Many explanations have been offered for the worldwide extinction of the dinosaurs at the end of the Mesozoic after 160 million years of existence. The most popular theory is that one or more asteroids or comets hit the earth, lifting massive amounts of debris and sulfur in the air and blocking the sunlight from reaching the earth's surface. The 1991 discovery of the Chicxulub crater on the Yucatán peninsula in Mexico lent support to this idea. The second currently popular theory is that the extinctions followed the huge volcanic eruptions that created the lava flows of the Deccan Traps in what is now India. (See mass extinction for more information.) No theory perfectly describes why dinosaurs, pterosaurs, and many marine organisms were affected by the extinction, when many mammals and other animals (e.g., turtles and crocodiles) survived. The extinction of the dinosaurs led to the geologically rapid evolution of mammals from a group of relatively small creatures to a diverse one that included many megafauna.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.