K/T extinction event

The Cretaceous–Tertiary extinction event, now called the Cretaceous–Palaeogene extinction event, was about 65.5 million years ago. It may be called the K/T extinction event or K/Pg event for short. This is the famous event which killed most of the dinosaurs at the end of the Cretaceous period.
It was a large-scale mass extinction of animal and plant species. The event marks the end of the Mesozoic era and the beginning of the Cainozoic era.
Effects.
Dinosaur fossils are only found below the K/T boundary. This shows they became extinct before, or during the event. Mosasaurs, plesiosaurs, pterosaurs and many species of plants and invertebrates also became extinct.
Mammalian and bird groups got through the event with some extinctions. Those that survived became widespread and varied during their later evolutionary radiation.
Causes.
The K/T extinctions were so sudden and far-reaching that they must have been caused by something sudden and powerful. One or more massive asteroid or meteor impacts, and increased volcanic activity have been suggested.
How quickly animals died out around the world is an important clue. Patterns in rocks also suggest causes. There are several impact craters and massive volcanic activity in the Deccan Traps in India dated to about the same time as the extinctions. Those impacts and volcanoes would have reduced sunlight and hindered photosynthesis, disrupting Earth's ecology.
The best supported theory is that the meteorite strike in the Yucatan was the main cause of the extinction at the end of the Mesozoic era.
Craters.
There were several impact events across the Cretaceous/Tertiary boundary, such as the Chicxulub crater in Mexico, Boltysh crater in Ukraine, Silverpit crater in North Sea, and the Shiva crater offshore western India. 
The Shiva crater is a sea floor structure under the continental shelf in the Indian Ocean, west of Mumbai, India. It was named by paleontologist Sankar Chatterjee after Shiva, the Hindu god of destruction and renewal.