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105-584: See text Eels are ray-finned fish belonging to the order Anguilliformes ( / æ ŋ ˈ ɡ w ɪ l ɪ f ɔːr m iː z / ), which consists of eight suborders, 20 families , 164 genera , and about 1000 species . Eels undergo considerable development from the early larval stage to the eventual adult stage and are usually predators . The term "eel" is also used for some other eel-shaped fish, such as electric eels (genus Electrophorus ), swamp eels (order Synbranchiformes ), and deep-sea spiny eels (family Notacanthidae). However, these other clades , with

210-555: A Berriasian–Barremian warm-dry phase, an Aptian–Santonian warm-wet phase, and a Campanian–Maastrichtian cool-dry phase. As in the Cenozoic, the 400,000 year eccentricity cycle was the dominant orbital cycle governing carbon flux between different reservoirs and influencing global climate. The location of the Intertropical Convergence Zone (ITCZ) was roughly the same as in the present. The cooling trend of

315-675: A cheap dish in the United Kingdom . During the 1990s, their numbers collapsed across Europe. They became a delicacy, and the UK's most expensive species. Eels, particularly the moray eel , are popular among marine aquarists . Eel blood is toxic to humans and other mammals, but both cooking and the digestive process destroy the toxic protein. High consumption of eels is seen in European countries leading to those eel species being considered endangered. In 2010, Greenpeace International added

420-459: A free-swimming larval stage. However other patterns of ontogeny exist, with one of the commonest being sequential hermaphroditism . In most cases this involves protogyny , fish starting life as females and converting to males at some stage, triggered by some internal or external factor. Protandry , where a fish converts from male to female, is much less common than protogyny. Most families use external rather than internal fertilization . Of

525-674: A straight shell, flourished in the seas along with reef-building rudist clams. Inoceramids were also particularly notable among Cretaceous bivalves, and they have been used to identify major biotic turnovers such as at the Turonian-Coniacian boundary. Predatory gastropods with drilling habits were widespread. Globotruncanid foraminifera and echinoderms such as sea urchins and starfish (sea stars) thrived. Ostracods were abundant in Cretaceous marine settings; ostracod species characterised by high male sexual investment had

630-742: A trait still present in Holostei ( bowfins and gars ). In some fish like the arapaima , the swim bladder has been modified for breathing air again, and in other lineages it have been completely lost. The teleosts have urinary and reproductive tracts that are fully separated, while the Chondrostei have common urogenital ducts, and partially connected ducts are found in Cladistia and Holostei. Ray-finned fishes have many different types of scales ; but all teleosts have leptoid scales . The outer part of these scales fan out with bony ridges, while

735-564: A ~0.6 °C increase in temperature. The latter warming interval, occurring at the very end of the Cretaceous, was triggered by the activity of the Deccan Traps. The LKEPCI lasted into the Late Palaeocene , when it gave way to another supergreenhouse interval. The production of large quantities of magma, variously attributed to mantle plumes or to extensional tectonics , further pushed sea levels up, so that large areas of

840-566: Is a monophyletic group that originated among the deep-sea eels. The earliest fossil eels are known from the Late Cretaceous ( Cenomanian ) of Lebanon . These early eels retain primitive traits such as pelvic fins and thus do not appear to be closely related to any extant taxa. Body fossils of modern eels do not appear until the Eocene , although otoliths assignable to extant eel families and even some genera have been recovered from

945-713: Is a traditional Māori food in New Zealand . In Italian cuisine , eels from the Valli di Comacchio , a swampy zone along the Adriatic coast, are especially prized, along with freshwater eels of Bolsena Lake and pond eels from Cabras, Sardinia . In northern Germany , the Netherlands , the Czech Republic , Poland , Denmark , and Sweden , smoked eel is considered a delicacy . Elvers, often fried, were once

1050-531: Is directly comparable to Hittite ellu-essar- "snake pit". This myth likely came to Greece via Anatolia. In the Hittite version of the myth, the dragon is called Illuyanka : the illuy- part is cognate to the word illa , and the -anka part is cognate to angu , a word for "snake". Since the words for "snake" (and similarly shaped animals) are often subject to taboo in many Indo-European (and non-Indo-European) languages, no unambiguous Proto-Indo-European form of

1155-545: Is divided into the infraclasses Holostei and Teleostei . During the Mesozoic ( Triassic , Jurassic , Cretaceous ) and Cenozoic the teleosts in particular diversified widely. As a result, 96% of living fish species are teleosts (40% of all fish species belong to the teleost subgroup Acanthomorpha ), while all other groups of actinopterygians represent depauperate lineages. The classification of ray-finned fishes can be summarized as follows: The cladogram below shows

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1260-619: Is found in England, northern France, the low countries , northern Germany , Denmark and in the subsurface of the southern part of the North Sea . Chalk is not easily consolidated and the Chalk Group still consists of loose sediments in many places. The group also has other limestones and arenites . Among the fossils it contains are sea urchins , belemnites , ammonites and sea reptiles such as Mosasaurus . In southern Europe,

1365-509: Is now used worldwide. In many parts of the world, alternative local subdivisions are still in use. From youngest to oldest, the subdivisions of the Cretaceous period are: The lower boundary of the Cretaceous is currently undefined, and the Jurassic–Cretaceous boundary is currently the only system boundary to lack a defined Global Boundary Stratotype Section and Point (GSSP). Placing a GSSP for this boundary has been difficult because of

1470-432: Is relatively rare and is found in about 6% of living teleost species; male care is far more common than female care. Male territoriality "preadapts" a species for evolving male parental care. There are a few examples of fish that self-fertilise. The mangrove rivulus is an amphibious, simultaneous hermaphrodite, producing both eggs and spawn and having internal fertilisation. This mode of reproduction may be related to

1575-542: Is used as a metaphor for Nazi atrocities, and the sight of eels being killed by a fisherman triggers the madness of the protagonist's mother. Sinister implications of eels fishing are also referenced in Jo Nesbø 's Cockroaches , the second book of the Harry Hole detective series. The book's background includes a Norwegian village where eels in the nearby sea are rumored to feed on the corpses of drowned humans, making

1680-662: The Campanian and Maastrichtian , indicating some level of diversification among the extant groups prior to the Cretaceous-Paleogene extinction , which is also supported by phylogenetic divergence estimates. One of these otolith taxa, the mud-dwelling Pythonichthys arkansasensis , appears to have thrived in the aftermath of the K-Pg extinction, based on its abundance. Taxonomy based on Eschmeyer's Catalog of Fishes : Order Anguilliformes In some classifications,

1785-506: The Cyprinidae (in goldfish and common carp as recently as 14 million years ago). Ray-finned fish vary in size and shape, in their feeding specializations, and in the number and arrangement of their ray-fins. In nearly all ray-finned fish, the sexes are separate, and in most species the females spawn eggs that are fertilized externally, typically with the male inseminating the eggs after they are laid. Development then proceeds with

1890-479: The European eel , Japanese eel , and American eel to its seafood red list. Japan consumes more than 70% of the global eel catch. The English name "eel" descends from Old English ǣl , Common Germanic *ēlaz . Also from the common Germanic are West Frisian iel , Dutch aal , German Aal , and Icelandic áll . Katz (1998) identifies a number of Indo-European cognates, among them

1995-713: The Mancos Shale of western North America. These shales are an important source rock for oil and gas , for example in the subsurface of the North Sea. In northwestern Europe, chalk deposits from the Upper Cretaceous are characteristic for the Chalk Group , which forms the white cliffs of Dover on the south coast of England and similar cliffs on the French Normandian coast. The group

2100-711: The North American Cordillera , as the Nevadan orogeny was followed by the Sevier and Laramide orogenies . Gondwana had begun to break up during the Jurassic Period, but its fragmentation accelerated during the Cretaceous and was largely complete by the end of the period. South America , Antarctica , and Australia rifted away from Africa (though India and Madagascar remained attached to each other until around 80 million years ago); thus,

2205-783: The Northeast . Freshwater eels, known as Kusia in Assamese , are eaten with curry, often with herbs. The European eel and other freshwater eels are mostly eaten in Europe and the United States , and is considered critically endangered. A traditional east London food is jellied eels , although the demand has significantly declined since World War II. The Spanish cuisine delicacy angulas consists of elver (young eels) sautéed in olive oil with garlic ; elvers usually reach prices of up to 1000 euro per kg. New Zealand longfin eel

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2310-553: The Selli Event . Early Aptian tropical sea surface temperatures (SSTs) were 27–32 °C, based on TEX 86 measurements from the equatorial Pacific. During the Aptian, Milankovitch cycles governed the occurrence of anoxic events by modulating the intensity of the hydrological cycle and terrestrial runoff. The early Aptian was also notable for its millennial scale hyperarid events in the mid-latitudes of Asia. The BAWI itself

2415-630: The Terrain Crétacé , using strata in the Paris Basin and named for the extensive beds of chalk ( calcium carbonate deposited by the shells of marine invertebrates , principally coccoliths ), found in the upper Cretaceous of Western Europe . The name Cretaceous was derived from the Latin creta , meaning chalk . The twofold division of the Cretaceous was implemented by Conybeare and Phillips in 1822. Alcide d'Orbigny in 1840 divided

2520-728: The Turonian Age, based on isotopic evidence. However, this has subsequently been suggested to be the result of inconsistent isotopic proxies, with evidence of polar rainforests during this time interval at 82° S. Rafting by ice of stones into marine environments occurred during much of the Cretaceous, but evidence of deposition directly from glaciers is limited to the Early Cretaceous of the Eromanga Basin in southern Australia . Flowering plants (angiosperms) make up around 90% of living plant species today. Prior to

2625-485: The caudal fin, forming a single ribbon running along much of the length of the animal. Eels swim by generating waves that travel the length of their bodies. They can swim backward by reversing the direction of the wave. Most eels live in the shallow waters of the ocean and burrow into sand, mud, or amongst rocks. Most eel species are nocturnal , and thus are rarely seen. Sometimes, they are seen living together in holes or "eel pits". Some eels also live in deeper water on

2730-488: The oviparous teleosts, most (79%) do not provide parental care. Viviparity , ovoviviparity , or some form of parental care for eggs, whether by the male, the female, or both parents is seen in a significant fraction (21%) of the 422 teleost families; no care is likely the ancestral condition. The oldest case of viviparity in ray-finned fish is found in Middle Triassic species of † Saurichthys . Viviparity

2835-663: The sister lineage of all other actinopterygians, the Acipenseriformes (sturgeons and paddlefishes) are the sister lineage of Neopterygii, and Holostei (bowfin and gars) are the sister lineage of teleosts. The Elopomorpha ( eels and tarpons ) appear to be the most basal teleosts. The earliest known fossil actinopterygian is Andreolepis hedei , dating back 420 million years ( Late Silurian ), remains of which have been found in Russia , Sweden , and Estonia . Crown group actinopterygians most likely originated near

2940-665: The slender giant moray , which reaches 4 m (13 ft). Eels begin life as flat and transparent larvae , called leptocephali . Eel larvae drift in the sea's surface waters, feeding on marine snow , small particles that float in the water. Eel larvae then metamorphose into glass eels and become elvers before finally seeking out their juvenile and adult habitats. Some individuals of anguillid elvers remains in brackish and marine areas close to coastlines, but most of them enter freshwater where they travel upstream and are forced to climb up obstructions, such as weirs , dam walls, and natural waterfalls. Gertrude Elizabeth Blood found that

3045-483: The tuatara ) disappeared from North America and Europe after the Early Cretaceous , and were absent from North Africa and northern South America by the early Late Cretaceous . The cause of the decline of Rhynchocephalia remains unclear, but has often been suggested to be due to competition with advanced lizards and mammals. They appear to have remained diverse in high-latitude southern South America during

3150-999: The Albian regularly expanded northward in tandem with expansions of subtropical high pressure belts. The Cedar Mountain Formation's Soap Wash flora indicates a mean annual temperature of between 19 and 26 °C in Utah at the Albian-Cenomanian boundary. Tropical SSTs during the Cenomanian-Turonian Thermal Maximum were at least 30 °C, though one study estimated them as high as between 33 and 42 °C. An intermediate estimate of ~33-34 °C has also been given. Meanwhile, deep ocean temperatures were as much as 15 to 20 °C (27 to 36 °F) warmer than today's; one study estimated that deep ocean temperatures were between 12 and 20 °C during

3255-571: The Cenozoic Era   —   the ichthyosaurs , last remaining temnospondyls ( Koolasuchus ), and nonmammalian cynodonts ( Tritylodontidae )   —   were already extinct millions of years before the event occurred. Coccolithophorids and molluscs , including ammonites , rudists , freshwater snails , and mussels , as well as organisms whose food chain included these shell builders, became extinct or suffered heavy losses. For example, ammonites are thought to have been

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3360-645: The Coniacian through the Maastrichtian. During the Cretaceous, the late- Paleozoic -to-early-Mesozoic supercontinent of Pangaea completed its tectonic breakup into the present-day continents , although their positions were substantially different at the time. As the Atlantic Ocean widened, the convergent-margin mountain building ( orogenies ) that had begun during the Jurassic continued in

3465-626: The Cretaceous is sharply defined, being placed at an iridium -rich layer found worldwide that is believed to be associated with the Chicxulub impact crater , with its boundaries circumscribing parts of the Yucatán Peninsula and extending into the Gulf of Mexico . This layer has been dated at 66.043 Mya. At the end of the Cretaceous, the impact of a large body with the Earth may have been

3570-514: The Cretaceous is usually a marine system consisting of competent limestone beds or incompetent marls . Because the Alpine mountain chains did not yet exist in the Cretaceous, these deposits formed on the southern edge of the European continental shelf , at the margin of the Tethys Ocean . During the Cretaceous, the present North American continent was isolated from the other continents. In

3675-537: The Cretaceous seas. Stagnation of deep sea currents in middle Cretaceous times caused anoxic conditions in the sea water leaving the deposited organic matter undecomposed. Half of the world's petroleum reserves were laid down at this time in the anoxic conditions of what would become the Persian Gulf and the Gulf of Mexico. In many places around the world, dark anoxic shales were formed during this interval, such as

3780-945: The Devonian-Carboniferous boundary. The earliest fossil relatives of modern teleosts are from the Triassic period ( Prohalecites , Pholidophorus ), although it is suspected that teleosts originated already during the Paleozoic Era . The listing below is a summary of all extinct (indicated by a dagger , †) and living groups of Actinopterygii with their respective taxonomic rank . The taxonomy follows Phylogenetic Classification of Bony Fishes with notes when this differs from Nelson, ITIS and FishBase and extinct groups from Van der Laan 2016 and Xu 2021. [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] Cretaceous The Cretaceous

3885-794: The French Cretaceous into five étages (stages): the Neocomian , Aptian, Albian, Turonian, and Senonian, later adding the Urgonian between Neocomian and Aptian and the Cenomanian between the Albian and Turonian. The Cretaceous is divided into Early and Late Cretaceous epochs , or Lower and Upper Cretaceous series . In older literature, the Cretaceous is sometimes divided into three series: Neocomian (lower/early), Gallic (middle) and Senonian (upper/late). A subdivision into 12 stages , all originating from European stratigraphy,

3990-672: The Jurassic, the North Atlantic already opened, leaving a proto-ocean between Europe and North America. From north to south across the continent, the Western Interior Seaway started forming. This inland sea separated the elevated areas of Laramidia in the west and Appalachia in the east. Three dinosaur clades found in Laramidia (troodontids, therizinosaurids and oviraptorosaurs) are absent from Appalachia from

4095-576: The LKEPCI. During this period of relatively cool temperatures, the ITCZ became narrower, while the strength of both summer and winter monsoons in East Asia was directly correlated to atmospheric CO 2 concentrations. Laramidia likewise had a seasonal, monsoonal climate. The Maastrichtian was a time of chaotic, highly variable climate. Two upticks in global temperatures are known to have occurred during

4200-532: The Late Cretaceous, where lizards remained rare, with their remains outnumbering terrestrial lizards 200:1. Choristoderes , a group of freshwater aquatic reptiles that first appeared during the preceding Jurassic, underwent a major evolutionary radiation in Asia during the Early Cretaceous, which represents the high point of choristoderan diversity, including long necked forms such as Hyphalosaurus and

4305-555: The Late Cretaceous-Early Palaeogene Cool Interval (LKEPCI). Tropical SSTs declined from around 35 °C in the early Campanian to around 28 °C in the Maastrichtian. Deep ocean temperatures declined to 9 to 12 °C, though the shallow temperature gradient between tropical and polar seas remained. Regional conditions in the Western Interior Seaway changed little between the MKH and

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4410-628: The MKH. Mean annual temperatures at the poles during the MKH exceeded 14 °C. Such hot temperatures during the MKH resulted in a very gentle temperature gradient from the equator to the poles; the latitudinal temperature gradient during the Cenomanian-Turonian Thermal Maximum was 0.54 °C per ° latitude for the Southern Hemisphere and 0.49 °C per ° latitude for the Northern Hemisphere, in contrast to present day values of 1.07 and 0.69 °C per ° latitude for

4515-526: The MKH. The poles were so warm that ectothermic reptiles were able to inhabit them. Beginning in the Santonian, near the end of the MKH, the global climate began to cool, with this cooling trend continuing across the Campanian. This period of cooling, driven by falling levels of atmospheric carbon dioxide, caused the end of the MKH and the transition into a cooler climatic interval, known formally as

4620-404: The Maastrichtian, bucking the trend of overall cooler temperatures during the LKEPCI. Between 70 and 69 Ma and 66–65 Ma, isotopic ratios indicate elevated atmospheric CO 2 pressures with levels of 1000–1400 ppmV and mean annual temperatures in west Texas between 21 and 23 °C (70 and 73 °F). Atmospheric CO 2 and temperature relations indicate a doubling of pCO 2 was accompanied by

4725-584: The Old English word for "hedgehog", which is igil (meaning "snake eater"), and perhaps in the egi- of Old High German egidehsa "wall lizard". According to this theory, the name Bellerophon ( Βελλεροφόντης , attested in a variant Ἐλλεροφόντης in Eustathius of Thessalonica ) is also related, translating to "the slayer of the serpent" ( ahihán ). In this theory, the ελλερο- is an adjective form of an older word, ελλυ, meaning "snake", which

4830-648: The Paleobiology Database: Freshwater eels ( unagi ) and marine eels ( conger eel , anago ) are commonly used in Japanese cuisine ; foods such as unadon and unajū are popular, but expensive. Eels are also very popular in Chinese cuisine , and are prepared in many different ways. Hong Kong eel prices have often reached 1000 HKD (128.86 US Dollars) per kg, and once exceeded 5000 HKD per kg. In India , eels are popularly eaten in

4935-419: The South Atlantic and Indian Oceans were newly formed. Such active rifting lifted great undersea mountain chains along the welts, raising eustatic sea levels worldwide. To the north of Africa the Tethys Sea continued to narrow. During most of the Late Cretaceous, North America would be divided in two by the Western Interior Seaway , a large interior sea, separating Laramidia to the west and Appalachia to

5040-514: The Southern and Northern hemispheres, respectively. This meant weaker global winds, which drive the ocean currents, and resulted in less upwelling and more stagnant oceans than today. This is evidenced by widespread black shale deposition and frequent anoxic events . Tropical SSTs during the late Albian most likely averaged around 30 °C. Despite this high SST, seawater was not hypersaline at this time, as this would have required significantly higher temperatures still. On land, arid zones in

5145-403: The Tethys to the Arctic Ocean and enabling biotic exchange between the two oceans. At the peak of the Cretaceous transgression , one-third of Earth's present land area was submerged. The Cretaceous is justly famous for its chalk ; indeed, more chalk formed in the Cretaceous than in any other period in the Phanerozoic . Mid-ocean ridge activity—or rather, the circulation of seawater through

5250-402: The adjacent diagram. The swim bladder is a more derived structure and used for buoyancy . Except from the bichirs , which just like the lungs of lobe-finned fish have retained the ancestral condition of ventral budding from the foregut , the swim bladder in ray-finned fishes derives from a dorsal bud above the foregut. In early forms the swim bladder could still be used for breathing,

5355-425: The ancestors of modern-day birds also diversified. They inhabited every continent, and were even found in cold polar latitudes. Pterosaurs were common in the early and middle Cretaceous, but as the Cretaceous proceeded they declined for poorly understood reasons (once thought to be due to competition with early birds , but now it is understood avian adaptive radiation is not consistent with pterosaur decline ). By

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5460-463: The bichirs and holosteans (bowfin and gars) in having gone through a whole-genome duplication ( paleopolyploidy ). The WGD is estimated to have happened about 320 million years ago in the teleosts, which on average has retained about 17% of the gene duplicates, and around 180 (124–225) million years ago in the chondrosteans. It has since happened again in some teleost lineages, like Salmonidae (80–100 million years ago) and several times independently within

5565-440: The bulkier, fleshy lobed fins of the sister class Sarcopterygii (lobe-finned fish). Resembling folding fans , the actinopterygian fins can easily change shape and wetted area , providing superior thrust-to-weight ratios per movement compared to sarcopterygian and chondrichthyian fins. The fin rays attach directly to the proximal or basal skeletal elements, the radials, which represent the articulation between these fins and

5670-408: The continental crust were covered with shallow seas. The Tethys Sea connecting the tropical oceans east to west also helped to warm the global climate. Warm-adapted plant fossils are known from localities as far north as Alaska and Greenland , while dinosaur fossils have been found within 15 degrees of the Cretaceous south pole . It was suggested that there was Antarctic marine glaciation in

5775-436: The continental shelves and over the slopes deep as 4,000 m (13,000 ft). Only members of the Anguilla regularly inhabit fresh water, but they, too, return to the sea to breed. The heaviest true eel is the European conger . The maximum size of this species has been reported as reaching a length of 3 m (10 ft) and a weight of 110 kg (240 lb). Other eels are longer, but do not weigh as much, such as

5880-706: The different actinopterygian clades (in millions of years , mya) are from Near et al., 2012. Jaw-less fishes ( hagfish , lampreys ) [REDACTED] Cartilaginous fishes ( sharks , rays , ratfish ) [REDACTED] Coelacanths [REDACTED] Lungfish [REDACTED] Amphibians [REDACTED] Mammals [REDACTED] Sauropsids ( reptiles , birds ) [REDACTED] Polypteriformes ( bichirs , reedfishes ) [REDACTED] Acipenseriformes ( sturgeons , paddlefishes ) [REDACTED] Teleostei [REDACTED] Amiiformes ( bowfins ) [REDACTED] Lepisosteiformes ( gars ) [REDACTED] The polypterids (bichirs and reedfish) are

5985-544: The early and mid-Cretaceous (becoming extinct during the late Cretaceous Cenomanian-Turonian anoxic event ), plesiosaurs throughout the entire period, and mosasaurs appearing in the Late Cretaceous. Sea turtles in the form of Cheloniidae and Panchelonioidea lived during the period and survived the extinction event. Panchelonioidea is today represented by a single species; the leatherback sea turtle . The Hesperornithiformes were flightless, marine diving birds that swam like grebes . Baculites , an ammonite genus with

6090-437: The east, then receded late in the period, leaving thick marine deposits sandwiched between coal beds. Bivalve palaeobiogeography also indicates that Africa was split in half by a shallow sea during the Coniacian and Santonian, connecting the Tethys with the South Atlantic by way of the central Sahara and Central Africa, which were then underwater. Yet another shallow seaway ran between what is now Norway and Greenland, connecting

6195-604: The eating of these eels verge on cannibalism. Ray-finned fish Actinopterygii ( / ˌ æ k t ɪ n ɒ p t ə ˈ r ɪ dʒ i aɪ / ; from actino-  'having rays' and Ancient Greek πτέρυξ (ptérux)  'wing, fins'), members of which are known as ray-finned fish or actinopterygians , is a class of bony fish that comprise over 50% of living vertebrate species. They are so called because of their lightly built fins made of webbings of skin supported by radially extended thin bony spines called lepidotrichia , as opposed to

6300-441: The eel fisheries at Ballisodare were greatly improved by the hanging of loosely plaited grass ladders over barriers, enabling elvers to ascend more easily. Several sets of classifications of eels exist; some, such as FishBase which divide eels into 20 families, whereas other classification systems such as ITIS and Systema Naturae 2000 include additional eel families, which are noted below. Genomic studies indicate that there

6405-535: The end of the AACS, which ended around 111 Ma with the Paquier/Urbino Thermal Maximum, giving way to the Mid-Cretaceous Hothouse (MKH), which lasted from the early Albian until the early Campanian. Faster rates of seafloor spreading and entry of carbon dioxide into the atmosphere are believed to have initiated this period of extreme warmth, along with high flood basalt activity. The MKH was punctuated by multiple thermal maxima of extreme warmth. The Leenhardt Thermal Event (LTE) occurred around 110 Ma, followed shortly by

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6510-448: The end of the Cretaceous. The high sea level and warm climate of the Cretaceous meant large areas of the continents were covered by warm, shallow seas, providing habitat for many marine organisms. The Cretaceous was named for the extensive chalk deposits of this age in Europe, but in many parts of the world, the deposits from the Cretaceous are of marine limestone , a rock type that is formed under warm, shallow marine conditions. Due to

6615-411: The end of the period only three highly specialized families remained; Pteranodontidae , Nyctosauridae , and Azhdarchidae . The Liaoning lagerstätte ( Yixian Formation ) in China is an important site, full of preserved remains of numerous types of small dinosaurs, birds and mammals, that provides a glimpse of life in the Early Cretaceous. The coelurosaur dinosaurs found there represent types of

6720-407: The enlarged ridges—enriched the oceans in calcium ; this made the oceans more saturated, as well as increased the bioavailability of the element for calcareous nanoplankton . These widespread carbonates and other sedimentary deposits make the Cretaceous rock record especially fine. Famous formations from North America include the rich marine fossils of Kansas 's Smoky Hill Chalk Member and

6825-399: The exception of deep-sea spiny eels, whose order Notacanthiformes is the sister clade to true eels, evolved their eel-like shapes independently from the true eels. As a main rule, most eels are marine. Exceptions are the catadromous genus Anguilla and the freshwater moray , which spend most of their life in freshwater, the anadromous rice-paddy eel , which spawns in freshwater, and

6930-528: The extinction fed on insects , larvae , worms , and snails, which in turn fed on dead plant and animal matter. Scientists theorise that these organisms survived the collapse of plant-based food chains because they fed on detritus . In stream communities , few groups of animals became extinct. Stream communities rely less on food from living plants and more on detritus that washes in from land. This particular ecological niche buffered them from extinction. Similar, but more complex patterns have been found in

7035-797: The family Cyematidae of bobtail snipe eels is included in the Anguilliformes, but in the FishBase system that family is included in the order Saccopharyngiformes . The electric eel of South America is not a true eel but is a South American knifefish more closely related to the carps and catfishes . Phylogeny based on Johnson et al. 2012. Protanguillidae Synaphobranchidae Heterenchelyidae Myrocongridae Muraenidae [REDACTED] Chlopsidae Derichthyidae Nettastomatidae Congridae [REDACTED] Ophichthidae Muraenesocidae Moringuidae Eurypharyngidae Saccopharyngidae [REDACTED] Monognathidae Cyematidae [REDACTED] Nemichthyidae Serrivomeridae Anguillidae [REDACTED] Based on

7140-505: The first records of the gharial-like Neochoristodera , which appear to have evolved in the regional absence of aquatic neosuchian crocodyliformes. During the Late Cretaceous the neochoristodere Champsosaurus was widely distributed across western North America. Due to the extreme climatic warmth in the Arctic, choristoderans were able to colonise it too during the Late Cretaceous. In the seas, rays , modern sharks and teleosts became common. Marine reptiles included ichthyosaurs in

7245-432: The fish's habit of spending long periods out of water in the mangrove forests it inhabits. Males are occasionally produced at temperatures below 19 °C (66 °F) and can fertilise eggs that are then spawned by the female. This maintains genetic variability in a species that is otherwise highly inbred. Actinopterygii is divided into the subclasses Cladistia , Chondrostei and Neopterygii . The Neopterygii , in turn,

7350-423: The freshwater snake eel Stictorhinus . Eels are elongated fish, ranging in length from 5 cm (2 in) in the one-jawed eel ( Monognathus ahlstromi ) to 4 m (13 ft) in the slender giant moray . Adults range in weight from 30 g (1 oz) to well over 25 kg (55 lb). They possess no pelvic fins , and many species also lack pectoral fins . The dorsal and anal fins are fused with

7455-427: The genus Berriasella , but its use as a stratigraphic indicator has been questioned, as its first appearance does not correlate with that of C. alpina . The boundary is officially considered by the International Commission on Stratigraphy to be approximately 145 million years ago, but other estimates have been proposed based on U-Pb geochronology, ranging as young as 140 million years ago. The upper boundary of

7560-625: The group Maniraptora , which includes modern birds and their closest non-avian relatives, such as dromaeosaurs , oviraptorosaurs , therizinosaurs , troodontids along with other avialans . Fossils of these dinosaurs from the Liaoning lagerstätte are notable for the presence of hair-like feathers . Insects diversified during the Cretaceous, and the oldest known ants , termites and some lepidopterans , akin to butterflies and moths , appeared. Aphids , grasshoppers and gall wasps appeared. Rhynchocephalians (which today only includes

7665-412: The high sea level, there was extensive space for such sedimentation . Because of the relatively young age and great thickness of the system, Cretaceous rocks are evident in many areas worldwide. Chalk is a rock type characteristic for (but not restricted to) the Cretaceous. It consists of coccoliths , microscopically small calcite skeletons of coccolithophores , a type of algae that prospered in

7770-494: The highest mountain streams . Extant species can range in size from Paedocypris , at 8 mm (0.3 in); to the massive ocean sunfish , at 2,300 kg (5,070 lb); and to the giant oarfish , at 11 m (36 ft). The largest ever known ray-finned fish, the extinct Leedsichthys from the Jurassic , has been estimated to have grown to 16.5 m (54 ft). Ray-finned fishes occur in many variant forms. The main features of typical ray-finned fish are shown in

7875-551: The highest rates of extinction and turnover. Thylacocephala , a class of crustaceans, went extinct in the Late Cretaceous. The first radiation of the diatoms (generally siliceous shelled, rather than calcareous ) in the oceans occurred during the Cretaceous; freshwater diatoms did not appear until the Miocene . Calcareous nannoplankton were important components of the marine microbiota and important as biostratigraphic markers and recorders of environmental change. The Cretaceous

7980-469: The impact of a large asteroid that formed the Chicxulub crater in the Gulf of Mexico. The end of the Cretaceous is defined by the abrupt Cretaceous–Paleogene boundary (K–Pg boundary), a geologic signature associated with the mass extinction that lies between the Mesozoic and Cenozoic Eras . The Cretaceous as a separate period was first defined by Belgian geologist Jean d'Omalius d'Halloy in 1822 as

8085-438: The inner part is crossed with fibrous connective tissue. Leptoid scales are thinner and more transparent than other types of scales, and lack the hardened enamel - or dentine -like layers found in the scales of many other fish. Unlike ganoid scales , which are found in non-teleost actinopterygians, new scales are added in concentric layers as the fish grows. Teleosts and chondrosteans (sturgeons and paddlefish) also differ from

8190-425: The internal skeleton (e.g., pelvic and pectoral girdles). The vast majority of actinopterygians are teleosts . By species count, they dominate the subphylum Vertebrata , and constitute nearly 99% of the over 30,000 extant species of fish . They are the most abundant nektonic aquatic animals and are ubiquitous throughout freshwater and marine environments from the deep sea to subterranean waters to

8295-767: The last epoch of the Jurassic, the Tithonian, continued into the Berriasian, the first age of the Cretaceous. The North Atlantic seaway opened and enabled the flow of cool water from the Boreal Ocean into the Tethys. There is evidence that snowfalls were common in the higher latitudes during this age, and the tropics became wetter than during the Triassic and Jurassic. Glaciation was restricted to high- latitude mountains, though seasonal snow may have existed farther from

8400-575: The late Valanginian (~ 134 million years ago) found in Israel and Italy, initially at low abundance. Molecular clock estimates conflict with fossil estimates, suggesting the diversification of crown-group angiosperms during the Late Triassic or the Jurassic, but such estimates are difficult to reconcile with the heavily sampled pollen record and the distinctive tricolpate to tricolporoidate (triple grooved) pollen of eudicot angiosperms. Among

8505-465: The late Cretaceous, and all else that depended on them suffered, as well. Herbivorous animals, which depended on plants and plankton as their food, died out as their food sources became scarce; consequently, the top predators , such as Tyrannosaurus rex , also perished. Yet only three major groups of tetrapods disappeared completely; the nonavian dinosaurs , the plesiosaurs and the pterosaurs . The other Cretaceous groups that did not survive into

8610-574: The latest Albian. Approximately 94 Ma, the Cenomanian-Turonian Thermal Maximum occurred, with this hyperthermal being the most extreme hothouse interval of the Cretaceous and being associated with a sea level highstand. Temperatures cooled down slightly over the next few million years, but then another thermal maximum, the Coniacian Thermal Maximum, happened, with this thermal event being dated to around 87 Ma. Atmospheric CO 2 levels may have varied by thousands of ppm throughout

8715-711: The l’Arboudeyesse Thermal Event (ATE) a million years later. Following these two hyperthermals was the Amadeus Thermal Maximum around 106 Ma, during the middle Albian. Then, around a million years after that, occurred the Petite Verol Thermal Event (PVTE). Afterwards, around 102.5 Ma, the Event 6 Thermal Event (EV6) took place; this event was itself followed by the Breistroffer Thermal Maximum around 101 Ma, during

8820-466: The main clades of living actinopterygians and their evolutionary relationships to other extant groups of fishes and the four-limbed vertebrates ( tetrapods ). The latter include mostly terrestrial species but also groups that became secondarily aquatic (e.g. whales and dolphins ). Tetrapods evolved from a group of bony fish during the Devonian period . Approximate divergence dates for

8925-517: The middle Cretaceous, becoming the dominant group of land plants by the end of the period, coincident with the decline of previously dominant groups such as conifers. The oldest known fossils of grasses are from the Albian , with the family having diversified into modern groups by the end of the Cretaceous. The oldest large angiosperm trees are known from the Turonian (c. 90 Mya) of New Jersey, with

9030-684: The middle of the Cretaceous. During the Early Cretaceous, flowering plants appeared and began to rapidly diversify, becoming the dominant group of plants across the Earth by the end of the Cretaceous, coincident with the decline and extinction of previously widespread gymnosperm groups. The Cretaceous (along with the Mesozoic) ended with the Cretaceous–Paleogene extinction event , a large mass extinction in which many groups, including non-avian dinosaurs, pterosaurs , and large marine reptiles , died out, widely thought to have been caused by

9135-408: The most promising candidates for fixing the Jurassic–Cretaceous boundary. In particular, the first appearance Calpionella alpina , coinciding with the base of the eponymous Alpina subzone, has been proposed as the definition of the base of the Cretaceous. The working definition for the boundary has often been placed as the first appearance of the ammonite Strambergella jacobi , formerly placed in

9240-824: The oceans. Extinction was more severe among animals living in the water column than among animals living on or in the seafloor. Animals in the water column are almost entirely dependent on primary production from living phytoplankton, while animals living on or in the ocean floor feed on detritus or can switch to detritus feeding. The largest air-breathing survivors of the event, crocodilians and champsosaurs , were semiaquatic and had access to detritus. Modern crocodilians can live as scavengers and can survive for months without food and go into hibernation when conditions are unfavorable, and their young are small, grow slowly, and feed largely on invertebrates and dead organisms or fragments of organisms for their first few years. These characteristics have been linked to crocodilian survival at

9345-653: The oldest records of Angiosperm macrofossils are Montsechia from the Barremian aged Las Hoyas beds of Spain and Archaefructus from the Barremian-Aptian boundary Yixian Formation in China. Tricolpate pollen distinctive of eudicots first appears in the Late Barremian, while the earliest remains of monocots are known from the Aptian. Flowering plants underwent a rapid radiation beginning during

9450-452: The poles. Many of the dominant taxonomic groups present in modern times can be ultimately traced back to origins in the Cretaceous. During this time, new groups of mammals and birds appeared, including the earliest relatives of placentals & marsupials ( Eutheria and Metatheria respectively), and the earliest crown group birds. Acanthomorph fish, the most diverse group of modern vertebrates, appeared in aquatic habitats around

9555-523: The poles. After the end of the first age, however, temperatures began to increase again, with a number of thermal excursions, such as the middle Valanginian Weissert Thermal Excursion (WTX), which was caused by the Paraná-Etendeka Large Igneous Province's activity. It was followed by the middle Hauterivian Faraoni Thermal Excursion (FTX) and the early Barremian Hauptblatterton Thermal Event (HTE). The HTE marked

9660-412: The principal food of mosasaurs , a group of giant marine lizards related to snakes that became extinct at the boundary. Omnivores , insectivores , and carrion -eaters survived the extinction event, perhaps because of the increased availability of their food sources. At the end of the Cretaceous, there seem to have been no purely herbivorous or carnivorous mammals . Mammals and birds that survived

9765-547: The punctuation mark at the end of a progressive decline in biodiversity during the Maastrichtian age. The result was the extinction of three-quarters of Earth's plant and animal species. The impact created the sharp break known as the K–Pg boundary (formerly known as the K–T boundary). Earth's biodiversity required substantial time to recover from this event, despite the probable existence of an abundance of vacant ecological niches . Despite

9870-744: The rise of angiosperms, during the Jurassic and the Early Cretaceous, the higher flora was dominated by gymnosperm groups, including cycads , conifers , ginkgophytes , gnetophytes and close relatives, as well as the extinct Bennettitales . Other groups of plants included pteridosperms or "seed ferns", a collective term that refers to disparate groups of extinct seed plants with fern-like foliage, including groups such as Corystospermaceae and Caytoniales . The exact origins of angiosperms are uncertain, although molecular evidence suggests that they are not closely related to any living group of gymnosperms. The earliest widely accepted evidence of flowering plants are monosulcate (single-grooved) pollen grains from

9975-765: The second part of the Latin word for eels, anguilla , attested in its simplex form illa (in a glossary only), and the Greek word for "eel", egkhelys (the second part of which is attested in Hesychius as elyes ). The first compound member, anguis ("snake"), is cognate to other Indo-European words for "snake" (compare Old Irish escung "eel", Old High German unc "snake", Lithuanian angìs , Greek ophis, okhis , Vedic Sanskrit áhi , Avestan aži , Armenian auj, iž , Old Church Slavonic *ǫžь , all from Proto-Indo-European *h₁ogʷʰis ). The word also appears in

10080-400: The severity of the K-Pg extinction event, there were significant variations in the rate of extinction between and within different clades . Species that depended on photosynthesis declined or became extinct as atmospheric particles blocked solar energy . As is the case today, photosynthesizing organisms, such as phytoplankton and land plants , formed the primary part of the food chain in

10185-422: The strong regionality of most biostratigraphic markers, and the lack of any chemostratigraphic events, such as isotope excursions (large sudden changes in ratios of isotopes ) that could be used to define or correlate a boundary. Calpionellids , an enigmatic group of planktonic protists with urn-shaped calcitic tests briefly abundant during the latest Jurassic to earliest Cretaceous, have been suggested as

10290-581: The terrestrial fauna of the late Cretaceous Hell Creek Formation . Other important Cretaceous exposures occur in Europe (e.g., the Weald ) and China (the Yixian Formation ). In the area that is now India, massive lava beds called the Deccan Traps were erupted in the very late Cretaceous and early Paleocene. Palynological evidence indicates the Cretaceous climate had three broad phases:

10395-873: The town is located. The daylight passage in the spring of elvers upstream along the Thames was at one time called "eel fare". The word 'elver' is thought to be a corruption of "eel fare". A famous attraction on the French Polynesian island of Huahine (part of the Society Islands ) is the bridge across a stream hosting three- to six-foot-long eels, deemed sacred by local culture. Eel fishing in Nazi -era Danzig plays an important role in Günter Grass ' novel The Tin Drum . The cruelty of humans to eels

10500-483: The trunk having a preserved diameter of 1.8 metres (5.9 ft) and an estimated height of 50 metres (160 ft). During the Cretaceous, ferns in the order Polypodiales , which make up 80% of living fern species, would also begin to diversify. On land, mammals were generally small sized, but a very relevant component of the fauna , with cimolodont multituberculates outnumbering dinosaurs in some sites. Neither true marsupials nor placentals existed until

10605-789: The ultimate end of the Tithonian-early Barremian Cool Interval (TEBCI). During this interval, precession was the dominant orbital driver of environmental changes in the Vocontian Basin. For much of the TEBCI, northern Gondwana experienced a monsoonal climate. A shallow thermocline existed in the mid-latitude Tethys. The TEBCI was followed by the Barremian-Aptian Warm Interval (BAWI). This hot climatic interval coincides with Manihiki and Ontong Java Plateau volcanism and with

10710-628: The very end, but a variety of non-marsupial metatherians and non-placental eutherians had already begun to diversify greatly, ranging as carnivores ( Deltatheroida ), aquatic foragers ( Stagodontidae ) and herbivores ( Schowalteria , Zhelestidae ). Various "archaic" groups like eutriconodonts were common in the Early Cretaceous, but by the Late Cretaceous northern mammalian faunas were dominated by multituberculates and therians , with dryolestoids dominating South America . The apex predators were archosaurian reptiles , especially dinosaurs , which were at their most diverse stage. Avians such as

10815-554: The word for eel can be reconstructed. It may have been *ēl(l)-u- , *ēl(l)-o- , or something similar. The large lake of Almere , which existed in the early Medieval Netherlands , got its name from the eels which lived in its water (the Dutch word for eel is aal or ael , so: " ael mere " = "eel lake"). The name is preserved in the new city of Almere in Flevoland , given in 1984 in memory of this body of water on whose site

10920-432: Was a period with a relatively warm climate , resulting in high eustatic sea levels that created numerous shallow inland seas . These oceans and seas were populated with now- extinct marine reptiles , ammonites , and rudists , while dinosaurs continued to dominate on land. The world was largely ice-free, although there is some evidence of brief periods of glaciation during the cooler first half, and forests extended to

11025-654: Was followed by the Aptian-Albian Cold Snap (AACS) that began about 118 Ma. A short, relatively minor ice age may have occurred during this so-called "cold snap", as evidenced by glacial dropstones in the western parts of the Tethys Ocean and the expansion of calcareous nannofossils that dwelt in cold water into lower latitudes. The AACS is associated with an arid period in the Iberian Peninsula . Temperatures increased drastically after

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