Middle Jurassic
 | This articleneeds additional citations forverification.(February 2024) |
| Middle Jurassic | |||||||||
|---|---|---|---|---|---|---|---|---|---|
 Map of the world during the Middle Jurassic[citation needed] | |||||||||
| Chronology | |||||||||
| |||||||||
| Etymology | |||||||||
| Name formality | Formal | ||||||||
| Usage information | |||||||||
| Celestial body | Earth | ||||||||
| Regional usage | Global (ICS) | ||||||||
| Time scale(s) used | ICS Time Scale | ||||||||
| Definition | |||||||||
| Chronological unit | Epoch | ||||||||
| Stratigraphic unit | Series | ||||||||
| Time span formality | Formal | ||||||||
| Lower boundary definition | FADof theAmmonitesLeioceras opalinumandLeioceras lineatum | ||||||||
| Lower boundary GSSP | Fuentelsaz,Spain 41°10′15″N1°50′00″W/ 41.1708°N 1.8333°W | ||||||||
| Lower GSSP ratified | 2000[2] | ||||||||
| Upper boundary definition | Not formally defined | ||||||||
| Upper boundary definition candidates | Horizon of AmmoniteCardioceras redcliffense. | ||||||||
| Upper boundary GSSP candidate section(s) | |||||||||
TheMiddle Jurassicis the secondepochof theJurassicPeriod.It lasted from about 174.1 to 161.5million years ago.Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relatively rare,[3]butgeological formationscontaining land animal fossils include theForest Marble Formationin England, theKilmaluag FormationinScotland,[4]theCalcaire de CaenofFrance,[5]theDaohugou Bedsin China, theItat FormationinRussia,theTiouraren FormationofNiger,[6]and theIsalo III Formationof westernMadagascar.
Paleogeography
[edit]During the Middle Jurassic Epoch,Pangaeabegan to separate intoLaurasiaandGondwana,and theAtlantic Oceanformed. Eastern Laurasia was tectonically active as theCimmerian platecontinued to collide with Laurasia's southern coast, completely closing thePaleo-Tethys Ocean.Asubduction zoneon the coast of western North America continued to create theAncestral Rocky Mountains.Significant subduction zones were active along practically all of the continental edges surrounding Pangea, as well as in southern Tibet, southeastern Europe, and other locations, to allow the formation of fresh seabed in the proto-Atlantic Ocean. Plate tectonic activity in subduction zones caused the construction of north-south mountain ranges such as the Rocky Mountains and the Andes all along the west coast of North, Central, and South America.[citation needed]
Fauna
[edit]The Middle Jurassic is one of the key periods in thehistory of lifeon Earth. Many groups, including dinosaurs andmammals,diversified during this time.[7][8]
Marine life
[edit]During this time,marine life(includingammonitesandbivalves) flourished.Ichthyosaurs,although common, are reduced in diversity; the top marine predators, thepliosaurs,grew to the size ofkiller whalesand larger (e.g.Pliosaurus,Liopleurodon).Plesiosaursbecame common at this time, andmetriorhynchidsfirst appeared. In the Jurassic seas, a wide range of animals swam. Cartilaginous and bony fish were plentiful. Large fish and marine reptiles were plentiful.[citation needed]
Terrestrial life
[edit]Many of the major groups ofdinosaursemerged during the Middle Jurassic, (includingcetiosaurs,brachiosaurs,megalosaursand primitiveornithopods).[7]
Descendants of thetherapsids,thecynodonts,were still flourishing along with the dinosaurs. These included thetritylodontsand mammals. Mammals remained quite small, but were diverse and numerous in faunas from around the world.[9][10]Tritylodonts were larger, and also had an almost global distribution.[11]The first crown-group mammals appeared in the late Early Jurassic. A group of cynodonts, thetrithelodonts,were becoming rare and eventually became extinct at the end of this epoch.[citation needed]
Flora
[edit]Coniferswere dominant in the Middle Jurassic. Otherplants,such asginkgoes,cycads,andfernswere also common.[citation needed]
References
[edit]
- ^"International Chronostratigraphic Chart"(PDF).International Commission on Stratigraphy.
- ^Cresta, S.; Goy, A.; Arias, C.; Barrón, E.; Bernad, J.; Canales, M.; García-Joral, F.; García-Romero, E; Gialanella, P.; Gómez, J.; González, J.; Herrero, C.; Martínez2, G.; Osete, M.; Perilli, N.; Villalaín, J. (September 2001)."The Global Boundary Stratotype Section and Point (GSSP) of the Toarcian-Aalenian Boundary (Lower-Middle Jurassic)"(PDF).Episodes.24(3): 166–175.doi:10.18814/epiiugs/2001/v24i3/003.Retrieved13 December2020.
{{cite journal}}:CS1 maint: numeric names: authors list (link) - ^Clark, James (June 2009)."Evolutionary Transitions Among Dinosaurs: Examples from the Jurassic of China".Evolution: Education and Outreach.2(2): 243–244.doi:10.1007/s12052-009-0137-0.
- ^British Geological Survey. 2011.Stratigraphic framework for the Middle Jurassic strata of Great Britain and the adjoining continental shelf: research report RR/11/06.British Geological Survey, Keyworth, Nottingham.
- ^Allain, Ronan (24 August 2010)."Discovery of megalosaur (Dinosauria, Theropoda) in the middle Bathonian of Normandy (France) and its implications for the phylogeny of basal Tetanurae".Journal of Vertebrate Paleontology.22(3): 548–563.doi:10.1671/0272-4634(2002)022[0548:DOMDTI]2.0.CO;2.S2CID85751613.Retrieved10 April2023.
- ^Rauhut; Lopez-Arbarello (15 January 2009)."Considerations on the age of the Tiouaren Formation (Iullemmeden Basin, Niger, Africa): Implications for Gondwanan Mesozoic terrestrial vertebrate faunas".Palaeogeography, Palaeoclimatology, Palaeoecology.271(3–4): 259–267.Bibcode:2009PPP...271..259R.doi:10.1016/j.palaeo.2008.10.019.Retrieved12 April2023.
- ^abBenson RBJ, Campione NE, Carrano MT, Mannion PD, Sullivan C, Upchurch P, and Evans DC. 2014.Rates of dinosaur body mass evolution indicate 170 million years of sustained ecological innovation on the avian stem lineage.PLoS Biology 12, no. 5: e1001853.
- ^Close, Roger A.; Friedman, Matt; Lloyd, Graeme T.; Benson, Roger B.J. (2015)."Evidence for a mid-Jurassic adaptive radiation in mammals".Current Biology.25(16): 2137–2142.doi:10.1016/j.cub.2015.06.047.PMID26190074.
- ^Kielan-Jaworowska, Z., Cifelli, R.L., and Luo, Z.-X. 2004. Mammals from the age of dinosaurs: origins evolution and structure. 630 pp. Columbia University Press, New York.
- ^Panciroli, E. 2017.The First MammalsArchived2020-08-03 at theWayback MachinePalaeontology Online.
- ^Kemp, T 2005.The Origin and Evolution of Mammals.Oxford University Press.
