Geologic Periods

                                                                                     Triassic Period

-The Triassic is a geologic period and system that extends from about 250 to 200 Mya (million years ago). As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events. The extinction event that closed the Triassic Period has recently been more accurately dated, but as with most older geologic periods, the rock beds that define the start and end are well identified, but the exact dates of the start and end of the period are uncertain by a few million years. The Triassic period ended with a mass extinction, which was particularly severe in the oceans; the conodonts disappeared, and all the marine reptiles except ichthyosaurs and plesiosaurs. Invertebrates like brachiopods, gastropods, and molluscs were severely affected. In the oceans, 22% of marine families and possibly about half of marine genera went missing according to University of Chicago paleontologist Jack Sepkoski. This was the era of the first dinosaurs and mammals.

 

                 Cretaceous Period

-The end of the Cretaceous defines the boundary between the Mesozoic and Cenozoic eras. The Cretaceous was a period with a relatively warm climate and high eustatic sea level. The oceans and seas were populated with now extinct marine reptiles, ammonites and rudists; and the land by dinosaurs. At the same time, new groups of mammals and birds as well as flowering plants appeared. The Cretaceous ended with one of the largest mass extinctions in Earth history, the K–T extinction, when many species, including non-avian dinosaurs, pterosaurs, and large marine reptiles, disappeared.

 

 

 

 

 

 

 

                                                                                       Jurassic Period

-Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by the major Triassic–Jurassic extinction event. However, the end of the Jurassic period did not witness any major extinction event. The start and end of the period are defined by carefully selected locations; the uncertainty in dating arises from trying to date these horizons. During the Jurassic period, the primary vertebrates living in the seas were fish and marine reptiles. The latter include ichthyosaurs who were at the peak of their diversity, plesiosaurs, pliosaurs, and marine crocodiles of the families Teleosauridae and Metriorhynchidae. During this period, flowers arose and birds started roaming the Earth.