Continental Vertebrate Extinctions at the Triassic-Jurassic and Cretaceous-Tertiary Boundaries: a Comparison

Abstract

Although similar causes (such as asteroid impact or flood basalt volcanism) have been suggested for both the Triassic-Jurassic (Tr/J) and Cretaceous-Tertiary (K/T) mass extinctions, a comparison of extinction patterns among continental vertebrates reveals significant differences between these two events. There is no discernible size factor at the Tr/J boundary, whereas the K/T extinction is marked by the disappearance of all large land vertebrates. Unlike what happened at the end of the Cretaceous, freshwater ecosystems were significantly affected at the end of the Triassic, with the extinction of the crocodile-like phytosaurs. Both dinosaurs and mammals survived the Tr/J event, but the large adaptive radiation of mammals had to wait until dinosaurs disappeared at the end of the Cretaceous. All these differences in pattern suggest that different processes were involved, and that what happened at the K/T boundary cannot be simply extrapolated to the Tr/J boundary. The need for closer studies of extinction patterns during major biotic crises is emphasized.