Jurassic

Jurassic
Name	Mesozoic Epoch: Middle Period
Time start	201.3 million years ago
Time end	145.0 million years ago
Major rock types	Marine limestones, sandstones, shales
Named by	Gideon Mantell
Region	Global

Jurassic

The interval spanning approximately 201.3 to 145.0 million years ago represents a pivotal period in Earth's deep time marked by tectonic reconfiguration, marine transgressions, and the diversification of many clades. Major faunal and floral turnovers during this interval shaped later Mesozoic ecosystems and set the stage for subsequent Cenozoic radiations. Landmark geological formations and iconic fossil assemblages from regions such as Europe, North America, Asia, Africa, and Gondwana-rich basins underpin much of modern paleontological knowledge.

Overview

This period follows the Triassic and precedes the Cretaceous in the Mesozoic, and is subdivided into Early, Middle, and Late epochs that correspond to regional series and chronostratigraphic stages such as the Hettangian, Toarcian, Aalenian, Bajocian, Callovian, Oxfordian, Kimmeridgian, and Tithonian. Biotic recoveries after the end-Triassic perturbation are documented in marine invertebrate groups like ammonite radiations, reef expansions involving scleractinian coral lineages, and diversification among temnospondyli survivors and new clades. Continental ecosystems saw the proliferation of sauropodomorpha and theropod dinosaurs, as well as gymnosperm-dominated floras such as cycadales, ginkgoales, and conifer forests.

Geology and Stratigraphy

Global sea-level highstands and regional regressions produced widespread deposition of marine limestones, siliciclastics, and evaporites preserved in stratigraphic units like the Marl Slate Formation equivalents, the Posidonia Shale, the Solnhofen Limestone, the Morrison Formation, and the Whitby Mudstone Formation. Lithostratigraphic successions are correlated using biostratigraphy based on index fossils such as ammonites, belemnites, and marine foraminifera, as well as magnetostratigraphy and radiometric dating from zircons in volcanic ash layers tied to events recorded in the Central Atlantic Magmatic Province and feedbacks from Large Igneous Province emplacement. Tectonostratigraphic units reflect fragmentation of the supercontinent Pangaea and development of rift basins along emergent margins like the proto-Atlantic.

Paleoclimate and Paleoenvironment

Paleoclimatic reconstructions integrate proxy records from oxygen isotopes in marine carbonates, paleosol geochemistry, and plant cuticle analyses from deposits in the Solnhofen Limestone, Green River Formation equivalents, and Gondwanan basins. The interval exhibits greenhouse tendencies with elevated atmospheric CO2 inferred from stomatal index studies on Ginkgo and Araucaria leaves, punctuated by cooler intervals such as the Early Toarcian oceanic anoxic event recorded in the Posidonia Shale and other European sections. Marine anoxia, shifts in carbonate platforms, and monsoonal patterns linked to the breakup of Pangaea influenced nutrient fluxes and biotic turnover in basins like the Tethys Sea margins and Western Interior Seaway predecessors.

Flora and Fauna

Terrestrial vegetation was dominated by gymnosperm groups including cycadales, ginkgoales, coniferophyta such as Araucariaceae and Podocarpaceae, with understory ferns like Matoniaceae and early fern allies. Early angiosperm-like pollen occurrences are controversial but definitive angiosperm dominance appears later in the Cretaceous. Vertebrate assemblages include abundant sauropods from formations like the Morrison Formation, theropods including dromaeosauridae-grade and basal coelurosaurs, as well as early aves precursors preserved in Lagerstätten such as the Solnhofen Limestone that yielded taxa like Archaeopteryx. Marine ecosystems hosted diverse ichthyosaur and plesiosaur reptiles, teleost and holostean fishes, and cephalopod faunas dominated by ammonite and belemnite taxa.

Biogeography and Plate Tectonics

Rifting of Pangaea produced distinct biogeographic provinces across Laurasia and Gondwana, with emergent seaways such as the expanding Tethys Sea facilitating dispersal and vicariance patterns evident in dinosaur clades between Europe, North America, and Asia. Continental fragmentation led to endemism in basins like the Ischigualasto Basin and Lorraine Basin equivalents; faunal provincialism is recorded in ornithischian and sauropod distributions linked to paleolatitude and climatic belts. Oceanic currents and continental configurations influenced migration corridors reflected in theropod and crocodylomorph occurrences across the Ouachita Mountains-adjacent basins and Eurasian archipelagos.

Major Fossil Sites and Lagerstätten

Exceptional preservation sites include the Solnhofen Limestone (Germany), the Liaoning deposits (China) including the Yixian Formation-equivalent sequences, the Morrison Formation (United States), the Posidonia Shale (Germany), the Kimmeridge Clay Formation (United Kingdom), and Gondwanan localities such as the Los Molles Formation and Ischigualasto Formation-adjacent units. These Lagerstätten have yielded soft-tissue impressions, articulated skeletons, feathered theropods, early birds, and complete marine reptiles that underpin taphonomic, functional, and evolutionary studies conducted by institutions such as the Natural History Museum, London, the American Museum of Natural History, and the Beijing Museum of Natural History.

Research History and Significance

Pioneering work by 19th-century geologists like Gideon Mantell and later syntheses by paleontologists at institutions including the Royal Society and the Geological Society of London established stage schemes and biostratigraphic frameworks. 20th- and 21st-century advances in isotope geochemistry, radiometric dating methods developed in laboratories at UC Berkeley and ETH Zurich, and phylogenetic analyses by researchers affiliated with Smithsonian Institution and Natural History Museum, London have clarified evolutionary patterns, extinction drivers, and paleoecological dynamics. Ongoing fieldwork in regions such as Patagonia, Inner Mongolia, and North Africa continues to refine correlations between tectonics, climate perturbations, and biotic responses across this critical Mesozoic interval.

Category:Mesozoic