Triassic vertebrates during this time. A specialized subgroup of archosaurs, called dinosaurs, first appeared in the Late Triassic but did not become dominant until the succeeding Jurassic Period. The first true mammals, themselves a specialized subgroup of therapsids, also evolved during this period, as well as the first flying vertebrates, the pterosaurs, who, like the dinosaurs, were a specialized subgroup of archosaurs. The vast supercontinent of Pangaea existed until the mid-Triassic, after which it began to gradually rift into two separate landmasses, Laurasia to the north and Gondwana to the south. The global climate during the Triassic was mostly hot and
Geology of the North Sea zone. The Triassic saw active crustal stretching via the rifting process, lower sea levels and volcanic activity. As the Jurassic (200–145 Ma) started, Pangaea began to break up into two continents, Gondwana and Laurasia. At this time sea levels rose. The burial of algae and bacteria below the mud of the sea floor during this time resulted in the formation of North Sea oil and natural gas, much of it trapped in overlying sandstone by deposits formed as the seas fell to form the swamps and salty lakes and lagoons that were home to dinosaurs. Volcanism and a rift system