sentences:  During the Mesozoic and Cenozoic other land animals followed as the dinosaurs disappeared, but much of the physical evidence from this era has been scraped away or buried by recent glaciation.The rock units that remain in Minnesota from this time period are of Cambrian and Ordovician age, from the Mount Simon Sandstone at the bottom of the sequence of sedimentary rocks to the Maquoketa Group at the top.In the Quaternary Period starting about two million years ago, glaciers expanded and retreated across the region.