Jurrasic
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Jurrasic
The Jurrasic Period is a major unit of the geologic timescale that extends from about 199.6 ± 0.6 Mya (million years ago) to 145.4 ± 4.0 Mya, the end of the Triassic to the beginning of the Cretaceous. As with other geologic periods, the rock beds that define the start and end of the period are well identified but the exact dates are uncertain by 5 - 10 million years. The Jurassic constitutes the middle period of the Mesozoic era, also known as the "Age of Dinosaurs". The start of the period is marked by the major Triassic-Jurassic extinction event.
The Jurassic was named by Alexandre Brogniart for the extensive marine limestone exposures of the Jura Mountains, in the region where Germany, France and Switzerland meet.
The Jurassic period of time is usually broken into Early, Middle, and Late subdivisions, also known as Lias, Dogger and Malm. The corresponding terms for the rocks are Lower, Middle, and Upper Jurassic.
On land, large archosaurian reptiles remained dominant. The Jurassic was the golden age of the great sauropods—Camarasaurus, Diplodocus, Brachiosaurus, and many others—that roamed the land late in the period; their mainstays were either the prairies of ferns, palm-like cycads and bennettitales, or the higher coniferous growth, according to their adaptations. They were preyed upon by large theropods (Ceratosaurs, Megalosaurs, and Allosaurs). All these belong to the 'lizard hipped' or saurischian branch of the dinosaurs.
During the Late Jurassic, the first birds evolved from small coelurosaur dinosaurs. Ornithischian dinosaurs were less predominant than saurischian dinosaurs, although some like stegosaurs and small ornithopods played important roles as small and medium-to-large (but not sauropod-sized) herbivores. In the air, pterosaurs were common; they ruled the skies, filling many ecological roles now taken by birds.
http://www.palaeos.com/Mesozoic/Jurassic/Jurassic.htm