The KT Event marks the end of the Cretaceous Period. Its is the mass extinction of nearly 70% of marine animals and 15% of landforms. Its also destroyed most vegetation. All animals over 50 pounds were wiped out, which included most dinosaurs. The only descendents of dinosaurs are modern day birds. he Ammonites, Belemnites, Icthyosaurs, Plesiosaurs, and Mosasaurs would become extinct forever.