What are Crurotarsans?
Crurotarsans (“cross-ankles”) are one of the two groups of archosaurs (a large clade of reptiles that includes birds, crocodilians, and dinosaurs), the other being ornithodirans (birds and dinosaurs). The only living crurotarsans are crocodilians, but during the early and middle Triassic, between about 250 and 200 million years ago, crurotarsans were responsible for most reptilian diversity. Crurotarsans have existed for almost 250 million years in total, often dominating swamp ecosystems in the form of large crocodilians, especially after the extinction of the dinosaurs 65 million years ago. Crurotarsans are defined as any taxa more closely related to present-day crocodiles than present-day birds, and by their unique croc-like ankle structure. Crurotarsans became the dominant vertebrates a few million years after the Permian-Triassic extinction 251 million years ago, which was the greatest mass extinction in the planet’s history. They followed the therapsids (ancestors of mammals), wh
