The extinction of non-avian dinosaurs except birds at the end of the Cretaceous has intrigued paleontologists for more than a century. One theory is that an asteroid impact 65 million years ago off the coast of Mexico generated massive tsunamis, with impact debris cutting off sunlight for months, stopping photosynthesis and causing freezing temperatures. Chemical reactions in the atmosphere caused acid rain and long-term global warming, all of which extinguished non-avian dinosaurs. However, at the same time, massive lava flows erupted across what is now southwest India. The eruptions probably caused many of the same effects as the asteroid impact. Although most scientists believe that the impact was the final blow for non-avian dinosaurs, both events could well have played a role. Created by American Museum of Natural History.

Were dinosaurs already undergoing a long-term decline before an asteroid hit at the end of the Cretaceous about 65.5 million years ago? A study led by Museum scientists gives a multifaceted answer. The findings, published in May, 2012, in the journal Nature Communications, suggest that in general, large-bodied, ƒ??bulk-feedingƒ?� herbivores were declining during the last 12 million years of the Cretaceous Period. But carnivorous dinosaurs and mid-sized herbivores were not. Created by American Museum of Natural History.