CRETACEOUS TETRAPOD FOOTPRINT BIOSTRATIGRAPHY,BIOCHRONOLOGY,AND ICHNOFACIES

The global record of Cretaceous tetrapod footprints is dominated by the tracks of non-avian dinosaurs and birds;fewer tracks are known of pterosaurs,crocodylians,turtles,mammals,and other tetrapods.The Cretaceous track record is best known from East Asia(especially China and Korea) and western North America.A moderately extensive record is also known from South America(primarily Argentina and Brazil),but Cretaceous track assemblages from Europe,Africa,and Australia are much more poorly known.Here,we re-examine two global footprint biochrons based on the Cretaceous tetrapod footprint record.An Early Cretaceous biochron is characterized by sauropod and ornithopod tracks.A Late Cretaceous biochron has fewer sauropod tracks but adds the tracks of hadrosaurs,tyrannosaurids,andceratopsians.Furthermore,the Cretaceous footprint record documents many important biostratigraphic data points,such as the mid-Cretaceous extirpation of sauropod dinosaurs in North America and the terminal Cretaceous extinction of dinosaurs.A growing Cretaceous footprint record from eastern Asia also provides the first glimpse of a more refined,provincial Cretaceous footprint biochronology,in which three or four Cretaceous footprint biochrons based on the stratigraphic distributions of endemic theropod dinosaur(including bird) ichnogenera may be recognizable.The abundance and endemism of this east Asian Cretaceous avian ichnofauna may indicate that a unique and prolific avian fauna existed in eastern Asia during the Cretaceous,a footprint-based hypothesis that merits further testing.