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.
Chilesaurus, a morphologically aberrant herbivorous dinosaur from the Late Jurassic of South America, has uncertain relationships to the three main groups of dinosaurs, having been recovered as a member of all three in different analyses.
Theropods 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. 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 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. Some coelurosaurs from the Late Jurassic of China including
Shishugounykus and
Haplocheirus are suggested to represent early
alvarezsaurs, however, this has been questioned.
Scansoriopterygids, a group of small feathered coelurosaurs with membraneous, bat-like wings for gliding, are known from the Middle to Late Jurassic of China. The oldest record of
troodontids is suggested to be
Hesperornithoides from the Late Jurassic of North America. Tooth remains suggested to represent those of
dromaeosaurs are known from the Jurassic, but no body remains are known until the Cretaceous. File:Ceratosaurus mounted white background.jpg|Skeleton of
Ceratosaurus, a ceratosaurid from the Late Jurassic of North America File:Monolophosaurus jiangi.jpg|Skeleton of
Monolophosaurus, a basal tetanuran from the Middle Jurassic of China File:Yi qi restoration.jpg|Restoration of
Yi qi, a scansoriopterygid from the Middle to Late Jurassic of China
Birds '' from the Late Jurassic (Tithonian) of Germany|alt=Fossil of complete Archaeopteryx, including indentations of feathers on wings and tail 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. ,'' a primitive ornithischian from the Early Jurassic of South Africa
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. The basal
neornithischian
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.
Ceratopsians first appeared in the Late Jurassic of China, represented by members of
Chaoyangsauridae.
Sauropodomorphs '' from the Middle-Late Jurassic of China
Sauropods became the dominant large herbivores in terrestrial ecosystems during the Jurassic. Some Jurassic sauropods reached gigantic sizes, becoming the largest organisms to have ever lived on land.
Basal bipedal
sauropodomorphs, such as
massospondylids, continued to exist into the Early Jurassic, but became extinct by the beginning of the Middle Jurassic.
Gravisaurian sauropods first appeared during the Early Jurassic, with the oldest definitive record being
Vulcanodon from Zimbabwe, likely of Sinemurian age.
Eusauropods first appeared during the late Early Jurassic (Toarcian) and diversified during the Middle Jurassic; and
mamenchisaurs.
Neosauropods such as
macronarians and
diplodocoids first appeared during the Middle Jurassic, before becoming abundant and globally distributed during the Late Jurassic.
Other reptiles Crocodylomorphs specimen of
Platysuchus, a
telosaurid thalattosuchian 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. 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. 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. The
Thalattosuchia, a clade of predominantly marine crocodylomorphs, first appeared during the Early Jurassic and became a prominent part of marine ecosystems. Within Thalattosuchia, the
Metriorhynchidae became highly adapted for life in the open ocean, including the transformation of limbs into flippers, the development of a tail fluke, and smooth, scaleless skin. The morphological diversity of crocodylomorphs during the Early and Middle Jurassic was relatively low compared to that in later time periods and was dominated by terrestrial small-bodied, long-legged
sphenosuchians, early
crocodyliforms and thalattosuchians. 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.
Turtles ,'' a
thalassochelydian sea turtle known from the Late Jurassic of Germany
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 (
Testudines),
Pleurodira and
Cryptodira, diverged by the beginning of the Late Jurassic. while the oldest unambiguous cryptodire,
Sinaspideretes, an early relative of
softshell turtles, is known from the Late Jurassic of China. The
Thalassochelydia, a diverse lineage of marine turtles unrelated to modern
sea turtles, are known from the Late Jurassic of Europe and South America.
Lepidosaurs Rhynchocephalians (the sole living representative being the
tuatara) had achieved a global distribution by the beginning of the Jurassic, Rhynchocephalians reached their highest morphological diversity in their evolutionary history during the Jurassic, occupying a wide range of lifestyles, including the aquatic
pleurosaurs with long snake-like bodies and reduced limbs, the specialized herbivorous
eilenodontines, as well as the
sapheosaurs which had broad tooth plates indicative of
durophagy. Rhynchocephalians disappeared from Asia after the Early Jurassic. The last common ancestor of living
squamates (which includes
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. Squamates first appear in the fossil record during the Middle Jurassic including members of modern clades such as
Scincomorpha, though many Jurassic squamates have unclear relationships to living groups.
Eichstaettisaurus from the Late Jurassic of Germany has been suggested to be an early relative of
geckos and displays adaptations for climbing.
Dorsetisaurus from the Late Jurassic of North America and Europe represents the oldest widely accepted record of
Anguimorpha.
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. File:Vadasaurus herzogi holotype (fossil).jpg|
Vadasaurus herzogi, a rynchocephalian from the Upper Jurassic
Solnhofen Limestone of Germany File:Homeosaurus maximiliani, lizard, Jurassic, Solnhofen Limestone, Eichstatt, Bavaria, Germany - Houston Museum of Natural Science - DSC01988.JPG|
Homeosaurus maximiliani, a rynchocephalian from the Solnhofen Limestone File:Pleurosaurus 783534.jpg|
Pleurosaurus,, an aquatic rhynchocephalian from the Late Jurassic of Europe File:Eichstaettisaurus schroederi.JPG|
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. 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 '' at the
Natural History Museum, London|alt=Skeleton of an icthyosaur in side view
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. 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 were already diverse in the earliest Jurassic, with the majority of plesiosaurs in the Hettangian-aged Blue Lias belonging to the
Rhomaleosauridae. Early plesiosaurs were generally small-bodied, with body size increasing into the Toarcian. There appears to have been a strong turnover around the Early–Middle Jurassic boundary, with
microcleidids and rhomaleosaurids becoming extinct and nearly extinct respectively after the end of the Toarcian with the first appearance of the dominant clade of plesiosaurs of the latter half of the Jurassic, the
Cryptoclididae during the Bajocian.
Pterosaurs '' at
Teylers Museum,
Haarlem|left
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
piscivorous.
Anurognathids, which first appeared in the Middle Jurassic, possessed short heads and densely furred bodies, and are thought to have been insectivores. Members of the family
Brachyopidae are known from Jurassic deposits in Asia, while the
chigutisaurid Siderops is known from the Early Jurassic of Australia. 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. 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,
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. 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.
Beiyanerpeton, 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 priscus 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
mammals, having originated from
cynodonts at the end of the Triassic, diversified extensively during the Jurassic. The
docodontan
Castorocauda was adapted to aquatic life, similarly to the
platypus and
otters. Some members of
Haramiyida and the
eutriconodontan tribe
Volaticotherini had a
patagium akin to those of
flying squirrels, allowing them to glide through the air. The
aardvark-like mammal
Fruitafossor, of uncertain taxonomy, was likely a specialist on colonial insects, similarly to living
anteaters.
Australosphenida, a group of mammals possibly related to living
monotremes, first appeared in the Middle Jurassic of Gondwana. The earliest records of
multituberculates, one of the longest lasting and most successful orders of mammals, are known from the Middle Jurassic.
Therian mammals, represented today by living
placentals and
marsupials, diversified meteorically during the Middle Jurassic. They have their earliest records during the early Late Jurassic, represented by
Juramaia, a
eutherian mammal closer to the ancestry of placentals than marsupials.
Juramaia is much more advanced than expected for its age, as other therian mammals are not known until the Early Cretaceous, 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 ,'' 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. End-Triassic conodonts were represented by only a handful of species and had been progressively declining through the Middle and Late Triassic.
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.
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.
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. 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 ,'' an
ichthyodectid stem-group teleost from the Late Jurassic Solnhofen Limestone of Germany, showing preserved colouration Ray-finned fish (
Actinopterygii) were major components of Jurassic freshwater and marine ecosystems. Archaic "
palaeoniscoid" fish, which were common in both marine and freshwater habitats during the preceding Triassic declined during the Jurassic, being largely replaced by more
derived actinopterygian lineages. The oldest known
Acipenseriformes, the group that contains living
sturgeon and
paddlefish, are from the Early Jurassic.
Amiiform fish (which today only includes the
bowfin) first appeared during the Early Jurassic, represented by
Caturus from the Pliensbachian of Britain; after their appearance in the western Tethys, they expanded to Africa, North America and Southeast and East Asia by the end of the Jurassic,
Pycnodontiformes, which first appeared in the western Tethys during the Late Triassic, expanded to South America and Southeast Asia by the end of the Jurassic, having a high diversity in Europe during the Late Jurassic. During the Jurassic, the
Ginglymodi, the only living representatives being
gars (Lepisosteidae) were diverse in both freshwater and marine environments. The oldest known representatives of anatomically modern gars appeared during the Late Jurassic. Stem-group
teleosts, which make up over 99% of living Actinopterygii, had first appeared during the Triassic in the western Tethys; they underwent a major diversification beginning in the Late Jurassic, with early representatives of modern teleost clades such as
Elopomorpha and
Osteoglossoidei appearing during this time. The
Pachycormiformes, a group of marine stem-teleosts, first appeared in the Early Jurassic and included both
tuna-like predatory and filter-feeding forms, the latter included the largest bony fish known to have existed:
Leedsichthys, with an estimated maximum length of over 15 metres, known from the late Middle to Late Jurassic.
Chondrichthyes '' from the Late Jurassic of Germany, a close relative of modern
angelsharks. During the Early Jurassic, the shark-like
hybodonts, which represented the dominant group of
chondrichthyans during the preceding Triassic, were common in both marine and freshwater settings; however, by the Late Jurassic, hybodonts had become minor components of most marine communities, having been largely replaced by modern
neoselachians, but remained common in freshwater and restricted marine environments. The Neoselachii, which contains all living sharks and rays, radiated beginning in the Early Jurassic. The oldest known ray (
Batoidea) is
Antiquaobatis from the Pliensbachian of Germany. Jurassic batoids known from complete remains retain a conservative,
guitarfish-like morphology. The oldest known
Hexanchiformes and
carpet sharks (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
catsharks.
Synechodontiformes, an extinct group of sharks closely related to Neoselachii, were also widespread during the Jurassic. The oldest remains of modern
chimaeras are from the Early Jurassic of Europe, with members of the living family
Callorhinchidae appearing during the Middle Jurassic. Unlike most living chimaeras, Jurassic chimeras are often found in shallow water environments. The closely related
myriacanthids and the flattened
Squaloraja are also known from the Jurassic of Europe.
Insects and arachnids '', an extinct
mesopsychid scorpionfly from the Late Jurassic of China There appears to have been no major extinction of insects at the Triassic–Jurassic boundary. The increasing diversity of insects in the Middle–Late Jurassic corresponds with a substantial increase in the diversity of
insect mouthparts. The Middle to Late Jurassic was a time of major diversification for
beetles, particularly for the suborder
Polyphaga, which represents 90% of living beetle species but which was rare during the preceding Triassic.
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.
Orthopteran diversity had declined during the Late Triassic, but recovered during the Early Jurassic, with the
Hagloidea, a superfamily of
ensiferan orthopterans today confined to a few living species, being particularly diverse during the Jurassic. The oldest known
lepidopterans (the group containing butterflies and moths) are known from the Triassic–Jurassic boundary, with wing scales belonging to the suborder
Glossata and
Micropterigidae-grade moths from the deposits of this age in Germany. Modern representatives of both
dragonflies and
damselflies also first appeared during the Jurassic. Although modern representatives are not known until the Cenozoic,
ectoparasitic insects thought to represent primitive
fleas, belonging to the family
Pseudopulicidae, are known from the Middle Jurassic of Asia. These insects are substantially different from modern fleas, lacking the specialised morphology of the latter and being larger.
Parasitoid wasps (
Apocrita) first appeared during the Early Jurassic and subsequently became widespread, reshaping terrestrial food webs. The Jurassic saw also saw the first appearances of several other groups of insects, including
Phasmatodea (stick insects),
Mantophasmatidae (gladiators),
Embioptera (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. '' 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, 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.
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. The only scorpion known from the Jurassic is
Liassoscorpionides from the Early Jurassic of Germany, of uncertain placement.
Eupnoi 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 filter feeders 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
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, which caused an associated drop in diversity in
decapod crustaceans. The earliest planktonic foraminifera, which constitute the suborder
Globigerinina, are known from the late Early Jurassic (mid-Toarcian) of the western Tethys, expanding across the whole Tethys by the Middle Jurassic and becoming globally distributed in tropical latitudes by the Late Jurassic.
Coccolithophores and
dinoflagellates, which had first appeared during the Triassic, radiated during the Early to Middle Jurassic, becoming prominent members of the
phytoplankton.
Microconchid tube worms, the last remaining order of
Tentaculita, a group of animals of uncertain affinities that were convergent on
Spirorbis tube worms, were rare after the Triassic and had become reduced to the single genus
Punctaconchus, which became extinct in the late Bathonian. The oldest known
diatom is from Late Jurassic–aged amber from Thailand, assigned to the living genus
Hemiaulus. 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.
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.
Crustaceans ,'' a
polychelidan decapod crustacean from the Late Jurassic of Germany. The Jurassic was a significant time for the evolution of
decapods. and
Eoprosopon klugi from the late Pliensbachian of Germany, which may belong to the living family
Homolodromiidae. Most Jurassic crabs are known only from
carapace pieces, which makes it difficult to determine their relationships. While rare in the Early and Middle Jurassic, crabs became abundant during the Late Jurassic as they expanded from their ancestral silty sea floor habitat into hard substrate habitats like reefs, with crevices in reefs providing refuge from predators. Early hermit crabs are associated with ammonite shells rather than those of gastropods.
Glypheids, which today are only known from two species, reached their peak diversity during the Jurassic, with around 150 species out of a total fossil record of 250 known from the period. Jurassic barnacles were of low diversity compared to present, but several important evolutionary innovations are known, including the first appearances of calcite shelled forms and species with an epiplanktonic mode of life.
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.
Rhynchonellida and
Terebratulida also declined during the Triassic–Jurassic extinction but rebounded during the Early Jurassic; neither clade underwent much morphological variation. Brachiopods substantially declined in the Late Jurassic; the causes are poorly understood. Proposed reasons include increased predation, competition with bivalves, enhanced
bioturbation or increased
grazing pressure.
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.
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 and
land snails 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.
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.
Cephalopods '' from the Middle Jurassic of France, formerly thought to be world's oldest known octopusAmmonites 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. Ammonite diversifications occurred coevally with
marine transgressions, while their diversity nadirs occurred during
marine regressions. The oldest definitive records of the squid-like
belemnites are from the earliest Jurassic (Hettangian–Sinemurian) of Europe and Japan; they expanded worldwide during the Jurassic. Belemnites were shallow-water dwellers, inhabiting the upper 200 metres of the water column on the
continental shelves and in the
littoral zone. They were key components of Jurassic ecosystems, both as predators and prey, as evidenced by the abundance of belemnite guards in Jurassic rocks. The earliest
vampyromorphs, of which the only living member is the
vampire squid, first appeared during the Early Jurassic. The earliest
octopuses appeared during the Middle Jurassic, having split from their closest living relatives, the vampyromorphs, during the Triassic to Early Jurassic. All Jurassic octopuses are solely known from the hard
gladius. Octopuses likely originated from bottom-dwelling (
benthic) ancestors which lived in shallow environments. ==References==