It is a common misconception that a giant meteor or comet-tail caused the Ice Age and the ensuing demise of all prehistoric life.
It was, in fact the appearance of a new type of dinosaur called the Chucknorrisaurus that suddenly appeared and wiped out all animal life. Scientists in Asia discovered a single fossil surrounded by a wealth of other skeletal remains, each with their craniums smashed to dust. The theory is that the dreaded Chucknorrisaurus was enjoying a meal, when it was interrupted by another dinosaur...mistake #1. Chucknorrisaurus was so angered by the intrusion that it snapped and started delivering roundhouse kicks to everything in sight. Other dinosaurs heard the commotion and came to investigate....mistake#2. The ensuing brawl ended up with every dinosaur dying in a hail of kicks, and their final breaths raised the CO2 levels to the point of creating a greenhouse effect and starting the Ice Age. This ice age only served to preserve the Chucknorrisaurus's DNA which combined with Simian} DNA and resulted in the creation of man.