Why Did Dinosaur Become Extinct?

About 180 million years ago the reptiles ruled the earth. In fact, there were so many of them and they were so powerful, that this period is known as the Era of Reptiles. The scientific name for this period is Mesozoic Era.
The largest of all the reptiles were the dinosaurs. And the largest dinosaurs were probably the biggest animals that ever walked the earth!
Yet about 60 million years ago the dinosaurs died out because changing conditions made life impossible for them.
The first dinosaurs were probably no bigger than a turkey, and, like a turkey, they walked on their hind legs. In time, some of them grew heavier and longer, and finally became so heavy that their legs would not support them on land. So they had to spend most of their lives in rivers and swamps, where water could keep their huge bodies afloat!
One of these giants was called "Brontosaurus". This dinosaur was 20 to 25 metres long and weighed about 38 tonnes. Other kinds of dinosaurs remained on land. For instance, "the Tyrannosaurus" was a monster about 14 metres long and 6 metres high. The Tyrannosaurus was probably the most ferocious animal that ever lived.
Dinosaurs developed in many different ways, but none of them ever developed a good brain. One reason dinosaurs disappeared may be that they were just not bright enough to know how to survive and escape from all their natural enemies.
Most scientists believe that changes in the earth and in climate killed off the dinosaurs. Swamps dried up, mountains appeared, and certain dinosaurs could not live on dry land. Also, changes in climate produced changes in vegetation, and since many dinosaurs were plant eaters, their food supply disappeared! And finally, as the earth began to have seasons, shifting from hot summers to snowy winters, dinosaurs could not fit themselves to these changes and gradually died out.

Dinosaurs were wiped out by a meteor, it hit in the gulf of mexico(the gulf of mexico is a crater formed by the metor that hit) when it hit the sun was blotted out buy the dust and reptiles like the dinosaurs can live in cold and plus thier food sources died because theres no sun for plants to grow, but the first mamals survived because they were warm blooded and could live out the cold, a few dinosaurs did survive that's why we have reptiles now