arid Triassic. It was marked by high extinction rates in marine organisms, but may have opened niches for the radiation of the dinosaurs. Norian Age The Norian is the second age of the Late Triassic, covering the time interval from about 227 to 208.5 million years ago. During this age, herbiverous sauropodomorphs diversified and began to displace the large herbivorous therapsids, perhaps because they were better able to adapt to the increasingly arid climate. However crurotarsans continued to occupy more ecological niches than dinosaurs. In the oceans, neopterygian fish proliferated at the expense of ceratitid ammonites. The Manicouagan impact event occurred 214 million years ago. However, no extinction event is associated with this impact. Rhaetian Age The Rhaetian Age was the final age of the Late Triassic, following the Norian Age, and it included the last major disruption of life until the end-Cretaceous mass extinction. This age of the Triassic is known for its extinction of marine reptiles, such as nothosaurs and shastasaurs with the ichthyosaurs, similar to today's dolphin. This age was concluded with the disappearance of many species that removed types of plankton from the ocean, as well as some organisms known for reef-building, and the pelagic conodonts. In addition to these species that became extinct, the straight-shelled nautiloids, placodonts, bivalves, and many types of reptiles did not survive through this age. Climate and environment during the Triassic Period During the beginning of the Triassic Period, the earth consisted of a giant landmass known as Pangea, which covered about a quarter of earth's surface. Towards the end of the period, continental drift occurred which separated Pangea. At this time, polar ice was not present because of the large differences between the equator and the poles. A single, large landmass similar to Pangea would be expected to have extreme seasons; however, evidence offers contradictions. Evidence suggests that there is arid climate as well as proof of strong precipitation. The planet's atmosphere and temperature components were mainly warm and dry, with other seasonal changes in certain ranges. The Middle Triassic was known to have consistent intervals of high levels of humidity. The circulation and movement of these humidity patterns, geographically, are not known however. The major Carnian Pluvial Event stands as one focus point of many studies. Different hypotheses of the events occurrence include eruptions, monsoonal effects, and changes caused by plate tectonics. Continental deposits also support certain ideas relative