This period is part of theMesozoic era. |
Triassic |
Jurassic |
Cretaceous |
The Jurassic is a Geologic period that extends from about 135 to 195 million years before the present. As other 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, is followed by the Cretaceous and constitutes the middle period of the Mesozoic Era -- the Age of Dinosaurs. The start of the Jurassic is marked by the major Triassic-Jurassic extinction event. The Jurassic is usually broken into Lower, Middle, and Upper subdivisions, also known as Lias, Dogger and Malm. The Faunal stages from youngest to oldest are:
- Malm
- Tithonian (141-135 M.y.)
- Kimmeridgean (146-141 M.y.)
- Oxfordian (154-146 M.y.)
- Dogger
- Callovian (160-154 M.y.)
- Batonian (164-160 M.y.)
- Bajocian (170-164 M.y.)
- Aalenian (175-170 M.y.)
- Lias
- Toarcian (184-175 M.y.)
- Pliensbachian (191-184 M.y.)
- Sinemurian (200-191 M.y.)
- Hettangian (203-200 M.y.)
During the Jurassic the "highest" life forms living in the seas were fish and marine reptiles marine. In the invertebrate world several new groups appeared, such as:
- planctonic foraminifera and calpionelids, of great stratigraphic relevance
- rudists, a reef-forming variety of bivalves
- belemnites and
- brachiopods of the terebratulid and rinchonelid groups
See also; Geologic timescale