Jurassic
The Jura is in the Earth's history, the average chronostratigraphic system ( or period in geochronology ) of the Mesozoic. The Jura began about 201.3 million years ago and ended about 145 million years ago. He thus took about 56.3 million years. The Jurassic is overlain by the Triassic below and of the Cretaceous.
History and naming
The name " Jura " was introduced in 1795 by Alexander von Humboldt for rock layers in the Jura Mountains in the scientific literature and in 1829 expanded by Alexandre Brongniart on the current system name. The Jura mountains consist mainly of deposits ( sediments ) that have been deposited during the system of the Jura on the edge of the former Tethys Sea.
Definition and GSSP
The beginning of the Jura is defined by the first appearance of the ammonite spelae Type Psiloceras. A final determination of the GSSP (roughly equivalent to a type profile and a type locality ) took place in 2010 at the Kuhjoch in the Karwendel mountains in Tirol near the border with Bavaria. The upper limit of the Jurassic and the lower limit of the Cretaceous (and thus the Berriasian stage) has not yet conclusively defined. It is expected to be placed in the vicinity of the Erstauftretens the ammonite species Berriasella jacobi.
Subdivision of the Jura
The Jurassic system is - as seen in the info box - divided into three series and a total of eleven stages.
The terms Jura Black, Brown and White Jura Jura or the Quenstedtsche breakdown in Lias, Dogger and Malm should no longer be used as names for the chronostratigraphic series of Jura. However, they are used as lithostratigraphic units in southern Germany Jura ( Jura Black, Brown and White Jura Jura ) or the North German Jurassic ( Lias, Dogger, Malm; provisional designations ). The boundaries of these units are purely lithostratigraphically, that is, only by changing to the rock characteristics defined. They therefore correspond only approximately to the chronostratigraphic units, since the lithostratigraphic boundaries do not coincide exactly with the system and series limits.
Most important index fossils in the Jurassic are the ammonites. These exclusively marine occurring distant relatives of today's squid were almost extinct at the end of the Triassic. Already in the Hettangian developed again a significant number of new genera, so that they are among the most common invertebrates that time. They can be found for example in southern Germany in the Posidonia shale and limestone beds in the Swabian Alb, Franconian Alb, or in the Alps together with the squid to the alternate end belemnites.
Paleogeography
During the early Jurassic of the supercontinent Pangea broke up further, this process had already indicated in the Upper Triassic to the formation of grave systems. The fragments formed North America, Eurasia and the southern Gondwana supercontinent. The early Atlantic and the Tethys Ocean were still narrow. In the late Jurassic and Gondwana began to break down.
Climate
The climate in the Jura was warm, traces of large domestic Seiss Childe were not found. As in the Triassic, but was also the Jura no fixed land near the geographic poles.
Development of the fauna
The law states the first heyday of the dinosaurs dar. In Central Europe footprints ( Barkhausen, Münchehagen ) and skeletal remains of dinosaurs from the Jurassic period ( Ohmdenosaurus, Compsognathus ) were discovered. The only big cats Compsognathus of Jachenhausen at Ried castle was long regarded as the smallest dinosaur.
The " first bird " Archaeopteryx was in rock strata of the Upper Jurassic ( Malm ) found so far exclusively in the Franconian Alb, especially in Solnhofen and Eichstätt.
From the Lower Jurassic of China also dates the discovery of a mammalian fossils, Hadrocodium wui, which is the oldest mammal in the strict sense. Recent finds from the Middle Jurassic in northeastern China Jiulongshan Mountains ( Inner Mongolia Ningcheng Province, Daohugou ) have changed the previous ideas about the world of the Mesozoic mammal sustainable. The genus Castorocauda lutrasimilis ( Docodonta ) that lived in the Middle Jurassic period 164 million years ago, resembled a beaver and already shows the evolution of mammals.
Famous " fossil Buildings" from the Jurassic of Germany are the Stotzen sponge reefs of the Swabian Alb. Reef formation on a smaller scale but also existed in northern Germany.
Development of Flora
The flora was dominated by gymnosperms ( including conifers such as pines and redwoods, but also Ginkgo trees and cycads ). The law is also known as the Age of Cycads ( cycads ), as these were very common. The understory of the forests were ferns and horsetails.
The Jurassic Period in Central Europe
At the beginning of the Jurassic sea, coming from the north transgredierte, initially in a relatively narrow area north and west of Germany to southern Germany. In East Germany and East Germany were sedimented continental deposits. In the Middle Jurassic, the sea stretched then further to the east. Almost the entire eastern platform was flooded. However, large parts of Scandinavia and parts of Bohemia and the Rhine island remained mainland during almost the entire Jura. Bohemian island and Rheinische mass have been during a regression in the upper Middle Jurassic to an island, separating North German and South German law. At the end of Jura Southern silted largely while in Northern Germany ruled on marine or brackish-water depositional environments.
Fossil sites
A well-known archaeological site for fossils of the Lower Jurassic Posidonia shale from the lineup (eg, ichthyosaurs, plesiosaurs, crocodiles, fish, crinoids, ammonites) is wood grubs in Kirchheim, at the foot of the Swabian Alb. The resident Urwelt Museum Hauff has worldwide recognition.
Jurassic Park
The English name for the Jurassic - Jurassic - made famous by the movie Jurassic Park and its successor the general public. However, many of the depicted in the movie dinosaurs, including Tyrannosaurus rex and Velociraptor, from the Cretaceous period come.