Jurassic
The Jurassic (/dʒʊˈræsɪk/ juurr-ASS-ik[2]) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period 201.4 million years ago (Mya) to the beginning of the Cretaceous Period, approximately 145 Mya. The Jurassic constitutes the middle period of the Mesozoic Era and is named after the Jura Mountains, where limestone strata from the period were first identified.
Jurassic
Formal
Global (ICS)
ICS Time Scale
Formal
First appearance of the ammonite Psiloceras spelae tirolicum.
Kuhjoch section, Karwendel mountains, Northern Calcareous Alps, Austria
47°29′02″N 11°31′50″E / 47.4839°N 11.5306°E
2010
Not formally defined
- Magnetic—base of Chron M18r
- Base of Calpionellid zone B
- FAD of ammonite Berriasella jacobi
None
The start of the Jurassic was marked by the major Triassic–Jurassic extinction event, associated with the eruption of the Central Atlantic Magmatic Province (CAMP). The beginning of the Toarcian Stage started around 183 million years ago and is marked by the Toarcian Oceanic Anoxic Event, a global episode of oceanic anoxia, ocean acidification, and elevated global temperatures associated with extinctions, likely caused by the eruption of the Karoo-Ferrar large igneous provinces. The end of the Jurassic, however, has no clear, definitive boundary with the Cretaceous and is the only boundary between geological periods to remain formally undefined.
By the beginning of the Jurassic, the supercontinent Pangaea had begun rifting into two landmasses: Laurasia to the north and Gondwana to the south. The climate of the Jurassic was warmer than the present, and there were no ice caps. Forests grew close to the poles, with large arid expanses in the lower latitudes.
On land, the fauna transitioned from the Triassic fauna, dominated jointly by dinosauromorph and pseudosuchian archosaurs, to one dominated by dinosaurs alone. The first birds appeared during the Jurassic, evolving from a branch of theropod dinosaurs. Other major events include the appearance of the earliest crabs and modern lizards, and the diversification of early mammals. Crocodylomorphs made the transition from a terrestrial to an aquatic life. The oceans were inhabited by marine reptiles such as ichthyosaurs and plesiosaurs, while pterosaurs were the dominant flying vertebrates. Modern sharks and rays first appeared and diversified during the period. The flora was dominated by ferns and gymnosperms, including conifers, of which many modern groups made their first appearance during the period, as well as other groups the extinct Bennettitales.
Flora[edit]
End-Triassic extinction[edit]
There is no evidence of a mass extinction of plants at the Triassic–Jurassic boundary.[83] At the Triassic–Jurassic boundary in Greenland, the sporomorph (pollen and spores) record suggests a complete floral turnover.[84] An analysis of macrofossil floral communities in Europe suggests that changes were mainly due to local ecological succession.[85] At the end of the Triassic, the Peltaspermaceae became extinct in most parts of the world, with Lepidopteris persisting into the Early Jurassic in Patagonia.[86] Dicroidium, a corystosperm seed fern that was a dominant part of Gondwanan floral communities during the Triassic, also declined at the Triassic–Jurassic boundary, surviving as a relict in Antarctica into the Early Jurassic.[87]
