Mosasaurs, Ichthyosaurs, and Plesiosaurs, oh my! These fierce marine reptiles ruled the oceans while T. rex was walking the land. What were these ancient reptiles doing in the middle of South Dakota 70 million years ago? Discover the answer with Danielle Serratos, Assistant Director of the Museum of Geology at the South Dakota School of Mines and Technology. Homestake Adams Research and Cultural Center; 12:00 p.m.; admission by donation.