Many dinosaur species became extinct during their prolonged 165-million-year-long evolution during the Mesozoic Era. Iconic dinosaurs like Triceratops and Stegosaurus became extinct millions of years apart. There are many hypotheses about what may have caused the large dinosaurs — together with many other species — to go extinct at the end of the Mesozoic Era. The last species of large Mesozoic dinosaurs became extinct during a dramatic event at the end of the era that caused the disappearance of nearly fifty percent of all life at the time. A large metiorite impacted the eath 65.5 million years ago creating devastating environmental disruptions that most likely drove the last remaining dinosaurs to extinction. However, dinosaur diversity had been diminishing for millions of years before the meteorite, so other factors that disrupted their environment and habitat probably contributed to their eventual extinction.