A dip in coi2 – not now but back then. 214 million years ago. The magic gas strikes again – see https://phys.org/news/2021-02-co2-dip-dinosaurs-south-america.html … which seems to be another case of geochronology causing problems and confusion. A PNAS study has been looking at the speed of dinosaur migrations in the Jurassic. TGhe sauropodomorphs were a group of long necked dinosaurs that are thought to have first appeared in South America around 230 million years ago. TYhe problem they have found for themselves is that rocks in Greenland don't show any sauropodomorphs before 214 million years ago. Why did it take such a long time to reach the top of North America? I don't suppose many people will show a lot of interest but it does illustrate a self made problem by the assumption the rocks are dated correctly. The mystery is further compounded as at the time Pangea was still mostly in existence. A quick trek up north would not have taken more than a few years – assuming there was plenty of food on the way. These were big guys. Why did it take 15 million years to get there? Not exactly the most important question one might ask but nevertheless one that seems to have required an explanation. They came up with the idea there was a dip in co2 and the sauropodomorphs were restricted from spreading as the tropics were cooler and presumably, lacking in the necessary vitamins to keep the big guys walking. In other words, were the tropics too cold. If so one might ask why it was lush in Greenland.
At https://phys.org/news/2021-02-comet-asteroid-dinosaurs.html …. this is about getting it all into proportion. Having accepted that a comet struck Chicxulub to kill off the dinosaurs the researchers decided to find out how it got here. Where did it come from? A bit of mulling and hey presto, it was diverted by Jupiter, as in a sling shot, hitting the earth instead of grazing the Sun, as most comets do.