Geological control on dinosaurs’ rise to dominance: Late Triassic ecosystem stress by relative sea level change

The Late Triassic is enigmatic in terms of how terrestrial life evolved: it was the time when new groups arose, such as dinosaurs, lizards, crocodiles and mammals. Also, it witnessed a prolonged period of extinctions, distinguishing it from other great mass extinction events, while the gradual rise of the dinosaurs during the Carnian to Norian remains unexplained. Here we show that key extinctions during the early Norian might have been triggered by major sea-level changes across the largest delta plain in Earth’s history situated in the Triassic Boreal Ocean, northern Pangea. Fossil and rock records display extensive marine inundations with floral turnover, demonstrating how susceptible widespread low-gradient delta plains were to transgressions. Landward shoreline translocation implies decrease in important coastal regions and ecological stress on the dominant Archosauria, thriving in these habitats, and we argue that these unique geological factors played an important role in dinosaurs gradual rise to dominance.