Jurassic

Jurassic stratigraphy is primarily based around of the use of ammonites as index fossils, with the First Appearance Datum of specific ammonite taxa being used to mark the beginnings of stages, and 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.[13]

Base Aalenian GSSP at Fuentelsaz

The oldest part of the Jurassic period has historically been referred to as the Lias or Liassic, roughly equivalent in extent to the Early Jurassic, but also including part of the preceding Rhaetian. The Hettangian stage was named by Swiss palaeontologist Eugène Renevier in 1864 after Hettange-Grande in North-Eastern France. The Global Boundary Stratotype Section and Point (GSSP) for the base of the Hettangian is located at Kuhjoch pass, Karwendel Mountains, Northern Calcareous Alps, Austria, which was ratified in 2010. The beginning of the Hettangian, and thus the Jurassic as a whole, is marked by the first appearance of the ammonite Psiloceras spelae tirolicum in the Kendlbach Formation exposed at Kuhjoch.[15] 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.[13]

The Sinemurian stage was defined and introduced into scientific literature by Alcide d'Orbigny in 1842. It takes its name from the French town of Semur-en-Auxois, near Dijon. The original definition of Sinemurian included what is now the Hettangian. The GSSP of the Sinemurian is located at a cliff face north of the hamlet of East Quantoxhead, 6 kilometres east of Watchet, Somerset, England, within the Blue Lias. The beginning of the Sinemurian is defined by the first appearance of the ammonite Vermiceras quantoxense.[13][16]

The Pliensbachian was named by German palaeontologist Albert Oppel in 1858 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. The beginning of the Pliensbachian is defined by the first appearance of the ammonite Bifericeras donovani.[17]

The Toarcian is named after the village Thouars (Latin: Toarcium), just south of Saumur in the Loire Valley of France, it was defined by Alcide d'Orbigny in 1842 originally from Vrines quarry around 2 km northwest of the village. The GSSP for the base of the Toarcian is located at Peniche, Portugal. The boundary is defined by the first appearance of ammonites belonging to the subgenus Dactylioceras (Eodactylioceras).[18]

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.[13] The GSSP for the base of the Aalenian is located at Fuentelsaz in the Iberian range near Guadalajara, Spain. The base of the Aalenian is defined by the first appearance of the ammonite Leioceras opalinum.[19]

The Bajocian is named after the town of Bayeux (Latin: Bajoce) in Normandy, France, and was defined by Alcide d'Orbigny in 1842. The GSSP for the base of the Bajocian is located at Murtinheira in Portugal, and was defined in 1997. The base of the Bajocian is defined by the first appearance of the ammonite Hyperlioceras mundum.[20]

The Bathonian is named after the city of Bath, England, introduced by Belgian geologist d'Omalius d'Halloy in 1843, after an incomplete section of oolitic limestones in several quarries in the region. The GSSP for the base of the Bathonian is Ravin du Bès, Bas-Auran area, Alpes de Haute Provence, France, which was defined 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.[21]

The Callovian is derived from the Latinized name of the village of Kellaways in Wiltshire, England, and was defined by Alcide d'Orbigny in 1852, originally with base at the contact between the Forest Marble Formation and the Cornbrash Formation. However, this boundary was later found to be situated within the upper part of the Bathonian. The base of the Callovian does not yet have a certified GSSP, as of 2019.[13]

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.[13]

The Kimmeridgian is named after the village of Kimmeridge on the coast of Dorset, England. It was named by Alcide d'Orbigny in 1842, in reference to the Kimmeridge Clay. Although not confirmed, the Flodigarry section at Staffin Bay on the Isle of Skye, Scotland has been submitted as the GSSP for the base of the Kimmeridgian.[22]

The Tithonian was introduced in scientific literature by Albert Oppel in 1865. The name Tithonian is unusual in geological stage names because it is derived from Greek mythology rather than a placename. Tithonus was the son of Laomedon of Troy and fell in love with Eos, the Greek goddess of dawn. His name was chosen by Albert Oppel for this stratigraphical stage because the Tithonian finds itself hand in hand with the dawn of the Cretaceous. The base of the Tithonian currently lacks a GSSP.[13] The upper boundary of the Jurassic is also currently undefined. Calpionellids, an enigmatic group of pelagic protists with urn shaped calcitic tests briefly abundant during the latest Jurassic to earliest Cretaceous, have been suggested to represent the most promising candidates for fixing the J/K boundary.[23]

The Kimmeridge Clay and equivalents are the major source rock for the North Sea oil.[24] The Arabian Intrashelf Basin, deposited from the late Middle to Upper Jurassic, is the setting of the world's largest oil reserves, including the Ghawar Field, the world largest oil field.[25] The Jurassic aged Sargelu[26] and Naokelekan Formations[27] are major source rocks for oil in Iraq. Over 1500 gigatons of Jurassic coal reserves are found in North-West China, primarily in the Turpan-Hami Basin and the Ordos Basin.[28]

Major impact craters include the Morokweng crater, a 70 km diameter crater buried beneath the Kalahari desert in northern South Africa. The impact is dated to the Jurassic-Cretaceous boundary, around 145 Ma. The Morokweng crater has been suggested to have had a role in the turnover at the Jurassic-Cretaceous transition.[29] Another major impact crater is the Puchezh-Katunki crater, 40-80 kilometres in diameter, buried beneath Nizhny Novgorod Oblast, Russia. The impact has been dated to the Sinemurian, around 192-196 Mya.[30]

The Toarcian Oceanic Anoxic Event (TOAE) was an episode of widespread oceanic anoxia during the early part of the Toarcian period, c. 183 Mya. It is marked by a globally documented high amplitude negative carbon isotope excursion,[45] as well as the deposition of black shales, and the extinction and collapse of carbonate producing marine organisms. The cause is often linked to the eruption of the Karoo-Ferrar large igneous provinces and the associated increase of carbon dioxide concentration in the atmosphere and the possible associated release of methane clathrates. This likely accelerated the hydrological cycle and increased silicate weathering. Groups affected include ammonites, ostracods, foraminifera, brachiopods, bivalves and cnidarians,[46][47] with the last two spire-bearing brachiopod orders Spiriferinida and Athyridida becoming extinct.[48] While the event had significant impact on marine invertebrates, it had little effect on marine reptiles.[49] During the TOAE, the Sichuan Basin was transformed into a giant lake, probably 3 times the size of Lake Superior, represented by the Da’anzhai Member of the Ziliujing Formation. The lake likely sequestered ∼460 Gigatons (Gt) of organic carbon and ∼1,200 Gt of inorganic carbon during the event.[50] 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.[51] This ocean acidification is what likely caused the collapse of carbonate production.[52][53]

The end-Jurassic transition was originally considered one of eight mass extinctions, but is now considered to be 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.[29]

The preceding end-Triassic extinction would result in the decline of Peltaspermaceae seed ferns, with Lepidopteris perisisting into the Early Jurassic in Patagonia.[54] At the Triassic-Jurassic boundary in Greenland, the sporomorph diversity suggests a complete floral turnover.[55] An analysis of macrofossil floral communities in Europe suggests no extinction over the Triassic-Jurassic boundary, and that changes were mainly due to local ecological succession.[56] Dicroidium, a seed fern that was a dominant part of Gondwanan floral communities during the Triassic, would decline at the T-J, boundary, surviving as a relict in Antarctica into the Sinemurian.[57]

Flowering plants, which make up 90% of living plant species, have no records from the Jurassic, with no claim of Jurassic representatives of the group having gained widespread acceptance.[58]

Petrified Araucaria maribilis cone

Trees of the Jurassic were dominated by conifers and modern conifier groups would diversify throughout the period.

Araucarian conifers were widespread across both hemispheres. The divergence between Araucaria and the branch containing Wollemia and Agathis is estimated to have taken place during the Mid-Jurassic, based on Araucaria mirabilis and Araucaria sphaerocarpa from the Middle Jurassic of Argentina and England respectively, which are early members of the Araucaria lineage. Representatives of Wollemia-Agathis lineage are not known until the Cretaceous.[59][60]

Also abundant during the Jurassic is the extinct family Cheirolepidiaceae, often recognised by their highly distinctive Classopolis pollen. Jurassic representatives include the pollen cone Classostrobus and the seed cone Pararaucaria. Both Araucarian and Cheirolepidiaceae confiers often occur in association.[61]

The oldest definitive record of the cypress family (Cupressaceae) is Austrohamia minuta from the Early Jurassic (Pliensbachian) of Patagonia, known from several elements.[62] Austrohamia is thought to have close affinities with Taiwania and Cunninghamia. By the Mid-Late Jurassic Cupressaceae were abundant in warm temperate-tropical regions of the Northern Hemisphere, most abundantly represented by the genus Elatides.[63] The seed cone Scitistrobus from the Middle Jurassic (Aalenian) of Scotland displays a mosaic of traits indicative of ancestral Voltziales and derived Cupressaceae.[64]

The oldest record of the pine family (Pinaceae) is the seed cone Eathiestrobus, known from the Late Jurassic (Kimmeridgian) also of Scotland.[65] During the Early Jurassic, the flora of the mid-latitudes of Eastern Asia were dominated by the extinct deciduous broad leafed conifer Podozamites, likely of voltzialean affinities, with its range extending northwards into polar latitudes of Siberia, but its range contracted northward in the Middle-Late Jurassic corresponding to the increasing aridity of the region.[66]

The earliest record of the yew family (Taxaceae) is Palaeotaxus rediviva, from the Hettangian of Sweden, suggested to be closely related to Austrotaxus, while Marskea jurassica from the Middle Jurassic of Yorkshire, England and material from the Callovian-Oxfordian Daohugou bed in China are thought to be closely related to Amentotaxus. The Daohugou material in particular is extremely similar to living Amentotaxus, only differing in having shorter seed-bearing axes.[67]

Podocarpaceae, today largely confined to the Southern Hemisphere occurs in the Northern Hemisphere during the Jurassic, including Podocarpophyllum from the Lower-Middle Jurassic of Central Asia and Siberia.[68] Scarburgia from the Middle Jurassic of Yorkshire,[69] and Harrisiocarpus from the Jurassic of Poland.[70]

Ginkgoales, which are currently represented by the single living species Ginkgo biloba, were more diverse during the Jurassic, they were among the most important components of Laurasian Jurassic floras, and were adapted to a wide variety of climatic conditions. Based on reproductive organs several lineages can be distinguished, including Yimaia, Grenana, Nagrenia and Karkenia, alongside Ginkgo. These lineages are associated with leaf morphotaxa such as Baiera, Ginkgoites and Sphenobaiera, some of which overlap with the morphological variability and growth stages of living Ginkgo biloba leaves and therefore cannot be used for reliable taxonomic identification.[71][72] Umaltolepis, historically thought to be ginkgoalean, and Vladimaria from the Jurassic of Asia have strap shaped ginkgo-like leaves (Pseudotorellia), with highly distinct reproductive structures with similarities to those of peltasperm and corystosperm seed ferns, and have been placed in the separate order Vladimariales, which may belong to a broader Ginkgoopsida.[73]

The ground cover was dominated by ferns, including members of the living families Dipteridaceae, Matoniaceae, Osmundaceae and Marattiaceae,[74] as well as horsetails. Polypodiales, which today make up 80% of living fern diversity, have no record from the Jurassic, and are thought to have diversified in the Cretaceous,[75] though the widespread Jurassic herbaceous fern genus Coniopteris, historically interpreted as a close relative of tree ferns of the family Dicksoniaceae, has recently been reinterpreted as an early relative of the group.[76]

A calicfied rhizome of an Osmundaceous fern from the Early Jurassic of Sweden belongs to the stem group of the living genus Osmundastrum, with the preservation showing the remains of chromosomes during cell division.[77] An analysis of the Osmundastrum rhizome found that it had been interacted with by numerous organisms, including lycopsid roots growing into the rhizome, probable peronosporomycetes as well as boring and coprolites likely by orbatid mites.[78]

The oldest remains of modern horsetails of the genus Equisetum first appear in the Early Jurassic, represented by Equisetum dimorphum from the Early Jurassic of Patagonia[79] and Equisetum laterale from the Early-Middle Jurassic of Australia.[80][81] Silicified remains of Equisetum thermale from the Late Jurassic of Argentina exhibit all the morphological characters of modern members of the genus.[82] The estimated split between Equisetum bogotense and all other living Equisetum is estimated to have occurred no later than the Early Jurassic.[81]

The Cyatheales, the group containing most modern tree ferns would appear during the Late Jurassic, represented by members of the genus Cyathocaulis, which are suggested to be early members of Cyatheaceae based on cladistic analysis.[83] Only a handful of possible records exist of the Hymenophyllaceae are known from the Jurassic, including Hymenophyllites macrosporangiatus from the Russian Jurassic.[84]

Bennettitales are a group of seed plants widespread throughout the Mesozoic with foliage bearing strong similarities to those of cycads, to the point of morphologically indistinguishable. Benettitales can be distinguished from cycads by the fact they have a different arrangement of stomata, and are not thought to be closely related.[85] Benettitales have morphologies varying from cycad-like to shubs and small trees. The Williamsoniaceae grouping is thought to have had a divaricate branching habit, similar to living Banksia, and adapted to growing in open habitats with poor soil nutrient conditions.[86] Benettitales exhibit complex, flower like reproductive structures that are thought to have been pollinated by insects. Several groups of insects that bear long proboscis, including extinct families like Kalligrammatid lacewings[87] and extant Acroceridae flies,[88] are suggested to have been pollinators of benettitales, feeding on nectar produced by bennettitalean cones.

Cycads were present during the Jurassic, the living groups of cycads have been suggested to have diverged from each other in the Early Jurassic,[89] though a later analysis placed this divergence during the Late Permian, which placed the diversification of the Zamiineae cycads during the Jurassic.[90] Cycads are difficult to distinguish from Bennettitales based on leaf morphology alone. Cycads are thought to have been a relatively minor component of mid-Mesozoic floras.[91] and mostly confined to tropical and subtropical latitudes.[92] Cycad foliage is assigned to morphogenera including Ctenis and Pterophyllum, but are not phylogenetically informative. Seeds from the late Callovian-early Oxfordian Oxford Clay are definitively assignable to the living family Cycadaceae.[93] While seeds found in the gut of the dinosaur Isaberrysaura from the Middle Jurassic of Argentina are assigned to Zamiineae, which includes all other living cycads.[94] The Nilssoniales, such as the leaf genus Nilssonia with leaves morphologically similar to those of cycads, have often been considered cycads or cycad relatives, but have been found to be distinct, perhaps more closely allied with Bennettitales.[92]

Protognetum from the Middle Jurassic of China is oldest known member of the gnetophytes and the only one known from the Jurassic. It exhibits characteristics of both Gnetum and Ephedra, and is placed in the monotypic family Protognetaceae.[95]

Sagenopteris phillipsi (Cayoniales) from the Middle Jurassic of Yorkshire, England

Seed ferns (Pteridospermatophyta) is a collective term to refer to disparate lineages of fern like plants that produce seeds, with uncertain affinities to living seed plant groups. Prominent groups of Jurassic seed ferns include Caytoniales, which includes the leaf taxon Sagenopteris, Caytonanthus pollen structures and Caytonia ovulate structures, often found in close association. They have frequently been suggested to have been closely related or perhaps ancestral to flowering plants, but no definitive evidence of this has been discovered.[96] The other prominent group is the Corystospermales, including genera like the leaf genus Pachypteris, prominent in the Jurassic of the Northern Hemisphere. As well as pollen organs belonging to Pteruchus and Umkomasia ovulate structures.[97][98]

Czekanowskiales, also known as Leptostrobales, are a group of gymnosperms of uncertain affinities with persistent leaves borne on deciduous short shoots, subtended by scale-like leaves, known from the Late Triassic (possibly Late Permian[99]) to Cretaceous.[100] They are thought to have had a tree or shrub like habit, and formed a conspicuous component of Mesozoic temperate and warm–temperate floras.[99] Jurassic genera include the leaf genera Czekanowskia, Phoenicopsis and Solenites, associated with the ovulate cone Leptostrobus.[100]

The Pentoxylales are a small group of gymnosperms of obscure affinities, known from the Jurassic and Cretaceous of Gondwana. These include the stems Pentoxylon, strap-shaped leaves Taeniopteris (more broadly used as a morphogenus representing other plant types) and Nipaniophyllum for well preserved leaves, Sahnia pollen organs, and Carnoconites seed-bearing structures. The habit of the group is uncertain, but may have been small trees.[100]

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.[101]

The moss Kulindobryum from the Middle Jurassic of Russia is thought to have affinites with the Splachnaceae, while Bryokhutuliinia from the same region is thought to have affinities with Dicranales.[102] Heinrichsiella from the Jurassic of Patagonia is thought to belong to the families Polytrichaceae or Timmiellaceae basal to Bryidae, and is the oldest representative of the grade.[103]

The liverwort Pellites hamiensis from the Middle Jurassic Xishanyao Formation of China is the oldest record of the family Pelliaceae.[104] Pallaviciniites sandaolingensis from the same deposit is thought to belong to the subclass Pallaviciniineae within the Pallaviciniales.[105] Ricciopsis sandaolingensis also from the same deposit is the only Jurassic record of Ricciaceae.[106]

In an analysis of the ferns of the Hettangian aged Mecsek Coal Formation found that the predominant groups of ferns by order of abundance belonged to the families Dipteridaceae (48% of collected specimens) Matoniaceae (25%), Osmundaceae (21%), Marattiaceae (6%) and 3 specimens of Coniopteris. They found that most of the ferns likely grew in monospecific thickets in disturbed areas.[74] The Middle-Late Jurassic Daohugou flora of China was dominated by Gymnosperms and ferns, with the most abundant group of gymnosperms being Bennettitales, followed by conifers and ginkgophytes.[107] High latitude floras of the New Zealand Jurassic were of low diversity, with only 43 species being recorded dominated by "conifers, ferns, bennettitaleans, pentoxylaleans and locally, equisetaleans" with Ginkgoales being entirely absent.[108] The flora of the Middle Jurassic Stonesfield Slate of England was dominated by "araucariacean and cheirolepidiacean conifers, bennettitaleans, and leaves of the possible gymnosperm Pelourdea" representing a coastal environment.[109]

During the Jurassic period, the primary vertebrates living in the sea were fish and marine reptiles. The latter include ichthyosaurs, which were at the peak of their diversity, plesiosaurs, including pliosaurs, and marine thalattosuchian crocodyliformes of the families Teleosauridae, Machimosauridae and Metriorhynchidae.[110]

Calcareous sabellids (Glomerula) appeared in the Early Jurassic.[111][112] The Jurassic also had diverse encrusting and boring (sclerobiont) communities, and it saw a significant rise in the bioerosion of carbonate shells and hardgrounds. Especially common is the ichnogenus (trace fossil) Gastrochaenolites.[113] During the Jurassic period, about four or five of the twelve clades of planktonic organisms that exist in the fossil record either experienced a massive evolutionary radiation or appeared for the first time.[14]

• 
  Ichthyosaurus from lower (early) Jurassic slates in southern Germany featured a dolphin-like body shape.
• 
  Plesiosaurs like Muraenosaurus roamed Jurassic oceans.
• 
  Gastropod and attached mytilid bivalves on a Jurassic limestone bedding plane in southern Israel.

Terrestrial environment of the Toarcian of Łęczna (Ciechocinek Formation, Lublin, Poland), based on the Bogdanka Coal Mine Flora. Dinosaurs are based on material found on various locations of the formation

On land, various archosaurian reptiles remained dominant. The Jurassic was a golden age for the large herbivorous dinosaurs known as the sauropods—Camarasaurus, Apatosaurus, Diplodocus, Brachiosaurus, and many others—that roamed the land late in the period; their foraging grounds were either the prairies of ferns, palm-like cycads and bennettitales, or the higher coniferous growth, according to their adaptations. The smaller Ornithischian herbivore dinosaurs, like stegosaurs and small ornithopods were less predominant, but played important roles. They were preyed upon by large theropods, such as Ceratosaurus, Megalosaurus, Torvosaurus and Allosaurus, all these belong to the 'lizard hipped' or saurischian branch of the dinosaurs.[114]

During the Late Jurassic, the first avialans, like Archaeopteryx, evolved from small coelurosaurian dinosaurs. In the air, pterosaurs were common; they ruled the skies, filling many ecological roles now taken by birds,[115] and may have already produced some of the largest flying animals of all time.[116][117] Within the undergrowth were various types of early mammals, as well as tritylodonts, lizard-like sphenodonts, and early lissamphibians. The rest of the Lissamphibia evolved in this period, introducing the first salamanders and caecilians.[118]

• 
  Diplodocus, reaching lengths over 30 m, was a common sauropod during the late Jurassic.
• 
  Allosaurus was one of the largest land predators of the Jurassic.
• 
  Stegosaurus is one of the most recognizable genera of dinosaurs and lived during the mid to late Jurassic.
• 
  Aurornis xui, which lived in the late Jurassic, may be the most primitive avialan dinosaur known to date, and is one of the earliest avialans found to date.

Cast of the holotype of Protosuchus

Holotype specimen of Platysuchus, a telosaurid

The T-J extinction decimated pseudosuchian diversity, with crocodylomorphs, which originated during the early Late Triassic (Norian), being the only group of pseudosuchians to survive the T-J extinction. The morphological diversity of crocodylomorphs during the Early Jurassic was around the same as those of Late Triassic pseudosuchians, but occupied different areas of morphospace, suggesting that they occupied different ecological niches to their Triassic counterparts, and that there was an extensive and rapid radiation of crocodylomorphs during this interval.[119] While living crocodilians are confined to an aquatic ambush predator lifestyle, Jurassic crocodyliformes exhibit a wide variety of life habits, with the earliest known herbivorous crocodylomorph being an unnamed species of protosuchid from the Early Jurassic of Arizona.[120] The earliest lineages of Crocodylomorpha are represented by the terrestrial small-bodied long-legged "sphenosuchians", one lineage of which, the Hallopodidae, perisisted into the Late Jurassic.[121][122] The Thalattosuchia, a clade of predominantly marine crocodylomorphs including both teleosaurioids and metriorhynchoids, first appeared during the Early Jurassic (Toarcian), and became prominent part of marine reptile communities during the Jurassic. During the Jurassic, the Neosuchia would appear, the Neosuchia are thought to be ancestrally freshwater aquatic, similar to living crocodilians.[123] 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 goniopholidid, 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.[123] 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.[124]

Stem-group turtles (Testudinata) would diversify during the Jurassic. Jurassic stem-turtles belong to two progressively more advanced clades, the Mesochelydia and Perichelydia.[125] It is thought that the ancestral condition for Mesochelydians is aquatic, as opposed to terrestrial for Testudinata.[126] The two modern groups of turtles (Testudines), Pleurodires and Cryptodires, would diverge by the Middle Jurassic.[127][128] Early cryptodire lineages like Xinjiangchelyidae are known from the Middle Jurassic,[129] while an early stem pleurodire lineage, the ocean-going Platychelyidae is known from the Late Jurassic.[130] The Thalassochelydia, a diverse lineage of sea-turtles, is known from the Late Jurassic (Oxfordian-Tithonian) of Europe and South America.[131]

Lepidosaurs, which include squamates (lizards and snakes) and rhynchocephalians (which today only includes the tuatara) would diversify during the Jurassic, however little can be said for diversity trends due to the poor fossil record during this interval.[132] Rynchocephalians reached their highest morphological diversity in their evolutionary history during the Jurassic, occupying a wide range of lifestyles, including aquatic taxa such as pleurosaurids, the specialized herbivorous "eilenodontines" as well as Oenosaurus, which had broad tooth plates indicative of durophagy. Cynosphenodon from the Early Jurassic of Mexico is suggested to be among the closest known relatives of the living tuatara.[133] Rhynchocephalians disappeared from Asia after the Early Jurassic.[134] Crown group squamates first appeared during the Middle Jurassic of Asia and Europe,[132] with the estimated origin of living squamates during the Early Jurassic (~190 Mya) and the divergence of most major squamate groups during the Early-Middle Jurassic.[135] Many Jurassic squamates have unclear relationships to living groups.[136] Early members of the snake lineage (Ophidia) appear during the Middle Jurassic,[137] as well as the Paramacellodidae, a family of lizards which are diagnosed by their distinctive covering of osteoderms, and are thought to be early members of Scincomorpha.[138] Eichstaettisaurus from the Late Jurassic of Germany has been suggested to be an early relative of geckos, and displays adaptations for climbing.[139] Dorsetisaurus from the Late Jurassic of North America and Europe represents the oldest widely accepted record of Anguimorpha.[140] Marmoretta from the Middle Jurassic of Britain represents a late surviving lepidosauromorph outside both groups.[141]

• 
  Vadasaurus herzogi, a rynchocephalian from the Upper Jurassic Solnhofen Limestone of Germany
• 
  Homeosaurus maximiliani a rynchocephalian from the Solnhofen Limestone
• 
  Pleurosaurus, an aquatic rhynchocephalian from the Late Jurassic of Europe
• 
  Eichstaettisaurus schroederi, an extinct lizard from the Solnhofen Limestone.

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 Cteniogenys, thought to be the most basal known choristodere, which is known from the Middle-Late Jurassic of Europe and Late Jurassic of North America, with similar remains also known from the upper Middle Jurassic of Kyrgyzstan, European Russia and western Siberia.[142] The other is Coeruleodraco from the Late Jurassic of China, which has close affinities to a clade of non-Neochoristodera from the Early Cretaceous of Asia as well as Lazarussuchus from the Cenozoic of Europe.[143]

Ichthyosaurus communis

Ichthyosaurs suffered an evolutionary bottleneck, with all non-neoichthyosaurians becoming extinct at the end of the Triassic. Ichthyosaurs would reach their apex of species diversity during the Early Jurassic, with an array of morphologies including the huge apex predator Temnodontosaurus and swordfish-like Eurhinosaurus. Jurassic ichthyosaurs were significantly less morphologically diverse than their Triassic counterparts, and would become less diverse and morphologically conservative after the Early Jurassic.[144] The fossil record of ichthyosaurs during the Middle Jurassic is poor.[145] The Ophthalmosauridae, which would represent all (with the exception of Malawania) ichthyosaurs from the late Middle Jurassic onwards, first appear in the early Middle Jurassic (Bajocian), before spreading worldwide by the Late Jurassic.[146]

Skull of Pliosaurus kevani, scale bar = 50 cm

Plesiosaurs originated at the end of the Triassic (Rhaetian). By the Triassic boundary, all other sauropterygians, including placodonts and nothosaurs had become extinct. At least six lineages of plesiosaur crossed the T-J boundary.[147] Plesiosaurs were already diverse in the earliest Jurassic, with the majority of plesiosaurs in the Hettangian aged Blue Lias belonging to the Rhomaleosauridae. Early plesiosaurs were generally small-bodied forms, with body size increasing into the Toarcian.[148] The Middle Jurassic saw the evolution of short necked and large headed thalassophonean pliosaurs from ancestrally small-headed long necked forms.[149] 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 among the largest predators of Jurassic oceans.[150] Cryptoclididae, a family of long-necked plesiosaurs, would radiate beginning in the Middle Jurassic.[151] Plesiosaurs would invade freshwater environments during the Jurassic, with indeterminate remains of small bodied pleisosaurs known from freshwater sediments from the Jurassic of China and Australia.[152][153]

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),[154] and are thought to have had piscivorous habits.[155]Anurognathids, which first appeared in the Middle Jurassic, possess short heads and densely furred bodies, and are thought to have been insectivores.[155] Derived monofenestratan pterosaurs, like wukongopterids appeared in the late Middle Jurassic. Advanced short-tailed pterodactyloids 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 feeding.[155] The bizarre Late Jurassic ctenochasmatoid Cycnorhamphus possessed a jaw with teeth only at the tips, with bent jaws like those of living openbill storks, which may have been used to hold and crush hard invertebrates.[155]

Dinosaurs, which had diversified in the Late Triassic, would experience a radiation 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.[156] 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.[157]

Advanced theropods belonging to Neotheropoda first appeared in the Late Triassic. Basal neotheropods, such as coelophysoids and "dilophosaurs", perisisted into the Early Jurassic.[158] 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.[159] The unusual ceratosaur Limusaurus from the Late Jurassic of China had a herbivorous diet with adults having edentuous beaked jaws,[160] making it the earliest known theropod to have converted from an ancestrally carnivorous diet.[161] The earliest members of the Tetanurae appeared during the early Middle Jurassic.[162] The Megalosauridae represent the oldest radiation of the Tetanurae, first appearing in Europe during the Bajocian.[163] The oldest member of Allosauroidea has been suggested to be Asfaltovenator from the Middle Jurassic of South America.[164] Coelurosaurs first appeared during the Middle Jurassic, including early tyrannosaurs such as Proceratosaurus from the Bathonian of Britain.[165] The earliest alvarezsaurs, a clade of coelurosaurs, first appeared during the Late Jurassic, represented by Shishugounykus and Haplocheirus from the Late Jurassic of China.[166] Scansoriopterygids, a group of small feathered coelurosaurs with membraneous, bat like wings for gliding, are known from the Middle-Late Jurassic of China.[167] 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.[168]

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  Skeleton of Ceratosaurus, a ceratosaurid from the Late Jurassic of North America.
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  Skeleton of Monolophosaurus, a basal tetanuran from the Middle Jurassic of China
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  Restoration of Yi qi, a scansoriopterygid from the Middle-Late Jurassic of China

Archaeopteryx lithographica from the Late Jurassic (Tithonian) of Germany

The earliest avialans, which include birds and their ancestors, appear during the Middle-Late Jurassic, definitively represented by Archaeopteryx from the Late Jurassic of Germany. Avialans belong to the clade Paraves within Coelurosuria, which also includes dromaeosaurs and troodontids. The Anchiornithidae from the Middle-Late Jurassic of China have frequently suggested to be avialans, but have also been found as a separate lineage of paravians.[162]

The earliest definitive ornithischians 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.[169] The basal neornithischian Kulindadromeus from the Middle Jurassic of Russia indicates that at least some ornithischians were covered in protofeathers.[170] The earliest members of Ankylopollexia, which would become prominent in the Cretaceous, appeared during the Late Jurassic, represented by bipedal forms such as Camptosaurus.[171] Ceratopsians first appeared in the Late Jurassic of China, represented by members of Chaoyangsauridae.[172]

Bipedal basal sauropodomorphs, such as massospondylids, continued to exist into the Early Jurassic. Quadrupedal sauropomorphs appeared during the Late Triassic. The quadupedal Ledumahadi from the earliest Jurassic of South Africa reached an estimated weight of 12 tons, far in excess of other known basal sauropodomorphs.[173] Gravisaurian sauropods first appeared during the Early Jurassic, with the oldest definitive record being Vulcanodon from Zimbabwe, likely of Sinemurian age.[174] Eusauropodan sauropods diverisfied during the Middle Jurassic, including cetiosaurids, turiasaurs,[175] and mamenchisaurs.[176] The earliest known member of Neosauropoda is Lingwulong, a dicraeosaurid diplodocoid from the Middle Jurassic of China. Neosauropods dispersed worldwide during the Late Jurassic.[177] The Late Jurassic saw the first appearance of several derived neosauropod groups, including Brachiosauridae[178] and Diplodocidae.[179] Jurassic sauropods would reach gigantic sizes, becoming the largest organisms to have ever lived on land up to that point.[180]

Skeleton of Karaurus sharovi, a stem-group salamander from the Middle to Late Jurassic of Kazakhstan

The vast majority of temnospondyls went extinct at the end of the Triassic, with only brachyopoids surviving into the Jurassic and beyond. Members of the family Brachyopidae are known from Jurassic deposits in Asia,[181] while the chigutisaurid Siderops is known from the Early Jurassic of Australia.[182] Modern lissamphibians would also begin 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.[183] Morphogically recognisable stem-frogs like Notobatrachus are known from the Middle Jurassic.[184] While the earliest salamander-line amphibians are known from the Triassic.[185] Crown group salamanders first appear during the Middle-Late Jurassic of Eurasia, alongside stem-group relatives. Many Jurassic stem-group salamanders, like Marmorerpeton and Kokartus are thought to have been neotenic.[186] Early representatives of crown group salamanders include Chunerpeton, Pangerpeton and Linglongtriton from the Middle-Late Jurassic Yanliao Biota of China, which belong to the Cryptobranchoidea, which contains living Asiatic and giant salamanders.[187] While Beiyanerpeton, also from the same biota is thought to be an early member of Salamandroidea, the group which contains all other living salamanders.[188] Salamanders would disperse into North America by the end of the Jurassic, as evidenced by Iridotriton found in the Late Jurassic Morrison Formation.[189] The oldest undisputed stem-caecilian is the Early Jurassic Eocaecilia from Arizona.[190] The fourth group of lissamphibians, the extinct albanerpetontids, would first appear in the Middle Jurassic, represented by Anoualerpeton priscus from the Bathonian of Britain, as well as indeterminate remains from equivalently aged sediments in France and the Anoual Formation of Morocco.[191]

Mammals, having originated from cynodonts at the end of the Triassic, diversified extensively during the Jurassic. Important groups of Jurassic mammals include Morganucodonta, Docodonta, Eutriconodonta, Dryolestida, Haramiyida and Multituberculata. While most Jurassic mammals are solely known from isolated teeth and jaw fragments, exceptionally preserved remains have revealed a variety of lifestyles.[192] The docodontan Castorocauda was adapted for aquatic life, similar to the platypus and otters.[193] Some members of Haramiyida[194] and the eutriconodontan tribe Volaticotherini[195] possessed a patagium akin to those of flying squirrels, allowing them to glide through the air. The aardvark like mammal Fruitafossor of uncertain affinities was likely a specialist on colonial insects, similar to living anteaters.[196] Early relatives of monotremes, the Australosphenida, first appear in the Middle Jurassic of Gondwana.[197] Theriiform mammals, represented today by living placentals and marsupials, would also appear during the early Late Jurassic, represented by Juramaia, a eutherian mammal closer to the ancestry of placentals than marsupials.[198] Juramaia is much more advanced than expected for its age, as other theriiform mammals do not appear until the Early Cretaceous.[199] Non-mammalian cynodonts of the families Tritheledontidae and Tritylodontidae survived the T-J extinction, and continued to exist into the Early Jurassic and Early Cretaceous, respectively.[200]

The last known species of conodont, a class of jawless fish-like animals whose hard teeth like elements are key index fossils, would finally become extinct during the earliest Jurassic after over 300 million years of evolutionary history, with an asynchronous extinction occurring first in the Tethys and eastern Panthalassia, with late survivors in the earliest Hettangian of Hungary and central Panthalassa.[201] End-Triassic conodonts were only represented by a handful of species, and had been progressively declining though the Middle and Late Triassic.[202]

Coelacanth from the Solnhofen Limestone

Lungfish (Dipnoi) were present in freshwater environments of both hemispheres during the Jurassic. Genera include Ceratodus and Ptychoceratodus which are more closely related to living South American and African lungfish than Queensland lungfish and Ferganoceratodus from the Jurassic of Asia, which is not closely related to either group of living lungfish.[203] Mawsoniids, a marine and freshwater/brackish group of coelacanths, which first appeared in North America during the Triassic, would expand into Europe and South America by the end of the Jurassic.[204] The marine Latimeriidae, which contains the living coelacanths of the genus Latimeria, were also present in the Jurassic, having originated in the Triassic.[205]

Head and forefin of Pachycormus, an extinct pachycormiform fish

Bony fish (Actinopterygii) were major components of Jurassic freshwater and marine ecosystems. Amiiform fish (which today only includes the bowfin) would first appear during the Early Jurassic, represented by Caturus from the Pliensbachian of Britain, after their first appearance in western Tethys, they would expand 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, would expand to South America and Southeast Asia by the end of the Jurassic, having a high diversity in Europe during the Late Jurassic.[206] Teleosts, which make up over 99% of living Actinopterygii, had first appeared during the Triassic in the western Tethys, underwent a major diversification beginning in the Late Jurassic, with early representatives of modern teleost clades such as Elopomorpha and Osteoglossoidei appearing during this time.[207][208] The Pachycormiformes, a group of fish closely allied to teleosts, first appeared in the Early Jurassic, and included both tuna-like predatory and filter feeding forms, the latter including the largest bony fish known to have existed, Leedsichthys, with an estimated maximum length of over 15 metres, known from the late Middle to Late Jurassic.[209]

Fossil of Palaeocarcharias, the oldest known lamniform shark

The Jurassic was a major time in the evolution of Chondrichthyes. Hybodonts, such as Hybodus were common in the Early Jurassic 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 would remain common in freshwater and restricted marine environments.[210] The Neoselachii, which contains all living sharks and rays, would radiate beginning in the Early Jurassic.[211] The oldest known Hexanchiformes are from the Early Jurassic (Pliensbachian) of Europe.[212] The oldest known ray (Batoidea) is Antiquaobatis from the Pliensbachian of Germany.[213] Jurassic batoids known from complete remains retain a conservative, guitarfish-like morphology.[214] The oldest known relatives of the Bullhead shark (Heterodontus) in the order Heterodontiformes first appear in the Early Jurassic, with representatives of the living genus appearing during the Late Jurassic.[215] Carpet sharks (Orectolobiformes) first appear during the Toarcian, represented by Folipistrix and Annea from Europe.[216] The oldest known mackerel sharks (Lamniformes) are known from the Middle Jurassic, represented by the genus Palaeocarcharias., which has an orectolobiform-like bodyform, but shares key similarities in tooth histology with lamniformes, including the absence of orthodentine.[217] The oldest record of Angelsharks (Squatiniformes) is Pseudorhina from the Oxfordian-Tithonian of Europe.[218] 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.[219] The oldest remains of chimaeras are known from the Early Jurassic of Europe, with members of the living family Callorhinchidae appearing during the Middle Jurassic. Unlike living chimaeras, these were found in shallow water settings.[220] The closely related Squaloraja and myriacanthoids are also known from the Jurassic of Europe.[221]

Numerous important insect fossil localities are known from the Jurassic of Eurasia, the most important being the Karabastau Formation of Kazakhstan, and the various Yanliao Biota deposits in Inner Mongolia, China, such as the Daohugou Bed, dating to the Callovian-Oxfordian. The diversity of insects was stagnant throughout the Early and Middle Jurassic, but during the latter third of the Jurassic origination rates increased substantially while extinction rates remained flat.[222] The Middle-Late Jurassic was a time of major diverisification for beetles.[223] Weevils first appear in the fossil record during the Middle-Upper Jurassic, but are suspected to have originated during the Late Triassic-Early Jurassic.[224] The oldest known lepidopterans (the group containing butterflies and moths) are known from the Triassic-Jurassic boundary, with wing scales belonging to the suborder Glossata and Micropterigidae-grade moths from the deposits of this age in Germany.[225] Although modern representatives are not known until the Cenozoic, ectoparasitic insects thought to represent a stem-group to fleas first appear during the Jurassic, such as Pseudopulex jurassicus. These insects are substantially different from modern fleas, lacking the specialised morphology of modern fleas and being larger in size.[226][227] The earliest group of Phasmatodea (stick insects), the winged Susumanioidea, an outgroup to living Phasmatodeans, first appear during the Middle Jurassic.[228] The oldest member of the Mantophasmatidae (gladiators) also appeared during this time.[229]

Only a handful of records of mites are known from the Jurassic, including Jureremus, an Oribatid mite belonging to the family Cymbaeremaeidae known from the Upper Jurassic of Britain and Russia.[230] Spiders would diversify through the Jurassic.[231] The Early Jurassic Seppo koponeni thought to possibly represent a stem-group to Palpimanoidea.[232] Eoplectreurys 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.[231] Mongolarachne from the Middle Jurassic of China is among the largest known fossil spiders, with legs over 5 centimetres in length.[233] The only scorpion known from the Jurassic is Liassoscorpionides from the Lower Jurassic of Germany, of uncertain placement.[234] Eupnoi Opiliones are known from the Middle Jurassic, including members of the family Sclerosomatidae.[235][236]

During the end-Triassic extinction, 46%-72% of all marine genera would become 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 would completely collapse during the event, and would not fully recover until much later in the Jurassic. Sessile filter feeders and photosymbiotic organisms were among most severely affected.[237]

Having declined at the T-J boundary. Reefs would substantially expand during the Late Jurassic, including both sponge reefs and scleractinian coral 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 would sharply decline at the close of the Jurassic.[238] which caused an associated drop in diversity in decapod crustaceans.[239] The earliest planktonic foraminifera are known from the late Early Jurassic (mid Toarcian) of the western Tethys, expanding across the whole Tethys by the Middle Jurassic, before being globally distributed in tropical latitudes by the Late Jurassic.[240] Coccolithophores and dinoflagellates, which had first appeared during the Triassic, would radiate during the Early-Middle Jurassic, becoming prominent members of the phytoplankton.[241] Microconchid tube worms, the last remaining order of Tentaculita, a group of animals of uncertain affinites that were convergent on Spirorbis tube worms, had become rare after the Triassic, and had become reduced to the single genus Punctaconchus, which became extinct in the late Bathonian.[242] The oldest known diatom is known from amber found in the Late Jurassic of Thailand, assigned to the living genus Hemiaulus.[243]

Reconstruction of Eocarcinus praecursor

The Jurassic was a significant time for the evolution of decapods.[239] The first true crabs (Brachyura) would appear during the Early Jurassic, with the earliest being Eocarcinus praecursor from the early Pliensbachian of England, which lacked the carcinisation of modern crabs.[244] and Eoprosopon klugi from the late Pliensbachian of Germany, which possibly belongs to the living family Homolodromiidae.[245] Most Jurassic crabs are only known from dorsal carapace pieces, which makes it difficult to determine their relationships.[246] While rare in the Early and Middle Jurassic, crabs would become abundant during the Late Jurassic as they expanded from their ancestral silty sea floor habitat into hard substrate habitats like reefs, with crevices in reefs helping to hide from predators[246][239] Hermit crabs would also first appear during the Jurassic, with the earliest known being Schobertella hoelderi from the late Hettangian of Germany.[247] Early hermit crabs are associated with ammonite shells rather than those of gastropods.[248] Glypheids, which today are only known from two species, reached their peak diversity during the Jurassic, with around 150 species out of a total fossil record of 250 being known from the period.[249] Thylacocephalans are an enigmatic group of arthropods known from the Silurian to the Cretaceous, with probable crustacean affinities. Remains of Jurassic thylacocephalans are among the best preserved members of the group.[250]

Brachiopod diversity declined during the T-J extinction. Spire bearing groups (Spiriferinida and Athyridida) would significantly decline at the T-J boundary and would not recover their biodiversity, becoming extinct in the TOAE.[48] Rhynchonellida and Terebratulida would also decline during the T-J extincton but would rebound during the Early Jurassic, neither clade would develop any significant morphological variation.[251] Brachiopods would substantially decline in the Late Jurassic, the causes of which are poorly understood. Proposed reasons include increased predation, competition with bivalves, enhanced bioturbation or increased grazing pressure.[252]

Ammonites were devastated by the end-Triassic extinction, with only the family Psiloceratidae of the suborder Phylloceratina surviving, and becoming ancestral to all later Jurassic and Cretaceous ammonites. Ammonites explosively diversified during the Early Jurassic, with the orders Psiloceratina, Ammonitina, Lytoceratina, Haploceratina, Perisphinctina and Ancyloceratina all appearing during the Jurassic. Ammonite faunas during the Jurassic were regional, being divided into around 20 distinguishable provinces and subprovinces in two realms, the northern high latitude Pan-Boreal realm, consisting of the Arctic, northern Panthalassa and northern Atlantic regions, and the equatorial-southern Pan-Tethyan realm, which included the Tethys and most of Panthalassa.[253]

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.[254] Rudists, the dominant reef building organisms of the Cretaceous, would first appear in the Late Jurassic (mid Oxfordian) in the northern margin of the western Tethys region, expanding to the eastern Tethys by the end of the Jurassic.[255]

The oldest definitive records of the squid-like belemnites are from the earliest Jurassic (Hettangian-Sinemurian) of Europe and Japan, and would expand worldwide during the Jurassic.[256] 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.[257]