Encyclopedia > Jurassic

  Article Content

Jurassic

The Jurassic is a Geologic period that extends from about 135 to 195 million Years before the present. 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 5-10 million years. The Jurassic was named by Alexandre Brongniart for extensive marine limestone exposures in the Jura Mountains in the region where Germany, France and Switzerland meet. The Jurassic follows the Triassic and is followed by the Cretaceous. The start of the Jurassic is marked by a major extinction event.

The Jurassic is usually broken into Lower, Middle, and Upper subdivisions. The Faunal stages from youngest to oldest are:

 Tithonian/Volgian/Portlandian (Malm/Morrison/Upper Jurassic)
 Kimmeridge (Malm/Morrison/Upper Jurassic)
 Oxfordian (Malm/Morrison/Upper Jurassic)
 Callovian/Druess (Dogger/Middle Jurassic)
 Batonian (Dogger/Middle Jurassic)
 Bajocian (Dogger/Middle Jurassic)
 Aalenian (Dogger/Middle Jurassic)
 Toarcian (Lias/Lower Jurassic)
 Pliensbachian (Lias/Lower Jurassic)
 Sinemurian (Lias/Lower Jurassic)
 Hettangian (Lias/Lower Jurassic)

The Jurassic is the middle Era of the Mesozoic Era -- the Age of Dinosaurs.

During the Early Jurassic, the supercontinent of Pangea broke up into North America, Eurasia and Gondwanaland. But the early Atlantic and Tethyan[?] seas were relatively narrow. In the late Jurassic, the Southern Continent -- Gondwanaland started to break up. Climates were warm with no evidence of glaciation. As in the Triassic, there was apparently no land near either pole. Jurassic marine deposits are well exposed in Western Europe. Marine beds are found along the West Coast. A shallow sea was present in parts of the northern plains of the United States and Canada. Most Jurassic exposures in North America are continental. Important Jurassic exposures are also found in Russia, India, South America, Japan, and Australasia.

During the Jurassic marine life continued the more or less stable state reached in the Triassic with the "highest" life forms being fish and marine reptiles. Among invertebrates brachiopods and mollusks remained common. Shelled cephalopods in particular were common and diverse. On land, large sophisticated reptiles remained dominant. Angiosperms (flowering plants) started to appear. The first birds may have evolved during the Jurassic.



All Wikipedia text is available under the terms of the GNU Free Documentation License

 
  Search Encyclopedia

Search over one million articles, find something about almost anything!
 
 
  
  Featured Article
History of Florida

... chiefs, promising them lands west of the Mississippi River if they agreed to leave Florida voluntarily. The remaining Seminole prepared for war. White settl ...