Introduction to the End-Cretaceous Cataclysm Approximately 66 million years ago, the Mesozoic Era was brought to an abrupt and violent close by a mass extinction event that eliminated roughly three-quarters of all plant and animal species on Earth.1 This event resulted in the extinction of all non-avian dinosaurs, pterosaurs, ammonites, rudists, and numerous marine reptiles, fundamentally altering the trajectory of biological evolution and inaugurating the Cenozoic Era, durin