Dinosaurs are reptiles(爬行动物) who lived mainly on the land during the Mesozoic era
(中生代). They are often huge. They are meat eaters or plant eaters. But they do not exist any more.

What killed the dinosaurs?
Evidence(证据) shows that a huge meteor(陨石) hit the earth about 65 million years ago. It raised millions of tons of dust into the sky, caused volcanoes to erupt(火山爆发), acid rain(酸雨) and even tsunamis(海啸). Scientists think that all the dinosaurs died because of these changes to the environment.

What does the word "dinosaur" mean and how are dinosaurs named?
Sir Richard Owen coined(造字) the word dinosaur, meaning "fearfully(极) great lizard," in 1842. In Greek, "deinos" means "fearfully great" and "sauros" means "lizard."
There are many different ways to choose a dinosaur name. Sometimes the dinosaur is given a name that describes something unusual about its body, head or feet. Some are named after the location(位置) where they are found. Others are named for their behaviour(行为) or size, and some are named to honour(尊敬) a person. The name has to be approved(批准) by the International Commission on Zoological Nomenclature(国际动物学命名委员会).