Laurasian

Biogeography

From the Triassic to the Early Jurassic, before the break-up of Pangaea, archosaurs (crurotarsans, pterosaurs and dinosaurs including birds) had a global distribution, especially crurotarsans, the group ancestral to the crocodilians. This cosmopolitanism ended as Gondwana fragmented and Laurasia was assembled. Pterosaur diversity reached a maximum in the Late Jurassic—Early Cretaceous and plate tectonics did not affect the distribution of these flying reptiles. Crocodilian ancestors also diversified during the Early Cretaceous but were divided into Laurasian and Gondwanan populations; true crocodilians evolved from the former. The distribution of the three major groups of dinosaurs – the sauropods, theropods, and ornithischians – was similar to that of the crocodilians. East Asia remained isolated with endemic species including psittacosaurs (horned dinosaurs) and Ankylosauridae (club-tailed, armoured dinosaurs).