Reptiles

Crocodylomorphs

The Triassic–Jurassic extinction decimated pseudosuchian diversity, with crocodylomorphs, which originated during the early Late Triassic, being the only group of pseudosuchians to survive. All other pseudosuchians, including the herbivorous aetosaurs and carnivorous "rauisuchians", became extinct.^[139] 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 ecological niches to their Triassic counterparts and that there was an extensive and rapid radiation of crocodylomorphs during this interval.^[140] While living crocodilians are mostly confined to an aquatic ambush predator lifestyle, Jurassic crocodylomorphs exhibited a wide variety of life habits. An unnamed protosuchid known from teeth from the Early Jurassic of Arizona represents the earliest known herbivorous crocodylomorph, an adaptation that appeared several times during the Mesozoic.^[141]

The Thalattosuchia, a clade of predominantly marine crocodylomorphs, first appeared during the Early Jurassic and became a prominent part of marine ecosystems.^[142] Within Thalattosuchia, the Metriorhynchidae became highly adapted for life in the open ocean, including the transformation of limbs into flippers, the development of a tail fluke, and smooth, scaleless skin.^[143] The morphological diversity of crocodylomorphs during the Early and Middle Jurassic was relatively low compared to that in later time periods and was dominated by terrestrial small-bodied, long-legged sphenosuchians, early crocodyliforms and thalattosuchians.^[144]^[142] The Neosuchia, a major group of crocodylomorphs, first appeared during the Early to Middle Jurassic. The Neosuchia represents the transition from an ancestrally terrestrial lifestyle to a freshwater aquatic ecology similar to that occupied by modern crocodilians.^[145] The timing of the origin of Neosuchia is disputed. The oldest record of Neosuchians has been suggested to be Calsoyasuchus, from the Early Jurassic of Arizona, which in many analyses has been recovered as the earliest branching member of the neosuchian family Goniopholididae, which radically alters times of diversification for crocodylomorphs. However, this placement has been disputed, with some analyses finding it outside Neosuchia, which would place the oldest records of Neosuchia in the Middle Jurassic.^[145] Razanandrongobe from the Middle Jurassic of Madagascar has been suggested the represent the oldest record of Notosuchia, a primarily Gondwanan clade of mostly terrestrial crocodylomorphs, otherwise known from the Cretaceous and Cenozoic.^[146]

Turtles

Stem-group turtles (Testudinata) diversified during the Jurassic. Jurassic stem-turtles belong to two progressively more advanced clades, the Mesochelydia and Perichelydia.^[147] It is thought that the ancestral condition for mesochelydians is aquatic, as opposed to terrestrial for testudinates.^[148] The two modern groups of turtles (Testudines), Pleurodira and Cryptodira, diverged by the beginning of the Late Jurassic.^[147] The oldest known pleurodires, the Platychelyidae, are known from the Late Jurassic of Europe and the Americas,^[149] while the oldest unambiguous cryptodire, Sinaspideretes, an early relative of softshell turtles, is known from the Late Jurassic of China.^[150] The Thalassochelydia, a diverse lineage of marine turtles unrelated to modern sea turtles, are known from the Late Jurassic of Europe and South America.^[151]

Lepidosaurs

Rhynchocephalians (the sole living representative being the tuatara) had achieved a global distribution by the beginning of the Jurassic,^[152] and represented the dominant group of small reptiles during the Jurassic globally.^[153] Rhynchocephalians reached their highest morphological diversity in their evolutionary history during the Jurassic, occupying a wide range of lifestyles, including the aquatic pleurosaurs with long snake-like bodies and reduced limbs, the specialized herbivorous eilenodontines, as well as the sapheosaurs which had broad tooth plates indicative of durophagy.^[154] Rhynchocephalians disappeared from Asia after the Early Jurassic.^[152] The last common ancestor of living squamates (which includes lizards and snakes) is estimated to have lived around 190 million years ago during the Early Jurassic, with the major divergences between modern squamate lineages estimated to have occurred during the Early to Middle Jurassic.^[155] Squamates first appear in the fossil record during the Middle Jurassic^[156] including members of modern clades such as Scincomorpha,^[157] though many Jurassic squamates have unclear relationships to living groups.^[158] Eichstaettisaurus from the Late Jurassic of Germany has been suggested to be an early relative of geckos and displays adaptations for climbing.^[159] Dorsetisaurus from the Late Jurassic of North America and Europe represents the oldest widely accepted record of Anguimorpha.^[160] Marmoretta 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.^[161]

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

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.^[162] The other is Coeruleodraco from the Late Jurassic of China, which is a more advanced choristodere, though still small and lizard-like in morphology.^[163]

Ichthyosaurs

Ichthyosaurs suffered an evolutionary bottleneck during the end-Triassic extinction, with all non-neoichthyosaurians becoming extinct. Ichthyosaurs reached their apex of species diversity during the Early Jurassic, with an array of morphologies including the huge apex predator Temnodontosaurus and swordfish-like Eurhinosaurus, though Early Jurassic ichthyosaurs were significantly less morphologically diverse than their Triassic counterparts.^[164]^[165] 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.^[166] 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.^[166]^[164]^[165]

Plesiosaurs

Plesiosaurs originated at the end of the Triassic (Rhaetian). By the end of the Triassic, all other sauropterygians, including placodonts and nothosaurs, had become extinct. At least six lineages of plesiosaur crossed the Triassic–Jurassic boundary.^[167] 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.^[168] There appears to have been a strong turnover around the Early–Middle Jurassic boundary, with microcleidids and rhomaleosaurids becoming extinct and nearly extinct respectively after the end of the Toarcian with the first appearance of the dominant clade of plesiosaurs of the latter half of the Jurassic, the Cryptoclididae during the Bajocian.^[166] The Middle Jurassic saw the evolution of short-necked and large-headed thalassophonean pliosaurs from ancestrally small-headed, long-necked forms.^[169]^[166] Some thalassophonean pliosaurs, such as some species of Pliosaurus, had skulls up to two metres in length with body lengths estimated around 10–12 meters(32-39 ft), making them the apex predators of Late Jurassic oceans.^[170]^[166] 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.^[171]^[172]

Pterosaurs

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);^[173] they are thought to been piscivorous.^[174] Anurognathids, which first appeared in the Middle Jurassic, possessed short heads and densely furred bodies, and are thought to have been insectivores.^[174] Derived monofenestratan pterosaurs such as 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.^[174] The bizarre Late Jurassic ctenochasmatoid Cycnorhamphus had a jaw with teeth only at the tips, with bent jaws like those of living openbill storks that may have been used to hold and crush hard invertebrates.^[174]

Dinosaurs

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.^[175]^[176] 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.^[177]

Theropods

Advanced theropods belonging to Neotheropoda first appeared in the Late Triassic. Basal neotheropods, such as coelophysoids and dilophosaurs, persisted into the Early Jurassic, but became extinct by the Middle Jurassic.^[178] 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.^[179] The unusual ceratosaur Limusaurus from the Late Jurassic of China had a herbivorous diet, with adults having edentulous beaked jaws,^[180] making it the earliest known theropod to have converted from an ancestrally carnivorous diet.^[181] The earliest members of the Tetanurae appeared during the late Early Jurassic or early Middle Jurassic.^[182] The Megalosauridae represent the oldest radiation of the Tetanurae, first appearing in Europe during the Bajocian.^[183] The oldest member of Allosauroidea has been suggested to be Asfaltovenator from the Middle Jurassic of South America.^[182] Coelurosaurs first appeared during the Middle Jurassic, including early tyrannosaurs such as Proceratosaurus from the Bathonian of Britain.^[184] Some coelurosaurs from the Late Jurassic of China including Shishugounykus and Haplocheirus are suggested to represent early alvarezsaurs,^[185] however, this has been questioned.^[186] Scansoriopterygids, a group of small feathered coelurosaurs with membraneous, bat-like wings for gliding, are known from the Middle to Late Jurassic of China.^[187] 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.^[188]

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

Birds

The earliest avialans, which include birds and their ancestors, appear during the Middle to Late Jurassic, definitively represented by Archaeopteryx from the Late Jurassic of Germany. Avialans belong to the clade Paraves within 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.^[189]

Ornithischians

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.^[190] The basal neornithischian Kulindadromeus from the Middle Jurassic of Russia indicates that at least some ornithischians were covered in protofeathers.^[191] The earliest members of Ankylopollexia, which become prominent in the Cretaceous, appeared during the Late Jurassic, represented by bipedal forms such as Camptosaurus.^[192] Ceratopsians first appeared in the Late Jurassic of China, represented by members of Chaoyangsauridae.^[193]

Sauropodomorphs

Sauropods became the dominant large herbivores in terrestrial ecosystems during the Jurassic.^[194] Some Jurassic sauropods reached gigantic sizes, becoming the largest organisms to have ever lived on land.^[195]

Basal bipedal sauropodomorphs, such as massospondylids, continued to exist into the Early Jurassic, but became extinct by the beginning of the Middle Jurassic.^[194] Quadrupedal sauropomorphs appeared during the Late Triassic. The quadrupedal Ledumahadi from the earliest Jurassic of South Africa reached an estimated weight of 12 tons, far in excess of other known basal sauropodomorphs.^[196] Gravisaurian sauropods first appeared during the Early Jurassic, with the oldest definitive record being Vulcanodon from Zimbabwe, likely of Sinemurian age.^[197] Eusauropods first appeared during the late Early Jurassic (Toarcian) and diversified during the Middle Jurassic;^[194] these included cetiosaurids, turiasaurs,^[198] and mamenchisaurs.^[199] Neosauropods such as macronarians and diplodocoids first appeared during the Middle Jurassic, before becoming abundant and globally distributed during the Late Jurassic.^[200]

Amphibians

The diversity of temnospondyls had progressively declined through the Late Triassic, with only brachyopoids surviving into the Jurassic and beyond.^[201] Members of the family Brachyopidae are known from Jurassic deposits in Asia,^[202] while the chigutisaurid Siderops is known from the Early Jurassic of Australia.^[203] Modern lissamphibians 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.^[204] Morphologically recognisable stem-frogs like the South American Notobatrachus are known from the Middle Jurassic,^[205] with modern crown-group frogs like Enneabatrachus and Rhadinosteus appearing by the Late Jurassic.^[206] While the earliest salamander-line amphibians are known from the Triassic,^[207] crown group 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 neotenic.^[208] 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 giant salamanders.^[209] Beiyanerpeton, and Qinglongtriton from the same biota are thought to be early members of Salamandroidea, the group which contains all other living salamanders.^[210]^[211] Salamanders dispersed into North America by the end of the Jurassic, as evidenced by Iridotriton, found in the Late Jurassic Morrison Formation.^[212] The stem-caecilian Eocaecilia is known from the Early Jurassic of Arizona.^[213] The fourth group of lissamphibians, the extinct salamander-like albanerpetontids, first appeared 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.^[214]

Thumb — *Henkelotherium,* a likely arboreal dyolestoid from the Late Jurassic of Portugal

Mammaliaformes

Mammaliaformes, including mammals, having originated from cynodonts at the end of the Triassic, diversified extensively during the Jurassic.^[215] While most Jurassic mammalaliaforms are solely known from isolated teeth and jaw fragments, exceptionally preserved remains have revealed a variety of lifestyles.^[215] The docodontan Castorocauda was adapted to aquatic life, similarly to the platypus and otters.^[216] Some members of Haramiyida^[217] and the eutriconodontan tribe Volaticotherini^[218] had a patagium akin to those of flying squirrels, allowing them to glide through the air. The aardvark-like mammal Fruitafossor, of uncertain taxonomy, was likely a specialist on colonial insects, similarly to living anteaters.^[219] Australosphenida, a group of mammals possibly related to living monotremes, first appeared in the Middle Jurassic of Gondwana.^[220] The earliest records of multituberculates, of the longest lasting and most successful orders of mammals, are known from the Middle Jurassic.^[221] Therian mammals, represented today by living placentals and marsupials, have their earliest records during the early Late Jurassic, represented by Juramaia, a eutherian mammal closer to the ancestry of placentals than marsupials.^[222] 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.^[223] 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.^[224]^[225]

Fish

Jawless fish

Thumb — Fossils and life restorations of the two species of *Yanliaomyzon ,* a lamprey known from the Middle Jurassic of China

The last known species of conodont, a class of jawless fish whose hard, tooth-like elements are key index fossils, finally became extinct during the earliest Jurassic after over 300 million years of evolutionary history, with an asynchronous extinction occurring first in the Tethys and eastern Panthalassa and survivors persisting into the earliest Hettangian of Hungary and central Panthalassa.^[226] End-Triassic conodonts were represented by only a handful of species and had been progressively declining through the Middle and Late Triassic.^[227] Yanliaomyzon 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.^[228]

Sarcopterygii

Lungfish (Dipnoi) were present in freshwater environments of both hemispheres during the Jurassic.^[229] Some studies have proposed that the last common ancestor of all living lungfish lived during the Jurassic.^[230] Mawsoniids, a marine and freshwater/brackish group of coelacanths, which first appeared in North America during the Triassic, expanded into Europe and South America by the end of the Jurassic.^[231] 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.^[232]

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.^[233] The oldest known Acipenseriformes, the group that contains living sturgeon and paddlefish, are from the Early Jurassic.^[234] Amiiform fish (which today only includes the bowfin) first appeared during the Early Jurassic, represented by Caturus from the Pliensbachian of Britain; after their appearance in the western Tethys, they expanded to Africa, North America and Southeast and East Asia by the end of the Jurassic,^[235] with the modern family Amiidae appearing during the Late Jurassic.^[236] Pycnodontiformes, which first appeared in the western Tethys during the Late Triassic, expanded to South America and Southeast Asia by the end of the Jurassic, having a high diversity in Europe during the Late Jurassic.^[235] During the Jurassic, the Ginglymodi, the only living representatives being gars (Lepisosteidae) were diverse in both freshwater and marine environments. The oldest known representatives of anatomically modern gars appeared during the Late Jurassic.^[237] Stem-group teleosts, which make up over 99% of living Actinopterygii, had first appeared during the Triassic in the western Tethys; they underwent a major diversification beginning in the Late Jurassic, with early representatives of modern teleost clades such as Elopomorpha and Osteoglossoidei appearing during this time.^[238]^[239] 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.^[240]

Chondrichthyes

During the Early Jurassic, the shark-like hybodonts, which represented the dominant group of chondrichthyans during the preceding Triassic, were common in both marine and freshwater settings; however, by the Late Jurassic, hybodonts had become minor components of most marine communities, having been largely replaced by modern neoselachians, but remained common in freshwater and restricted marine environments.^[241]^[242] The Neoselachii, which contains all living sharks and rays, radiated beginning in the Early Jurassic.^[243] The oldest known ray (Batoidea) is Antiquaobatis from the Pliensbachian of Germany.^[244] Jurassic batoids known from complete remains retain a conservative, guitarfish-like morphology.^[245] The oldest known Hexanchiformes and carpet sharks (Orectolobiformes) are from the Early Jurassic (Pliensbachian & Toarcian, respectively) of Europe.^[246]^[247] 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.^[248] The oldest known mackerel sharks (Lamniformes) are from the Middle Jurassic, represented by the genus Palaeocarcharias, which has an orectolobiform-like body but shares key similarities in tooth histology with lamniformes, including the absence of orthodentine.^[249] 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.^[250] 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.^[251] Synechodontiformes, an extinct group of sharks closely related to Neoselachii, were also widespread during the Jurassic.^[252] The oldest remains of modern chimaeras are from the Early Jurassic of Europe, with members of the living family Callorhinchidae appearing during the Middle Jurassic. Unlike most living chimaeras, Jurassic chimeras are often found in shallow water environments.^[253] The closely related Squaloraja and myriacanthoids are also known from the Jurassic of Europe.^[254]

Insects and arachnids

There appears to have been no major extinction of insects at the Triassic–Jurassic boundary.^[83] 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.^[255] The increasing diversity of insects in the Middle–Late Jurassic corresponds with a substantial increase in the diversity of insect mouthparts.^[256] The Middle to Late Jurassic was a time of major diversification for beetles,^[257] particularly for the suborder Polyphaga, which represents 90% of living beetle species but which was rare during the preceeding Triassic.^[258] Weevils first appear in the fossil record during the Middle to Late Jurassic, but are suspected to have originated during the Late Triassic to Early Jurassic.^[259] Orthopteran diveristy had declined during the Late Triassic, but recovered during the Early Jurassic,^[260] with the Hagloidea, a superfamily of ensiferan orthopterans today confined to a few living species, being particularly diverse during the Jurassic.^[261] 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.^[262] Modern representatives of both dragonflies and damselflies also first appeared during the Jurassic.^[263] Although modern representatives are not known until the Cenozoic, ectoparasitic insects thought to represent primitive fleas, belonging to the family Pseudopulicidae, are known from the Middle Jurassic of Asia. These insects are substantially different from modern fleas, lacking the specialised morphology of the latter and being larger.^[264]^[265] Parasitoid wasps (Apocrita) first appeared during the Early Jurassic and subsequently became widespread, reshaping terrestrial food webs.^[266] The Jurassic saw also saw the first appearances of several other groups of insects, including Phasmatodea (stick insects),^[267] Mantophasmatidae (gladiators),^[268] Embioptera (webspinners),^[269] and Raphidioptera (snakeflies).^[270]

Thumb — *Mongolarachne* from the Late Jurassic of China

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 Late Jurassic of Britain and Russia,^[271] and a member of the still living orbatid genus Hydrozetes from the Early Jurassic of Sweden.^[272] Spiders diversified through the Jurassic.^[273] The Early Jurassic Seppo koponeni may represent a stem group to Palpimanoidea.^[274] 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 of China.^[273] Mongolarachne from the Middle Jurassic of China is among the largest known fossil spiders, with legs over 5 centimetres long.^[275] The only scorpion known from the Jurassic is Liassoscorpionides from the Early Jurassic of Germany, of uncertain placement.^[276] Eupnoi harvestmen (Opiliones) are known from the Middle Jurassic of China, including members of the family Sclerosomatidae.^[277]^[278]

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 filter feeders and photosymbiotic organisms were among those most severely affected.^[279]

Marine ecosystems

Having declined at the Triassic–Jurassic boundary, reefs substantially expanded 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 sharply declined at the close of the Jurassic,^[280] which caused an associated drop in diversity in decapod crustaceans.^[281] 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.^[282] Coccolithophores and dinoflagellates, which had first appeared during the Triassic, radiated during the Early to Middle Jurassic, becoming prominent members of the phytoplankton.^[283] Microconchid tube worms, the last remaining order of Tentaculita, a group of animals of uncertain affinities that were convergent on Spirorbis tube worms, were rare after the Triassic and had become reduced to the single genus Punctaconchus, which became extinct in the late Bathonian.^[284] The oldest known diatom is from Late Jurassic–aged amber from Thailand, assigned to the living genus Hemiaulus.^[285]

Echinoderms

Crinoids diversified throughout the Jurassic, reaching their peak Mesozoic diversity during the Late Jurassic, primarily due to the radiation of sessile forms belonging to the orders Cyrtocrinida and Millericrinida.^[286] Echinoids (sea urchins) underwent substantial diversification beginning in the Early Jurassic, primarily driven by the radiation of irregular (asymmetrical) forms, which were adapting to deposit feeding. Rates of diversification sharply dropped during the Late Jurassic.^[287]

Crustaceans

The Jurassic was a significant time for the evolution of decapods.^[281] The first true crabs (Brachyura) are known from the Early Jurassic, with the earliest being Eocarcinus praecursor from the early Pliensbachian of England, which lacked the crab-like morphology (carcinisation) of modern crabs,^[288] and Eoprosopon klugi from the late Pliensbachian of Germany, which may belong to the living family Homolodromiidae.^[289] Most Jurassic crabs are known only from carapace pieces, which makes it difficult to determine their relationships.^[290] 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.^[290]^[281] Hermit crabs also first appeared during the Jurassic, with the earliest known being Schobertella hoelderi from the late Hettangian of Germany.^[291] Early hermit crabs are associated with ammonite shells rather than those of gastropods.^[292] Glypheids, which today are only known from two species, reached their peak diversity during the Jurassic, with around 150 species out of a total fossil record of 250 known from the period.^[293] Jurassic barnacles were of low diversity compared to present,^[294] but several important evolutionary innovations are known, including the first appearances of calcite shelled forms and species with an epiplanktonic mode of life.^[295]

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.^[296] Rhynchonellida and Terebratulida also declined during the Triassic–Jurassic extinction but rebounded during the Early Jurassic; neither clade underwent much morphological variation.^[297] 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.^[298]

Bryozoans

Like the preceding Triassic, bryozoan diversity was relatively low compared to the Paleozoic. The vast majority of Jurassic bryozoans are members of Cyclostomatida, which experienced a radiation during the Middle Jurassic, with all Jurassic representatives belonging to the suborders Tubuliporina and Cerioporina. Cheilostomata, the dominant group of modern bryozoans, first appeared during the Late Jurassic.^[299]

Molluscs

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.^[300] Bivalve family level diversity after the Early Jurassic was static, though genus diversity experienced a gradual increase throughout the period.^[301] Rudists, the dominant reef-building organisms of the Cretaceous, first appeared in the Late Jurassic (mid-Oxfordian) in the northern margin of the western Tethys, expanding to the eastern Tethys by the end of the Jurassic.^[302]

Cephalopods

Ammonites were devastated by the end-Triassic extinction, with only a handful of genera belonging to the family Psiloceratidae of the suborder Phylloceratina surviving and becoming ancestral to all later Jurassic and Cretaceous ammonites. Ammonites explosively diversified during the Early Jurassic, with the orders Psiloceratina, Ammonitina, Lytoceratina, Haploceratina, Perisphinctina and Ancyloceratina all appearing during the Jurassic. Ammonite faunas during the Jurassic were regional, being divided into around 20 distinguishable provinces and subprovinces in two realms, the northern high latitude Pan-Boreal realm, consisting of the Arctic, northern Panthalassa and northern Atlantic regions, and the equatorial–southern Pan-Tethyan realm, which included the Tethys and most of Panthalassa.^[303] Ammonite diversifications occurred coevally with marine transgressions, while their diversity nadirs occurred during marine regressions.^[304]

The oldest definitive records of the squid-like belemnites are from the earliest Jurassic (Hettangian–Sinemurian) of Europe and Japan; they expanded worldwide during the Jurassic.^[305] 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.^[306]

The earliest vampyromorphs, of which the only living member is the vampire squid, first appeared during the Early Jurassic.^[307] The earliest octopuses appeared during the Middle Jurassic, having split from their closest living relatives, the vampyromorphs, during the Triassic to Early Jurassic.^[308] All Jurassic octopuses are solely known from the hard gladius.^[308]^[309] Octopuses likely originated from bottom-dwelling (benthic) ancestors which lived in shallow environments.^[308] Proteroctopus from the late Middle Jurassic La Voulte-sur-Rhône lagerstätte, previously interpreted as an early octopus, is now thought to be a basal taxon outside the clade containing vampyromorphs and octopuses.^[310]