Scientists have found that increasing oxygen levels are linked to the rise of North American dinosaurs around 215 M years ago. A new technique for measuring oxygen levels in ancient rocks shows that oxygen levels in North American rocks leapt by nearly a third in just a couple of million years, possibly setting the scene for a dinosaur expansion into the tropics of North America and elsewhere. This is presented in a Keynote talk at the Goldschmidt Geochemistry conference, in Barcelona.
source https://phys.org/news/2019-08-dinosaurs-linked-oxygen.html