiahe Formation (T3x3) in the Sichuan Basin are the earliest records of dinosaurs from China. Hitherto, little has been known about dinosaurs from the Late Triassic of eastern Tethys and their geochronological ages. Here, we report abundant new dinosaur tracks from the Upper Triassic Tianquan track site, in Ya’an city, western Sichuan Basin. The tracks are assigned to cf. Pengxianpus isp., cf. Kayentapus isp. and elements of the Grallator-Anchisauripus-Eubrontes plexus based on morphospace analysis of key traits. These tracks were all produced by small theropod dinosaurs. The track-bearing beds are dated to 218.4 ± 4.7 Ma, a mid-Norian age, based on a group of the youngest detrital zircons. These earliest dinosaurs in the eastern Tethys appear to have migrated in from regions in western Tethys at similar paleolatitudes, and their movements may have been limited by substantially fluctuating paleoclimates. These theropod tracks from eastern Tethys provide additional evidence of the rise of dinosaurs to ecological dominance at a time of fluctuating paleoclimatic conditions corresponding to the mid-Norian Warming Event.