Dinosaur

Dinosaur is a group of reptile-like vertebrates whose name comes from the Greek words deinos, meaning terrible, and sauros, meaning lizard. Dinosaurs are classified as members of the clade Dinosauria, which first appeared in the fossil record during the Triassic period, about 230 to 245 million years ago, and dominated many ecosystems for more than 160 million years.

Dinosaurs occupied a wide range of ecological roles, from top carnivores to giant long-necked herbivores and smaller omnivores. They exhibited a variety of body shapes and sizes, with some lineages evolving upright stances and specialized limb structures. Modern evidence shows that many theropod dinosaurs had feathers, and some non-avian groups retained insulating or display feathers or proto-feathers. The fossil record documents growth from hatchlings to adults and reveals diverse reproductive strategies, including egg laying and nesting behaviors.

Taxonomically, dinosaurs are divided into two major clades: Saurischia (lizard-hipped) and Ornithischia (bird-hipped). Saurischia includes theropods, which leads to birds, and sauropodomorphs, the long-necked giants. Ornithischia encompasses several herbivorous groups such as hadrosaurs, ceratopsians, and stegosaurs. Birds are considered the only surviving dinosaurs, having evolved from small theropods in the Mesozoic and surviving the mass extinction event at the end of the Cretaceous.

The non-avian dinosaurs became extinct about 66 million years ago, likely due to a combination of a large asteroid impact and volcanic activity. The study of dinosaurs has significantly influenced paleontology, evolutionary biology, and our understanding of vertebrate life’s history.