The Late Triassic is the third and final epoch of the Triassic Period in the geologic time scale, spanning the time between Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch. The corresponding series of rock beds is known as the Upper Triassic. The Late Triassic is divided into the Carnian, Norian and Rhaetian Ages. Many of the first dinosaurs evolved during the Late Triassic, including Plateosaurus, Coelophysis, and Eoraptor. The Triassic–Jurassic extinction event began during this epoch and is one of the five major mass extinction events of the Earth. Etymology The Triassic was named in 1834 by Friedrich von Alberti, after a succession of three distinct rock layers (Greek meaning 'triad') that are widespread in southern Germany: the lower Buntsandstein (colourful sandstone), the middle Muschelkalk (shell-bearing limestone) and the upper Keuper (coloured clay). The Late Triassic Series corresponds approximately to the middle and upper Keuper. Dating and subdivisions On the geologic time scale, the Late Triassic is usually divided into the Carnian, Norian, and Rhaetian Ages, and the corresponding rocks are referred to as the Carnian, Norian, and Rhaetian Stages. Triassic chronostratigraphy was originally based on ammonite fossils, beginning with the work of Edmund von Mojsisovics in the 1860s. The base of the Late Triassic (which is also the base of the Carnian) is set at the first appearance of an ammonite, Daxatina canadensis. In the 1990s, conodonts became increasingly important in the Triassic timescale, and the base of the Rhaetian is now set at the first appearance of a conodont, Misikella posthernsteini. , the base of the Norian has not yet been established, but will likely be based on conodonts. The late Triassic is also divided into land-vertebrate faunachrons. These are, from oldest to youngest, the Berdyankian, Otischalkian, Adamanian, Revueltian and Apachean. Carnian Age The Carnian is the first age of the Late Triassic, covering the time interval from 237 to 227 million years ago. The earliest true dinosaurs likely appeared during the Carnian and rapidly diversified. They emerged in a world dominated by crurotarsan archosaurs (ancestors of crocodiles), predatory phytosaurs, herbivorous armored aetosaurs, and giant carnivorous rauisuchians, which the dinosaurs gradually began to displace. The emergence of the first dinosaurs came at about the same time as the Carnian pluvial episode, at 234 to 232 Ma. This was a humid interval in the generally