Cretaceous–Tertiary extinction event

The Cretaceous–Tertiary event was the catastrophic mass extinction of extant animal species in a comparatively short period of time, approximately 65.5 million years ago. It is widely known as the K–T extinction event, and its geological signature, usually a thin band dated to that time and found in various parts of the world, is called the K–T boundary. (K is the traditional abbreviation for the Cretaceous Period, to avoid confusion with the Carboniferous Period, denoted C, and the Cambrian Period, denoted C.)

Most, if not all, non-avian dinosaurs became extinct during or possibly a few years after the event. Non-avian dinosaur fossils are not found later than the K–T boundary, except for a few controversial exceptions. Many other groups of animals and plants, including mosasaurs, plesiosaurs, pterosaurs, and some invertebrates, also became extinct at the K–T boundary. The event marks the end of the Mesozoic Era, and the beginning of the Cenozoic Era.

Most of the extinctions occurred in a relatively short time because extensive weather changes reduced photosynthesis, thereby decreasing the amount of plant material available to herbivorous animals. This change in food supply caused a massive disruption in Earth's ecology.

The cause of the event has centered on an large impact event, increased volcanic activity or other causes (in combination or separately). Several impact craters and massive volcanic activity in the Deccan traps have all been dated to the approximate time of the extinction event.