They were not spread across the entire planet, though, far from it. They lived in what is now Western North America and used to be an island continent called La

They were not spread across the entire planet, though, far from it. They lived in what is now Western North America and used to be an island continent called Laramidia[1]. [1] https://en.wikipedia.org/wiki/Laramidia https://en.wikipedia.org/wiki/Laramidia