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 arid expanses 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
Muschelkalk of Southern Germany, but he erroneously concluded that they were older. He then named them Jura-Kalkstein ('Jura limestone') in 1799.
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".
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, but none has retained its original definition. The 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.
The 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.
Tidwell Member of the Morrison Formation (Upper Jurassic), Colorado
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.
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,
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
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
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.
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
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.
The village of
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
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 during the Middle and Late 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
Major impact structures include the
Morokweng impact structure, a 70 km diameter impact structure buried beneath the Kalahari desert in northern South Africa. The impact is dated to the Tithonian, approximately 146.06 ± 0.16 Mya. Another major structure is the
Puchezh-Katunki crater, 40 kilometres in diameter, buried beneath
Nizhny Novgorod Oblast in western Russia. The impact has been dated to the Sinemurian, 195.9 ± 1.0 Ma.
At the beginning of the Jurassic, all of the world's major landmasses were coalesced into the
supercontinentPangaea, which during the Early Jurassic began to break up into northern supercontinent
Laurasia and the southern supercontinent
Gondwana. The rifting between North America and Africa was the first to initiate, beginning in the early 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 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. During the Jurassic, both the North and South Pole were covered by oceans. 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, also known as the Hispanic Corridor, which connected the North Atlantic Ocean with eastern Panthalassa. 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
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.
During the Early Jurassic the world's oceans transitioned from an
aragonite sea to a
calcite sea chemistry, favouring the dissolution of
aragonite and precipitation of
calcite. The rise of calcareous
plankton during the Middle Jurassic profoundly altered ocean chemistry, with the deposition of
biomineralized plankton on the ocean floor acting as a
buffer against large CO2 emissions.
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. Intermittent "cold snap" intervals are known to have occurred during this time period, however, interrupting the otherwise warm greenhouse climate. 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 and scrubland in the lower latitudes between 40° N and S of the equator.
Tropical rainforest and
tundra biomes are likely to have been rare or absent.
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. It has been proposed that glaciation was present in the Northern Hemisphere during the late Pliensbachian. There was a 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 warm interval extending to the end of the Toarcian 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, with the Callovian-Oxfordian boundary at the end of this interval witnessing particularly notable global cooling, potentially even an ice age. This is followed by the Kimmeridgian Warm Interval between 164 and 150 million years ago. The Pangaean 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. A prominent drop in temperatures occurred during the Tithonian, known as the Early Tithonian Cooling Event (ETCE). 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.
The Toarcian Oceanic Anoxic Event (TOAE), also known as the Jenkyns Event, was an episode of widespread
oceanic anoxia during the early part of the Toarcian Age, 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, associated with a major rise in global temperatures.
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, as evidenced by an increased amount of organic matter of terrestrial origin found in marine deposits during the TOAE. Groups affected include ammonites,ostracods,foraminifera,bivalves,cnidarians, and especially
brachiopods, for which the TOAE represented one of the most severe extinctions in their evolutionary history. 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 the probable cause of the collapse of carbonate production. Additionally, anoxic conditions were exacerbated by enhanced recycling of phosphorus back into ocean water as a result of high ocean acidity and temperature inhibiting its mineralisation into apatite; the abundance of phosphorus in marine environments caused further eutrophication and consequent anoxia in a positive feedback loop.
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 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
Araucarian conifers have their first unambiguous records during the Early Jurassic, and members of 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.
Members of the extinct genus Schizolepidopsis which likely represent a
stem-group to the pine family (
Pinaceae), were widely distributed across Eurasia during the Jurassic. The oldest unambiguous record of Pinaceae is the
pine coneEathiestrobus, known from the Late Jurassic (Kimmeridgian) of Scotland, which remains the only known unequivocal fossil of the group before the Cretaceous. Despite being the earliest known member of the Pinaceae, Eathiestrobus appears to be a member of the
pinoidclade 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, with the latter material assigned to the modern genus, indicating that Taxaceae had substantially diversified by the end of the Jurassic.
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 from the Jurassic of Asia has strap-shaped ginkgo-like leaves with highly distinct reproductive structures with similarities to those of peltasperm and corystosperm seed ferns, has been suggested to be a member of Ginkgoales sensu lato.
Restoration of a member of
Bennettitales belonging to Williamsoniaceae.
Bennettitales, having first become widespread during the preceding Triassic, were diverse and abundant members of Jurassic floras across both hemispheres. 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. Jurassic Bennettitales predominantly belong to the group
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 some of which 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, with the Bennettitales and
Nilssoniales, which have cycad-like foliage, being dominant. The Nilssoniales have 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. 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 and phylogenetic stem group age estimates for individual early diverging angiosperm orders, there are no widely accepted Jurassic fossil 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. A variety of other Jurassic seed ferns of uncertain placement are known, including Pachypteris from Europe, which has sometimes been allied with the corystosperms.
Czekanowskiales, also known as Leptostrobales, are a group of seed plants uncertain affinities with persistent heavily dissected 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 Northern Hemisphere Mesozoic temperate and warm-temperate floras. The genus Phoenicopsis was widespread in Early-Middle Jurassic floras of Eastern Asia and Siberia.
Pentoxylales, a small but clearly distinct group of
liana-like seed plants of obscure affinities, first appeared during the Jurassic. Their distribution appears to have been confined to Eastern Gondwana.
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.
The Triassic–Jurassic extinction decimated
pseudosuchian diversity, with
crocodylomorphs, which originated during the early Late Triassic, being the only group of pseudosuchians to survive, with all others, including the herbivorous
aetosaurs and carnivorous "
rauisuchians" becoming extinct. 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.
Thalattosuchia, a clade of predominantly marine crocodylomorphs, first appeared during the Early Jurassic and became a prominent part of marine ecosystems. Within Thalattosuchia, the
Metriorhynchidae became highly adapted for life in the open ocean, including the transformation of limbs into flippers, the development of a tail fluke, and smooth, scaleless skin. 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
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. Rhynchocephalians disappeared from Asia after the Early Jurassic. The last common ancestor of living
squamates (which includes
snakes) is estimated to have lived around 190 million years ago during the Early Jurassic, with the major divergences between modern squamate lineages estimated to have occurred during the Early to Middle Jurassic. Squamates first appear in the fossil record during the Middle Jurassic including members of modern clades such as
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.Tamaulipasaurus from Early Jurassic of Mexico and Marmoretta from the Middle Jurassic of Britain represents late surviving
lepidosauromorphs outside both Rhynchocephalia and Squamata.
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 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 Jurassic 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
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
microcleidids and rhomaleosaurids becoming extinct and nearly extinct respectively after the end of the Toarcian with 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.
theropods belonging to
Neotheropoda first appeared in the Late Triassic. Basal neotheropods, such as
dilophosaurs, persisted into the Early Jurassic, but became extinct by the Middle Jurassic. The earliest
averostrans appear during the Early Jurassic, with the earliest known member of
Ceratosauria being Saltriovenator from the early Sinemurian (199.3–197.5 million years ago) of Italy. The unusual ceratosaur Limusaurus from the Late Jurassic of China had a herbivorous diet, with adults having
edentulous beaked jaws, making it the earliest known theropod to have converted from an ancestrally carnivorous diet. The earliest members of the
Tetanurae appeared during the late Early Jurassic or early Middle Jurassic. The
Megalosauridae represent the oldest radiation of the Tetanurae, first appearing in Europe during the Bajocian. The oldest member of
Allosauroidea has been suggested to be Asfaltovenator from the Middle Jurassic of South America.Coelurosaurs first appeared during the Middle Jurassic, including early
tyrannosaurs such as Proceratosaurus from the Bathonian of Britain. Some coelurosaurs from the Late Jurassic of China including Shishugounykus and Haplocheirus are suggested to represent early
alvarezsaurs, however, this has been questioned.Scansoriopterygids, a group of small feathered coelurosaurs with membraneous, bat-like wings for gliding, are known from the Middle to Late Jurassic of China. The oldest record of
troodontids is suggested to be Hesperornithoides from the Late Jurassic of North America. Tooth remains suggested to represent those of
dromaeosaurs are known from the Jurassic, but no body remains are known until the Cretaceous.
Skeleton of Ceratosaurus, a ceratosaurid from the Late Jurassic of North America
Skeleton of Monolophosaurus, a basal tetanuran from the Middle Jurassic of China
Restoration of Yi qi, a scansoriopterygid from the Middle to Late Jurassic of China
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 Coelurosauria, which also includes dromaeosaurs and troodontids. The
Anchiornithidae from the Middle-Late Jurassic of Eurasia have frequently suggested to be avialans, but have also alternatively found as a separate lineage of paravians.
Skeleton of Heterodontosaurus, a primitive ornithischian from the Early Jurassic of South Africa
Sauropods became the dominant large herbivores in terrestrial ecosystems during the Jurassic. Some Jurassic sauropods reached gigantic sizes, becoming the largest organisms to have ever lived on land.
Henkelotherium, a likely arboreal dyolestoid from the Late Jurassic of Portugal
Mammaliaformes, having originated from
cynodonts at the end of the Triassic, diversified extensively during the Jurassic. Important groups of Jurassic Mammaliaformes include
Multituberculata. While most Jurassic mammalaliaformes are solely known from isolated teeth and jaw fragments, exceptionally preserved remains have revealed a variety of lifestyles. The docodontan Castorocauda was adapted to aquatic life, similarly to the
otters. Some members of Haramiyida and the eutriconodontan tribe
Volaticotherini had a
patagium akin to those of
flying squirrels, allowing them to glide through the air. The
aardvark-like mammal Fruitafossor, of uncertain taxonomy, was likely a specialist on colonial insects, similarly to living
anteaters.Australosphenida, a group of mammals possibly related to monotremes, first appeared in the Middle Jurassic of Gondwana.Therian mammals, represented today by living
marsupials, appear during the early Late Jurassic, represented by Juramaia, a
eutherian mammal closer to the ancestry of placentals than marsupials.Juramaia is much more advanced than expected for its age, as other therian mammals are not known until the Early Cretaceous. Two groups of non-mammalian cynodonts persisted beyond the end of the Triassic. The insectiviorous
Tritheledontidae has a few records from the Early Jurassic. The
Tritylodontidae, a herbiviorous group of cynodonts that first appeared during the Rhaetian, has abundant records from the Jurassic, overwhelmingly from the Northern Hemisphere.
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.
Fossil of Thrissops, an
ichthyodectid stem-group teleost from the Late Jurassic Solnhofen Limestone of Germany, showing preserved colouration
Ray-finned fish (
Actinopterygii) were major components of Jurassic freshwater and marine ecosystems. Archaic "
palaeoniscoid" fish, which were common in both marine and freshwater habitats during the preceding Triassic declined during the Jurassic, being largely replaced by more
derived actinopterygian lineages. The oldest known
Acipenseriformes, the group that contains living
paddlefish, are from the Early Jurassic.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. During the Jurassic, the
Ginglymodi, the only living representatives being
gars (Lepisosteidae) were diverse in both freshwater and marine environments. The oldest known representatives of anatomically modern gars appeared during the Upper Jurassic. Stem-group
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
Osteoglossoidei appearing during this time. The
Pachycormiformes, a group of marine stem-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, the shark-like
hybodonts, which represented the dominant group of
chondrichthyans during the preceding Triassic, 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 ray (
Batoidea) is Antiquaobatis from the Pliensbachian of Germany. Jurassic batoids known from complete remains retain a conservative,
guitarfish-like morphology. The oldest known
carpet sharks (Orectolobiformes) are from the Early Jurassic (Pliensbachian & Toarcian, respectively) of Europe. The oldest known members of the Heterodontiformes, the only living member of which is the
bullhead shark (Heterodontus), first appeared in the Early Jurassic, with representatives of the living genus appearing during the Late Jurassic. 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 Late Jurassic (Oxfordian–Tithonian) of Europe, which already has a bodyform similar to living members of the order. 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.Synechodontiformes, an extinct group of sharks closely related to Neoselachii, were also widespread during the Jurassic. The oldest remains of modern
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 corresponds 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
Micropterigidae-grade moths from the deposits of this age in Germany. Modern representatives of both
damselflies also first appeared during the Jurassic. Although modern representatives are not known until the Cenozoic,
ectoparasitic insects thought to represent primitive
fleas, belonging to the family
Pseudopulicidae, are known from the Middle Jurassic of Asia. These insects are substantially different from modern fleas, lacking the specialised morphology of the latter and being larger.Parasitoid wasps (
Apocrita) first appeared during the Early Jurassic and subsequently became widespread, reshaping terrestrial food webs. The Jurassic saw also saw the first appearances of several other groups of insects, including
Phasmatodea (stick insects),Mantophasmatidae,Embioptera (webspinners), and
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, which constitute the suborder
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.
Crinoids diversified throughout the Jurassic, reaching their peak Mesozoic diversity during the Late Jurassic, primarily due to the radiation of sessile forms belonging to the orders
Millericrinida.Echinoids (sea urchins) underwent substantial diversification beginning in the Early Jurassic, primarily driven by the radiation of irregular (asymmetrical) forms, which were adapting to deposit feeding. Rates of diversification sharply dropped during the Late Jurassic.
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. Jurassic barnacles were of low diversity compared to present, but several important evolutionary innovations are known, including the first appearances of calcite shelled forms and species with an epiplanktonic mode of life.
Brachiopod diversity declined during the Triassic–Jurassic extinction. Spire-bearing brachiopods (
Athyridida) 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
Like the preceding Triassic,
bryozoan diversity was relatively low compared to the Paleozoic. The vast majority of Jurassic bryozoans are members of
Cyclostomatida, which experienced a radiation during the Middle Jurassic, with all Jurassic representatives belonging to the suborders
Cheilostomata, the dominant group of modern bryozoans, first appeared during the Late Jurassic.
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. Bivalve family level diversity after the Early Jurassic was static, though genus diversity experienced a gradual increase throughout the period.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.
Fossil specimen of Proteroctopus from the Middle Jurassic of France, formerly thought to be worlds oldest known octopus
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
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 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.
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. Octopuses likely originated from bottom-dwelling (
benthic) ancestors which lived in shallow environments.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.
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