Pliosaurus

{{Short description|Extinct genus of marine reptiles}} {{redirect|Predator X}} {{Automatic taxobox | fossil_range = Late Jurassic to Lower Cretaceous (Kimmeridgian to Valanginian), {{Fossil range|154|137|ref=<ref name="Knutsen2012"/><ref name="Zverkov2015"/><ref name="ICS">{{cite web|first1=K. M.|last1=Cohen|first2=S.|last2=Finney|first3=P. L.|last3=Gibbard|title=International Chronostratigraphic Chart|year=2015|publisher=International Commission on Stratigraphy|url=http://www.stratigraphy.org/ICSchart/ChronostratChart2015-01.pdf}}</ref>}}Possible Oxfordian record<ref name="Bensonetal2013"/> | image = Dinosaurium,_Pliosaurus_rossicus_1.jpg | image_upright = | image_caption = Skeletal mount of a ''P. rossicus'' exhibited in Dinosaurium, Prague | taxon = Pliosaurus | authority = Owen, 1841 | type_species = †'''''Plesiosaurus brachydeirus''''' | type_species_authority = Owen, 1841 | subdivision_ranks = Other species | subdivision = {{collapsible list| ;Recognised species * †'''''P. rossicus''''' {{Small|Novozhilov, 1948}} * †'''''P. funkei''''' {{Small|Knutsen et al., 2012}} * †'''''P. kevani''''' {{Small|Benson et al., 2013}} * †'''''P. westburyensis''''' {{Small|Benson et al., 2013}} * †'''''P. carpenteri''''' {{Small|Benson et al., 2013}} ;Disputed species * †'''''P. patagonicus''''' {{Small|Gasparini & O'Gorman, 2014}} * †'''''P. almanzaensis''''' {{Small|O'Gorman et al., 2018}}}} | synonyms = {{collapsible list|title=List of synonyms|{{collapsible list|title=Synonyms of genus<ref name="Noeetal2004"/><ref name="Knutsen2012"/><ref name="Bensonetal2013"/>| * ''Pleiosaurus'' Owen, 1841 * ''Stretosaurus'' Tarlo, 1959 * ''Spondylosaurus'' Fischer, 1845 * ''Strongylokrotaphus'' Novozhilov, 1964}} {{collapsible list|title=Synonyms of ''P. brachydeirus''<ref name="Knutsen2012"/><ref name="Bensonetal2013"/>| * ''Plesiosaurus giganteus'' Conybeare, 1824 * ''Plesiosaurus (Pleiosaurus) brachydeirus'' Owen, 1841 * ''Pleiosaurus brachydeirus'' Phillips, 1871 * ''Pliosaurus brachydirus'' Lydekker, 1889}} {{collapsible list|title=Synonyms of ''P. rossicus''<ref name="Knutsen2012"/>| * ''Pliosaurus irgisensis'' ? Novozhilov, 1948 * ''Strongylokrotaphus irgisensis'' ? Novozhilov, 1964 * ''Liopleurodon rossicus'' Tarlo, 1971}}}} }}

'''''Pliosaurus''''' is the type genus (defining example) of the pliosaurs, one of the major group of the plesiosaurs, an extinct group of aquatic marine reptiles. It lived from the Upper Jurassic to the Lower Cretaceous in what is now Europe and South America. The first known fossil consists of a partial skeleton of an immature specimen collected by William Buckland in Market Rasen, England. Although initially mentioned in a 1824 paper by William Daniel Conybeare, it was not until 1841 that it was first formally described by Richard Owen as belonging to a new species of ''Plesiosaurus'', before being given its own genus by the same author later that year. The genus name ''Pliosaurus'' means "more lizard", Owen naming the taxon of because its appearance being more reminiscent of crocodilians than to ''Plesiosaurus''. While many species have been assigned to ''Pliosaurus'' in the past, only six are firmly recognised as valid since a 2013 paper. Two additional species from Argentina were named in 2014 and 2018, but their assignment to the genus has not been fully confirmed in subsequent classifications.

The largest species, ''P. funkei'' and ''P. kevani'', are among the largest pliosaurs ever discovered, with maximum sizes estimated at around {{convert|10|m|ft}} long and weighing nearly {{convert|11|t|ST}}. Even before both species were described in the scientific literature, their imposing size led some scientists to assign them various nicknames, the most famous being "Predator X", used to refer to the second known specimen of ''P. funkei''. However, a large specimen composed entirely of cervical vertebrae discovered in Abingdon and putatively assigned to the genus could have reached a length exceeding {{convert|11|m|ft}}. The elongated skull of ''Pliosaurus'' is robust, and those of the largest known species exceed {{convert|2|m|ft}} in length. The teeth are also robust and are trihedral in cross-section, which is one of the main diagnostic traits of the genus. The neck is one of the most recognizable features of the taxon, being relatively short compared to other plesiosaurs, having only 18 cervical vertebrae. The limbs of ''Pliosaurus'' were modified into flippers, with the anterior flippers of ''P. funkei'' reaching up to {{convert|3|m|ft}} in length.

Phylogenetic classifications place ''Pliosaurus'' in a relatively derived position within the Thalassophonea, with the genus often being recovered as related to ''Gallardosaurus''. Like other plesiosaurs, ''Pliosaurus'' was well-adapted to aquatic life, using its flippers for a method of swimming known as subaqueous flight. Pliosaurid skulls are reinforced to better withstand the stresses of their feeding. The long, robust snouts of the various ''Pliosaurus'' species were used to capture large prey, piercing them with the numerous trihedral teeth at the back of the jaws. ''P. kevani'' would have achieved a bite force ranging from {{convert|9,600|to|48,000|newtons|lbf|-1}} depending on the area of the jaws. The rostrum of some species contains internal structures that likely housed a neurovascular system capable of detecting the movements of nearby prey in the water. The fossil record shows that ''Pliosaurus'' shared its habitat with a variety of other animals, including invertebrates, fish, thalattosuchians, ichthyosaurs, and other plesiosaurs, which would undoubtedly have constituted prey for the larger species.

== Research history == === Discovery and identification ===

In 1824, William Daniel Conybeare established a new species of the genus ''Plesiosaurus'', ''Plesiosaurus giganteus'', to include all plesiosaurian specimens with shortened cervical vertebrae. Among the specimens that were classified in this taxon was a partial skeleton discovered in Market Rasen, Lincolnshire, England, collected by William Buckland.<ref name="Conybeare1824">{{cite journal|last=Conybeare|first=W. D.|year=1824|title=On the discovery of an almost perfect skeleton of the ''Plesiosaurus''|journal=Transactions of the Geological Society of London|volume=2|issue=2|pages=381–389|doi=10.1144/transgslb.1.2.38|doi-broken-date=11 January 2026|s2cid=129024288|url=https://zenodo.org/record/2463676}}</ref> This specimen has since been stored in the Oxford University Museum of Natural History, where it has since been catalogued as OUMNH J.9245. Other fossils associated with this same individual are also stored in the museum, but their records tend to vary depending on the studies describing them since.<ref name="Tarlo1960"/><ref name="Knutsen2012"/><ref name="Bensonetal2013"/> Together it consists of teeth, a mandible, upper jaw, a partial spinal column, a femur, a tibia, and a fibula.<ref name="Phillips1871"/><ref name="Tarlo1960"/> Its ontogenetic stage is unknown, but the incomplete ossification of the proximal convexity of the tibia suggests that it is a juvenile or subadult specimen.<ref name="Bensonetal2013"/> In his article, Conybeare only refers specimens to this species, designating no type specimens and giving no detailed anatomical descriptions.<ref name="Conybeare1824"/> As the referred specimens were then insufficiently characterized, the name ''Plesiosaurus giganteus'' was generally perceived as invalid in subsequent works,<ref name="Tarlo1960"/> having since become a ''nomen oblitum''.<ref name="Bensonetal2013"/>

In 1841, Richard Owen described the anatomy of the jaws of the Market Rasen specimen. Based on several distinctive features, he decided to make it the holotype of a subgenus accompanying a new species of ''Plesiosaurus'', which he named ''Plesiosaurus (Pleiosaurus) brachydeirus''.<ref name="Owen1841a">{{cite book|last=Owen|first=R.|year=1841|title=Odontography|volume=v. 1|publisher=Hippolyte Baillière|location=London|pages=282–285|url=https://www.biodiversitylibrary.org/item/55014#page/381/mode/1up}}</ref> The name ''Pleiosaurus'' comes from the Ancient Greek πλειων (''pleion'', "more"), and σαῦρος (''saûros'', "lizard"),<ref name="Liddell&Scott1980">{{cite book|last1=Liddell|first1=H. G.|author-link1=Henry Liddell|last2=Scott|first2=R.|author-link2=Robert Scott (philologist)|year=1980|orig-year=1871|edition=abridged|title=A Greek-English Lexicon|publisher=Oxford University Press|location=Oxford|isbn=978-0-19-910207-5 |url=https://archive.org/details/lexicon00lidd|url-access=registration}}</ref>{{rp|564, 630}}<ref name="Meaning">{{cite web|title=Ben Creisler's Plesiosaur Pronunciation Guide|year=2012|last=Creisler|first=B.|website=Oceans of Kansas|url=http://oceansofkansas.com/Creisler_Plesiosaurs2.html|access-date=26 June 2021}}</ref> Owen named it this way because the appearance of the specimen described is closer to those of crocodilians than to those of other species then attributed to ''Plesiosaurus''.<ref name="Owen1841a"/><ref name="Owen1841b"/> The specific name ''brachydeirus'' also comes from Ancient Greek and comes from the words βραχύς (''brakhús'', "short"), and δειρή (''deirḗ'', "neck" or "throat"),<ref name="Liddell&Scott1980"/>{{rp|135, 153}} in reference to its cervical vertebrae.<ref name="Owen1841a"/> Later that same year, Owen described the postcranial parts of the skeleton and relegated this taxon to a separate genus, but spelling it as ''Pliosaurus''.<ref name="Owen1841b">{{cite book|last=Owen|first=R.|chapter=Report on British Fossil Reptiles. Part II|chapter-url=https://archive.org/details/reportofeleventh42lond/page/n99/mode/1up|year=1842|title=Report of the Eleventh Meeting of the British Association for the Advancement of Science; Held at Plymouth in July 1841|url=https://archive.org/details/reportofeleventh42lond/page/n4/mode/1up|location=London|publisher=John Murray|page=[https://archive.org/details/reportofeleventh42lond/page/n99/mode/2up 60–65]|lccn=99030427|oclc=1015526268}}</ref> In 1869, the same author erroneously claimed that another species formerly attributed to ''Pliosaurus'', ''P. grandis'', would be the type species of this genus.<ref name="Owen1869">{{cite journal|last=Owen|first=R.|title=Monographs on the British Fossil Reptilia from the Kimmeridge Clay|journal=Monographs of the Palaeontographical Society|year=1869|volume=22|issue=98|pages=1–12|doi=10.1080/02693445.1869.12113233|url=https://www.biodiversitylibrary.org/item/113749#page/361/mode/1up}}</ref> In 1871, John Phillips corrected most of Owen's taxonomic errors, recognizing ''P. brachydeirus'' as the type species and using the original spelling ''Pleiosaurus''.<ref name="Phillips1871">{{cite book|last=Phillips|first=J.|title=Geology of Oxford and the valley of the Thames|publisher=Oxford: Clarendon Press|location=London|year=1871|pages=341–354|url=https://www.biodiversitylibrary.org/item/76959#page/397/mode/1up}}</ref> Furthermore, the holotypic material of ''P. grandis'' is considered by many authors to be non-diagnostic and cannot be proven to belong to the genus.<ref name="Lydekker1889a">{{cite book|last=Lydekker|first=R.|author-link=Richard Lydekker|title=Catalogue of the Fossil Reptilia and Amphibia in the British Museum (Natural History)|volume=2|location=London|publisher=The British Museum (Natural History)|year=1889|page=123|url=https://www.biodiversitylibrary.org/item/125714#page/152/mode/2up}}</ref><ref name="Tarlo1960">{{cite journal|last=Tarlo|first=L. B.|year=1960|title=A review of the Upper Jurassic pliosaurs|journal=Bulletin of the British Museum (Natural History)|volume=4|issue=5|pages=145–189|url=https://ia801305.us.archive.org/5/items/biostor-118792/biostor-118792.pdf}}</ref><ref name="Knutsen2012"/> However, despite Phillips's requirement, the genus name ''Pliosaurus'' has since entered into universal usage and must be maintained according to the rule of article 33.3.1 of the ICZN.<ref name="Bensonetal2013"/> Currently, only the holotype and the fossils attributed to it constitute the only known specimen of this species.<ref name="Knutsen2012"/><ref name="Bensonetal2013"/>

=== Later discoveries and other species === thumb|upright=1.5|alt=Two photos showing the left and right sides of a fossil skull of a marine reptile on display in a museum|View in two sides of the holotype skull of ''P. rossicus'' (PIN 304/1)

In 1948, Nestor Novozhilov named the species ''P. rossicus'' on the basis of two more or less partial specimens discovered in two mines in the Lower Volga Basin in Russia (hence the name), and which have since been housed in the paleontological collections of the country's scientific academy. The holotype consists of a skull and postcranial remains from a relatively small specimen,<ref name="Novozhilov1948">{{cite journal|last=Novozhilov|first=N. I.|year=1948|title=Два новых плиозавра из нижнего волжского яруса Поволжья|trans-title=Two new pliosaurs from the lower Volgian stage of the Volga region|journal=Doklady Akademii Nauk SSSR|volume=60|pages=115–118|language=Russian|url=https://undor-muz.ru/wp-content/uploads/2019/08/Novozhilov-1948.pdf}}</ref> since catalogued as PIN 304/1. This same specimen, which was originally a complete skeleton, was largely destroyed ten years earlier due to the exploitation of the oil shale from which it was discovered.<ref name="Storrsetal2000">{{citation|last1=Storrs|first1=G. W.|last2=Arkhangel'skii|first2=M. S.|last3=Efimov|first3=V. M.|year=2000|chapter=Mesozoic marine reptiles of Russia and other former Soviet republics|editor-last1=Benton|editor-first1=M. J.|editor-link1=Michael J. Benton|editor-last2=Shishkin|editor-first2=M. A.|editor-last3=Unwin|editor-first3=D. M.|editor-last4=Kurochkin|editor-first4=E. N.|title=The Age of Dinosaurs in Russia and Mongolia|location=Cambridge, UK|publisher=Cambridge University Press|pages=187–210|chapter-url=https://www.researchgate.net/publication/259842825|isbn=978-0-521-55476-3|url={{google books|plainurl=yes|id=NzVGpo3M998C}}}}</ref> However, pectoral elements associated with the latter are described by the same author in 1964.<ref name="Novozhilov1964">{{citation|language=Russian|last=Novozhilov|first=N. I.|chapter=Отряд Завроптеригии|trans-chapter=Order Sauropterygia|editor1-last=Rozhdestvensky|editor1-first=A. N.|editor2-last=Tatarinov|editor2-first=L. P.|editor-link2=Leonid Petrovich Tatarinov|title=Основы палеонтологии: Справочник для палеонтологов и геологов СССР. Земноводные, пресмыкающиеся и птицы|trans-title=Fundamentals of paleontology: Handbook for paleontologists and geologists of the USSR. Amphibians, reptiles and birds|location=Moscow|publisher=Nauka|year=1964|volume=12|pages=309–333|url=https://www.geokniga.org/bookfiles/geokniga-osnovypaleontologii12.pdf}}</ref> Based on its small size and poorly developed anatomical elements on the scapula, the holotype is interpreted as a juvenile.<ref name="Halstead1971"/><ref name="Storrsetal2000"/><ref name="Knutsen2012"/> The second specimen, more imposing and since catalogued as PIN 2440/1,<ref name="Storrsetal2000"/><ref name="Knutsen2012"/> was discovered in May 1945 as a complete skeleton, but like the holotype, it was largely destroyed by mining operations. The only surviving remains of the latter are a rostrum, a proximal part of a humerus, a phalanx, and ribs fragments, which were originally described in 1947 as coming from a ''P. grandis'' by Anatoly Rozhdestvensky.<ref name="Rozhdestvensky1947">{{cite journal|language=Russian|last1=Rozhdestvensky|first1=A. N.|title=Новая находка гигантского плиозавра в Заволжье|trans-title=New discovery of giant ''Pliosaurus'' in Zavolzhe (left bank of Volga)|journal=Doklady Akademii Nauk SSSR|year=1947|volume=56|issue=2|pages=197–199|url=https://jurassic.ru/pdf/rozhdestvensky1947.pdf}}</ref> In 1971, Beverly Halstead reclassified this species in the genus ''Liopleurodon'' because of its short mandibular symphysis (where the two halves of the lower jaw connect), and assigned the second specimen a complete hindlimb.<ref name="Halstead1971">{{cite journal|last=Halstead|first=L. B.|year=1971|title=''Liopleurodon rossicus'' (Novozhilov): A pliosaur from the lower Volgian of the Moscow Basin|journal=Palaeontology|volume=14|issue=4|pages=566–570|url=https://www.biodiversitylibrary.org/page/49714258#page/294/mode/2up}}</ref> However, it later turned out that this hindlimb actually originates from the holotype of the contemporary species ''P. irgisensis'',<ref name="Storrsetal2000"/> which has since been recognised as a dubious.{{efn|Initially named ''Peloneustes irgisensis'' by Novozhilov in the same publication in which he described ''P. rossicus'', the taxon is based on a single specimen (PIN 426) from the same locality, consisting of a partial skeleton that includes a large but incomplete skull, vertebrae, a partial hindlimb, and preserved stomach contents.<ref name="Novozhilov1948"/> In 1960, Halstead (then called Tarlo) considered the species too distinct to belong to ''Peloneustes'' and provisionally placed it in ''Pliosaurus'', suggesting that Novozhilov may have been mistaken in believing it to be the only long-snouted pliosaurid.<ref name="Tarlo1960"/> Four years later, in 1964, Novozhilov erected the genus ''Strongylokrotaphus'',<ref name="Novozhilov1964"/> but subsequent studies, agreeing with Halstead’s assessment, reassigned the species to ''Pliosaurus'',<ref name="Storrsetal2000"/> with some even suggesting it may represent a junior synonym of ''P. rossicus''.<ref name="Knutsen2012"/> More recent research has regarded the taxon as a ''nomen dubium'' due to the non-diagnostic nature of the holotype, while nevertheless recommending a redescription of the material.<ref name="Knutsen2012"/><ref name="Bensonetal2013"/> However, this suggestion risks being tainted by the current state of conservation of the specimen, the skull and notably the mandible having since been seriously damaged by pyrite decay, and the associated elements being noted as lost.<ref name="Storrsetal2000"/><ref name="Knutsen2012"/>}}<ref name="Knutsen2012"/><ref name="Bensonetal2013"/> Although Halstead's classification was long recognised as valid, it was questioned in a 2001 thesis by Leslie F. Noè, who noted that, due to the shape of the teeth and the length of the mandibular symphysis, the species might represent a new genus.<ref name="Noe2001">{{cite thesis|last=Noè|first=L. F.|year=2001|title=A taxonomic and functional study of the Callovian (Middle Jurassic) Pliosauroidea (Reptilia, Sauropterygia)|publisher=University of Derby|location=Chicago|type=PhD}}</ref> In a revision published in 2012, Espen M. Knutsen nevertheless reassigned the species to its original genus on the basis of diagnostic features shared with other lineages within the genus.<ref name="Knutsen2012">{{cite journal|last1=Knutsen|first1=E. M.|title=A taxonomic revision of the genus ''Pliosaurus'' (Owen, 1841a) Owen, 1841b|journal=Norwegian Journal of Geology|volume=92|pages=259–276|year=2012|issn=0029-196X|url=http://njg.geologi.no/images/NJG_articles/NJG_2_3_2012_14_Knutsen_Scr.pdf}}</ref>

The species ''P. funkei'' was described in 2012 by Knutsen and colleagues based on two large specimens discovered in the Norwegian archipelago of Svalbard. The holotype, catalogued as PMO 214.135, consists of a partial skeleton preserving the anterior part of the jaws with teeth, various more or less preserved vertebrae, a complete right coracoid, a nearly complete right flipper, as well as ribs and gastralia (abdominal ribs). The larger referred specimen, catalogued as PMO 214.136, includes a partial skull preserving mostly its left posterior part, a few vertebrae and several unidentifiable fragmentary bones. Based on various morphological and histological characteristics, particularly in terms of increased bone density, these two specimens appear to have been adults. The fossils were collected at {{cvt|2|km}} intervals during eight seasons of fieldwork conducted from 2004 to 2012 by Jørn Hurum in the southern Sassenfjorden.<ref name="Knutsenetal2012"/> More precisely, they were discovered in 2006, excavated over the following two years,<ref name="Hurumetal2012"/> and officially reported at a Society of Vertebrate Paleontology conference in 2009, where their affinity with the genus ''Pliosaurus'' was already noted.<ref name="Knutsenetal2009">{{cite journal|last1=Knutsen|first1=E. M.|last2=Druckenmiller|first2=P. S.|last3=Hurum|first3=J. H.|last4=Nakrem|first4=H. A.|title=Preliminary account of new Late Jurassic pliosaurid material from Svalbard, Norway|journal=Journal of Vertebrate Paleontology|year=2009|volume=29|issue=suppl. to 3|page=128A|doi=10.1080/02724634.2009.10411818|issn=0272-4634|url=https://vertpaleo.org/wp-content/uploads/2021/03/SVP09AbstractsFULL_WEB.pdf}}</ref><ref name="Smith2011"/> Due to the Arctic climate of Svalbard, the specimens were subjected to repeated freeze-thaw cycles before collection, extensively fracturing and degrading the material. The specific name honours Bjørn Funke, the discoverer of the holotype, and his wife May-Liss Knudsen Funke, for their years of voluntary service to the paleontological collections of the University of Oslo Natural History Museum, where the specimens have since been housed. In their article, Knutsen and colleagues conclude that it cannot be definitively excluded that ''P. funkei'' and ''P. rossicus'' would represent different ontogenetic stages of the same species based on the available material. Nevertheless, the two taxa are still maintained as distinct on the basis that their respective holotypes exhibit proportionally very different humeral lengths.{{efn|This specific distinction is based on the fact that other plesiosaurian taxa such as ''Leptocleidus'' have body-to-limb length ratios that are identical in both juveniles and adults within the same species. Since both known specimens of ''P. funkei'' are adults and the holotype of ''P. rossicus'' is seen as a juvenile, this precise difference is then seen as sufficient to maintain the distinction.<ref name="Knutsenetal2012"/>}}<ref name="Knutsenetal2012">{{cite journal|last1=Knutsen|first1=E. M.|last2=Druckenmiller|first2=P. S.|last3=Hurum|first3=J. H.|title=A new species of ''Pliosaurus'' (Sauropterygia: Plesiosauria) from the Middle Volgian of central Spitsbergen, Norway|journal=Norwegian Journal of Geology|year=2012|volume=92|pages=235–258|issn=0029-196X|url=https://njg.geologi.no/images/NJG_articles/NJG_2_3_2012_13_Knutsen_etal_Scr.pdf}}</ref> The rather remarkable size of the fossils led the Hurum's paleontological teams to nickname them "The Monster" for the holotype and "Predator X" for the referred specimen, which gave the taxon significant media coverage even before they were firmly described.<ref name="BBC2009">{{cite web|publisher=BBC|title=Arctic sea monster's giant bite|website=BBC News|date=March 17, 2009|url=https://news.bbc.co.uk/2/hi/science/nature/7948670.stm|url-status=live|archive-url=https://web.archive.org/web/20230407022418/http://news.bbc.co.uk/2/hi/science/nature/7948670.stm|archive-date=April 7, 2023}}</ref><ref name="Smith2011">{{cite web|first=A. S.|last=Smith|title=Mine's bigger than yours! The Monster of Aramberri, Predator X, and other monster pliosaurs in the media|url=https://plesiosauria.com/mines-bigger-than-yours-the-monster-of-aramberri-predator-x-and-other-monster-pliosaurs-in-the-media/|website=The Plesiosaur Directory|date=May 5, 2011|archive-url=https://web.archive.org/web/20240727184022/https://plesiosauria.com/mines-bigger-than-yours-the-monster-of-aramberri-predator-x-and-other-monster-pliosaurs-in-the-media/|archive-date=July 27, 2024}}</ref><ref name="Black2012">{{Cite web|last=Black|first=R.|author-link=Riley Black|date=October 15, 2012|title=Paleontologists Reveal the Identity of 'Predator X'|website=National Geographic|url=https://www.nationalgeographic.com/science/article/paleontologists-reveal-identity-of-predator-x|archive-url=https://web.archive.org/web/20250127121943/https://www.nationalgeographic.com/science/article/paleontologists-reveal-identity-of-predator-x|archive-date=January 27, 2025}}</ref> This popularity led the species to appear in a 2009 documentary broadcast on the American television channel History, then in a 2010 low-budget science fiction horror film.<ref name="Black2012"/>

thumb|left|upright=1.15|alt=Photo showing the right side of the fossil skull (in black) of a large marine reptile on display in a museum|Holotype skull of ''P. kevani'' (DORCM G.13,675)

In a 2013 paper published in the mega journal ''PLOS ONE'', Roger B. J. Benson and colleagues described three additional species of ''Pliosaurus'', all of whose fossils were discovered in England. The first of these three species described was ''P. kevani'', whose holotype consists of a large, nearly complete skull of a probable adult, which was discovered in a cliff at Osmington Mills Bay, Dorset. This specimen was collected over a period of eight years via fragmented parts weighing up to {{cvt|60|kg}}. Most of the fossils comprising the skull were taken without prior permission from loose or fallen boulders, while others were collected locally and purchased from landowners. The specimen was quickly identified as a pliosaurid by geologist Richard Edmonds.<ref name="Bensonetal2013"/> The remarkable size and completeness of this specimen, like "The Monster" and "Predator X", gave it widespread media coverage, to the point of earning the nickname "Weymouth Bay pliosaur" before its official description.<ref name="Smith2011"/> The Dorset Museum's acquisition of the specimen was publicly announced in 2009, where it has since been catalogued as DORCM G.13,675. However, it was not officially opened by David Attenborough until July 2011. This discrepancy is due in part to the time taken to prepare the fossils, which took 200 hours for the lower jaw and over 365 hours for the rest of the skull. The specific name for this taxon honours Kevan Sheehan, owner of a small cafe overlooking the sea at Osmington Mills, who collected most of the holotype specimen during daily walks along the shore. In addition to the holotype skull, Benson and colleagues tentatively assigned two other large pliosaurid specimens discovered in the Cambridgeshire as ''P.'' cf. ''kevani'' os the basis of their tooth morphology. The first consists of a large, mostly postcranial skeleton catalogued as CAMSM J.35990, discovered in Stretham,{{efn|Discovered in 1952, this specimen was successively studied by Halstead (then called Tarlo), who published several articles about it. Initially, it was assigned in 1958 to ''P. macromerus'',<ref name="Tarlo1958">{{cite journal|last1=Tarlo|first1=L. B.|year=1958|title=The scapula of ''Pliosaurus macromerus'' Phillips|journal=Palaeontology|volume=1|issue=3|pages=193–199|url=https://palass.org/sites/default/files/media/publications/palaeontology/volume_1/vol1_part3_pp193-199.pdf}}</ref> but the morphology of this specimen, particularly of a bone interpreted by the author as a scapula, led Halstead to place the species in its own genus, ''Stretosaurus'', the following year.<ref name="Tarlo1959">{{cite journal|last1=Tarlo|first1=L. B.|year=1959|title=''Stretosaurus'' gen. nov., a giant pliosaur from the Kimmeridge Clay|journal=Palaeontology|volume=2|issue=1|pages=39–55|url=https://palass.org/sites/default/files/media/publications/palaeontology/volume_2/vol2_part1_pp39-55.pdf}}</ref><ref name="Tarlo1960"/> In subsequent works, however, he reassigned the species to ''Liopleurodon'', citing the short mandibular symphysis of the referred specimens.<ref name="Halstead1971"/><ref name="Halstead1989">{{cite journal|last=Halstead|first=L. B.|year=1989|title=Plesiosaur locomotion|journal=Journal of the Geological Society|volume=146|pages=37–40|doi=10.1144/gsjgs.146.1.0037|s2cid=219541473|doi-access=free}}</ref> Since 2004, ''Stretosaurus'' has been regarded as a junior synonym of ''Pliosaurus'', based on its tooth morphology.<ref name="Noeetal2004">{{cite journal|last1=Noè|first1=L. F.|last2=Smith|first2=D. T. J.|last3=Watson|first3=D. I.|year=2004|title=A new species of Kimmeridgian pliosaur (Reptilia; Sauropterygia) and its bearing on the nomenclature of ''Liopleurodon macromerus''|journal=Proceedings of the Geologists' Association|volume=115|issue=1|pages=13–24|doi=10.1016/S0016-7878(04)80031-2|s2cid=84565047}}</ref> In his 2012 revision, Knutsen not only supported this interpretation but also demonstrated that the bone previously identified as a scapula in the Stretham specimen is in fact an ilium.<ref name="Knutsen2012"/>}} while the second is a single tooth catalogued as LEICT G418.1965.108, discovered in Ely, which are stored at the Sedgwick Museum of Earth Sciences and the Leicester Museum & Art Gallery respectively.<ref name="Bensonetal2013">{{cite journal|last1=Benson|first1=R. B. J.|last2=Evans|first2=M.|last3=Smith|first3=A. S.|last4=Sassoon|first4=J.|last5=Moore-Faye|first5=S.|last6=Ketchum|first6=H. F.|last7=Forrest|first7=R.|year=2013|title=A giant pliosaurid skull from the Late Jurassic of England|journal=PLOS ONE|volume=8|issue=5|article-number=e65989|doi=10.1371/journal.pone.0065989|pmid=23741520|pmc=3669260|bibcode=2013PLoSO...865989B|doi-access=free}}</ref>

thumb|upright=1.25|alt=Photo showing the left side of the fossil skull (in brown) of a large marine reptile on display in a museum. The bottom left of the image shows numerous teeth belonging to this same skull.|Holotype skull of ''P. westburyensis'' (BRSMG Cc332).

The other two species described in the 2013 paper are ''P. westburyensis'' and ''P. carpenteri'', both of whose holotypes were discovered in a quarry near Westbury, Wiltshire, and were subsequently donated to the Bristol Museum & Art Gallery, where they have since been catalogued as BRSMG Cc332 and BRSMG Cc6172, respectively. The holotype of the first species consists of a skull with some postcranial remains, while the second consists of a partial skeleton,<ref name="Bensonetal2013"/> respectively discovered on July 2, 1980,<ref name="Taylor&Cruickshank1993"/> and May 12, 1994.<ref name="Grangeetal1996"/><ref name="Sassoonetal2012"/> Informally dubbed as the "first Westbury pliosaur",<ref name="Sassoonetal2010"/><ref name="Sassoonetal2012"/> BRSMG Cc332 was first described in a 1993 paper by Michael A. Taylor and Arthur Cruickshank, in which they identified it as a specimen of ''P. brachyspondylus''.<ref name="Taylor&Cruickshank1993">{{cite journal|first1=M. A.|last1=Taylor|first2=A. R. I.|last2=Cruickshank|title=Cranial anatomy and functional morphology of ''Pliosaurus brachyspondylus'' (Reptilia: Plesiosauria) from the Upper Jurassic of Westbury, Wiltshire|journal=Philosophical Transactions of the Royal Society B|volume=341|issue=1298|pages=399–418|year=1993|doi=10.1098/rstb.1993.0124|s2cid=85378579|bibcode=1993RSPTB.341..399T|url=https://royalsocietypublishing.org/doi/pdf/10.1098/rstb.1993.0124|archive-url=https://web.archive.org/web/20191026194618/https://royalsocietypublishing.org/doi/pdf/10.1098/rstb.1993.0124|archive-date=October 26, 2019}}</ref> The first anatomical description of BRSMG Cc6172 was not carried out until much later, by Judyth Sassoon and colleagues in 2012,<ref name="Sassoonetal2012"/> although some historical details relating to its excavation had already been published in earlier works.<ref name="Grangeetal1996">{{cite journal|last1=Grange|first1=D. R.|last2=Storrs|first2=G. W.|last3=Carpenter|first3=S.|last4=Etches|first4=S.|year=1996|title=An important marine vertebrate-bearing locality from the Lower Kimmeridge Clay (Upper Jurassic) of Westbury, Wiltshire|journal=Proceedings of the Geologists' Association|volume=107|issue=2|pages=107–116|doi=10.1016/S0016-7878(96)80004-6|s2cid=140674312|bibcode=1996PrGA..107..107G|url=https://www.academia.edu/2379914}}</ref><ref name="Sassoonetal2010">{{cite journal|last1=Sassoon|first1=J.|last2=Vaughan|first2=R.|last3=Carpenter|first3=S.|last4=Noè|first4=L. F.|year=2010|title=The second Westbury pliosaur: excavation, collection and preparation|journal=The Geological Curator|volume=9|issue=3|pages=117–126|doi=10.55468/GC218|s2cid=251122996|doi-access=free}}</ref> In their publication, these two specimens are both classified in ''Pliosaurus'', although without a species assignment,<ref name="Sassoonetal2012">{{cite journal|first1=J.|last1=Sassoon|first2=L. F.|last2=Noè|first3=M. J.|last3=Benton|title=Cranial anatomy, taxonomic implications and palaeopathology of an Upper Jurassic Pliosaur (Reptilia: Sauropterygia) from Westbury, Wiltshire, UK|journal=Palaeontology|volume=55|issue=4|pages=743–773|year=2012|doi=10.1111/j.1475-4983.2012.01151.x|bibcode=2012Palgy..55..743S|s2cid=86254473|doi-access=free}}</ref> a point of view also followed in the genus revision conducted by Knutsen in the same year.<ref name="Knutsen2012"/> Based on their morphological differences and their close stratigraphic levels within the same quarry, Sassoon and colleagues described these specimens as exhibiting intraspecific variation, and possibly sexual dimorphism within the same species, interpreting BRSMG Cc332 as a young male and BRSMG Cc6172 as an old female.<ref name="Sassoonetal2012"/> However, in the article published the following year, Benson and his colleagues consider that the differences between them are relatively significant when observed in the context of specimens from other localities, and therefore justify a specific distinction. The specific name of the first cited species refers to the town of Westbury, while that of the second honours Simon Carpenter, discoverer of the holotype of the latter species.<ref name="Bensonetal2013"/> From June 2017 to February 2018, the holotype specimen of ''P. carpenteri'', then nicknamed "Doris", was temporarily mounted as part of a special exhibition at Bristol Museum & Art Gallery.<ref name="Larkinetal2021">{{cite journal|first1=N. R.|last1=Larkin|first2=S.|last2=Dey|first3=D.|last3=Hutchinson|title=Mounting the type specimen of ''Pliosaurus carpenteri'' Benson et al., 2013, an 8m-long fossil pliosaur skeleton, including the 3D-printed 1.8m-long replica of the skull for Bristol Museum & Art Gallery|journal=Journal of Natural Science Collections|year=2021|volume=8|pages=3–12|url=https://www.natsca.org/sites/default/files/publications/JoNSC-Vol8-Larkin_Dey_and_Hutchinson_2021_0.pdf}}</ref>

The South American species ''P. patagonicus'' and ''P. almanzaensis'' were described in 2014 and 2018, respectively, from fossils discovered in different localities of Neuquén Province, Argentina.<ref name="Gasparini&O'Gorman2014">{{cite journal|first1=Z.|last1=Gasparini|first2=J. P.|last2=O'Gorman|year=2014|title=A new species of ''Pliosaurus'' (Sauropterygia, Plesiosauria) from the Upper Jurassic of northwestern Patagonia, Argentina|journal=Ameghiniana|volume=51|issue=4|pages=269–283|doi=10.5710/amgh.03.04.2014.2225|s2cid=130194647|bibcode=2014Amegh..51..269G|hdl=11336/9372|hdl-access=free}}</ref><ref name="O'Gormanetal2018">{{cite journal|first1=J. P.|last1=O'Gorman|first2=Z.|last2=Gasparini|first3=L. A.|last3=Spalletti|year=2018|title=A new ''Pliosaurus'' species (Sauropterygia, Plesiosauria) from the Upper Jurassic of Patagonia: new insights on the Tithonian morphological disparity of mandibular symphyseal morphology|journal=Journal of Paleontology|volume=92|issue=2|pages=240–253|doi=10.1017/jpa.2017.82|bibcode=2018JPal...92..240O|s2cid=134813424|hdl=11336/81697|hdl-access=free}}</ref> The holotype of ''P. patagonicus'' consists of a partial skull discovered in 1975 by Zulma Gasparini and a team from the La Plata Museum, in the Zapala Department. The specimen, since catalogued as MLP 80-V-29-1 within the museum, was prepared using acid, a technique frequently employed at the time, but its application was incorrect. Although the mandible had been partially well exposed, the palate and the other cranial bones, originally crushed dorsoventrally, were so damaged that they became difficult to identify. As a result, the taxonomic identity of the specimen remained uncertain for more than three decades.<ref name="Gasparini&O'Gorman2014"/> Thus, in works led by Gasparini, the specimen was first assigned to ''Stretosaurus'' sp. from 1982 to 1992,<ref name="Gasparinietal1982">{{cite journal|last1=Gasparini|first1=Z.|last2=Goñi|first2=R.|last3=Molina|first3=O.|year=1982|title=Un plesiosaurio (Reptilia) tithoniano de Cerro Lotena, Neuquén, Argentina|trans-title=A Tithonian plesiosaur (Reptilia) from Cerro Lotena, Neuquén, Argentina|journal=Actas Quinto Congreso Latinoamericano de Geología|volume=5|pages=33–47|language=Spanish}}</ref><ref name="Gasparini1985">{{cite journal|last1=Gasparini|first1=Z.|year=1985|title=Los reptiles marinos jurásicos de América del Sur|trans-title=The Jurassic marine reptiles of South America|journal=Ameghiniana|volume=22|issue=1–2|pages=23–34|url=https://www.ameghiniana.org.ar/index.php/ameghiniana/article/view/1737|language=Spanish}}</ref><ref name="Gasparini1992">{{citation|last=Gasparini|first=Z.|year=1992|title=Marine reptiles of the Circum-Pacific region|editor-last1=Westermann|editor-first=G. E. G.|chapter=Marine reptiles of the Circum-Pacific region|publisher=Cambridge University Press|location=Cambridge|series=World and regional geology|pages=361–364|isbn=978-0-511-52937-5|doi=10.1017/CBO9780511529375.028|s2cid=128203700|url=https://www.geokniga.org/bookfiles/geokniga-thejurassicofthecircumpacificworldandregionalgeologygerd.pdf}}</ref> then referred to as ''Liopleurodon'' cf. ''macromerus'' in 1997,<ref name="Gasparini&Fernández1997">{{citation|last1=Gasparini|first1=Z.|last2=Fernández|first2=M.|year=1997|chapter=Tithonian marine reptiles of the Eastern Pacific|title=Ancient Marine Reptiles|editor-last1=Callaway|editor-first1=J. M.|editor-last2=Nicholls|editor-first2=E. L.|editor-link2=Elizabeth Nicholls|publisher=Academic Press|location=San Diego|pages=435–440|isbn=978-0-12-155210-7|doi=10.1016/B978-012155210-7/50023-5|s2cid=132674969}}</ref> before being classified simply as ''Liopleurodon'' sp. from 2007 to 2011.<ref name="Gasparini2007">{{citation|last=Gasparini|first=Z.|year=2007|chapter=Plesiosauria|title=Patagonian Mesozoic Reptiles|editor-last1=Gasparini|editor-first1=Z.|editor-last2=Salgado|editor-first2=L.|editor-link2=Leonardo Salgado|editor-first3=R. A.|editor-last3=Coria|editor-link3=Rodolfo Coria|publisher=Indiana University Press|location=Bloomington|pages=292–313|isbn=978-0-253-34857-9}}</ref><ref name="Gasparini&Fernández2011">{{cite journal|last1=Gasparini|first1=Z.|last2=Fernández|first2=M.|year=2011|title=Reptiles marinos mesozoicos|trans-title=Mesozoic marine reptiles|journal=Relatorio del XVIII Congreso Geológico Argentino|volume=1|pages=529–536|url=https://rdi.uncoma.edu.ar/handle/uncomaid/18054|language=es}}</ref> A new preparation of the specimen allowed Gasparini and José P. O'Gorman to reidentify it as a new species of the genus ''Pliosaurus'', ''P. patagonicus'', the specific epithet referring to Patagonia, the region where the holotype was discovered.<ref name="Gasparini&O'Gorman2014"/> The holotype of ''P. almanzaensis'' consists of a large, relatively well-preserved skull followed by several vertebrae and skeletal elements from the flippers. It was discovered in 1986 by brothers Sergio and Rafael Cocca in the locality of Cajón de Almanza (hence the name), about {{cvt|10|km}} east of the village of Loncopué. A field mission was subsequently carried out the same year by the team of the Provincial Museum of Natural Sciences of Zapala, accompanied by Gasparini, in order to determine the possible position of the skull. In February 1987, the entire specimen, later catalogued as MOZ 3728P within the museum, was finally collected, and Luis A. Spalletti precisely determined its stratigraphic position in January 1988. However, the specimen was only formally described in 2018 by O'Gorman, Gasparini, and Spalletti as representing a new species of ''Pliosaurus'', contemporaneous with ''P. patagonicus''.<ref name="O'Gormanetal2018"/>

== Description == Plesiosaurs are usually categorized as belonging to the small-headed, long-necked "plesiosauromorph" morphotype or the large-headed, short-necked "pliosauromorph" morphotype, ''Pliosaurus'' belonging to the latter category.<ref name="O'Keefe2001a">{{cite journal|last=O'Keefe|first=F. R.|year=2001|title=Ecomorphology of plesiosaur flipper geometry|journal=Journal of Evolutionary Biology|volume=14|issue=6|pages=987–991|doi=10.1046/j.1420-9101.2001.00347.x|s2cid=53642687|doi-access=free |bibcode=2001JEBio..14..987O }}</ref><ref name="Bensonetal2013"/> Like all other plesiosaurs, it had a short tail, a barrel-shaped body, and all of its limbs modified into large flippers.<ref name="Martilletal2023">{{cite journal|last1=Martill|first1=D. M.|last2=Jacobs|first2=M. L.|last3=Smith|first3=R. E.|title=A truly gigantic pliosaur (Reptilia, Sauropterygia) from the Kimmeridge Clay Formation (Upper Jurassic, Kimmeridgian) of England|journal=Proceedings of the Geologists' Association|year=2023|volume=134|issue=3|pages=361–373|doi=10.1016/j.pgeola.2023.04.005|s2cid=258630597|bibcode=2023PrGA..134..361M|doi-access=free}}</ref>

=== Size === [[File:Pliosaurus_funkei21DB.jpg|thumb|upright=1.1|alt=An artist's impression of a large, bluish prehistoric marine reptile on a white background, with its size compared to the silhouette of a diver|Life restoration of ''P. funkei'']]

''P. funkei'' and ''P. kevani'' are the largest known species of the genus and are among the largest pliosaurs ever discovered in the world.<ref name="Knutsenetal2012"/><ref name="Black2012"/><ref name="Bensonetal2013"/><ref name="Foffaetal2014b"/> Even before their fossils were formally described in the scientific literature, the media estimated their lengths as ranging from {{cvt|13 to 15|m}} for the ''P. funkei'' specimens and from {{cvt|12 to 16|m}} for the holotype of ''P. kevani''.<ref name="Smith2011"/> However, more serious estimates published from 2012 reduce these estimates by {{cvt|10 to 13|m}} for a skull exceeding {{cvt|2|m}} in length.<ref name="Knutsenetal2012"/><ref name="Bensonetal2013"/> In 2023, David Martill and colleagues described four posterior cervical vertebrae from a large specimen putatively assigned as ''Pliosaurus'' sp., discovered in the Kimmeridge Clay of Abingdon, Oxfordshire. Based on comparisons made with other pliosaurid genera, the authors gave a body length estimate of {{cvt|9.8 to 14.4|m}}.<ref name="Martilletal2023"/> In 2026, Ruizhe Jackevan Zhao compared the specimens attributed to ''P.'' cf. ''kevani'' and ''P. funkei'', and concluded that both would not be significantly different in terms of measurements, with an estimated body length of {{cvt|9.8|m}} and body mass of approximately {{cvt|10.7|-|10.9|t}}.<ref name="Zhao2026">{{cite journal|last=Zhao |first=R. J. |year=2026 |title=Body reconstruction and size estimation of plesiosaurs |journal=PeerJ |volume=14 |article-number=e21146 |pmc=13089226 |pmid=42004715 |doi=10.7717/peerj.21146 |doi-access=free }}</ref>

Few estimates have been given for other species. The immature status of the holotype specimen of ''P. brachydeirus'' suggests that it could have reached larger measurements as an adult.<ref name="Bensonetal2013"/> The temporary skeletal mount of the holotype of ''P. carpenteri'' suggests a size of about {{cvt|8|m}} long for a skull reaching {{cvt|1.8|m}}.<ref name="Larkinetal2021"/> The holotype skull of ''P. westburyensis'' is {{cvt|1.7|m}} long, making it slightly smaller than ''P. carpenteri''.<ref name="Sassoonetal2012"/><ref name="Bensonetal2013"/>

=== Teeth === thumb|upright=0.75|alt=|Multi-angle view of two teeth from the holotype of ''P. kevani''

One of the main identifying features of ''Pliosaurus'' is that the teeth are often trihedral in cross-section, with flat and smooth labial surfaces (the side facing lips), but convex lingual surfaces (the side facing the tongue) bearing longitudinal enamel ridges. However, ''P. kevani'' is the only recognized species in which the teeth are sub-trihedral in shape, possessing slightly flattened labial surfaces with finely distributed enamel ridges. In some species such as ''P. kevani'' and ''P. carpenteri'', the premaxillary teeth are anisodont, meaning they vary in size, which is not the case in ''P. brachydeirus'' or ''P. westburyensis''.<ref name="Knutsen2012"/><ref name="Knutsenetal2012"/><ref name="Bensonetal2013"/>

The different species of ''Pliosaurus'' can also be distinguished by the number of teeth present in the premaxillae, maxillae (the latter two sometimes bearing caniniform dentition), the mandibular symphysis, and the dentary as a whole. However, since not all fossils are sufficiently well preserved, the dental counts of some species remain uncertain: ''P. brachydeirus'' possessed four to six premaxillary teeth, twenty-two or more maxillary teeth, thirty-five to thirty-seven dentary teeth, and more than seven to thirteen pairs of symphyseal teeth; ''P. rossicus'' had six premaxillary teeth and six pairs of symphyseal teeth; ''P. funkei'' had at least five premaxillary teeth and six pairs of symphyseal teeth; ''P. kevani'' had six premaxillary teeth, about twenty-five maxillary teeth, more than twenty-eight to thirty-seven dentary teeth, and more than six to fifteen pairs of symphyseal teeth; ''P. westburyensis'' had more than five premaxillary teeth, about twenty-five maxillary teeth, more than twenty-one dentary teeth, and possibly nine pairs of symphyseal teeth; and ''P. carpenteri'' had six premaxillary teeth, more than twenty-seven maxillary teeth, twenty-seven dentary teeth, and eight to nine pairs of symphyseal teeth.<ref name="Knutsen2012"/><ref name="Knutsenetal2012"/><ref name="Bensonetal2013"/>

=== Postcranial skeleton ===

The vast majority of recognized ''Pliosaurus'' species do not preserve any sufficiently complete postcranial skeletons, making comparisons difficult. A possible exception is ''P. kevani'', one of whose referred specimens consists of a large postcranial skeleton. However, this skeleton cannot be diagnosed with certainty as belonging to a distinct or already known species, despite its current attribution.<ref name="Bensonetal2013"/> Thus, the postcranial anatomy of ''Pliosaurus'' is primarily known from vertebrae and limb elements documented in the holotype specimens of ''P. brachydeirus'', ''P. funkei'', and ''P. carpenteri'', although rare diagnostic postcranial elements have also been reported in ''P. rossicus'' and ''P. westburyensis''.<ref name="Knutsen2012"/><ref name="Knutsenetal2012"/><ref name="Bensonetal2013"/>

The cervical vertebrae of ''Pliosaurus'' are massive, short, and possess flattened centra that are subcircular to slightly oval in shape. The ventral surface of these vertebrae is an important criterion for distinguishing species. In ''P. brachydeirus'', the ventral surface of the cervical vertebrae is marked by a pronounced longitudinal ridge, a feature absent in ''P. westburyensis'' and ''P. carpenteri''. The cervical vertebrae of ''P. rossicus'' and ''P. funkei'' have rugose ventral surfaces lacking median ridges.<ref name="Knutsen2012"/><ref name="Knutsenetal2012"/><ref name="Bensonetal2013"/> Like other pliosaurids that lived during the Jurassic, ''Pliosaurus'' likely possessed double-headed cervical ribs.<ref name="Tarlo1960"/><ref name="Knutsen2012"/><ref name="Knutsenetal2012"/> Like other pliosaurids, the pectoral vertebrae of ''P. funkei'' bear articulations for their respective ribs, partially on both the centra and neural arches. The dorsal vertebrae are approximately as long as they are wide, in contrast to the cervical vertebrae.<ref name="Knutsenetal2012"/> Although the caudal vertebrae are poorly known in the genus, with only one documented in ''P. brachydeirus'',<ref name="Tarlo1960"/> they likely supported a tail fin, as documented in other plesiosaurs.<ref name="Massare1988"/><ref name="CaudalFins"/>

The few known elements of the pectoral girdle in the genus are currently documented only in ''P. rossicus'' and ''P. funkei''.<ref name="Novozhilov1964"/><ref name="Knutsenetal2012"/> These elements are also present in ''P. carpenteri'', but they have not been described in detail in studies concerning this species.<ref name="Sassoonetal2010"/><ref name="Bensonetal2013"/><ref name="Larkinetal2021"/> The scapula of ''P. rossicus'' features a dorsally directed process, and the longitudinal axes of the scapulocoracoid openings intersect at an angle greater than 140°.<ref name="Novozhilov1964"/> The coracoid of ''P. funkei'' is among the largest identified in pliosaurids. In dorsal view, it is longer than wide, with its width tapering anteriorly. This coracoid also has a more elongate anteromedial process than that of ''P. rossicus'', although this may be explained by ontogenetic factors.<ref name="Knutsenetal2012"/>

Limb proportions also vary between species. For example, ''P. funkei'' is distinguished by particularly elongated forelimbs, which could reach up to {{convert|3|m|ft}}, with humeri whose length exceeds seven times the average width of the cervical vertebrae. In comparison, ''P. rossicus'' has proportionally shorter limbs, with humeri less than 4.5 times the width of the cervical vertebrae. The radius and ulna of ''P. funkei'' are nearly equal in proportions, being about twice as long as they are wide. The phalanges are hourglass-shaped, becoming shorter and narrower distally.<ref name="Knutsen2012"/><ref name="Knutsenetal2012"/> The tibia and fibula of ''P. brachydeirus'' are shorter than they are wide, a feature generally observed only in polycotylids.<ref name="Tarlo1960"/> In ''P. carpenteri'', the radius, ulna, tibia, and fibula are characterized by highly convex proximal articular surfaces.<ref name="Bensonetal2013"/>

== Classification == === History of taxonomy === thumb|alt=Artist's impression of a grayish prehistoric marine reptile on a white background|Life restoration of ''P. brachydeirus''.

Although being the type genus of pliosaurids, ''Pliosaurus'' was for nearly two centuries a poorly understood taxon due to the lack of an adequate description of the holotype of ''P. brachydeirus''.<ref name="Sassoonetal2012"/> This led in particular to many pliosaur genera since recognised as distinct being sometimes considered species, or even junior synonyms, of ''Pliosaurus''. In 1960, Halstead (then called Tarlo) revised the taxonomy of Late Jurassic pliosaurids, making the first revision of the type genus. In his paper, he considered the following three species as valid: ''P. brachydeirus'', ''P. brachyspondylus'', and the newly described ''P. andrewsi''.<ref name="Tarlo1960"/> Simultaneously with the publication of the official description of ''P. funkei'' in 2012,<ref name="Knutsenetal2012"/><ref name="Hurumetal2012"/> Another article written by Knutsen alone and concerning the taxonomic revision of the genus ''Pliosaurus'' as a whole is published. According to him, the species ''P. brachydeirus'', ''P. brachyspondylus'', ''P. macromerus'', ''P. rossicus''{{efn|When he described the proposed neotype of ''P. macromerus'', Knutsen suggested that ''P. rossicus'' might be a synonym, noting the shared presence of only six symphyseal tooth sockets and five premaxillary tooth sockets. However, he maintained the validity of both taxa, as their stratigraphic ranges do not overlap and the specimens have not been adequately described.<ref name="Knutsen2012"/> The following year, Benson and colleagues observed that the proposed neotype of ''P. macromerus'' actually possesses seven symphyseal tooth sockets, and that it may originally have had as many as nine in life. Thus, this difference was considered sufficient to distinguish it from ''P. rossicus''. The authors of this study even provisionally classify a specimen historically attributed to ''P. macromerus'', discovered in Cumnor, Oxfordshire, as belonging to ''P. rossicus'' on the basis of the number of symphyseal tooth sockets.<ref name="Bensonetal2013"/>}} and ''P. funkei'' are valid. However, he maintains the validity of both species ''P. brachyspondylus'' and ''P. macromerus'' on the basis of proposed neotypes, their original type specimens being deemed non-diagnostic. ''P. andrewsi'', which was long considered a valid species of the genus, turns out to have too many morphological differences to be placed in ''Pliosaurus''.<ref name="Knutsen2012"/> In 2013, Benson and colleagues recognised the validity of the following six species: ''P. brachydeirus'', ''P. rossicus'', ''P. funkei'', ''P. kevani'', ''P. westburyensis'', and ''P. carpenteri''. As no formal petition to ICZN was made to designate the neotypes of ''P. brachyspondylus'' and ''P. macromerus'', these two species are then considered as dubious.<ref name="Bensonetal2013"/>

=== Systematics and phylogeny ===

In 1874, Harry Govier Seeley named a new family of plesiosaurs, Pliosauridae, to contain forms similar to ''Pliosaurus''.<ref name="Seeley1874">{{cite journal|last=Seeley|first=H. G.|year=1874|title=Note on some of the generic modifications of the plesiosaurian pectoral arch|doi=10.1144/gsl.jgs.1874.030.01-04.48|journal=Quarterly Journal of the Geological Society|volume=30|issue=1–4|pages=436–449|bibcode=1874QJGS...30..436S|s2cid=128746688|url=https://zenodo.org/record/1448521}}</ref> Exactly how pliosaurids are related to other plesiosaurs is uncertain. In 1940, palaeontologist Theodore E. White considered pliosaurids to be close relatives of Elasmosauridae based on shoulder anatomy.<ref name="White1940">{{cite journal|last=White|first=T. E.|year=1940|title=Holotype of ''Plesiosaurus longirostris'' Blake and classification of the plesiosaurs|journal=Journal of Paleontology|volume=14|issue=5|pages=451–467|jstor=1298550}}</ref> However, in 1943, Samuel P. Welles thought that pliosaurids were more similar to Polycotylidae, as they both had large skulls and short necks, among other characteristics. He grouped these two families into the superfamily Pliosauroidea, with other plesiosaurs forming the superfamily Plesiosauroidea.<ref name="Welles1943">{{cite journal|last=Welles|first=S. P.|title=Elasmosaurid plesiosaurs with description of new material from California and Colorado|journal=Memoir of the University of California|volume=13|issue=3|pages=125–254|year=1943|url=https://plesiosauria.com/pdf/welles_1943_elasmosaurid_plesiosaurs.pdf}}</ref><ref name="Persson1963">{{cite journal|first=P. O.|last=Perssons|year=1963|title=A revision of the classification of the Plesiosauria with a synopsis of the stratigraphical and geographical distribution of the group|journal=Lunds Universitets Arsskrift|volume=59|issue=1|pages=1–59|url=https://paleoarchive.com/literature/Persson1963-RevisionClassificationPlesiosauria.pdf}}</ref> Another plesiosaur family, Rhomaleosauridae, has since been assigned to Pliosauroidea,<ref name="Smith&Dyke2008">{{cite journal|last1=Smith|first1=A. S.|last2=Dyke|first2=G. J.|title=The skull of the giant predatory pliosaur ''Rhomaleosaurus cramptoni'': Implications for plesiosaur phylogenetics|journal=Naturwissenschaften|year=2008|volume=95|issue=10|pages=975–980|doi=10.1007/s00114-008-0402-z|pmid=18523747|bibcode=2008NW.....95..975S|s2cid=12528732|url=http://doc.rero.ch/record/16503/files/PAL_E3603.pdf}}</ref><ref name="O'Keefe2001b">{{cite journal|first=F. R.|last=O’Keefe|year=2001|title=A cladistic analysis and taxonomic revision of the Plesiosauria (Reptilia: Sauropterygia)|journal=Acta Zoologica Fennica|volume=213|pages=1–63|url=https://mds.marshall.edu/cgi/viewcontent.cgi?referer=https://scholar.google.com/&httpsredir=1&article=1051&context=bio_sciences_faculty}}</ref> while Polycotylidae has been reassigned to Plesiosauroidea.<ref name="Carpenter1997">{{cite book|year=1997|editor1-last=Callaway|editor1-first=I. M.|editor2-last=Nicholls|editor2-first=E. L.|title=Ancient Marine Reptiles|publisher=Academic Press|pages=191–216|chapter=Comparative cranial anatomy of two North American Cretaceous plesiosaurs|last=Carpenter|first=K.|chapter-url=https://www.researchgate.net/publication/285685402}}</ref><ref name="Benson2012">{{cite journal|last1=Benson|first1=R. B. J.|last2=Evans|first2=M.|last3=Druckenmiller|first3=P. S.|year=2012|title=High diversity, low disparity and small body size in Plesiosaurs (Reptilia, Sauropterygia) from the Triassic–Jurassic boundary|journal=PLOS ONE|volume=7|issue=3|article-number=e31838|doi=10.1371/journal.pone.0031838|pmid=22438869|pmc=3306369|bibcode=2012PLoSO...731838B|doi-access=free}}</ref> However, in 2012, Benson and colleagues recovered a different topology, with Pliosauridae being more closely related to Plesiosauroidea than Rhomaleosauridae. This pliosaurid-plesiosauroid clade was termed Neoplesiosauria.<ref name="Benson2012" />

In 1960, Halstead considered ''Pliosaurus'' to be a close relative of ''Peloneustes'', since both taxa had elongated mandibular symphyses. According to him, the genus ''Pliosaurus'' would comprise a chronospecific sequence represented, in order of succession, by the species ''P. andrewsi'', ''P. brachyspondylus'', and ''P. brachydeirus''.<ref name="Tarlo1960" /> In 2001, F. Robin O’Keefe recovered ''Pliosaurus'' as the sister taxon of ''Brachauchenius''.<ref name="O'Keefe2001b" /> However, in 2008, Adam S. Smith and Gareth J. Dyke considered ''Pliosaurus'' to be the sister taxon of ''Peloneustes''.<ref name="Smith&Dyke2008"/> In 2012, Patrick S. Druckenmiller and Knutsen recovered the genus ''Pliosaurus'' as a monophyletic group comprising the species ''P. brachydeirus'', ''P. rossicus'', ''P. funkei'', ''P. brachyspondylus'', and ''P. macromerus'', although their cladogram also included an unspecified specimen catalogued as NHMUK R2439.<ref name="Druckenmiller&Knutsen2012">{{cite journal|last1=Druckenmiller|first1=P. S.|last2=Knutsen|first2=E. M.|title=Phylogenetic relationships of Upper Jurassic (Middle Volgian) plesiosaurians (Reptilia: Sauropterygia) from the Agardhfjellet Formation of central Spitsbergen, Norway|journal=Norwegian Journal of Geology|year=2012|volume=92|pages=277–284|url=https://foreninger.uio.no/ngf/ngt/pdf-nye/NJG_2_3_2012_15_Druckenmiller_Knutsen_Pr.pdf}}</ref> In 2013, Benson and Druckenmiller named a new clade within Pliosauridae, Thalassophonea. This clade included the "classic", short-necked pliosaurids while excluding the earlier, long-necked, more gracile forms. Since the publication of this study, ''Pliosaurus'' has since been seen as being related to ''Gallardosaurus''.<ref name="Benson2013">{{cite journal|last1=Benson|first1=R. B. J.|last2=Druckenmiller|first2=P. S.|year=2013|title=Faunal turnover of marine tetrapods during the Jurassic–Cretaceous transition|journal=Biological Reviews|volume=89|issue=1|pages=1–23|doi=10.1111/brv.12038|pmid=23581455|s2cid=19710180}}</ref> In the same year, in order to keep the genus ''Pliosaurus'' as monophyletic again, Benson and colleagues removed ''Gallardosaurus'', ''P. rossicus'' and its potential junior synonym ''P. irgisensis'' from their cladogram.<ref name="Bensonetal2013"/> The inclusion of the species ''P. patagonicus'' and ''P. almanzaensis'' within the genus ''Pliosaurus'' has been discussed by some authors. In 2019, María Páramo-Fonseca and colleagues considered that these two taxa do not appear to form a monophyletic group with the European species of the genus.<ref name="Páramo-Fonsecaetal2019">{{cite journal|first1=M. E.|last1=Páramo-Fonseca|first2=C. D.|last2=Benavides-Cabra|first3=I. E.|last3=Gutiérrez|year=2019|title=A new specimen of ''Stenorhynchosaurus munozi'' Páramo-Fonseca et al., 2016 (Plesiosauria, Pliosauridae), from the Barremian of Colombia: new morphological features and ontogenetic implications|journal=Journal of Vertebrate Paleontology|volume=39|issue=4|article-number=e1663426|doi=10.1080/02724634.2019.1663426|bibcode=2019JVPal..39E3426P|s2cid=208561823}}</ref> In 2023, Valentin Fischer and colleagues recovered ''P. almanzaensis'' within the genus in their cladograms, but placed ''P. patagonicus'' among the Brachaucheninae, a subgroup of thalassophoneans whose representatives mainly lived during the Cretaceous. Some of their alternative cladograms even recover the species as the sister taxon of the Russian genus ''Luskhan''.<ref name="Fischeretal2023">{{cite journal|last1=Fischer |first1=V.|last2=Benson|first2=R. B. J.|first3=N. G.|last3=Zverkov|first4=M. S.|last4=Arkhangelsky|first5=I M.|last5=Stenshin|first6=G. N.|last6=Uspensky|first7=N. E.|last7=Prilepskaya|title=Anatomy and relationships of the bizarre Early Cretaceous pliosaurid ''Luskhan itilensis''|journal=Zoological Journal of the Linnean Society|volume=198|issue=1|pages=220–256|year=2023|doi=10.1093/zoolinnean/zlac108|s2cid=257573659|doi-access=free}}</ref>

The following cladogram follows the Bayesian analysis made by Fischer et al. (2023),<ref name="Fischeretal2023"/> although the species ''P. brachyspondylus'', ''P. macromerus'' and ''P. irgisensis'' are considered as doubious.<ref name="Bensonetal2013"/>

{{clade|style=font-size:85%; line-height:85%; |label1=Pliosauridae |1={{clade |1=''Attenborosaurus conybeari'' |2={{clade |1=''Thalassiodracon hawkinsi'' |2={{clade |1={{clade |1=''Hauffiosaurus zanoni'' |2=''Hauffiosaurus tomistomimus'' |3=''Hauffiosaurus longirostris'' }} |4={{clade |1=''Anguanax zignoi'' |2=''Marmornectes candrewi'' |label3=Thalassophonea |3={{clade |1=''Peloneustes philarchus'' |2={{clade |1=''"Pliosaurus" andrewsi'' |2={{clade |1=''Simolestes vorax'' |2={{clade |1=''Liopleurodon ferox'' |2={{clade |1=''Gallardosaurus iturraldei'' |2={{clade |1='''''Pliosaurus almanzaensis''''' |2='''''Pliosaurus irgisensis''''' |3='''''Pliosaurus rossicus''''' |4='''''Pliosaurus brachyspondylus''''' |5='''''Pliosaurus macromerus''''' |6='''''Pliosaurus brachydeirus''''' |7='''''Pliosaurus carpenteri''''' |8='''''Pliosaurus westburyensis''''' |9='''''Pliosaurus funkei''''' |10={{clade |1='''''Pliosaurus kevani''''' |2='''''Pliosaurus''''' '''cf.''' '''''kevani'''''}}}} |label3=Brachaucheninae |3={{clade |1='''''Pliosaurus patagonicus''''' |2={{clade |1=''Luskhan itilensis'' |2={{clade |1={{clade |1=''Makhaira rossica'' |2=''Stenorhynchosaurus munozi'' }} |3={{clade |1=''Acostasaurus pavachoquensis'' |2={{clade |1=''Sachicasaurus vitae'' |2={{clade |1=''Monquirasaurus boyacensis'' |2=''Kronosaurus-Eiectus'' |3={{clade |1=QM F51291 |2={{clade |1=''Brachauchenius'' MNA |2=''Brachauchenius lucasi'' |3=''Megacephalosaurus eulerti'' |4=''Polyptychodon'' sp.}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}

== Paleobiology == thumb|alt=|Life restoration of ''P. rossicus'' Plesiosaurs were well-adapted to marine life.<ref name="Fleischleetal2018"/><ref name="Fleischleetal2019"/> They grew at rates comparable to those of birds and had high metabolisms, indicating homeothermy<ref name="Houssaye2013">{{cite journal|first=A.|last=Houssaye|title=Bone histology of aquatic reptiles: What does it tell us about secondary adaptation to an aquatic life?|journal=Biological Journal of the Linnean Society|volume=108|issue=1|year=2013|pages=3–21|doi=10.1111/j.1095-8312.2012.02002.x|s2cid=82741198|doi-access=free}}</ref> or even endothermy.<ref name="Fleischleetal2018">{{cite journal|first1=C. V.|last1=Fleischle|first2=T.|last2=Wintrich|first3=P. M.|last3=Sander|year=2018|title=Quantitative histological models suggest endothermy in plesiosaurs|journal=PeerJ|volume=6|article-number=e4955|doi=10.7717/peerj.4955|pmid=29892509|pmc=5994164|doi-access=free}}</ref> A 2019 study by palaeontologist Corinna Fleischle and colleagues found that plesiosaurs had enlarged red blood cells, based on the morphology of their vascular canals, which would have aided them while diving.<ref name="Fleischleetal2019">{{cite journal|first1=C. V.|last1=Fleischle|first2=P. M.|last2=Sander|first3=T.|last3=Wintrich|first4=K. R.|last4=Caspar|year=2019|title=Hematological convergence between Mesozoic marine reptiles (Sauropterygia) and extant aquatic amniotes elucidates diving adaptations in plesiosaurs|journal=PeerJ|volume=7|article-number=e8022|doi=10.7717/peerj.8022|pmid=31763069|pmc=6873879|doi-access=free}}</ref> Plesiosaurs such as ''Pliosaurus'' employed a method of swimming known as subaqueous flight, using their flippers as hydrofoils. Plesiosaurs are unusual among marine reptiles in that they used all four of their limbs, but not movements of the vertebral column, for propulsion. The short tail, while unlikely to have been used to propel the animal, could have helped stabilise or steer the plesiosaur.<ref name="Massare1988">{{cite journal|last=Massare|first=J. A.|title=Swimming Capabilities of Mesozoic Marine Reptiles: Implications for Method of Predation|journal=Paleobiology|volume=14|issue=2|year=1988|pages=187–205|doi=10.1017/S009483730001191X|bibcode=1988Pbio...14..187M |s2cid=85810360 }}</ref><ref name="CaudalFins">{{cite journal|last=Smith|first=A. S.|year=2013|title=Morphology of the caudal vertebrae in ''Rhomaleosaurus zetlandicus'' and a review of the evidence for a tail fin in Plesiosauria|journal=Paludicola|volume=9|issue=3|pages=144–158|url=https://plesiosauria.com/pdf/smith_2013_plesiosaur_tail_fin.pdf}}</ref> Computer modelling by Susana Gutarra and colleagues in 2022 found that due to their large flippers, a plesiosaur would have produced more drag than a comparably-sized cetacean or ichthyosaur. However, plesiosaurs counteracted this with their large trunks and body size.<ref name="Gutarra2022">{{cite journal|last1=Gutarra|first1=S.|last2=Stubbs|first2=T. L.|last3=Moon|first3=B. C.|last4=Palmer|first4=C.|last5=Benton|first5=M.J.|title=Large size in aquatic tetrapods compensates for high drag caused by extreme body proportions|journal=Communications Biology|volume=5|pages=380|year=2022|issue=1 |doi=10.1038/s42003-022-03322-y|pmid=35484197 |pmc=9051157 }}</ref> Due to the reduction in drag by their shorter, deeper bodies, Judy Massare proposed in 1988 that plesiosaurs could actively search for and pursue their food instead of having to lie in wait for it.<ref name="Massare1988" />

=== Feeding mechanics ===

''Pliosaurus'' is interpreted by palaeontologists as a marine predator at the top of the food chain, with powerful cranial musculature that gave it an exceptionally strong bite, although its skull was relatively weak against twisting or lateral bending. Unlike basal thalassophoneans such as ''Peloneustes'' and ''Luskhan'', which were better adapted to small, mobile prey, ''Pliosaurus'' appeared to favor a predatory strategy based on short, targeted bites, delivered to the back of the jaw where the force of pressure was greatest. This anatomical configuration suggests that it avoided violently shaking or twisting its prey, which could compromise the integrity of its skull. It likely captured a wide variety of marine prey, ranging from medium-sized fish to smaller marine reptiles, which it subdued by firmly immobilizing with its robust jaws before crushing or swallowing them in dismemberment. This strategy of combining muscular power and attack precision allowed it to adapt to a wide range of prey, characteristic of a generalist predator of the Jurassic seas.<ref name="Massare1987">{{cite journal|last=Massare|first=J. A.|year=1987|title=Tooth morphology and prey preference of Mesozoic marine reptiles|journal=Journal of Vertebrate Paleontology|volume=7|issue=2|pages=121–137|doi=10.1080/02724634.1987.10011647|bibcode=1987JVPal...7..121M|s2cid=83647928}}</ref><ref name="Taylor&Cruickshank1993"/><ref name="Bensonetal2013"/><ref name="Foffaetal2014b"/><ref name="Fischeretal2017">{{cite journal|last1=Fischer|first1=V.|last2=Benson|first2=R. B. J.|last3=Zverkov|first3=N. G.|last4=Soul|first4=L. C.|last5=Arkhangelsky|first5=M. S.|last6=Lambert|first6=O.|last7=Stenshin|first7=I. M.|last8=Uspensky|first8=G. N.|last9=Druckenmiller|first9=P. S.|year=2017|title=Plasticity and Convergence in the Evolution of Short-Necked Plesiosaurs|journal=Current Biology|volume=27|issue=11|pages=1667–1676|doi=10.1016/j.cub.2017.04.052|pmid=28552354|s2cid=39217763|doi-access=free}}</ref>

The second study focuses on bite force. By modeling the mandibular musculature and reconstructing the geometry of the skull using computed tomography and finite element analysis techniques, the researchers determined that the force exerted ranged from {{convert|9,600|to|48,000|newtons|lbf|-1}} depending on the area of the lower jaws, a force comparable to, or even greater than, that of the largest living crocodilians. Since this power was concentrated in the back of the jaw, this suggests that ''P. kevani'' used a biting strategy designed to puncture or crush robust prey. However, despite this impressive force, the cranial structure has certain weaknesses when faced with bending or lateral torsional stresses. This also indicates that ''P. kevani'' did not kill its prey by violent jerks, but by a direct and powerful bite, optimized to quickly incapacitate large prey without excessive head movements.<ref name="Foffaetal2014b">{{cite journal|first1=D.|last1=Foffa|first2=A. R.|last2=Cuff|first3=J.|last3=Sassoon|first4=E. J.|last4=Rayfield|first5=M. N.|last5=Mavrogordato|first6=M. J.|last6=Benton|title=Functional anatomy and feeding biomechanics of a giant Upper Jurassic pliosaur (Reptilia: Sauropterygia) from Weymouth Bay, Dorset, UK|journal=Journal of Anatomy|year=2014|volume=225|issue=2|pages=209–219|doi=10.1111/joa.12200|pmc=4111928|pmid=24925465|doi-access=free}}</ref> Such behavior was also suggested for the holotype of ''P. westburyensis'' in 1993.<ref name="Taylor&Cruickshank1993"/> A ''Pliosaurus''-like pliosaur has also been suggested to have inflicted bite marks upon an indeterminate ophthalmosaurid ichthyosaur by Nikolay Zverkov and colleagues in 2015.<ref name="Zverkovetal2015">{{cite journal|first1=N. G.|last1=Zverkov|first2=M.|last2=Arkhangelsky|first3=I. M.|last3=Stenshin|title=A review of Russian Upper Jurassic ichthyosaurs with an intermedium/humeral contact. Reassessing ''Grendelius'' McGowan, 1976|journal=Proceedings of the Zoological Institute RAS|volume=318|issue=2|pages=148–167|year=2015|doi=10.31610/trudyzin/2015.319.4.558|s2cid=56362895|doi-access=free}}</ref>

=== Sensory functions === Pliosaurs are generally regarded as visually oriented predators. The cranial anatomy of the holotype specimen of ''P. westburyensis'' reveals greatly enlarged orbits, indicative of large eyes and suggesting a high degree of visual acuity. Sclerotic rings known from other pliosaurs support this interpretation and point to vision specifically adapted to aquatic environments. In contrast, the lack of acoustic isolation in the auditory capsules indicates that, unlike modern cetaceans, pliosaurs did not possess echolocation. The size and arrangement of the orbits further suggest that their vision was effective under low-light conditions, such as in the turbid waters of coastal seas or the deeper part of the photic zone.<ref name="Taylor&Cruickshank1993"/> Similarly, ''P. carpenteri'' is thought to have possessed limited stereoscopic vision but a wide lateral field of view.<ref name="Sassoonetal2012"/> The nasal cavities of ''Pliosaurus'' are remarkably small relative to the size of the skull, too reduced to provide effective respiration. This peculiarity has led to the hypothesis that these structures were not primarily involved in ventilation but instead had a sensory function. By analogy with ''Rhomaleosaurus'', it has been suggested that the nares were used for aquatic olfaction, with water passing through inverted palatal grooves toward the internal choanae. This interpretation would explain why the size of the nares did not scale proportionally with that of the animal, as their role was related to chemical detection rather than respiration.<ref name="Taylor&Cruickshank1993"/>

In another study published slightly earlier in 2014, Foffa and colleagues also described the internal anatomy of the rostrum of the ''P. kevani'' holotype, again using computed CT scans. These revealed a neurovascular system within the premaxillae, whose canals, filled with sediment and pyrite, were clearly distinguishable from digital models of the surrounding bone. The largest canals reach {{cvt|23|mm}} in diameter, while the finest branches, about {{cvt|2|mm}} wide, extend to the periphery of the rostrum. At the level of the sixth premaxillary tooth socket, there is evidence of a major branching from which a second canal arises, a feature also observed in theropod dinosaurs of the spinosaurid group, such as ''Spinosaurus'' and ''Baryonyx''. The canals connect the interior of the bones to more than two hundred small foramina visible on the surface, primarily on the premaxillae and maxillae. Some of these canals open near the tooth alveoli, while others emerge directly on the dorsal and lateral surfaces of the snout. Together, they form a complex neurovascular system indicating dense innervation and developed vascularization in the rostral region. This network is interpreted as the termination of branches of the trigeminal nerve, which would have transmitted sensory information from the skin to the animal’s brain. Such neurovascular systems are comparable to those observed in several extant and extinct animals, including crocodilians, ''Spinosaurus'', lepidosauromorphs, ichthyosaurs, and other sauropterygians (the group including plesiosaurs and their close relatives). The authors of the study emphasize, however, that the exact function of the neurovascular network in ''P. kevani'' remains uncertain, although the very high number of innervated pits on its rostrum suggests a sensory role likely related to detecting movements in the water, a valuable adaptation for hunting in low-light conditions.<ref name="Foffaetal2014a">{{cite journal|first1=D.|last1=Foffa|first2=J.|last2=Sassoon|first3=A. R.|last3=Cuff|first4=M. N.|last4=Mavrogordato|first5=M. J.|last5=Benton|year=2014|title=Complex rostral neurovascular system in a giant pliosaur|journal=Naturwissenschaften|volume=101|issue=5|pages=453–456|doi=10.1007/s00114-014-1173-3|pmid=24756202|bibcode=2014NW....101..453F| s2cid=7406418|url=https://www.researchgate.net/publication/261759750}}</ref> Similar rostral structures have been reported in the holotype specimens of ''P. carpenteri'' and ''P. westburyensis'',<ref name="Taylor&Cruickshank1993"/><ref name="Sassoonetal2012"/><ref name="Bensonetal2013"/> but these have not yet been described in detail.<ref name="Foffaetal2014a"/>

=== Paleopathology ===

In their 2012 publication describing the cranial anatomy of the future holotype of ''P. carpenteri'', Sassoon and colleagues identified several bone pathologies that had affected the animal during adulthood. Detailed observations revealed erosive osteoarthritis of the mandibular joint, particularly at the articular glenoid surfaces, which led to a progressive misalignment of the lower jaw: the joint surfaces are irregularly hollowed and show extensive deformation consistent with advanced articular degeneration. This type of lesion is interpreted as analogous to osteoarthritis in modern vertebrates. Among other anomalies observed in the specimen are the presence of callus-like bone growth around certain tooth alveoli and irregular lateral cavities in the mandible, suggesting repeated episodes of stress or trauma affecting the jaw bones. Together, these pathological modifications indicate not only age-related degenerative disease, but also long-term mechanical consequences—such as asymmetric biting caused by the altered joint—which likely influenced the animal’s ability to capture and process prey over time.<ref name="Sassoonetal2012"/>

When Taylor and Cruickshank described in 1993 what would later become the holotype specimen of ''P. westburyensis'', they interpreted an asymmetric rugosity of the parietal crest as a pathological feature, possibly related to a tumor or to a reaction following trauma, such as an infection or a wound.<ref name="Taylor&Cruickshank1993"/> However, as similar structures have been observed in other pliosaurs, Sassoon and colleagues instead proposed that it represents a variable character, even suggesting the possibility of sexual dimorphism, in line with their interpretation of specimens BRSMG Cc332 and BRSMG Cc6172,<ref name="Sassoonetal2012"/> although this latter view has since been contradicted by Benson et al. (2013). In this same latter study, the authors also report the presence of a pronounced and irregular depression on the ventral surface of the fused squamosal bones of the holotype skull of ''P. kevani''. This feature could correspond to a pathology, a bite mark, or an alteration of the bone surface that occurred during the specimen's biostratinomic history.<ref name="Bensonetal2013"/>

== Paleoecology == === England === [[File:Paleogeography and paleoclimate of the Late Jurassic - 150 Ma with dinosaur fossil localities.png|thumb|left|upright=1.2|alt=map of the world in the Jurassic, indicating the Kimmeridge Clay Formation was located near a warm temperate climate|Map of the world in the Jurassic, the Kimmeridge Clay Formation is located at E1]]

''P. brachydeirus'', ''P. kevani'', ''P. westburyensis'', ''P. carpenteri'' and a possible specimen of ''P. rossicus'' are known from the Kimmeridgian and Tithonian stages of the Upper Jurassic in the Kimmeridge Clay Formation, England.<ref name="Bensonetal2013"/> This formation was deposited in a deep-sea marine environment reaching about {{cvt|150 to 200|m}} depth, known as the Jurassic Sub-Boreal Seaway.<ref name="Gallois2004">{{cite journal|last=Gallois|first=R. W.|title=The Kimmeridge Clay: the most intensively studied formation in Britain|journal=Open University Geological Journal|year=2004|volume=25|issue=2|pages=33–38|url=https://www.researchgate.net/publication/277850785}}</ref><ref name="Foffaetal2018">{{cite journal|last1=Foffa|first1=D.|last2=Young|first2=M. T.|last3=Stubbs|first3=T. L.|last4=Dexter|first4=K. G.|last5=Brusatte|first5=S. L.|year=2018|title=The long-term ecology and evolution of marine reptiles in a Jurassic seaway|journal=Nature Ecology & Evolution|volume=2|issue=10 |pages=1548–1555|doi=10.1038/s41559-018-0656-6|pmid=30177805|bibcode=2018NatEE...2.1548F |s2cid=52147976 |url=https://www.research.ed.ac.uk/en/publications/789aa9d0-076f-41bc-bd78-213a3313ebbe }}</ref><ref name="Foffaetal2019">{{cite journal|last1=Foffa|first1=D.|last2=Johnson|first2=M. M.|last3=Young|first3=M. T.|last4=Steel|first4=L.|last5=Brusatte|first5=S. L.|year=2019|title=Revision of the Late Jurassic deep-water teleosauroid crocodylomorph ''Teleosaurus megarhinus'' Hulke, 1871 and evidence of pelagic adaptations in Teleosauroidea|journal=PeerJ|volume=7|article-number=e6646|doi=10.7717/peerj.6646|pmid=30972249|pmc=6450380|doi-access=free |bibcode=2019PeerJ...7e6646F }}</ref> Known invertebrates are mainly represented by ammonites and crustaceans.<ref name="Wignall1990">{{cite book|first=P. B.|last=Wignall|title=Benthic palaeoecology of the late Jurassic Kimmeridge Clay of England|series=Special Papers in Palaeontology|volume=43|publisher=The Palaeontological Association|location=London|year=1990|isbn=978-0-901702-42-5|url=http://rogov.zwz.ru/Wignall,%201990_Bentic%20palaeoecology_Kimmeridge%20clay.pdf|archive-url=https://web.archive.org/web/20110826085319/http://rogov.zwz.ru/Wignall%2C%201990_Bentic%20palaeoecology_Kimmeridge%20clay.pdf|archive-date=2011-08-26}}</ref>

=== Slavic regions ===

In Russia, the first two known specimens of ''P. rossicus'' were discovered in Tithonian rocks of the Lower Volga Basin.<ref name="Rozhdestvensky1947"/><ref name="Novozhilov1948"/><ref name="Novozhilov1964"/> Due to the abundant presence of the ammonite ''Dorsoplanites panderi'' in the type locality of the taxon, the stratigraphic unit thus bears this name.<ref name="Storrsetal2000"/><ref name="Knutsen2012"/><ref name="Rogov2013">{{cite journal|first=M. A.|last=Rogov|title=Ammonites and infrazonal subdivision of the ''Dorsoplanites panderi'' zone (Volgian Stage, Upper Jurassic) of the European part of Russia|journal=Doklady Earth Sciences|year=2013|volume=451|issue=2|pages=803–808|doi=10.1134/S1028334X13080059|bibcode=2013DokES.451..803R |s2cid=128426221|url=https://www.researchgate.net/publication/260502275}}</ref> Little is known or published about Volga fossils from this period, although a fairly large number of invertebrates have been recorded. These include ammonites, bivalves, radiolarians, and dinoflagellates.<ref name="Rogovetal2024">{{cite journal|first1=M. A.|last1=Rogov|first2=V. A.|last2=Zakharov|first3=E. B.|last3=Pestchevitskaya|first4=V. S.|last4=Vishnevskaya|first5=N. G.|last5=Zverkov|first6=E. Yu.|last6=Baraboshkin|title=Upper Jurassic Volgian Stage and Lower Cretaceous Ryazanian Stage of the Panboreal Biogeographic Superrealm|journal=Stratigraphy and Geological Correlation|year=2024|volume=32|issue=6|pages=672–706|doi=10.1134/S0869593824700187|bibcode=2024SGC....32..672R|s2cid=274076675|url=https://www.researchgate.net/publication/385411605}}</ref> Except ''P. rossicus'' and the dubious ''P. irgisensis'',<ref name="Knutsen2012"/> fossils of several contemporary marine reptiles have been discovered, including several species of ichthyosaurs in the region, notably the ophthalmosaurids ''Arthropterygius'', ''Grendelius'', ''Nannopterygius'' and ''Undorosaurus''.<ref name="Zverkovetal2015"/><ref name="Zverkov&Efimov2019">{{cite journal|first1=N. G.|last1=Zverkov|first2=V. M.|last2=Efimov|year=2019|title=Revision of ''Undorosaurus'', a mysterious Late Jurassic ichthyosaur of the Boreal Realm|journal=Journal of Systematic Palaeontology|volume=17|issue=14|pages=963–993|doi=10.1080/14772019.2018.1515793|bibcode=2019JSPal..17.1183Z |s2cid=91912834|url=https://figshare.com/articles/Revision_of_i_Undorosaurus_i_a_mysterious_Late_Jurassic_ichthyosaur_of_the_Boreal_Realm/7624868}}</ref><ref name="Zverkov&Jacobs2020"/> In addition, fossils belonging to a metriorhynchid thalattosuchian are also known from contemporary sediments in this region.<ref name="Rogovetal2024"/> In 2015, a single tooth discovered at the summit of {{ill|Mount Sheludivaya|ru|Шелудивая}} in Crimea was attributed to ''Pliosaurus'' by Zverkov on the basis of the typical trihedral shape of the genus. Dating to the late Valanginian of the Early Cretaceous, it represents the most recent known occurrence of the genus in the fossil record. Prior to this find, brachauchenines were the only pliosaurids thought to have persisted across the Jurassic–Cretaceous boundary.<ref name="Zverkov2015">{{cite conference|last=Zverkov|first=N. G.|title=On a typically Late Jurassic pliosaur from the Lower Cretaceous of Crimea|publisher=The International Scientific Conference on the Jurassic/Cretaceous boundary|year=2015|pages=89–94|url=https://www.researchgate.net/publication/281746764}}</ref><ref name="Zverkovetal">{{cite journal|first1=N. G.|last1=Zverkov|first2=V.|last2=Fischer|first3=D.|last3=Madzia|first4=R. B. J.|last4=Benson|year=2018|title=Increased pliosaurid dental disparity across the Jurassic-Cretaceous transition|journal=Palaeontology|volume=61|issue=6|pages=825–846|doi=10.1111/pala.12367|hdl=2268/221241|s2cid=134889277|hdl-access=free|doi-access=free |bibcode=2018Palgy..61..825Z }}</ref>

=== Svalbard === [[File:Keilhauia-1.png|thumb|upright=1.1|alt=|Geological map of central Svalbard, Norway. The Agardhfjellet Formation, from which ''P. funkei'' is known, is shown in dark blue]]

In Svalbard, ''P. funkei'' is known from Tithonian-aged rocks of the Slottsmøya Member of the Agardhfjellet Formation.<ref name="Knutsenetal2009"/><ref name="Knutsen2012"/><ref name="Knutsenetal2012"/><ref name="Druckenmiller&Knutsen2012"/> This unit consists of a mix of shales and siltstones and was deposited in a shallow water methane seep environment.<ref name="Hurumetal2012">{{cite journal|first1=J. H.|last1=Hurum|first2=H. A.|last2=Nakrem|first3=Ø.|last3=Hammer|first4=E. M.|last4=Knutsen|first5=P. S.|last5=Druckenmiller|first6=K.|last6=Hryniewicz|first7=L. K.|last7=Novis|title=An Arctic Lagerstätte – the Slottsmøya Member of the Agardhfjellet Formation (Upper Jurassic-Lower Cretaceous) of Spitsbergen|journal=Norwegian Journal of Geology|volume=92|pages=55–64|year=2012|issn=0029-196X|url=http://www.geologi.no/images/NJG_articles/NJG_2_3_2012_1_Hurum_Pr.pdf}}</ref> The seafloor, which was located about {{cvt|150|m}} below the surface, seems to have been relatively dysoxic, or oxygen-poor, although it was periodically oxygenated by clastic sediments.<ref name="Delsettetal2016">{{Citation|last1=Delsett|first1=L. L.|last2=Novis|first2=L. K.|last3=Roberts|first3=A. J.|last4=Koevoets|first4=M. J.|last5=Hammer|first5=Ø.|last6=Druckenmiller|first6=P. S.|last7=Hurum|first7=J. H.|year=2016|chapter=The Slottsmøya marine reptile ''Lagerstätte'': depositional environments, taphonomy and diagenesis|editor1-first=B. P.|editor1-last=Kear|editor2-first=J.|editor2-last=Lindgren|editor3-first=J. H.|editor3-last=Hurum|editor4-first=J.|editor4-last=Milán|editor5-first=V.|editor5-last=Vajda|title=Mesozoic Biotas of Scandinavia and its Arctic Territories|series=Special Publications|publisher=Geological Society|location=London|volume=434|pages=165–188|isbn=978-1-862-39748-4|doi=10.1144/SP434.2|doi-access=free|s2cid=130478320|hdl=10037/25235|hdl-access=free}}</ref> Despite this, near the top of the member, various diverse assemblages of invertebrates associated with cold seeps have been discovered; these include ammonites, lingulate brachiopods, bivalves, rhynchonellate brachiopods, tubeworms, belemnoids, tusk shells, sponges, crinoids, sea urchins, brittle stars, starfish, crustaceans and gastropods.<ref name="Hryniewiczetal2015">{{Cite journal|last1=Hryniewicz|first1=K.|last2=Nakrem|first2=H. A.|last3=Hammer|first3=Ø.|last4=Little|first4=C. T. S.|last5=Kaim|first5=A.|last6=Sandy|first6=M. R.|last7=Hurum|first7=J. H.|year=2015|title=The palaeoecology of the latest Jurassic–earliest Cretaceous hydrocarbon seep carbonates from Spitsbergen, Svalbard|journal=Lethaia|volume=48|issue=3|pages=353–374|doi=10.1111/let.12112|bibcode=2015Letha..48..353H|s2cid=140717795}}</ref> Though direct evidence from Slottsmøya is currently lacking, the high latitude of this site and relatively cool global climate of the Tithonian mean that sea ice was likely present at least in the winter.<ref name="Price1999">{{Cite journal|last=Price|first=G. D.|year=1999|title=The evidence and implications of polar ice during the Mesozoic|journal=Earth-Science Reviews|volume=48|issue=3|pages=183–210|doi=10.1016/S0012-8252(99)00048-3|bibcode=1999ESRv...48..183P|s2cid=129329306|url=https://doc.rero.ch/record/16181/files/PAL_E3386.pdf}}</ref><ref name="Gallowayetal2013">{{Cite journal|last1=Galloway|first1=J. M.|last2=Sweet|first2=A. R.|last3=Swindles|first3=G. T.|last4=Dewing|first4=K.|last5=Hadlari|first5=T.|last6=Embry|first6=A. F.|last7=Sanei|first7=H.|year=2013|title=Middle Jurassic to Lower Cretaceous paleoclimate of Sverdrup Basin, Canadian Arctic Archipelago inferred from the palynostratigraphy|journal=Marine and Petroleum Geology|volume=44|pages=240–255|doi=10.1016/j.marpetgeo.2013.01.001|bibcode=2013MarPG..44..240G|s2cid=128901561|url=https://www.academia.edu/10878733}}</ref> A considerable number of plesiosaurs and ichthyosaurs are known from the Slottsmøya Member. As a large apex predator, ''P. funkei'' may have included some of them in its diet.<ref name="Knutsenetal2012"/><ref name="Hurumetal2012"/><ref name="Delsettetal2016"/> Aside from ''P. funkei'' itself, the other plesiosaurs reported are ''Colymbosaurus'', ''Djupedalia'', ''Ophthalmothule'', and ''Spitrasaurus'', all of which belong to the family Cryptoclididae.<ref name="Delsettetal2016"/><ref name="Roberts2020">{{Cite journal|last1=Roberts|first1=A. J.|last2=Druckenmiller|first2=P. S.|last3=Cordonnier|first3=B.|last4=Delsett|first4=L. L.|last5=Hurum|first5=J. H.|year=2020|title=A new plesiosaurian from the Jurassic–Cretaceous transitional interval of the Slottsmøya Member (Volgian), with insights into the cranial anatomy of cryptoclidids using computed tomography|journal=PeerJ|volume=8|article-number=e8652|doi=10.7717/peerj.8652|pmid=32266112|pmc=7120097|doi-access=free}}</ref> The contemporary ichthyosaurs known from the Slottsmøya Member are ophthalmosaurids of the genera ''Arthropterygius'', ''Brachypterygius'', ''Undorosaurus'', and ''Nannopterygius''.<ref name="Angstetal2010">{{Cite journal|last1=Angst|first1=D.|last2=Buffetaut|first2=É.|last3=Tabouelle|first3=J.|last4=Tong|first4=H.|year=2010|title=An ichthyosaur skull from the Late Jurassic of Svalbard|journal=Bulletin de la Société géologique de France|volume=181|issue=5|pages=453–458|doi=10.2113/gssgfbull.181.5.453|s2cid=130286705|url=https://www.researchgate.net/publication/230777838}}</ref><ref name="Zverkov&Efimov2019"/><ref name="Delsettetal2019">{{Cite journal|last1=Delsett|first1=L. L.|last2=Roberts|first2=A. J.|last3=Druckenmiller|first3=P. S.|last4=Hurum|first4=J. H.|year=2019|title=Osteology and phylogeny of Late Jurassic ichthyosaurs from the Slottsmøya Member Lagerstätte (Spitsbergen, Svalbard)|journal=Acta Palaeontologica Polonica|volume=64|issue=4|pages=717–743|doi=10.4202/app.00571.2018|s2cid=210294877|doi-access=free}}</ref><ref name="Zverkov&Jacobs2020">{{Cite journal|last1=Zverkov|first1=N. G.|last2=Jacobs|first2=M. L.|year=2020|title=Revision of ''Nannopterygius'' (Ichthyosauria: Ophthalmosauridae): reappraisal of the 'inaccessible' holotype resolves a taxonomic tangle and reveals an obscure ophthalmosaurid lineage with a wide distribution|journal=Zoological Journal of the Linnean Society|volume=191|issue=1|pages=228–275|doi=10.1093/zoolinnean/zlaa028|s2cid=225881928|doi-access=free}}</ref> Many of the fossils of these marine reptiles are preserved in three dimensions and partially articulated, a condition correlated with the high abundance of organic material in the sediments in which they were buried, as well as the absence of local invertebrates.<ref name="Delsettetal2016"/>

==Notes== {{notelist}} ==References== {{Reflist}} {{Plesiosauria|Pliosauroidea}} {{Taxonbar|from=Q134771}}

Category:Pliosauridae Category:Kimmeridgian genus first appearances Category:Tithonian genus extinctions Category:Late Jurassic plesiosaurs of Europe Category:Jurassic England Category:Fossils of England Category:Jurassic Norway Category:Fossils of Svalbard Category:Agardhfjellet Formation Category:Jurassic Russia Category:Fossils of Russia Category:Fossil taxa described in 1841 Category:Taxa named by Richard Owen Category:Sauropterygian genera