The Jurassic (
The start of the Jurassic was marked by the major Triassic–Jurassic extinction event, associated with the eruption of the Central Atlantic Magmatic Province (CAMP). The beginning of the Toarcian Age started around 183 Ma and is marked by the Toarcian Oceanic Anoxic Event, a global episode of Anoxic event, ocean acidification, and elevated global temperatures associated with extinctions, likely caused by the eruption of the Karoo-Ferrar. The end of the Jurassic, however, has no clear, definitive boundary with the Cretaceous and is the only boundary between geological periods to remain formally undefined.
By the beginning of the Jurassic, the supercontinent Pangaea had begun 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.
On land, the fauna transitioned from the Triassic fauna, dominated jointly by Dinosauromorpha and , to one dominated by alone. The first Stem group birds appeared during the Jurassic, evolving from a branch of theropod dinosaurs. Other major events include the appearance of the earliest and modern , and . Mammaliaformes, one of the few Cynodontia lineages to survive the end of the Triassic, continued to diversify throughout the period, with the Jurassic seeing the emergence of the first crown group . Crocodylomorpha made the transition from a terrestrial to an aquatic life. The oceans were inhabited by marine reptiles such as Ichthyosauria and , while were the dominant flying vertebrates. Modern sharks and rays first appeared and diversified during the period, while the first known crown-group teleost fish (the dominant group of modern fish) appeared near the end of the period. The flora was dominated by and , including , of which many modern groups made their first appearance during the period, as well as other groups like the extinct Bennettitales.
Etymology and history
The chronostratigraphic term "Jurassic" is linked to the
Jura Mountains, a forested
mountain range that mainly follows the France–Switzerland border. The name "Jura" is derived from the
Celtic languages root *jor via
Gaulish *iuris "wooded mountain", which was borrowed into
Latin as a name of a place and evolved into
Juria and finally
Jura.
During a tour of the region in 1795, German naturalist Alexander von Humboldt recognized Carbonate rock deposits within the Jura Mountains as geologically distinct from the Triassic aged 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 Oolite in Britain, thus coining and publishing the term "Jurassic".[ From p. 221, footnote 2: "Souvent aussi calcaire oolithique moyen ou principal (great oolithe ) ; mais le nom de terrains jurassiques nous paroît préférable … analogue à celle de la chaîne du Jura." (Often also middle or principal oolitic limestone (great oolithe); but the name of "Jurassic terrains" seems to us preferable, because it is more general, because it indicates a terrain composed of different rocks, being in a geognostic position analogous to that of the Jura chain.)]
The German geologist Leopold von Buch in 1839 established the three-fold division of the Jurassic, originally named from oldest to the youngest: the Black Jurassic, Brown Jurassic, and White Jurassic.[von Buch, L., 1839. Über den Jura in Deutschland. Der Königlich Preussischen Akademie der Wissenschaften, Berlin, p. 87.] The term "Lias Group" had previously been used for strata of equivalent age to the Black Jurassic in England by William Conybeare and William Phillips in 1822. William Phillips, the geologist, worked with William Conybeare to find out more about the Black Jurassic in England.
The French palaeontologist Alcide 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 Biostratigraphy zones, based primarily on ammonites. Most of the modern stages of the Jurassic were formalized at the Colloque du Jurassique à Luxembourg in 1962.
Geology
The Jurassic Period is divided into three epochs: Early, Middle, and Late. Similarly, in
stratigraphy, the Jurassic is divided into the
Lower Jurassic,
Middle Jurassic, and
Upper Jurassic series. Geologists divide the rocks of the Jurassic into a
Stratigraphy set of units called stages, each formed during corresponding time intervals called ages.
Stages can be defined globally or regionally. For global stratigraphic correlation, the International Commission on Stratigraphy (ICS) ratify global stages based on a Global Boundary Stratotype Section and Point (GSSP) from a single formation (a stratotype) identifying the lower boundary of the stage.[Cohen, K.M., Finney, S.C., Gibbard, P.L. & Fan, J.-X. (2013; updated) The ICS International Chronostratigraphic Chart. Episodes 36: 199–204.]
Stratigraphy
Jurassic stratigraphy is primarily based on the use of ammonites as index fossils. The first appearance datum of specific ammonite
Taxon 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.
]]
Early Jurassic
The oldest part of the Jurassic Period has historically been referred to as the Lias or Liassic, roughly equivalent in extent to the Early Jurassic, but also including part of the preceding
Rhaetian. The Hettangian Stage was named by Swiss palaeontologist Eugène Renevier in 1864 after
Hettange-Grande in north-eastern France.
The GSSP for the base of the Hettangian is located at the Kuhjoch Pass,
Karwendel, 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 in the Kendlbach Formation exposed at Kuhjoch.
The base of the Jurassic was previously defined as the first appearance of
Psiloceras planorbis by Albert Oppel in 1856–58, but this was changed as the appearance was seen as too localised an event for an international boundary.
The Sinemurian Stage was first defined and introduced into scientific literature by Alcide d'Orbigny in 1842. It takes its name from the French town of Semur-en-Auxois, near Dijon. The original definition of Sinemurian included what is now the Hettangian. The GSSP of the Sinemurian is located at a cliff face north of the hamlet of East Quantoxhead, 6 kilometres east of Watchet, Somerset, England, within the Blue Lias, and was ratified in 2000. The beginning of the Sinemurian is defined by the first appearance of the ammonite Vermiceras.
Albert Oppel in 1858 named the Pliensbachian Stage after the hamlet of Pliensbach in the community of Zell unter Aichelberg in the Swabian Alb, near Stuttgart, Germany. The GSSP for the base of the Pliensbachian is found at the Wine Haven locality in Robin Hood's Bay, Yorkshire, England, in the Redcar Mudstone Formation, and was ratified in 2005. The beginning of the Pliensbachian is defined by the first appearance of the ammonite Bifericeras.
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 Dactylioceras .
Middle Jurassic
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
Iron 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.
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.
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, at the base of the Zigzagiceras ammonite zone .
The Callovian is derived from the Latinized name of the village of Kellaways in Wiltshire, England, and was named by Alcide d'Orbigny in 1852, originally the base at the contact between the Forest Marble Formation and the Cornbrash Formation. However, this boundary was later found to be within the upper part of the Bathonian.
Late Jurassic
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 (then placed in the genus
Vertumniceras). Subsequent proposals have suggested the first appearance of
Cardioceras 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 on the Isle of Skye, Scotland,
The Tithonian was introduced in scientific literature by Albert Oppel in 1865. The name Tithonian is unusual in geological stage names because it is derived from Greek mythology rather than a place name. Tithonus was the son of Laomedon of Troy and fell in love with Eos, the Greek goddess of dawn. His name was chosen by Albert Oppel for this Stratigraphy 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 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. , an enigmatic group of 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
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
Ordos Plateau.
Impact structures
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 Ma.
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.
Paleogeography and tectonics
At the beginning of the Jurassic, all of the world's major landmasses were coalesced into the
supercontinent Pangaea, 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.
During the Callovian, the
Turgai Strait formed, creating a marine barrier between Europe and Asia.
Madagascar and Antarctica began to rift away from Africa during the late Early Jurassic in association with the eruption of the
Karoo-Ferrar, 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.
As part of the Nevadan orogeny, which began during the Triassic, the Cache Creek Ocean closed, and various including the large Wrangellia Terrane accreted onto the western margin of North America.
During the Early Jurassic, around 190 million years ago, the Pacific Plate originated at the triple junction of the Farallon Plate, Phoenix Plate, and Izanagi Plate Plate tectonics, the three main Oceanic crust of Panthalassa. The previously stable triple junction had converted to an unstable arrangement surrounded on all sides by because of a kink in one of the plate boundaries, resulting in the formation of the Pacific Plate at the centre of the junction.
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.
Climate
The climate of the Jurassic was generally warmer than that of present, by around , with atmospheric carbon dioxide likely about 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.
and
in northeastern
Siberia during the Early to Middle Jurassic indicate cold winters.
[ Alt URL] The ocean depths were likely warmer than present, and
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 Jurassic also witnessed the decline of the Pangaean megamonsoon that had characterised the preceding Permian and Triassic periods.
Variation in the frequency of
wildfire activity in the Jurassic was governed by the 405 kyr eccentricity cycle.
Thanks to the breakup of Pangaea, the hydrological cycle during the Jurassic was significantly enhanced.
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.
Climatic events
Toarcian Oceanic Anoxic Event
The Toarcian Oceanic Anoxic Event (TOAE), also known as the Jenkyns Event, was an episode of widespread
Anoxic event during the early part of the Toarcian Age, c. 183 Ma. It is marked by a globally documented high amplitude negative carbon isotope excursion,
as well as the deposition of black
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.
End-Jurassic transition
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.
Flora
End-Triassic extinction
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.
, a corystosperm 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 Early Jurassic.
Floral composition
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
Voltziales ancestors.
Araucariaceae 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 from the Early Jurassic (Pliensbachian) of Patagonia, known from many parts of the plant.
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 earliest record of the yew family (Taxaceae) is Palaeotaxus, from the Hettangian of Sweden, suggested to be closely related to the living Austrotaxus, while Marskea 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.
The oldest unambiguous members of Podocarpaceae are known from the Jurassic, found across both hemispheres, including Scarburgia and Harrisiocarpus from the Middle Jurassic of England, as well as unnamed species from the Middle-Late Jurassic of Patagonia.
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.
Ginkgoales
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
Ovule 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
Karkeniaceae. These lineages are associated with
Ginkgo-like leaves, but are distinguished from living and fossil representatives of
Ginkgo by having differently arranged reproductive structures.
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.
Bennettitales
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
, 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
Kalligrammatidae lacewings
and extant ones such as
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 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.
The relationships of most Mesozoic cycads to living groups are ambiguous,
with no Jurassic cycads belonging to either of the two modern groups of cycads, though some Jurassic cycads possibly represent
stem-group relatives of modern
Cycadaceae, like the leaf genus
Paracycas known Europe, and
Zamiaceae, like some European species of the leaf genus
Pseudoctenis. Also widespread during the Jurassic was the extinct
Ctenis lineage, which appears to be distantly related to modern cycads.
Modern cycads are pollinated by beetles, and such an association is thought to have formed by the Early Jurassic.
Other seed plants
Although there have been several claimed records, there are no widely accepted Jurassic fossil records of
, which make up 90% of living plant species, and fossil evidence suggests that the group diversified during the following Cretaceous.
The earliest known gnetophytes, one of the four main living groups of , appeared by the end of the Jurassic, with the oldest unequivocal gnetophyte being the seed Dayvaultia from the Late Jurassic of North America.
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
The 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.[Pattemore, G.A., Rigby, J.F. and Playford, G., 2015. Triassic-Jurassic pteridosperms of Australasia: speciation, diversity and decline. Boletín Geológico y Minero, 126 (4): 689–722]
Ferns and allies
Living families of ferns widespread during the Jurassic include
Dipteridaceae,
Matoniaceae,
Gleicheniaceae,
Osmundaceae and
Marattiaceae.
, which make up 80% of living fern diversity, have no record from the Jurassic and are thought to have diversified in the Cretaceous,
though the widespread Jurassic
Herbaceous plant fern genus
Coniopteris, historically interpreted as a close relative of
of the family
Dicksoniaceae, has recently been reinterpreted as an early relative of the group.
The Cyatheales, the group containing most modern tree ferns, appeared during the Late Jurassic, represented by members of the genus Cyathocaulis, which are suggested to be early members of Cyatheaceae on the basis of cladistic analysis.
The oldest remains of modern Equisetaceae of the genus Equisetum first appear in the Early Jurassic, represented by Equisetum dimorphum from the Early Jurassic of Patagonia[Gould, R. E. 1968. Morphology of Equisetum laterale Phillips, 1829, and E. bryanii sp. nov. from the Mesozoic of south‐eastern Queensland. Australian Journal of Botany 16: 153–176.]
Lower plants
Isoetes 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 moss Kulindobryum from the Middle Jurassic of Russia, which was found associated with dinosaur bones, is thought to be related to the Splachnaceae, which grow on animal caracasses.
The liverwort Pellites from the Middle Jurassic Xishanyao Formation of China is the oldest record of the family Pelliaceae.
Fauna
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.
, 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
Advanced
Theropoda belonging to
Neotheropoda first appeared in the Late Triassic. Basal neotheropods, such as
Coelophysoidea and
Dilophosauridae, persisted into the Early Jurassic, but became extinct by the Middle Jurassic.
The earliest
appear during the Early Jurassic, with the earliest known member of
Ceratosauria being
Saltriovenator from the early Sinemurian (199.3–197.5 Ma) 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.
first appeared during the Middle Jurassic, including early
Tyrannosauroidea 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
Alvarezsauroidea,
[Qin, Z., Clark, J., Choiniere, J., & Xu, X. (2019). A new alvarezsaurian theropod from the Upper Jurassic Shishugou Formation of western China. Scientific Reports, 9: 11727. ] 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
Troodontidae is suggested to be
Hesperornithoides from the Late Jurassic of North America. Tooth remains suggested to represent those of
Dromaeosauridae are known from the Jurassic, but no body remains are known until the Cretaceous.
, a ceratosaurid from the Late Jurassic of North America]]
, a basal tetanuran from the Middle Jurassic of China]]
Birds
The earliest
Avialae, 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.
Ornithischians
The earliest definitive
appear during the Early Jurassic, represented by basal ornithischians like
Lesothosaurus, heterodontosaurids, and early members of
Thyreophora. The earliest members of
Ankylosauria and
Stegosauria appear during the Middle Jurassic.
The basal
Kulindadromeus from the Middle Jurassic of Russia indicates that at least some ornithischians were covered in protofeathers.
The earliest members of
Ankylopollexia, which become prominent in the Cretaceous, appeared during the Late Jurassic, represented by bipedal forms such as
Camptosaurus.
first appeared in the Late Jurassic of China, represented by members of
Chaoyangsauridae.
Sauropodomorphs
Sauropoda 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.
Basal bipedal Sauropodomorpha, such as Massospondylidae, continued to exist into the Early Jurassic, but became extinct by the beginning of the Middle Jurassic.
Other reptiles
Crocodylomorphs
The Triassic–Jurassic extinction decimated
diversity, with
Crocodylomorpha, which originated during the early Late Triassic, being the only group of pseudosuchians to survive. All other pseudosuchians, including the herbivorous
and carnivorous "
rauisuchians", became extinct.
The morphological diversity of crocodylomorphs during the Early Jurassic was around the same as that of Late Triassic pseudosuchians, but they occupied different areas of morphospace, suggesting that they occupied different
to their Triassic counterparts and that there was an extensive and rapid radiation of crocodylomorphs during this interval.
While living
are mostly confined to an aquatic ambush predator lifestyle, Jurassic crocodylomorphs exhibited a wide variety of life habits. An unnamed
Protosuchidae known from teeth from the Early Jurassic of Arizona represents the earliest known herbivorous crocodylomorph, an adaptation that appeared several times during the Mesozoic.
The Thalattosuchia, a clade of predominantly marine crocodylomorphs, first appeared during the Early Jurassic and became a prominent part of marine ecosystems.
Turtles
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 testudinates.
The two modern groups of turtles (
Turtle),
Pleurodira and
Cryptodira, diverged by the beginning of the Late Jurassic.
The oldest known pleurodires, the
Platychelyidae, are known from the Late Jurassic of Europe and the Americas,
while the oldest unambiguous cryptodire,
Sinaspideretes, an early relative of
Trionychidae, is known from the Late Jurassic of China.
The
Thalassochelydia, a diverse lineage of marine turtles unrelated to modern
, are known from the Late Jurassic of Europe and South America.
Lepidosaurs
(the sole living representative being the
tuatara) had achieved a global distribution by the beginning of the Jurassic,
and represented the dominant group of small reptiles during the Jurassic globally.
Rhynchocephalians reached their highest morphological diversity in their evolutionary history during the Jurassic, occupying a wide range of lifestyles, including the aquatic
Pleurosauridae with long snake-like bodies and reduced limbs, the specialized herbivorous
Eilenodontinae, as well as the
sapheosaurs which had broad tooth plates indicative of
durophagy.
Rhynchocephalians disappeared from Asia after the Early Jurassic.
The last common ancestor of living
Squamata (which includes
and
) 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.
from the Late Jurassic of Germany has been suggested to be an early relative of
and displays adaptations for climbing.
from the Late Jurassic of North America and Europe represents the oldest widely accepted record of
Anguimorpha.
from the Middle Jurassic of Britain has been suggested to represent a late surviving lepidosauromorph outside both Rhynchocephalia and Squamata, though some studies have recovered it as a stem-squamate.
, a rynchocephalian from the Upper Jurassic Solnhofen Limestone of Germany]]
, a rynchocephalian from the Solnhofen Limestone]]
,'', an aquatic rhynchocephalian from the Late Jurassic of Europe]]
Choristoderes
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
Ichthyosauria suffered an evolutionary bottleneck during the end-Triassic extinction, with all non-
becoming extinct. Ichthyosaurs reached their apex of species diversity during the Early Jurassic, with an array of morphologies including the huge
apex predator Temnodontosaurus 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
Plesiosauria originated at the end of the Triassic (Rhaetian). By the end of the Triassic, all other
, including
Placodontia and
, 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
Microcleididae 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
Thalassophonea 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 , 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.
Pterosaurs
first appeared in the Late Triassic. A major radiation of Jurassic pterosaurs is the Rhamphorhynchidae, which first appeared in the late Early Jurassic (Toarcian);
they are thought to been
Piscivore.
, which first appeared in the Middle Jurassic, possessed short heads and densely furred bodies, and are thought to have been insectivores.
Derived
pterosaurs such as
Wukongopteridae appeared in the late Middle Jurassic. Advanced short-tailed
Pterodactyloidea first appeared at the Middle–Late Jurassic boundary. Jurassic pterodactyloids include the ctenochasmatids, like
Ctenochasma, which have closely spaced needle-like teeth that were presumably used for
Filter feeder.
The bizarre Late Jurassic ctenochasmatoid
Cycnorhamphus had a jaw with teeth only at the tips, with bent jaws like those of living
that may have been used to hold and crush hard invertebrates.
Amphibians
The diversity of
Temnospondyli had progressively declined through the Late Triassic, with only
Brachyopoidea surviving into the Jurassic and beyond.
Members of the family
Brachyopidae are known from Jurassic deposits in Asia,
while the
Chigutisauridae Siderops is known from the Early Jurassic of Australia.
Modern
began to diversify during the Jurassic. The Early Jurassic
Prosalirus thought to represent the first frog relative with a morphology capable of hopping like living frogs.
Morphologically recognisable stem-frogs like the South American
Notobatrachus are known from the Middle Jurassic,
with modern crown-group frogs like
Enneabatrachus and
Rhadinosteus appearing by the Late Jurassic.
While the earliest salamander-line amphibians are known from the Triassic,
salamanders first appear during the Middle to Late Jurassic in Eurasia, alongside stem-group relatives. Many Jurassic stem-group salamanders, such as
Marmorerpeton and
Kokartus, are thought to have been
Neoteny.
Early representatives of crown group salamanders include
Chunerpeton, Pangerpeton and
Linglongtriton from the Middle to Late Jurassic
Yanliao Biota of China. Some of these are suggested to belong to Cryptobranchoidea, which contains living Asiatic and
.
, and
Qinglongtriton from the same biota are thought to be early members of
Salamandroidea, the group which contains all other living salamanders.
Salamanders dispersed into North America by the end of the Jurassic, as evidenced by
Iridotriton, found in the Late Jurassic Morrison Formation.
The stem-
caecilian Eocaecilia is known from the Early Jurassic of Arizona.
The fourth group of lissamphibians, the extinct salamander-like albanerpetontids, first appeared in the Middle Jurassic, represented by
Anoualerpeton from the Bathonian of Britain, as well as indeterminate remains from equivalently aged sediments in France and the
Anoual Formation of Morocco.
,'' a likely arboreal dyolestoid from the Late Jurassic of Portugal]]
Mammaliaformes
Mammaliaformes, including
, having originated from
at the end of the Triassic, diversified extensively during the Jurassic.
While most Jurassic mammalaliaforms are solely known from isolated teeth and jaw fragments, exceptionally preserved remains have revealed a variety of lifestyles.
The
Castorocauda was adapted to aquatic life, similarly to the
platypus and
.
Some members of
Haramiyida and the
tribe
Volaticotherini[Meng, J.; Hu, Y.-M.; Wang, Y.-Q.; Wang, X.-L.; Li, C.-K. (2007). "Corrigendum: A Mesozoic gliding mammal from northeastern China". Nature 446 (7131): 102. . .] had a
patagium akin to those of
, 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
.
, a group of mammals possibly related to living
, first appeared in the Middle Jurassic of Gondwana.
The earliest records of
Multituberculata, one of the longest lasting and most successful orders of mammals, are known from the Middle Jurassic.
mammals, represented today by living
Placentalia and
, diversified meteorically during the Middle Jurassic.
They have their earliest records during the early Late Jurassic, represented by
Juramaia, a
mammal closer to the ancestry of placentals than marsupials.
[ Electronic supplementary material] Juramaia is much more advanced than expected for its age, as other therian mammals are not known until the Early Cretaceous, and it has been suggested that
Juramaia may also originate from the Early Cretaceous instead.
Two groups of non-mammaliaform 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.
Fish
Jawless fish
The last known species of
conodont, a class of
Agnatha 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.
from the Middle Jurassic of China represents the oldest post Paleozoic
lamprey, and the oldest lamprey to have the toothed feeding apparatus and likely the three stage life cycle typical of modern members of the group.
Sarcopterygii
Lungfish (Dipnoi) were present in freshwater environments of both hemispheres during the Jurassic.
Some studies have proposed that the last common ancestor of all living lungfish lived during the Jurassic.
, a marine and freshwater/brackish group of
, which first appeared in North America during the Triassic, expanded into Europe and South America by the end of the Jurassic.
The marine
Latimeriidae, which contains the living coelacanths of the genus
Latimeria, were also present in the Jurassic, having originated in the Triassic, with a number of records from the Jurassic of Europe including
Swenzia, thought to be the closest known relative of living coelacanths.
Actinopterygii
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
sturgeon and
paddlefish, are from the Early Jurassic.
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,
with the modern family
Amiidae appearing during the Late Jurassic.
, 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
(Lepisosteidae) were diverse in both freshwater and marine environments. The oldest known representatives of anatomically modern gars appeared during the Late Jurassic.
Stem-group
, which make up over 99% of living Actinopterygii, had first appeared during the Triassic in the western Tethys; they underwent a major diversification beginning in the Late Jurassic, with early representatives of modern teleost clades such as
Elopomorpha and
Osteoglossoidei appearing during this time.
[Arratia G. Mesozoic halecostomes and the early radiation of teleosts. In: Arratia G, Tintori A, editors. Mesozoic Fishes 3 – Systematics, Paleoenvironments and Biodiversity. München: Verlag Dr. Friedrich Pfeil; 2004. p. 279–315.] 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.
[Liston, J., Newbrey, M., Challands, T., and Adams, C., 2013, "Growth, age and size of the Jurassic pachycormid Leedsichthys problematicus (Osteichthyes: Actinopterygii) in: Arratia, G., Schultze, H. and Wilson, M. (eds.) Mesozoic Fishes 5 – Global Diversity and Evolution. Verlag Dr. Friedrich Pfeil, München, Germany, pp. 145–175]
Chondrichthyes
During the Early Jurassic, the shark-like
Hybodontiformes, which represented the dominant group of
Chondrichthyes 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
Neoselachii, 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
Hexanchiformes and
(Orectolobiformes) are from the Early Jurassic (Pliensbachian and Toarcian, respectively) of Europe.
The oldest known members of the Heterodontiformes, the only living members of which are the
bullhead shark (
Heterodontus), first appeared in the Early Jurassic, with representatives of the living genus appearing during the Late Jurassic.
The oldest record of angelsharks (
Squatiniformes) is
Pseudorhina from the Late Jurassic (Oxfordian–Tithonian) of Europe, which already has a bodyform similar to members of the only living genus of the order,
Squatina.
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
Scyliorhinidae.
Synechodontiformes, an extinct group of sharks closely related to Neoselachii, were also widespread during the Jurassic.
The oldest remains of modern
are from the Early Jurassic of Europe, with members of the living family
Callorhinchidae appearing during the Middle Jurassic. Unlike most living chimaeras, Jurassic chimeras are often found in shallow water environments.
The closely related
Myriacanthidae and the flattened
Squaloraja are also known from the Jurassic of Europe.
Insects and arachnids
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
,
particularly for the suborder
Polyphaga, which represents 90% of living beetle species but which was rare during the preceding Triassic.
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.
diversity had declined during the Late Triassic, but recovered during the Early Jurassic,
with the
Hagloidea, a superfamily of
orthopterans today confined to a few living species, being particularly diverse during the Jurassic.
The oldest known
(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.
Modern representatives of both
Dragonfly and
Damselfly also first appeared during the Jurassic.
Although modern representatives are not known until the Cenozoic,
ectoparasitic insects thought to represent primitive
, 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.
(
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),
(gladiators),
(webspinners),
and
Raphidioptera (snakeflies).
The earliest
scale insect (Coccomorpha)
is known from amber dating to the Late Jurassic, though the group probably originated earlier during the Triassic.
Only a handful of records of mites are known from the Jurassic, including
Jureremus, an
Oribatida mite belonging to the family
Cymbaeremaeidae known from the Late Jurassic of Britain and Russia,
and a member of the still living orbatid genus
Hydrozetes from the Early Jurassic of Sweden.
Spiders diversified through the Jurassic.
The Early Jurassic
Seppo koponeni may represent a stem group to
Palpimanoidea.
from the Middle Jurassic of China is considered a stem lineage of
Synspermiata. The oldest member of the family
Archaeidae,
Patarchaea, is known from the Middle Jurassic of China.
from the Middle Jurassic of China is among the largest known fossil spiders, with legs over 5 centimetres long.
The only scorpion known from the Jurassic is
Liassoscorpionides from the Early Jurassic of Germany, of uncertain placement.
harvestmen (
Opiliones) are known from the Middle Jurassic of China, including members of the family
Sclerosomatidae.
Marine invertebrates
End-Triassic extinction
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. Sessile
and
photosymbiotic organisms were among those most severely affected.
Marine ecosystems
Having declined at the Triassic–Jurassic boundary, reefs substantially expanded during the Late Jurassic, including both
and
. Late Jurassic reefs were similar in form to modern reefs but had more microbial carbonates and hypercalcified
, and had weak biogenic binding. Reefs sharply declined at the close of the Jurassic,
which caused an associated drop in diversity in
Decapoda 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.
and
, which had first appeared during the Triassic, radiated during the Early to Middle Jurassic, becoming prominent members of the
phytoplankton.
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.
Echinoderms
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
Cyrtocrinida and
Millericrinida.
(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.
Crustaceans
The Jurassic was a significant time for the evolution of
Decapoda.
The first true crabs (
Crab) are known from the Early Jurassic, with the earliest being
Eocarcinus from the early Pliensbachian of England, which lacked the crab-like morphology (
carcinisation) of modern crabs,
and
Eoprosopon 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.
also first appeared during the Jurassic, with the earliest known being
Schobertella from the late Hettangian of Germany.
Early hermit crabs are associated with ammonite shells rather than those of gastropods.
, 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.
Brachiopods
Brachiopod diversity declined during the Triassic–Jurassic extinction. Spire-bearing brachiopods (
Spiriferinida and
Athyridida) did not recover their biodiversity, becoming extinct in the TOAE.
and
Terebratulida also declined during the Triassic–Jurassic extinction but rebounded during the Early Jurassic; neither clade underwent much morphological variation.
Brachiopods substantially declined in the Late Jurassic; the causes are poorly understood. Proposed reasons include increased predation, competition with bivalves, enhanced
bioturbation or increased
grazing pressure.
Bryozoans
Like the preceding Triassic,
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
Tubuliporina and Cerioporina.
Cheilostomata, the dominant group of modern bryozoans, first appeared during the Late Jurassic.
Molluscs
Gastropods
Marine gastropods were significantly affected by the T-J extinction, with around 56% of genera going extinct, with
Neritimorpha being particularly strongly effected, while
Heterobranchia suffered much lower losses than other groups.
While present, the diversity of
Freshwater snail and
was much lower during the Jurassic than in contemporary ecosystems, with the diversity of these groups not reaching levels comparable to modern times until the following Cretaceous.
Bivalves
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.
, 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.
Cephalopods
'' from the Middle Jurassic of France, formerly thought to be world's 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
Psiloceratina,
Ammonitina,
Lytoceratina,
Haploceratoidea,
Perisphinctoidea 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.
Ammonite diversifications occurred coevally with marine transgressions, while their diversity nadirs occurred during marine regressions.
The oldest definitive records of the squid-like Belemnitida are from the earliest Jurassic (Hettangian–Sinemurian) of Europe and Japan; they expanded worldwide during the Jurassic.
The earliest Vampyromorphida, of which the only living member is the vampire squid, first appeared during the Early Jurassic.
Citations
External links
