Excellent question Megan.
So, there are a couple of reasons why we think dinosaurs went extinct.
1. A giant object (meteor or asteroid) could have hit earth, killing a lot of animals with the shock and then blocking out the sun, sokilling most of the food for whoever survived.
2. It could have been a much slower change in the climate of the earth, maybe from a volcanic eruption here on earth, which changed the atmosphere so much that most of the dinosaurs died.
These kind of ‘Mass Extinction Events’ have happened a few times in the history of the earth. Some are because of these huge things, but others are much slower and are caused by changes to the earths orbit or something else we’re not quite sure of.
However, not all dinosaurs went extinct! All birds came from dinosaurs originally. And did you know that crocodiles and alligators were probably around at the same time as dinosaurs! So were turtles! Though not of the same group as dinosaurs biologically, this kinda makes them dinosaurs right?!
Yet another great question from you Megan! Excellent 🙂 We don’t really know what caused dinosaurs to all die off, but there’s a few theories about this. It might have been a big meteorite that crashed into Earth and changed the climatic conditions so dramatically that dinosaurs could not survive. Perhaps ash and gas spewing from volcanoes suffocated many of the dinosaurs, diseases wiped out entire populations of dinosaurs, and food chain imbalances might have lead to the starvation of dinosaurs. Hope that helped 🙂