The reason the dinosaurs died out is believed to have happened during The Cretaceous–Paleogene extinction event about 65-66 million years ago. While many theories have been stated, the most credible is one from an asteroid/meteor impact. The force of the impacts was terrible enough, but a dust cloud formation blocked sunlight for years leaving catastrophic consequences for all life when plants and plankton had little sunlight for their photosynthesis. It’s believed about 75% of all species vanished after the event.