Question about Hell Creek and the Western Interior Seaway

[crankydinosaur]

Okay I'm confused. If the Hell Creek was parts of Montana, North / South Dakota and Wyoming but the Western Interior Seaway covered those areas.... where did the fauna live. I know it was a shallow sea but..... I'm confused.

[SBell]

They were different times in the late Cretaceous--the WIS stretched from the Yukon south at some points, but by the latest Cretaceous had receded such that areas like Montana and Saskatchewan were now (more or less) on the western shore of the seaway, while the seaway itself was further east and/or south.