Dinosaurs were a diverse group of reptiles that lived on Earth for millions of years, including both herbivores and carnivors. Dinosaurs had a variety of body shapes and sizes, some walked on two legs, others on four, and many had feathers. The earliest known dinosaurs, like Eoraptor, lived in the Late Triassic period. The extinction event that wiped out most dinosaur species is thought to have been caused by an asteroid impact and/or volcanic eruptions. Fossils provide valuable information about dinosaurs, including their size, shape, and diet.