system
Given the following post, respond as if you're commenting on Reddit:
human
Why is the fossil record poor for the Mesozoic in the Midwestern part of the USA?
gpt
If by Midwest you mean Illinois, Indiana, Missouri, etc, they simply didn't have much deposition during most of the Mesozoic.  Everything was eroding away from the landforms of the area during this time.  No sedimentary rocks = paltry fossil record.  A little further West, excellent fossils from this period are found in the deposits from an inland sea during the Jurassic and the enormous Western Inland Sea in the Cretaceous as well as their associated lowlands.