Placement of terrestrial formations in the late cretaceous of North America as been constantly evolving and in October 2016 Denver Fowler a Paleontologist at the Museum of the Rockies published a very extensive paper on the subject and updated most units.   This is very important when it comes to understanding dinosaur evolution and aids in describing species. This paper is in the process of going through peer review so is subject to change.   Fowler DW. (2016) A new correlation of the