Dinosaurs are a diverse group of animals of the clade Dinosauria. They first appeared during the Triassic period, 231.4 million years ago, and were the dominant terrestrial vertebrates for 135 million years, from the beginning of the Jurassic (about 201 million years ago) until the end of the Cretaceous (66 million years ago), when the Cretaceous–Paleogene extinction eventled to the extinction of most dinosaur groups at the close of the Mesozoic Era. The fossil record indicates that birds evolved from
theropod dinosaurs during the Jurassic Period and, consequently, they are considered a subgroup of dinosaurs by many paleontologists. Some birds survived the extinction event that occurred 66 million years ago, and their descendants continue the dinosaur lineage to the present day.[
Dinosaurs had adaptations which helped make them successful. The first known dinosaurs were small predators that walked on two legs. All their descendents had an upright posture, with the legs underneath the body. This transformed their whole life-style. There were other features. Most of the smaller dinosaurs had feathers, and were probably warm-blooded. This would make them active, with a higher metabolism than modern reptiles. Social interaction, with living in herds and co-operation seems very likely for some types.
The first dinosaur fossils were found in the early 19th century. They are major attractions at museums around the world. Dinosaurs also became part of popular culture. There have been many best-selling books and movies. New discoveries are widely covered in the media.