Dinosaurs are a diverse group of animals of the clade Dinosauria. They first appeared during the Triassic period, approximately 230 million years ago, and became the dominant terrestrial vertebrates for 135 million years, from the beginning of the Jurassic (about 200 million years ago) until the end of the Cretaceous (65.5 million years ago), when theCretaceous–Paleogene extinction event led 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, and consequently they are considered a type of dinosaur in modern classification systems. Some birds survived the extinction event that occurred 65 million years ago, and continue the dinosaur lineage to the present day.
Triassic–Jurassic extinction event (End Triassic): 205 Ma at the Triassic-Jurassic transition. About 23% of all families and 48% of all genera (20% of marine families and 55% of marine genera) went extinct. Most non-dinosaurian archosaurs, most therapsids, and most of the large amphibians were eliminated, leaving dinosaurs with little terrestrial competition. Non-dinosaurian archosaurs continued to dominate aquatic environments, while non-archosaurian diapsidscontinued to dominate marine environments. The Temnospondyl lineage of large amphibians also survived until the Cretaceous in Australia (e.g., Koolasuchus).