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 present, and there were no ice caps. Forests grew close to the poles, with large expanses of desert in the lower latitudes of the continents.
Thirty years later, in 1829, the French naturalist Alexandre Brongniart published a survey on the different terrains that constitute the crust 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" for the first time. The German geologist Leopold von Buch in 1839 established the three-fold division of the Jurassic, originally named from oldest to youngest, the Black Jurassic, Brown Jurassic and White Jurassic. The term "Lias" had previously been used for strata of equivalent age to the Black Jurassic in England by William Conybeare and Phillips in 1822. French palaeontologistAlcide d'Orbigny in papers between 1842 and 1852 divided the Jurassic into ten étages (stages) based on ammonite and other fossil assemblages in England and France, of which seven are still used, 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 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 á 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 Kuhjoch pass, Karwendel Mountains, Northern Calcareous Alps, Austria, which 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 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, which 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, which 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 with the base at the contact between the Forest Marble Formation and the Cornbrash Formation. However, this boundary was later found to be situated 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 placename. 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 also currently undefined, and the Jurassic-Cretaceous boundary is currently the only system boundary to lack a defined GSSP. Placing a GSSP for the J/K boundary has been difficult, due to 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 J/K boundary.
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 Ma. 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 early Jurassic, the supercontinentPangaea began to break up into northern supercontinent Laurasia and the southern supercontinent Gondwana. The rifting between North American and Africa, was the first to initiate, beginning in the earliest Jurassic, associated with the emplacement of the Central Atlantic Magmatic Province. During the Jurassic, the North Atlantic Ocean remained relatively narrow, while the South Atlantic did not open until the following Cretaceous period. 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 several hundred kilometer wide passage between the Baltic Shield and Greenland.
Madagascar and Antarctica began to rift away from Africa during the late Early Jurassic associated 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 had rifted apart, forming the Caribbean Seaway, connecting the north Atlantic Ocean with eastern Panthalassa, however palaeontological data suggests that the seaway had been open since the Early Jurassic. During the Early Jurassic, around 190 million years ago, the Pacific Plate originated at the triple junction of the Farallon, Phoenix, and Izanagitectonic plates, the three main oceanic plates of Panthalassa. The previously stable triple junction had converted to an unstable arrangement surrounded on all sides by transform faults, due to a kink in one of the plate boundaries, resulting in the formation of the Pacific Plate at the centre of the junction, which began to expand. During the Middle to early Late Jurassic, the Sundance Seaway, a shallow epicontinental sea covered much of northwest North America.
Based on estimated sea level curves, the eustatic sea level was 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 drops by several tens of metres. The sea level progressively rose from the Aalenian onwards, aside from dips of a few tens of metres in the Bajocian and around the Callovian-Oxfordian boundary, culminating in a sea level 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. Sea level within the long-term trend was cyclical with 64 fluctuations through the Jurassic, 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 rise of calcareous plankton during the Middle Jurassic profoundly altered ocean chemistry, with the deposition of biomineralizing plankton on the ocean floor acting as a buffer against large CO2 emissions.
The climate of the Jurassic was generally warmer than at present, by around 5 °C to 10 °C. Atmospheric carbon dioxide levels were likely four times higher than present. Forests likely grew near the poles, and experienced warm summers and cold, sometimes snowy winters, and there were unlikely to have been ice sheets given the high summer temperatures that prevented the accumulation of snow, though mountain glaciers may have existed.Dropstones and glendonites in northeastern Siberia during the Early-Mid Jurassic indicate cold winters. The ocean depths were likely 8 °C warmer than present, and 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, with the average temperature being several degrees above 0 °C. This was ended by the spike in global temperatures by 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 164-150 million years ago. The Pangean interior had less severe seasonal swings than previous warm periods due to the expansion of the Central Atlantic and western Indian Ocean providing 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 cause is often linked to the eruption of the Karoo-Ferrar large igneous provinces and the associated increase of carbon dioxide concentration in the atmosphere and 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 3 times the size of 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. During the TOAE, 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 T-J, 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 araucarian conifers 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 by their highly distinctive Classopolis pollen. Jurassic representatives include the pollen cone Classostrobus and the seed cone Pararaucaria. Both 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 Mid-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 prior to 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 is recognised 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, with its range extending northwards into polar latitudes of Siberia, but its range contracted northward in the Middle-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, only differing in having shorter seed-bearing axes.
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, and 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, which 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 based on morphology alone. Leaves of Bennettitales can be distinguished from those of cycads by the fact they have a 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 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 like Kalligrammatid lacewings and extant Acroceridae 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, with their foliage being confused with that of Bennettitales and other "cycadophytes". 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. While 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. 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.
Seed ferns (Pteridospermatophyta) is a collective term to refer to disparate lineages of fern like plants that produce seeds, with 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. They have frequently 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 the 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 appear during the Jurassic. Their distribution appears to have been confined to Gondwana.
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.
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 based on cladistic analysis. Only a handful of possible records exist of the Hymenophyllaceae are known 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.
In an analysis of the ferns of the Hettangian aged Mecsek Coal Formation found that the predominant groups of ferns by order of abundance belonged to the families Dipteridaceae (48% of collected specimens) Matoniaceae (25%), Osmundaceae (21%), Marattiaceae (6%) and 3 specimens of Coniopteris. They found that most of the ferns likely grew in monospecific thickets in disturbed areas. The Middle-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 locally, equisetaleans" with Ginkgoales being entirely absent. The flora of the Middle Jurassic Stonesfield Slate of England was dominated by "araucariacean and cheirolepidiacean conifers, bennettitaleans, and leaves of the possible gymnosperm Pelourdea" representing a coastal environment.
The T-J extinction decimated pseudosuchian diversity, with crocodylomorphs, which originated during the early Late Triassic (Norian), being the only group of pseudosuchians to survive the T-J extinction. The morphological diversity of crocodylomorphs during the Early Jurassic was around the same as those of Late Triassic pseudosuchians, but 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 exhibit a wide variety of life habits, with the earliest known herbivorous crocodylomorph being an unnamed species of protosuchid from the Early Jurassic of Arizona. The earliest lineages of Crocodylomorpha are represented by the terrestrial small-bodied long-legged "sphenosuchians", one lineage of which, the Hallopodidae, perisisted into the Late Jurassic.
The Thalattosuchia, a clade of predominantly marine crocodylomorphs including both teleosaurioids and metriorhynchoids, first appeared during the Early Jurassic, and became prominent part of marine reptile communities. The Neosuchia, a major group of crocodylmorphs, first appeared during the Early-Middle Jurassic. The Neosuchia represents the transition from an ancestrally terrestrial lifestyle to a freshwater aquatic ecology similar to 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.
Stem-group turtles (Testudinata) diversified during the Jurassic. Jurassic stem-turtles belong to two progressively more advanced clades, the Mesochelydia and Perichelydia. It is thought that the ancestral condition for Mesochelydians is aquatic, as opposed to terrestrial for Testudinata. The two modern groups of turtles (Testudines), Pleurodira and Cryptodira, diverged by the Middle Jurassic. Early cryptodire lineages like Xinjiangchelyidae are known from the Middle Jurassic, while an early pleurodire lineage, the ocean-going Platychelyidae is known from the Late Jurassic. The Thalassochelydia, a diverse lineage of sea-turtles, is known from the Late Jurassic (Oxfordian-Tithonian) of Europe and South America.
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-Middle Jurassic. Squamates first appear in the fossil record during the Middle Jurassic, including 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, which is known from the Middle-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 Triassic boundary, all other sauropterygians, including placodonts and nothosaurs had become extinct. At least six lineages of plesiosaur crossed the T-J 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 forms, 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 thalassophoneanpliosaurs 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-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-like animals whose hard teeth 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, with late survivors in the earliest Hettangian of Hungary and central Panthalassa. End-Triassic conodonts were only represented by 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 first 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, 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 including 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 appear in the Early Jurassic, with representatives of the living genus appearing during the Late Jurassic.Carpet sharks (Orectolobiformes) first appear during the Toarcian, represented by Folipistrix and Annea from Europe. The oldest known mackerel sharks (Lamniformes) are known from the Middle Jurassic, represented by the genus Palaeocarcharias., which has an orectolobiform-like bodyform, 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 known 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. Numerous 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 was stagnant throughout the Early and Middle Jurassic, but during the latter third of the Jurassic origination rates increased substantially while extinction rates remained flat. The Middle-Late Jurassic was a time of major diversification for beetles.Weevils first appear in the fossil record during the Middle-Upper Jurassic, but are suspected to have originated during the Late Triassic-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 a stem-group to fleas first appear during the Jurassic, such as Pseudopulex jurassicus. These insects are substantially different from modern fleas, lacking the specialised morphology of modern fleas and being larger in size. The earliest group of Phasmatodea (stick insects), the winged Susumanioidea, an outgroup to living Phasmatodeans, first appear 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 completely 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 T-J 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, before being globally distributed in tropical latitudes by the Late Jurassic.Coccolithophores and dinoflagellates, which had first appeared during the Triassic, radiated during the Early-Middle Jurassic, becoming prominent members of the phytoplankton.Microconchid tube worms, the last remaining order of Tentaculita, a group of animals of uncertain affinites that were convergent on Spirorbis tube worms, had become 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 known 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 possibly belongs to the living family Homolodromiidae. Most Jurassic crabs are only known from dorsal 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 helping to hide 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 being known from the period.
Brachiopod diversity declined during the T-J extinction. Spire bearing groups (Spiriferinida and Athyridida) significantly declined at the T-J boundary and did not recover their biodiversity, becoming extinct in the TOAE.Rhynchonellida and Terebratulida also declined during the T-J extinction but rebounded during the Early Jurassic, neither clade developed any significant morphological variation. Brachiopods substantially declined in the Late Jurassic, the causes of which 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, and 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 octopods. Octopuses likely originated from bottom dwelling (benthic) ancestors which lived in shallow water environments.
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