By the beginning of the Jurassic, the supercontinentPangaea 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 expanses of desert in the lower latitudes.
During a tour of the region in 1795, German naturalist Alexander von Humboldt recognized carbonate deposits within the Jura Mountains as geologically distinct from the Triassic aged Muschelkalk of Southern Germany, though he erroneously concluded they were older. He then named them Jura-Kalkstein ('Jura limestone') in 1799.
Thirty years later, in 1829, the French naturalist Alexandre Brongniart published a book entitled Description of the Terrains that Constitute the Crust of the Earth or Essay on the Structure of the Known Lands of the Earth. In this book, Brongniart used the phrase terrains jurassiques when correlating the "Jura-Kalkstein" of Humboldt with similarly aged oolitic limestones in Britain, thus coining and publishing the term "Jurassic".
French palaeontologistAlcide d'Orbigny in papers between 1842 and 1852 divided the Jurassic into ten stages based on ammonite and other fossil assemblages in England and France, of which seven are still used even though none retain the original definition. German geologist and palaeontologist Friedrich August von Quenstedt in 1858 divided the three series of von Buch in the Swabian Jura into six subdivisions defined by ammonites and other fossils.
German palaeontologist Albert Oppel in his studies between 1856 and 1858 altered d'Orbigny's original scheme and further subdivided the stages into biostratigraphic zones, based primarily on ammonites. Most of the modern stages of the Jurassic were formalized at the Colloque du Jurassique à Luxembourg in 1962.
Middle to Upper Jurassic strata, San Rafael Swell, Emery County, Utah.
Middle to Upper Jurassic strata, Island Park, Dinosaur National Monument, Uintah County, Utah.
Jurassic stratigraphy is primarily based on the use of ammonites as index fossils. The first appearance datum of specific ammonite taxa is used to mark the beginnings of stages, as well as smaller timespans within stages, referred to as "ammonite zones"; these, in turn, are also sometimes subdivided further into subzones. Global stratigraphy is based on standard European ammonite zones, with other regions being calibrated to the European successions.
Base Aalenian GSSP at Fuentelsaz
The oldest part of the Jurassic period has historically been referred to as the Lias or Liassic, roughly equivalent in extent to the Early Jurassic, but also including part of the preceding Rhaetian. The Hettangian stage was named by Swiss palaeontologist Eugène Renevier in 1864 after Hettange-Grande in north-eastern France.
The GSSP for the base of the Hettangian is located at the Kuhjoch Pass, Karwendel Mountains, Northern Calcareous Alps, Austria; it was ratified in 2010. The beginning of the Hettangian, and thus the Jurassic as a whole, is marked by the first appearance of the ammonite Psiloceras spelae tirolicum in the Kendlbach Formation exposed at Kuhjoch. The base of the Jurassic was previously defined as the first appearance of Psiloceras planorbis by Albert Oppel in 1856-58, but this was changed as the appearance was seen as too localised an event for an international boundary.
The Sinemurian stage was first defined and introduced into scientific literature by Alcide d'Orbigny in 1842. It takes its name from the French town of Semur-en-Auxois, near Dijon. The original definition of Sinemurian included what is now the Hettangian. The GSSP of the Sinemurian is located at a cliff face north of the hamlet of East Quantoxhead, 6 kilometres east of Watchet, Somerset, England, within the Blue Lias, and was ratified in 2000. The beginning of the Sinemurian is defined by the first appearance of the ammonite Vermiceras quantoxense.
The village Thouars (Latin: Toarcium), just south of Saumur in the Loire Valley of France, lends its name to the Toarcian stage. The Toarcian was named by Alcide d'Orbigny in 1842, with the original locality being Vrines quarry around 2 km northwest of Thouars. The GSSP for the base of the Toarcian is located at Peniche, Portugal, and was ratified in 2014. The boundary is defined by the first appearance of ammonites belonging to the subgenus Dactylioceras(Eodactylites).
The Aalenian is named after the city of Aalen in Germany. The Aalenian was defined by Swiss geologist Karl Mayer-Eymar in 1864. The lower boundary was originally between the dark clays of the Black Jurassic and the overlying clayey sandstone and ferruginous oolite of the Brown Jurassic sequences of southwestern Germany. The GSSP for the base of the Aalenian is located at Fuentelsaz in the Iberian range near Guadalajara, Spain, and was ratified in 2000. The base of the Aalenian is defined by the first appearance of the ammonite Leioceras opalinum.
Alcide d'Orbigny in 1842 named the Bajocian stage after the town of Bayeux (Latin: Bajoce) in Normandy, France. The GSSP for the base of the Bajocian is located in the Murtinheira section at Cabo Mondego, Portugal; it was ratified in 1997. The base of the Bajocian is defined by the first appearance of the ammonite Hyperlioceras mundum.
The Bathonian is named after the city of Bath, England, introduced by Belgian geologist d'Omalius d'Halloy in 1843, after an incomplete section of oolitic limestones in several quarries in the region. The GSSP for the base of the Bathonian is Ravin du Bès, Bas-Auran area, Alpes de Haute Provence, France; it was ratified in 2009. The base of the Bathonian is defined by the first appearance of the ammonite Gonolkites convergens, at the base of the Zigzagiceras zigzag ammonite zone.
The Callovian is derived from the Latinized name of the village of Kellaways in Wiltshire, England, and was named by Alcide d'Orbigny in 1852, originally the base at the contact between the Forest Marble Formation and the Cornbrash Formation. However, this boundary was later found to be within the upper part of the Bathonian. The base of the Callovian does not yet have a certified GSSP. The working definition for the base of the Callovian is the first appearance of ammonites belonging to the genus Kepplerites.
The Oxfordian is named after the city of Oxford in England and was named by Alcide d'Orbigny in 1844 in reference to the Oxford Clay. The base of the Oxfordian lacks a defined GSSP. W. J. Arkell in studies in 1939 and 1946 placed the lower boundary of the Oxfordian as the first appearance of the ammonite Quenstedtoceras mariae (then placed in the genus Vertumniceras). Subsequent proposals have suggested the first appearance of Cardioceras redcliffense as the lower boundary.
Kimmeridge on the coast of Dorset, England, is the origin of the name of the Kimmeridgian. The stage was named by Alcide d'Orbigny in 1842 in reference to the Kimmeridge Clay. The GSSP for the base of the Kimmeridgian is the Flodigarry section at Staffin Bay on the Isle of Skye, Scotland, which was ratified in 2021. The boundary is defined by the first appearance of ammonites marking the boreal Bauhini Zone and the subboreal Baylei Zone.
The Tithonian was introduced in scientific literature by Albert Oppel in 1865. The name Tithonian is unusual in geological stage names because it is derived from Greek mythology rather than a place name. Tithonus was the son of Laomedon of Troy and fell in love with Eos, the Greek goddess of dawn. His name was chosen by Albert Oppel for this stratigraphical stage because the Tithonian finds itself hand in hand with the dawn of the Cretaceous. The base of the Tithonian currently lacks a GSSP. The working definition for the base of the Tithonian is the first appearance of the ammonite genus Gravesia.
The upper boundary of the Jurassic is currently undefined, and the Jurassic-Cretaceous boundary is currently the only system boundary to lack a defined GSSP. Placing a GSSP for this boundary has been difficult because of the strong regionality of most biostratigraphic markers, and lack of any chemostratigraphic events, such as isotope excursions (large sudden changes in ratios of isotopes), that could be used to define or correlate a boundary. Calpionellids, an enigmatic group of planktonicprotists with urn-shaped calcitic tests briefly abundant during the latest Jurassic to earliest Cretaceous, have been suggested to represent the most promising candidates for fixing the Jurassic-Cretaceous boundary In particular, the first appearance Calpionella alpina, co-inciding with the base of the eponymous Alpina subzone, has been proposed as the definition of the base of the Cretaceous. The working definition for the boundary has often been placed as the first appearance of the ammonite Strambergella jacobi, formerly placed in the genus Berriasella, but its use as a stratigraphic indicator has been questioned, as its first appearance does not correlate with that of C. alpina.
Mineral and hydrocarbon deposits
The Kimmeridge Clay and equivalents are the major source rock for the North Sea oil. The Arabian Intrashelf Basin, deposited from the late Middle to Upper Jurassic, is the setting of the world's largest oil reserves, including the Ghawar Field, the world's largest oil field. The Jurassic-aged Sargelu and Naokelekan Formations are major source rocks for oil in Iraq. Over 1500 gigatons of Jurassic coal reserves are found in north-west China, primarily in the Turpan-Hami Basin and the Ordos Basin.
Major impact craters include the Morokweng crater, a 70 km diameter crater buried beneath the Kalahari desert in northern South Africa. The impact is dated to the Jurassic-Cretaceous boundary, around 145 Mya. The Morokweng crater has been suggested to have had a role in the turnover at the Jurassic-Cretaceous transition. Another major impact crater is the Puchezh-Katunki crater, 40-80 kilometres in diameter, buried beneath Nizhny Novgorod Oblast, Russia. The impact has been dated to the Sinemurian, around 192-196 Mya.
During the Jurassic, the North Atlantic Ocean remained relatively narrow, while the South Atlantic did not open until the Cretaceous. The continents were surrounded by Panthalassa, with the Tethys Ocean between Gondwana and Asia. At the end of the Triassic, there was a marine transgression in Europe, flooding most parts of central and western Europe transforming it into an archipelago of islands surrounded by shallow seas. Beginning in the Early Jurassic, the Boreal Ocean was connected to the proto-Atlantic by the "Viking corridor" or Transcontinental Laurasian Seaway, a passage between the Baltic Shield and Greenland several hundred kilometers wide.
Madagascar and Antarctica began to rift away from Africa during the late Early Jurassic in association with the eruption of the Karoo-Ferrar large igneous provinces, opening the western Indian Ocean and beginning the fragmentation of Gondwana. At the beginning of the Jurassic, North and South America remained connected, but by the beginning of the Late Jurassic they had rifted apart to form the Caribbean Seaway, which connected the north Atlantic Ocean with eastern Panthalass. Palaeontological data suggest that the seaway had been open since the Early Jurassic.
Grainstone with calcitic ooids and sparry calcite cement; Carmel Formation, Middle Jurassic, of southern Utah, USA.
The eustatic sea level is estimated to have been close to present levels during the Hettangian and Sinemurian, rising several tens of metres during the late Sinemurian-Pliensbachian before regressing to near present levels by the late Pliensbachian. There seems to have been a gradual rise to a peak of ~75 m above present sea level during the Toarcian. During the latest part of the Toarcian, the sea level again dropped by several tens of metres. It progressively rose from the Aalenian onwards, aside from dips of a few tens of metres in the Bajocian and around the Callovian-Oxfordian boundary, peaking possibly as high as 140 metres above present sea level at the Kimmeridgian-Tithonian boundary. The sea levels falls in the late Tithonian, perhaps to around 100 metres, before rebounding to around 110 metres at the Tithonian-Berriasian boundary.
The sea level within the long-term trends across the Jurassic was cyclical, with 64 fluctuations, 15 of which were over 75 metres. The most noted cyclicity in Jurassic rocks is fourth order, with a periodicity of approximately 410,000 years.
The climate of the Jurassic was generally warmer than that of present, by around 5 °C to 10 °C, with atmospheric carbon dioxide likely four times higher. Forests likely grew near the poles, where they experienced warm summers and cold, sometimes snowy winters; there were unlikely to have been ice sheets given the high summer temperatures that prevented the accumulation of snow, though there may have been mountain glaciers.Dropstones and glendonites in northeastern Siberia during the Early to Middle Jurassic indicate cold winters. The ocean depths were likely 8 °C warmer than present, and coral reefs grew 10° of latitude further north and south. The Intertropical Convergence Zone likely existed over the oceans, resulting in large areas of desert in the lower latitudes.
The beginning of the Jurassic was likely marked by a thermal spike corresponding to the Triassic-Jurassic extinction and eruption of the Central Atlantic magmatic province. The first part of the Jurassic was marked by the Early Jurassic cool interval between 199 and 183 million years ago. This was ended by the spike in global temperatures of around 4-8 °C during the early part of the Toarcian corresponding to the Toarcian Oceanic Anoxic Event and the eruption of the Karoo-Ferrar large igneous provinces in southern Gondwana, with the Toarcian warm interval extending to the end of the stage around 174 million years ago.
During the Toarcian warm interval, ocean surface temperatures likely exceeded 30 °C, and equatorial and subtropical (30°N-30°S) regions are likely to have been extremely arid, with temperatures in the interior of Pangea likely in excess of 40 °C. The Toarcian warm interval is followed by the Middle Jurassic cool interval between 174 and 164 million years ago. This is followed by the Kimmeridgian warm interval between 164 and 150 million years ago. The Pangean interior had less severe seasonal swings than in previous warm periods as the expansion of the Central Atlantic and western Indian Ocean provided new sources of moisture. The end of the Jurassic was marked by the Tithonian-early Barremian cool interval, beginning 150 million years ago and continuing into the Early Cretaceous.
Toarcian Oceanic Anoxic Event
The Toarcian Oceanic Anoxic Event (TOAE) was an episode of widespread oceanic anoxia during the early part of the Toarcian period, c. 183 Mya. It is marked by a globally documented high amplitude negative carbon isotope excursion, as well as the deposition of black shales and the extinction and collapse of carbonate-producing marine organisms.
The TOAE is often attributed to the eruption of the Karoo-Ferrar large igneous provinces and the associated increase of carbon dioxide concentration in the atmosphere, as well as the possible associated release of methane clathrates. This likely accelerated the hydrological cycle and increased silicate weathering. Groups affected include ammonites, ostracods, foraminifera, brachiopods, bivalves and cnidarians, with the last two spire-bearing brachiopod orders, Spiriferinida and Athyridida, becoming extinct. While the event had significant impact on marine invertebrates, it had little effect on marine reptiles. During the TOAE, the Sichuan Basin was transformed into a giant lake, probably three times the size of modern-day Lake Superior, represented by the Da'anzhai Member of the Ziliujing Formation. The lake likely sequestered ~460 gigatons (Gt) of organic carbon and ~1,200 Gt of inorganic carbon during the event. Seawater pH, which had already substantially decreased prior to the event, increased slightly during the early stages of the TOAE, before dropping to its lowest point around the middle of the event. This ocean acidification is what likely caused the collapse of carbonate production.
The end-Jurassic transition was originally considered one of eight mass extinctions, but is now considered to be a complex interval of faunal turnover, with the increase in diversity of some groups and decline in others, though the evidence for this is primarily European, probably controlled by changes in eustatic sea level.
There is no evidence of a mass extinction of plants at the Triassic-Jurassic boundary. At the Triassic-Jurassic boundary in Greenland, the sporomorph (pollen and spores) record suggests a complete floral turnover. An analysis of macrofossil floral communities in Europe suggests that changes were mainly due to local ecological succession. 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.Dicroidium, a 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 Sinemurian.
Conifers formed a dominant component of Jurassic floras. The Late Triassic and Early Jurassic was a major time of diversification of conifers, with most modern conifer groups appearing in the fossil record by the end of the Jurassic, having evolved from voltzialean ancestors.
Araucarian conifers have their first unambiguous records during the Early Jurassic, and ones closely related to the modern genus Araucaria were widespread across both hemispheres by the Middle Jurassic.
Also abundant during the Jurassic is the extinct family Cheirolepidiaceae, often recognised through their highly distinctive Classopolis pollen. Jurassic representatives include the pollen cone Classostrobus and the seed cone Pararaucaria. Araucarian and Cheirolepidiaceae conifers often occur in association.
The oldest definitive record of the cypress family (Cupressaceae) is Austrohamia minuta from the Early Jurassic (Pliensbachian) of Patagonia, known from many parts of the plant. The reproductive structures of Austrohamia have strong similarities to those of the primitive living cypress genera Taiwania and Cunninghamia. By the Middle to Late Jurassic Cupressaceae were abundant in warm temperate-tropical regions of the Northern Hemisphere, most abundantly represented by the genus Elatides.
The oldest record of the pine family (Pinaceae) is the pine coneEathiestrobus, known from the Late Jurassic (Kimmeridgian) of Scotland, which remains the only known fossil of the group before the Cretaceous. Despite being the earliest known member of the Pinaceae, Eathiestrobus appears to be a member of the pinoid clade of the family, suggesting that the initial diversification of Pinaceae occurred earlier than has been found in the fossil record.
During the Early Jurassic, the flora of the mid-latitudes of Eastern Asia were dominated by the extinct deciduous broad leafed conifer Podozamites, which appears to not be closely related to any living family of conifer. Its range extended northwards into polar latitudes of Siberia and then contracted northward in the Middle to Late Jurassic, corresponding to the increasing aridity of the region.
The earliest record of the yew family (Taxaceae) is Palaeotaxus rediviva, from the Hettangian of Sweden, suggested to be closely related to the living Austrotaxus, while Marskea jurassica from the Middle Jurassic of Yorkshire, England and material from the Callovian-Oxfordian Daohugou Bed in China are thought to be closely related to Amentotaxus. The Daohugou material in particular is extremely similar to living Amentotaxus, differing only in having shorter seed-bearing axes.
Podocarpaceae, today largely confined to the Southern Hemisphere, occurred in the Northern Hemisphere during the Jurassic, Examples include Podocarpophyllum from the Early to Middle Jurassic of Central Asia and Siberia,Scarburgia from the Middle Jurassic of Yorkshire, and Harrisiocarpus from the Jurassic of Poland.
Ginkgoales, of which the sole living species is Ginkgo biloba, were more diverse during the Jurassic: they were among the most important components of Eurasian Jurassic floras and were adapted to a wide variety of climatic conditions. The earliest representatives of the genus Ginkgo, represented by ovulate and pollen organs similar to those of the modern species, are known from the Middle Jurassic in the Northern Hemisphere. Several other lineages of ginkgoaleans are known from Jurassic rocks, including Yimaia, Grenana, Nagrenia and Karkenia. These lineages are associated with Ginkgo-like leaves, but are distinguished from living and fossil representatives of Ginkgo by having differently arranged reproductive structures.Umaltolepis, historically thought to be ginkgoalean, and Vladimaria from the Jurassic of Asia have strap-shaped ginkgo-like leaves with highly distinct reproductive structures with similarities to those of peltasperm and corystosperm seed ferns; these have been placed in the separate order Vladimariales, which may be related to Ginkgoales.
Bennettitales are a group of seed plants widespread throughout the Mesozoic that reached a peak diversity during the Triassic and Jurassic periods. The foliage of Bennettitales bears strong similarities to those of cycads, to such a degree that they cannot be reliably distinguished on the basis of morphology alone. Leaves of Bennettitales can be distinguished from those of cycads their different arrangement of stomata, and the two groups are not thought to be closely related. All Jurassic Bennettitales belong to the grouping Williamsoniaceae, which grew as shrubs and small trees. The Williamsoniaceae are thought to have had a divaricate branching habit, similar to that of living Banksia, and adapted to growing in open habitats with poor soil nutrient conditions. Bennettitales exhibit complex, flower-like reproductive structures that are thought to have been pollinated by insects. Several groups of insects that bear long proboscis, including extinct families such as kalligrammatid lacewings and extant ones such as acrocerid flies, are suggested to have been pollinators of bennettitales, feeding on nectar produced by bennettitalean cones.
Cycads reached their apex of diversity during the Jurassic and Cretaceous periods. Despite the Mesozoic sometimes being called the "Age of Cycads", cycads are thought to have been a relatively minor component of mid-Mesozoic floras, their foliage being confused with that of Bennettitales and other "cycadophytes". The Nilssoniales have leaves morphologically similar to those of cycads, and often been considered cycads or cycad relatives, but have been found to be distinct on chemical grounds, and perhaps more closely allied with Bennettitales. Cycads are thought to have been mostly confined to tropical and subtropical latitudes throughout their evolutionary history. The relationships of most Mesozoic cycads to living groups are ambiguous. Seeds from Jurassic of England and Haida Gwaii, Canada, are early members of the Cycadaceae, the only living genus of which is Cycas. Seeds found in the gut of the dinosaur Isaberrysaura from the Middle Jurassic of Argentina are assigned to Zamiineae, which includes all other living cycad genera. Modern cycads are pollinated by beetles, and such an association is thought to have formed by the Early Jurassic.
Other seed plants
Although there have been several claimed records, there are no widely accepted Jurassic records of flowering plants, which make up 90% of living plant species, and fossil evidence suggests that the group diversified during the following Cretaceous.
"Seed ferns" (Pteridospermatophyta) is a collective term to refer to disparate lineages of fern like plants that produce seeds but have uncertain affinities to living seed plant groups. A prominent group of Jurassic seed ferns is the Caytoniales, which reached their zenith during the Jurassic, with widespread records in the Northern Hemisphere, though records in the Southern Hemisphere remain rare. Due to their berry-like seed-bearing capsules, they have often been suggested to have been closely related or perhaps ancestral to flowering plants, but the evidence for this is inconclusive. Records of the corystosperms, a seed fern group primarily known from the Triassic of Gondwana, become rare after the Triassic and the decline of Dicroidium, though there appear to be Jurassic records of the group from the Northern Hemisphere.
Czekanowskiales, also known as Leptostrobales, are a group of seed plants uncertain affinities with persistent leaves borne on deciduous short shoots, subtended by scale-like leaves, known from the Late Triassic (possibly Late Permian) to Cretaceous. They are thought to have had a tree- or shrub-like habit and formed a conspicuous component of Mesozoic temperate and warm-temperate floras. Jurassic genera include the leaf genera Czekanowskia, Phoenicopsis and Solenites, associated with the ovulate cone Leptostrobus.
The Pentoxylales, a small but clearly distinct group of seed plants of obscure affinities, first appeared during the Jurassic. Their distribution appears to have been confined to Gondwana.
The Cyatheales, the group containing most modern tree ferns, appeared during the Late Jurassic, represented by members of the genus Cyathocaulis, which are suggested to be early members of Cyatheaceae on the basis of cladistic analysis. Only a handful of possible records exist of the Hymenophyllaceae from the Jurassic, including Hymenophyllites macrosporangiatus from the Russian Jurassic.
Quillworts virtually identical to modern species are known from the Jurassic onwards. Isoetites rolandii from the Middle Jurassic of Oregon is the earliest known species to represent all major morphological features of modern Isoetes. More primitive forms such as Nathorstiana, which retain an elongated stem, persisted into the Early Cretaceous.
An analysis of the ferns of the Hettangian-aged Mecsek Coal Formation found that the predominant groups of ferns belonged to Dipteridaceae (48% of collected specimens), Matoniaceae (25%), Osmundaceae (21%), Marattiaceae (6%) and Coniopteris (three specimens). Most of the ferns likely grew in monospecific thickets in disturbed areas. The Middle to Late Jurassic Daohugou flora of China was dominated by gymnosperms and ferns, with the most abundant group of gymnosperms being Bennettitales, followed by conifers and ginkgophytes. High-latitude floras of the New Zealand Jurassic were of low diversity, with only 43 species being recorded, dominated by conifers, ferns, bennettitaleans, pentoxylaleans and equisetaleans, with Ginkgoales being entirely absent. The flora of the Middle Jurassic Stonesfield Slate of England, representing a coastal environment, was dominated by araucariacean and cheirolepidiacean conifers, bennettitaleans, and the possible gymnosperm Pelourdea.
The Triassic-Jurassic extinction decimated pseudosuchian diversity, with crocodylomorphs, which originated during the early Late Triassic, being the only group of pseudosuchians to survive. The morphological diversity of crocodylomorphs during the Early Jurassic was around the same as those of Late Triassic pseudosuchians, but they occupied different areas of morphospace, suggesting that they occupied different ecological niches to their Triassic counterparts and that there was an extensive and rapid radiation of crocodylomorphs during this interval. While living crocodilians are confined to an aquatic ambush predator lifestyle, Jurassic crocodylomorphs exhibited a wide variety of life habits. An unnamed protosuchid known from teeth from the Early Jurassic of Arizona represents the earliest known herbivorous crocodylomorph, an adaptation that appeared several times during the Mesozoic.
The Thalattosuchia, a clade of predominantly marine crocodylomorphs, first appeared during the Early Jurassic and became a prominent part of marine ecosystems. The morphological diversity of crocodylomorphs during the Early and Middle Jurassic was relatively low compared to that in later time periods and was dominated by terrestrial small-bodied, long-legged sphenosuchians, early crocodyliforms and thalattosuchians. The Neosuchia, a major group of crocodylomorphs, first appeared during the Early to Middle Jurassic. The Neosuchia represents the transition from an ancestrally terrestrial lifestyle to a freshwater aquatic ecology similar to that occupied by modern crocodilians. The timing of the origin of Neosuchia is disputed. The oldest record of Neosuchians has been suggested to be Calsoyasuchus, from the Early Jurassic of Arizona, which in many analyses has been recovered as the earliest branching member of the neosuchian family Goniopholididae, which radically alters times of diversification for crocodylomorphs. However, this placement has been disputed, with some analyses finding it outside Neosuchia, which would place the oldest records of Neosuchia in the Middle Jurassic.Razanandrongobe from the Middle Jurassic of Madagascar has been suggested the represent the oldest record of Notosuchia, a primarily Gondwanan clade of mostly terrestrial crocodylomorphs, otherwise known from the Cretaceous and Cenozoic.
Rhynchocephalians (the sole living representative being the tuatara) had achieved a global distribution by the beginning of the Jurassic. Rhynchocephalians reached their highest morphological diversity in their evolutionary history during the Jurassic, occupying a wide range of lifestyles, including the aquatic pleurosaurs with long snake-like bodies and reduced limbs, the specialized herbivorous eilenodontines, as well as Oenosaurus, which had broad tooth plates indicative of durophagy. Cynosphenodon from the Early Jurassic of Mexico is suggested to be among the closest known relatives of the living tuatara. Rhynchocephalians disappeared from Asia after the Early Jurassic. The last common ancestor of living squamates (which includes lizards and snakes) is estimated to have lived around 190 million years ago during the Early Jurassic, with the major divergences between squamate lineages estimated to have occurred during the Early to Middle Jurassic. Squamates first appear in the fossil record during the Middle Jurassic and included early members of the snake lineage (Ophidia) and Scincomorpha, though many Jurassic squamates have unclear relationships to living groups.Eichstaettisaurus from the Late Jurassic of Germany has been suggested to be an early relative of geckos and displays adaptations for climbing.Dorsetisaurus from the Late Jurassic of North America and Europe represents the oldest widely accepted record of Anguimorpha.Marmoretta from the Middle Jurassic of Britain represents a late surviving lepidosauromorph outside both groups.
The earliest known remains of Choristodera, a group of freshwater aquatic reptiles with uncertain affinities to other reptile groups, are found in the Middle Jurassic. Only two genera of choristodere are known from the Jurassic. One is the small lizard-like Cteniogenys, thought to be the most basal known choristodere; it is known from the Middle to Late Jurassic of Europe and Late Jurassic of North America, with similar remains also known from the upper Middle Jurassic of Kyrgyzstan, European Russia and western Siberia. The other is Coeruleodraco from the Late Jurassic of China, which is a more advanced choristodere, though still small and lizard-like in morphology.
Ichthyosaurs suffered an evolutionary bottleneck during the end-Triassic extinction, with all non-neoichthyosaurians becoming extinct. Ichthyosaurs reached their apex of species diversity during the Early Jurassic, with an array of morphologies including the huge apex predatorTemnodontosaurus and swordfish-like Eurhinosaurus, though Early Jurassic ichthyosaurs were significantly less morphologically diverse than their Triassic counterparts. At the Early-Middle Triassic boundary, between the end of the Toarcian and the beginning of the Bajocian, most lineages of ichythosaur appear to have become extinct, with the first appearance of the Ophthalmosauridae, the clade that would encompass almost all ichthyosaurs from then on, during the early Bajocian. Ophthalmosaurids were diverse by the Late Jurassic, but failed to fill many of the niches that had been occupied by ichthyosaurs during the Early Jurassic.
Plesiosaurs originated at the end of the Triassic (Rhaetian). By the end of the Triassic, all other sauropterygians, including placodonts and nothosaurs, had become extinct. At least six lineages of plesiosaur crossed the Triassic-Jurassic boundary. Plesiosaurs were already diverse in the earliest Jurassic, with the majority of plesiosaurs in the Hettangian-aged Blue Lias belonging to the Rhomaleosauridae. Early plesiosaurs were generally small-bodied, with body size increasing into the Toarcian. There appears to have been a strong turnover around the Early-Middle Jurassic boundary, with the extinction of the previously widespread rhomaleosaurids and microcleidids after the end of the Toarcian and the first appearance of the dominant clade of plesiosaurs of the latter half of the Jurassic, the Cryptoclididae, during the Bajocian. The Middle Jurassic saw the evolution of short-necked and large-headed thalassophonean pliosaurs from ancestrally small-headed, long-necked forms. Some thalassophonean pliosaurs, such as some species of Pliosaurus, had skulls up to two metres in length with body lengths estimated around 10-12 metres, making them the apex predators of Late Jurassic oceans. Plesiosaurs invaded freshwater environments during the Jurassic, with indeterminate remains of small-bodied pleisosaurs known from freshwater sediments from the Jurassic of China and Australia.
Dinosaurs, which had morphologically diversified in the Late Triassic, experienced a major increase in diversity and abundance during the Early Jurassic in the aftermath of the end-Triassic extinction and the extinction of other reptile groups, becoming the dominant vertebrates in terrestrial ecosystems.Chilesaurus, a morphologically aberrant herbivorous dinosaur from the Late Jurassic of South America, has uncertain relationships to the three main groups of dinosaurs, having been recovered as a member of all three in different analyses.
The earliest avialans, which include birds and their ancestors, appear during the Middle to Late Jurassic, definitively represented by Archaeopteryx from the Late Jurassic of Germany. Avialans belong to the clade Paraves within Coelurosuria, which also includes dromaeosaurs and troodontids. The Anchiornithidae from the Middle-Late Jurassic of China have frequently suggested to be avialans, but have also alternatively found as a separate lineage of paravians.
The last known species of conodont, a class of jawless fish whose hard tooth-like elements are key index fossils, finally became extinct during the earliest Jurassic after over 300 million years of evolutionary history, with an asynchronous extinction occurring first in the Tethys and eastern Panthalassa and survivors persisting into the earliest Hettangian of Hungary and central Panthalassa. End-Triassic conodonts were represented by only a handful of species and had been progressively declining through the Middle and Late Triassic.
Head and forefin of Pachycormus, an extinct pachycormiform fish
Bony fish (Actinopterygii) were major components of Jurassic freshwater and marine ecosystems. Amiiform fish (which today only includes the bowfin) first appeared during the Early Jurassic, represented by Caturus from the Pliensbachian of Britain; after their appearance in the western Tethys, they expanded to Africa, North America and Southeast and East Asia by the end of the Jurassic. Pycnodontiformes, which first appeared in the western Tethys during the Late Triassic, expanded to South America and Southeast Asia by the end of the Jurassic, having a high diversity in Europe during the Late Jurassic.Teleosts, which make up over 99% of living Actinopterygii, had first appeared during the Triassic in the western Tethys; they underwent a major diversification beginning in the Late Jurassic, with early representatives of modern teleost clades such as Elopomorpha and Osteoglossoidei appearing during this time. The Pachycormiformes, a group of fish closely allied to teleosts, first appeared in the Early Jurassic and included both tuna-like predatory and filter-feeding forms. The latter included the largest bony fish known to have existed: Leedsichthys, with an estimated maximum length of over 15 metres, known from the late Middle to Late Jurassic.
During the Early Jurassic, Hybodonts, such as Hybodus, were common in both marine and freshwater settings; however, by the Late Jurassic, hybodonts had become minor components of most marine communities, having been largely replaced by modern neoselachians, but remained common in freshwater and restricted marine environments. The Neoselachii, which contains all living sharks and rays, radiated beginning in the Early Jurassic. The oldest known Hexanchiformes are from the Early Jurassic (Pliensbachian) of Europe. The oldest known ray (Batoidea) is Antiquaobatis from the Pliensbachian of Germany. Jurassic batoids known from complete remains retain a conservative, guitarfish-like morphology. The oldest known relatives of the bullhead shark (Heterodontus) in the order Heterodontiformes first appeared in the Early Jurassic, with representatives of the living genus appearing during the Late Jurassic.Carpet sharks (Orectolobiformes) first appeared during the Toarcian, represented by Folipistrix and Annea from Europe. The oldest known mackerel sharks (Lamniformes) are from the Middle Jurassic, represented by the genus Palaeocarcharias, which has an orectolobiform-like body but shares key similarities in tooth histology with lamniformes, including the absence of orthodentine. The oldest record of angelsharks (Squatiniformes) is Pseudorhina from the Oxfordian-Tithonian of Europe. The oldest known remains of Carcharhiniformes, the largest order of living sharks, first appear in the late Middle Jurassic (Bathonian) of the western Tethys (England and Morocco). Known dental and exceptionally preserved body remains of Jurassic Carchariniformes are similar to those of living catsharks. The oldest remains of chimaeras are from the Early Jurassic of Europe, with members of the living family Callorhinchidae appearing during the Middle Jurassic. Unlike living chimaeras, these were found in shallow water settings. The closely related Squaloraja and myriacanthoids are also known from the Jurassic of Europe.
There appears to have been no major extinction of insects at the Triassic-Jurassic boundary. Many important insect fossil localities are known from the Jurassic of Eurasia, the most important being the Karabastau Formation of Kazakhstan and the various Yanliao Biota deposits in Inner Mongolia, China, such as the Daohugou Bed, dating to the Callovian-Oxfordian. The diversity of insects stagnated throughout the Early and Middle Jurassic, but during the latter third of the Jurassic origination rates increased substantially while extinction rates remained flat. The increasing diversity of insects in the Middle-Late Jurassic corrersponds with a substantial increase in the diversity of insect mouthparts. The Middle to Late Jurassic was a time of major diversification for beetles.Weevils first appear in the fossil record during the Middle to Late Jurassic, but are suspected to have originated during the Late Triassic to Early Jurassic. The oldest known lepidopterans (the group containing butterflies and moths) are known from the Triassic-Jurassic boundary, with wing scales belonging to the suborder Glossata and Micropterigidae-grade moths from the deposits of this age in Germany. Although modern representatives are not known until the Cenozoic, ectoparasitic insects thought to represent primitive relatives of modern fleas, such as Pseudopulex jurassicus, first appeared during the Jurassic. These insects are substantially different from modern fleas, lacking the specialised morphology of the latter and being larger. The earliest group of Phasmatodea (stick insects)--the winged Susumanioidea, an outgroup to living Phasmatodeans--first appeared during the Middle Jurassic. The oldest member of the Mantophasmatidae (gladiators) also appeared during this time.
During the end-Triassic extinction, 46%-72% of all marine genera became extinct. The effects of the end Triassic extinction were greatest at tropical latitudes and were more severe in Panthalassa than the Tethys or Boreal oceans. Tropical reef ecosystems collapsed during the event, and would not fully recover until much later in the Jurassic. Sessilefilter feeders and photosymbiotic organisms were among most severely affected.
Having declined at the Triassic-Jurassic boundary, reefs substantially expanded during the Late Jurassic, including both sponge reefs and scleractiniancoral reefs. Late Jurassic reefs were similar in form to modern reefs but had more microbial carbonates and hypercalcified sponges, and had weak biogenic binding. Reefs sharply declined at the close of the Jurassic, which caused an associated drop in diversity in decapod crustaceans. The earliest planktonic foraminifera, Globigerinina, are known from the late Early Jurassic (mid-Toarcian) of the western Tethys, expanding across the whole Tethys by the Middle Jurassic and becoming globally distributed in tropical latitudes by the Late Jurassic.Coccolithophores and dinoflagellates, which had first appeared during the Triassic, radiated during the Early to Middle Jurassic, becoming prominent members of the phytoplankton.Microconchid tube worms, the last remaining order of Tentaculita, a group of animals of uncertain affinities that were convergent on Spirorbis tube worms, were rare after the Triassic and had become reduced to the single genus Punctaconchus, which became extinct in the late Bathonian. The oldest known diatom is from Late Jurassic-aged amber from Thailand, assigned to the living genus Hemiaulus.
The Jurassic was a significant time for the evolution of decapods. The first true crabs (Brachyura) are known from the Early Jurassic, with the earliest being Eocarcinus praecursor from the early Pliensbachian of England, which lacked the crab-like morphology (carcinisation) of modern crabs, and Eoprosopon klugi from the late Pliensbachian of Germany, which may belong to the living family Homolodromiidae. Most Jurassic crabs are known only from carapace pieces, which makes it difficult to determine their relationships. While rare in the Early and Middle Jurassic, crabs became abundant during the Late Jurassic as they expanded from their ancestral silty sea floor habitat into hard substrate habitats like reefs, with crevices in reefs providing refuge from predators.Hermit crabs also first appeared during the Jurassic, with the earliest known being Schobertella hoelderi from the late Hettangian of Germany. Early hermit crabs are associated with ammonite shells rather than those of gastropods.Glypheids, which today are only known from two species, reached their peak diversity during the Jurassic, with around 150 species out of a total fossil record of 250 known from the period.
Brachiopod diversity declined during the Triassic-Jurassic extinction. Spire-bearing groups (Spiriferinida and Athyridida) declined at the Triassic-Jurassic boundary and did not recover their biodiversity, becoming extinct in the TOAE.Rhynchonellida and Terebratulida also declined during the Triassic-Jurassic extinction but rebounded during the Early Jurassic; neither clade underwent much morphological variation. Brachiopods substantially declined in the Late Jurassic; the causes are poorly understood. Proposed reasons include increased predation, competition with bivalves, enhanced bioturbation or increased grazing pressure.
Ammonites were devastated by the end-Triassic extinction, with only a handful of genera belonging to the family Psiloceratidae of the suborder Phylloceratina surviving and becoming ancestral to all later Jurassic and Cretaceous ammonites. Ammonites explosively diversified during the Early Jurassic, with the orders Psiloceratina, Ammonitina, Lytoceratina, Haploceratina, Perisphinctina and Ancyloceratina all appearing during the Jurassic. Ammonite faunas during the Jurassic were regional, being divided into around 20 distinguishable provinces and subprovinces in two realms, the northern high latitude Pan-Boreal realm, consisting of the Arctic, northern Panthalassa and northern Atlantic regions, and the equatorial-southern Pan-Tethyan realm, which included the Tethys and most of Panthalassa.
The end-Triassic extinction had a severe impact on bivalve diversity, though it had little impact on bivalve ecological diversity. The extinction was selective, having less of an impact on deep burrowers, but there is no evidence of a differential impact between surface-living (epifaunal) and burrowing (infaunal) bivalves.Rudists, the dominant reef-building organisms of the Cretaceous, first appeared in the Late Jurassic (mid-Oxfordian) in the northern margin of the western Tethys, expanding to the eastern Tethys by the end of the Jurassic.
The oldest definitive records of the squid-like belemnites are from the earliest Jurassic (Hettangian-Sinemurian) of Europe and Japan; they expanded worldwide during the Jurassic. Belemnites were shallow-water dwellers, inhabiting the upper 200 metres of the water column on the continental shelves and in the littoral zone. They were key components of Jurassic ecosystems, both as predators and prey, as evidenced by the abundance of belemnite guards in Jurassic rocks.
The earliest vampyromorphs, of which the only living member is the vampire squid, first appeared during the Early Jurassic. The earliest octopuses appeared during the Middle Jurassic, having split from their closest living relatives, the vampyromorphs, during the Triassic to Early Jurassic. All Jurassic octopuses are solely known from the hard gladius.Proteroctopus from the late Middle Jurassic La Voulte-sur-Rhône lagerstätte, previously interpreted as an early octopus, is now thought to be a basal taxon outside the clade containing vampyromorphs and octopuses. Octopuses likely originated from bottom-dwelling (benthic) ancestors which lived in shallow environments.
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