Plesiosaur

Plesiosauria Temporal range: Ma[1] PreꞒ Ꞓ O S D C P T J K Pg N
Restored skeleton of Plesiosaurus
Skeletal mount of Peloneustes
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Superorder:	†Sauropterygia
Clade:	†Pistosauria
Order:	†Plesiosauria Blainville, 1835
Subgroups
†Anningasaura †Lindwurmia †Zahrisaurus †Termatosaurus? †Alexeyisaurus? †Neoplesiosauria †Plesiosauroidea †Pliosauroidea

The Plesiosauria (/ˌpliːsiəˈsɔːriə, -zi-/ PLEE-see-ə-SOR-ee-ə, -⁠zee-;^[2][3] Greek: πλησίος, plesios, meaning "near to" and sauros, meaning "lizard")^[4] or plesiosaurs are an order or clade of extinct Mesozoic marine reptiles, belonging to the Sauropterygia.

Plesiosaurs first appeared in the latest

Plesiosaurs were among the first fossil reptiles discovered. In the beginning of the nineteenth century, scientists realised how distinctive their build was and they were named as a separate order in 1835. The first plesiosaurian genus, the eponymous Plesiosaurus, was named in 1821. Since then, more than a hundred valid species have been described. In the early twenty-first century, the number of discoveries has increased, leading to an improved understanding of their anatomy, relationships and way of life.

Plesiosaurs had a broad flat body and a short tail. Their limbs had evolved into four long flippers, which were powered by strong muscles attached to wide bony plates formed by the shoulder girdle and the pelvis. The flippers made a flying movement through the water. Plesiosaurs breathed air, and bore live young; there are indications that they were warm-blooded.

Plesiosaurs showed two main morphological types. Some species, with the "plesiosauromorph" build, had (sometimes extremely) long necks and small heads; these were relatively slow and caught small sea animals. Other species, some of them reaching a length of up to seventeen metres, had the "pliosauromorph" build with a short neck and a large head; these were apex predators, fast hunters of large prey. The two types are related to the traditional strict division of the Plesiosauria into two suborders, the long-necked Plesiosauroidea and the short-neck Pliosauroidea. Modern research, however, indicates that several "long-necked" groups might have had some short-necked members or vice versa. Therefore, the purely descriptive terms "plesiosauromorph" and "pliosauromorph" have been introduced, which do not imply a direct relationship. "Plesiosauroidea" and "Pliosauroidea" today have a more limited meaning. The term "plesiosaur" is properly used to refer to the Plesiosauria as a whole, but informally it is sometimes meant to indicate only the long-necked forms, the old Plesiosauroidea.

History of discovery

Early finds

Skeletal elements of plesiosaurs are among the first fossils of extinct reptiles recognised as such.

During the eighteenth century, the number of English plesiosaur discoveries rapidly increased, although these were all of a more or less fragmentary nature. Important collectors were the reverends William Mounsey and Baptist Noel Turner, active in the Vale of Belvoir, whose collections were in 1795 described by John Nicholls in the first part of his The History and Antiquities of the County of Leicestershire.^[11] One of Turner's partial plesiosaur skeletons is still preserved as specimen BMNH R.45 in the British Museum of Natural History; this is today referred to Thalassiodracon.^[7]

Naming of Plesiosaurus

In the early nineteenth century, plesiosaurs were still poorly known and their special build was not understood. No systematic distinction was made with

Soon afterwards, the morphology became much better known. In 1823, Thomas Clark reported an almost complete skull, probably belonging to Thalassiodracon, which is now preserved by the British Geological Survey as specimen BGS GSM 26035.^[7] The same year, commercial fossil collector Mary Anning and her family uncovered an almost complete skeleton at Lyme Regis in Dorset, England, on what is today called the Jurassic Coast. It was acquired by the Duke of Buckingham, who made it available to the geologist William Buckland. He in turn let it be described by Conybeare on 24 February 1824 in a lecture to the Geological Society of London,^[15] during the same meeting in which for the first time a dinosaur was named, Megalosaurus. The two finds revealed the unique and bizarre build of the animals, in 1832 by Professor Buckland likened to "a sea serpent run through a turtle". In 1824, Conybeare also provided a specific name to Plesiosaurus: dolichodeirus, meaning "longneck". In 1848, the skeleton was bought by the British Museum of Natural History and catalogued as specimen BMNH 22656.^[7] When the lecture was published, Conybeare also named a second species: Plesiosaurus giganteus. This was a short-necked form later assigned to the Pliosauroidea.^[16]

Plesiosaurs became better known to the general public through two lavishly illustrated publications by the collector

During the first half of the nineteenth century, the number of plesiosaur finds steadily increased, especially through discoveries in the sea cliffs of Lyme Regis. Sir Richard Owen alone named nearly a hundred new species. The majority of their descriptions were, however, based on isolated bones, without sufficient diagnosis to be able to distinguish them from the other species that had previously been described. Many of the new species described at this time have subsequently been invalidated. The genus Plesiosaurus is particularly problematic, as the majority of the new species were placed in it so that it became a wastebasket taxon. Gradually, other genera were named. Hawkins had already created new genera, though these are no longer seen as valid. In 1841, Owen named Pliosaurus brachydeirus. Its etymology referred to the earlier Plesiosaurus dolichodeirus as it is derived from πλεῖος, pleios, "more fully", reflecting that according to Owen it was closer to the Sauria than Plesiosaurus. Its specific name means "with a short neck".^[21] Later, the Pliosauridae were recognised as having a morphology fundamentally different from the plesiosaurids. The family Plesiosauridae had already been coined by John Edward Gray in 1825.^[22] In 1835, Henri Marie Ducrotay de Blainville named the order Plesiosauria itself.^[23]

American discoveries

In the second half of the nineteenth century, important finds were made outside of England. While this included some German discoveries, it mainly involved plesiosaurs found in the sediments of the American Cretaceous

In 1867, physician Theophilus Turner near

Around the turn of the century, most plesiosaur research was done by a former student of Marsh, Professor Samuel Wendell Williston. In 1914, Williston published his Water reptiles of the past and present.^[33] Despite treating sea reptiles in general, it would for many years remain the most extensive general text on plesiosaurs.^[34] In 2013, a first modern textbook was being prepared by Olivier Rieppel. During the middle of the twentieth century, the USA remained an important centre of research, mainly through the discoveries of Samuel Paul Welles.

Recent discoveries

Whereas during the nineteenth and most of the twentieth century, new plesiosaurs were described at a rate of three or four novel genera each decade, the pace suddenly picked up in the 1990s, with seventeen plesiosaurs being discovered in this period. The tempo of discovery accelerated in the early twenty-first century, with about three or four plesiosaurs being named each year.^[35] This implies that about half of the known plesiosaurs are relatively new to science, a result of a far more intense field research. Some of this is taking place away from the traditional areas, e.g. in new sites developed in New Zealand, Argentina, Chile,^[36] Norway, Japan, China and Morocco, but the locations of the more original discoveries have proven to be still productive, with important new finds in England and Germany. Some of the new genera are a renaming of already known species, which were deemed sufficiently different to warrant a separate genus name.

In 2002, the "

In 2006, a combined team of American and Argentinian investigators (the latter from the Argentinian Antarctic Institute and the La Plata Museum) found the skeleton of a juvenile plesiosaur measuring 1.5 metres (4 ft 11 in) in length on Vega Island in Antarctica.^[43] The fossil is currently on display at the geological museum of South Dakota School of Mines and Technology.^[44]

In 2008, fossil remains of an undescribed plesiosaur that was named

In December 2017, a large skeleton of a plesiosaur was found in the continent of Antarctica, the oldest creature on the continent, and the first of its species in Antarctica.[47]

Not only has the number of field discoveries increased, but also, since the 1950s, plesiosaurs have been the subject of more extensive theoretical work. The methodology of cladistics has, for the first time, allowed the exact calculation of their evolutionary relationships. Several hypotheses have been published about the way they hunted and swam, incorporating general modern insights about biomechanics and ecology. The many recent discoveries have tested these hypotheses and given rise to new ones.^{[original research?]}

Evolution

The Plesiosauria have their origins within the

From the earliest

In the middle of the Jurassic, very large Pliosauridae evolved. These were characterized by a large head and a short neck, such as Liopleurodon and Simolestes. These forms had skulls up to three metres (ten feet) long and reached a length of up to seventeen metres (56 feet) and a weight of ten tonnes. The pliosaurids had large, conical teeth and were the dominant marine carnivores of their time. During the same time, approximately 160 million years ago, the Cryptoclididae were present, shorter species with a long neck and a small head.^[54]

The Leptocleididae radiated during the Early Cretaceous. These were rather small forms that, despite their short necks, might have been more closely related to the Plesiosauridae than to the Pliosauridae. Later in the Early Cretaceous, the Elasmosauridae appeared; these were among the longest plesiosaurs, reaching up to fifteen metres (fifty feet) in length due to very long necks containing as many as 76 vertebrae, more than any other known vertebrate. Pliosauridae were still present as is shown by large predators, such as Kronosaurus.^[54]

At the beginning of the Late Cretaceous, the Ichthyosauria became extinct; perhaps a plesiosaur group evolved to fill their niches: the Polycotylidae, which had short necks and peculiarly elongated heads with narrow snouts. During the Late Cretaceous, the elasmosaurids still had many species.^[54]

All plesiosaurs became

The following cladogram follows an analysis by Benson & Druckenmiller (2014).^[57]

Description

Size

While plesiosaurs varied little in the build of the trunk, and can be called "conservative" in this respect, there were major differences between the subgroups as regards the form of the neck and the skull. Plesiosaurs can be divided into two major morphological types that differ in head and

The tooth form and number was very variable. Some forms had hundreds of needle-like teeth. Most species had larger conical teeth with a round or oval cross-section. Such teeth numbered four to six in the premaxilla and about fourteen to twenty-five in the maxilla; the number in the lower jaws roughly equalled that of the skull. The teeth were placed in tooth-sockets, had vertically wrinkled enamel and lacked a true cutting edge or carina. With some species, the front teeth were notably longer, to grab prey.^[69]

Soft tissues

Soft tissue remains of plesiosaurs are rare, but sometimes, especially in

Food

The probable food source of plesiosaurs varied depending on whether they belonged to the long-necked "plesiosauromorph" forms or the short-necked "pliosauromorph" species.

The extremely long necks of "plesiosauromorphs" have caused speculation as to their function from the very moment their special build became apparent. Conybeare had offered three possible explanations. The neck could have served to intercept fast-moving fish in a pursuit. Alternatively, plesiosaurs could have rested on the sea bottom, while the head was sent out to search for prey, which seemed to be confirmed by the fact the eyes were directed relatively upwards. Finally, Conybeare suggested the possibility that plesiosaurs swam on the surface, letting their necks plunge downwards to seek food at lower levels. All these interpretations assumed that the neck was very flexible. The modern insight that the neck was, in fact, rather rigid, with limited vertical movement, has necessitated new explanations. One hypothesis is that the length of the neck made it possible to surprise schools of fish, the head arriving before the sight or pressure wave of the trunk could alert them. "Plesiosauromorphs" hunted visually, as shown by their large eyes, and perhaps employed a directional sense of olfaction. Hard and soft-bodied cephalopods probably formed part of their diet. Their

Plesiosaurs were themselves prey for other carnivores, as shown by bite marks left by a shark that have been discovered on a fossilized plesiosaur fin[84] and the fossilized remains of a mosasaur's stomach contents that are thought to be the remains of a plesiosaur.^[85]

Skeletons have also been discovered with

In Robinson's model, both the downstroke and the upstroke would have been powerful. In 1982, she was criticised by Samuel Tarsitano, Eberhard Frey and Jürgen Riess, who claimed that, while the muscles at the underside of the shoulder and pelvic plates were clearly powerful enough to pull the limbs downwards, comparable muscle groups on the top of these plates to elevate the limbs were simply lacking, and, had they been present, could not have been forcefully employed, their bulging carrying the danger of hurting the internal organs. They proposed a more limited flying model in which a powerful downstroke was combined with a largely unpowered recovery, the flipper returning to its original position by the momentum of the forward moving and temporarily sinking body.^[101][102] This modified flying model became a popular interpretation. Less attention was given to an alternative hypothesis by Stephen Godfrey in 1984, which proposed that both the forelimbs and hindlimbs performed a deep paddling motion to the rear combined with a powered recovery stroke to the front, resembling the movement made by the forelimbs of sea-lions.^[103]

In 2010,

Like all

The interpretation by Frey & Riess became the dominant one, but was challenged in 2004 by Sanders, who showed experimentally that, whereas an alternate movement might have caused excessive pitching, a simultaneous movement would have caused only a slight pitch, which could have been easily controlled by the hind flippers. Of the other axial movements, rolling could have been controlled by alternately engaging the flippers of the right or left side, and yaw by the long neck or a vertical tail fin. Sanders did not believe that the hind pair was not used for propulsion, concluding that the limitations imposed by the hip joint were very relative.^[107] In 2010, Sanders & Carpenter concluded that, with an alternating gait, the turbulence caused by the front pair would have hindered an effective action of the hind pair. Besides, a long gliding phase after a simultaneous engagement would have been very energy efficient.^[104] It is also possible that the gait was optional and was adapted to the circumstances. During a fast steady pursuit, an alternate movement would have been useful; in an ambush, a simultaneous stroke would have made a peak speed possible. When searching for prey over a longer distance, a combination of a simultaneous movement with gliding would have cost the least energy.^[108] In 2017, a study by Luke Muscutt, using a robot model, concluded that the rear flippers were actively employed, allowing for a 60% increase of the propulsive force and a 40% increase of efficiency. There would not have been a single optimal phase for all conditions, the gait likely having been changed as the situation demanded.^[109]

Speed

In general, it is hard to determine the maximum speed of extinct sea creatures. For plesiosaurs, this is made more difficult by the lack of consensus about their flipper stroke and gait. There are no exact calculations of their

Diving

Few data are available that show exactly how deep plesiosaurs dived. That they dived to some considerable depth is proven by traces of decompression sickness. The heads of the humeri and femora with many fossils show necrosis of the bone tissue, caused by a too rapid ascent after deep diving. However, this does not allow to deduce some exact depth as the damage could have been caused by a few very deep dives, or alternatively by a great number of relatively shallow descents. The vertebrae show no such damage: they were probably protected by a superior blood supply, made possible by the arteries entering the bone through the two foramina subcentralia, large openings in their undersides.^[114]

Descending would have been helped by a negative

Gastroliths have been suggested as a method to increase weight^[115] or even as means to attain neutral buoyancy, swallowing or spitting them out again as needed.^[116] They might also have been used to increase stability.^[117]

The relatively large eyes of the

Cryptocleididae have been seen as an adaptation to deep diving.^[118]

Tail role

A 2020 study has posited that sauropterygians relied on vertical tail strokes much like

cetaceans. In plesiosaurs the trunk was rigid so this action was more limited and in conjunction with the flippers.^[75]

Metabolism

Traditionally, it was assumed that extinct reptile groups were cold-blooded like modern reptiles. New research during the past decades has led to the conclusion that some groups, such as

parsimonious to assume that the more derived pistosaurians, the plesiosaurs, also had a faster metabolism. A paper published in 2018 claimed that plesiosaurs had resting metabolic rates (RMR) in the range of birds based on quantitative osteohistological modelling.^[121] However, these results are problematic in view of general principles of vertebrate physiology (see Kleiber's law); evidence from isotope studies of plesiosaur tooth enamel indeed suggests endothermy at lower RMRs, with inferred body temperatures of ca. 26 °C (79 °F).^[122]

Reproduction

As reptiles in general are

Richard Anthony Thulborn showed that Seeley had been deceived by a "doctored" fossil of a nest of crayfish.^[125]

An actual plesiosaur specimen found in 1987 eventually proved that plesiosaurs gave birth to live young:

K-strategy in reproduction.^[127] Little is known about growth rates or a possible sexual dimorphism

.

Social behaviour and intelligence

From the parental care indicated by the large size of the young, it can be deduced that social behaviour in general was relatively complex.[126] It is not known whether plesiosaurs hunted in packs. Their relative brain size seems to be typical for reptiles. Of the senses, sight and smell were important, hearing less so; elasmosaurids have lost the stapes completely. It has been suggested that with some groups the skull housed electro-sensitive organs.^[128][129]

Paleopathology

Some plesiosaur fossils show

pathologies, the result of illness or old age. In 2012, a mandible of Pliosaurus was described with a jaw joint clearly afflicted by arthritis, a typical sign of senescence.^[130]

Distribution

Plesiosaur fossils have been found on every continent, including Antarctica.^[131]

Timeline of Plesiosauria Species

Stratigraphic distribution

Main article: List of plesiosaur-bearing stratigraphic units

The following is a list of geologic formations that have produced plesiosaur fossils.

Name	Age	Location	Notes
Agardhfjellet Formation	Tithonian	Norway	Pliosaurus funkei, Spitrasaurus
Akrabou Formation	Turonian	Morocco	Manemergus, Thililua, Libonectes
Al'Hisa Phosphorite Formation	Campanian-Maastrichtian	Jordan	Plesiosaurus mauritanicus
Allen Formation	Campanian-Maastrichtian	Argentina
Al-Sawwanah al-Sharqiyah, Phosphate mine	Santonian-Campanian-Maastrichtian	Syria	Plesiosaurus[132]
Ampthill Clay Formation	Oxfordian	UK	Liopleurodon pachydeirus
Bearpaw Formation	Campanian	Canada  US	Dolichorhynchops herschelensis, Terminonatator
Blue Lias Formation	Rhaetian-Hettangian	UK	"Rhomaleosaurus" megacephalus, Stratesaurus, Thalassiodracon
Britton Formation	Coniacian	US	Libonectes
Bückeberg Formation	Berriasian	Germany	Gronausaurus
Bulldog Shale Formation	Aptian-Albian	Australia	Opallionectes, Umoonasaurus
Calcaire à Bélemnites	Pliensbachian	France	Cryonectes
Carlile Formation	Turonian	US	Megacephalosaurus
Charmouth Mudstone Formation	Sinemurian	UK	Archaeonectrus, Attenborosaurus
Chichali Formation		Pakistan
Clearwater Formation	Albian	Canada	Nichollssaura, Wapuskanectes
Conway Formation	Campanian-Maastrichtian	New Zealand	Mauisaurus, Alexandronectes
Coral Rag Formation	Oxfordian	UK	"Pliosaurus" grossouvrei
Exter Formation	Rhaetian	Germany	Rhaeticosaurus mertensi, perhaps a basal Pliosaur[133]
Favret Formation	Anisian	US	Augustasaurus
Fencepost limestone	Turonian	US	Trinacromerum
Franciscan Formation		US
Graneros Shale	Cenomanian	US	Thalassomedon
Greenhorn Limestone	Turonian	US	Brachauchenius, Pahasapasaurus
Guanling Formation	Anisian	China
Hiccles Cove Formation	Callovian	Canada	Borealonectes
Horseshoe Canyon Formation	Maastrichtian	Canada	Leurospondylus
Jagua Formation	Oxfordian	Cuba	Gallardosaurus, Vinialesaurus
Jagüel Formation	Maastrichtian	Argentina	Tuarangisaurus cabazai
Katiki Formation	Maastrichtian	New Zealand	Kaiwhekea
Kimmeridge Clay	Kimmeridgian	UK	Pliosaurus westburyensis
Kingsthorp	Toarcian	UK	Rhomaleosaurus thorntoni
Kiowa Shale	Albian	US	Apatomerus
La Colonia Formation	Campanian	Argentina	Sulcusuchus
Lake Waco Formation		US
Los Molles Formation	Bajocian	Argentina	Maresaurus
Maree Formation	Aptian	Australia
Leicestershire	late Sinemurian	UK	Eretmosaurus
Lücking clay pit	early Pliensbachian	Germany	Westphaliasaurus
Marnes feuilletés	Toarcian	France	Occitanosaurus
Mooreville Chalk Formation	Santonian - Campanian	US
Moreno Formation	Albian	US	Fresnosaurus, Hydrotherosaurus, Morenosaurus
Muschelkalk	Anisian	Germany	Pistosaurus
Naknek Formation	Kimmeridgian	US	Megalneusaurus
Niobrara Formation	Santonian	US	Styxosaurus snowii[135][136]
Oxford Clay	Callovian	UK  France	"Pliosaurus" andrewsi, Picrocleidus, Simolestes, Tricleidus
Oulad Abdoun Basin	late Maastrichtian	Morocco	Zarafasaura
Paja Formation	Aptian	Colombia	Kronosaurus boyacensis
Paso del Sapo Formation	Maastrichtian	Argentina	Aristonectes
Pierre Shale	Campanian	US	Hydralmosaurus
Posidonia Shale	Toarcian	Germany	Hauffiosaurus zanoni, Hydrorion, Meyerasaurus, Plesiopterys, Seeleyosaurus
Rio del Lago Formation	early Carnian	Italy	Bobosaurus
São Gião Formation	Toarcian	Portugal	Lusonectes
Smoky Hill Chalk	Campanian	US	Dolichorhynchops osborni
Sundance Formation	Oxfordian	US	Megalneusaurus, Pantosaurus, Tatenectes
Sundays River Formation	Valanginian	South Africa	Leptocleidus capensis
Tahora Formation	Campanian	New Zealand	Tuarangisaurus keyesi
Tamayama Formation	Santonian	Japan	Futabasaurus
Thermopolis Shale	Albian	US	Edgarosaurus
Toolebuc Formation	Albian	Australia	Kronosaurus queenslandicus
Tropic Shale Formation	Turonian	US	B. lucasi), Scalamagnus, Eopolycotylus, Palmulasaurus, Trinacromerum sp.
Vectis Formation	Aptian	UK	Vectocleidus
Wadhurst Clay Formation	Valanginian	UK	Hastanectes
Wallumbilla Formation	Aptian-Albian	Australia	Styxosaurus glendowerensis
Weald Clay	Barremian	UK	Leptocleidus superstes
Whitby Mudstone Formation	Toarcian	UK	Rhomaleosaurus zetlandicus, Sthenarosaurus
Wilczek Formation	Norian	Russia	Alexeyisaurus
Xintiangou Formation	Middle Jurassic	China	Yuzhoupliosaurus
Zhenzhuchong Formation		China
Ziliujing Formation	Toarcian	China	Bishanopliosaurus, Sinopliosaurus

In contemporary culture

Main article: Loch Ness Monster

See also: Sea monster

The belief that plesiosaurs are dinosaurs is a common misconception, and plesiosaurs are often erroneously depicted as dinosaurs in popular culture.^[137][138]

It has been suggested that

cryptozoological proposal has been rejected by the scientific community at large, which considers it to be based on fantasy and pseudoscience. Purported plesiosaur carcasses have been shown to be partially decomposed corpses of basking sharks instead.^{[139][140][141]}

While the

cold-blooded reptile to be able to survive easily, the fact that the osteology of the plesiosaur's neck makes it absolutely safe to say that the plesiosaur could not lift its head like a swan out of water as the Loch Ness monster does, the assumption that air-breathing animals would be easy to see whenever they appear at the surface to breathe,^[142] the fact that the loch is too small and contains insufficient food to be able to support a breeding colony of large animals, and finally the fact that the lake was formed only 10,000 years ago at the end of the last ice age, and the latest fossil appearance of plesiosaurs dates to over 66 million years ago.^[143] Frequent explanations for the sightings include waves, floating inanimate objects, tricks of the light, swimming known animals and practical jokes.^[144] Nevertheless, in the popular imagination, plesiosaurs have come to be identified with the Monster of Loch Ness. This has made plesiosaurs better known to the general public.^[145]

See also

• List of plesiosaur type specimens
• List of plesiosaurs

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Further reading

• Callaway, J. M.; Nicholls, E. L. (1997). "Sauropterygia". Ancient Marine Reptiles. Academic Press.
  ISBN 978-0-12-155210-7
  .
• Carpenter, K (1996). "A review of short-necked plesiosaurs from the Cretaceous of the western interior, North America" (PDF). Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen. 201 (2): 259–287.
  doi:10.1127/njgpa/201/1996/259
  .
• Carpenter, K. 1997. Comparative cranial anatomy of two North American Cretaceous plesiosaurs. Pp 91–216, in Calloway J. M. and E. L. Nicholls, (eds.), Ancient Marine Reptiles, Academic Press, San Diego.
• Carpenter, K (1999). "Revision of North American elasmosaurs from the Cretaceous of the western interior". Paludicola. 2 (2): 148–173.
• Cicimurri, D.; Everhart, M. (2001). "An Elasmosaur with Stomach Contents and Gastroliths from the Pierre Shale (Late Cretaceous) of Kansas". Trans. Kans. Acad. Sci. 104 (3 & 4): 129–143.
  S2CID 86037286
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• Cope, E. D. (1868). "Remarks on a new enaliosaurian, Elasmosaurus platyurus". Proceedings of the Academy of Natural Sciences of Philadelphia. 20: 92–93.
• Ellis, R. 2003: Sea Dragons (
  Kansas University Press
  )
• Everhart, M. J. (2002). "Where the elasmosaurs roamed". Prehistoric Times. 53: 24–27.
• Everhart, M.J. 2005. "Where the Elasmosaurs roamed," Chapter 7 in Oceans of Kansas: A Natural History of the Western Interior Sea, Indiana University Press, Bloomington, 322 p.
• Everhart, M.J. 2005. Oceans of Kansas: A Natural History of the Western Interior Sea. Indiana University Press, Bloomington, 322 pp.
• Everhart, M.J. (2005). "Gastroliths associated with plesiosaur remains in the Sharon Springs Member (Late Cretaceous) of the Pierre Shale, Western Kansas". Kansas Acad. Sci. Trans. 103 (1–2): 58–69.
• Everhart, Michael J (2006). "The Occurrence of Elasmosaurids (Reptilia: Plesiosauria) in the Niobrara Chalk of Western Kansas". Paludicila. 5 (4): 170–183.
• Hampe, O., 1992: Courier Forsch.-Inst. Senckenberg 145: 1-32
• Lingham-Soliar, T. (1995). "in". Phil. Trans. R. Soc. Lond. 347: 155–180.
• O'Keefe, F. R. (2001). "A cladistic analysis and taxonomic revision of the Plesiosauria (Reptilia: Sauropterygia);". Acta Zool. Fennica. 213: 1–63.
• ( ), 1997: in Reports of the National Center for Science Education, 17.3 (May/June 1997) pp 16–28.
• Kaddumi, H. F., 2009. Fossils of the Harrana Fauna and the adjacent areas. Publications of the Eternal River Museum of Natural History, Jordan. 324 pp.
• Storrs, G. W., 1999. An examination of Plesiosauria (Diapsida: Sauropterygia) from the Niobrara Chalk (Upper Cretaceous) of central North America, University of Kansas Paleontologcial Contributions, (N.S.), No. 11, 15 pp.
• Welles, S. P. 1943. Elasmosaurid plesiosaurs with a description of the new material from California and Colorado. University of California Memoirs 13:125-254. figs.1-37., pls.12-29.
• Welles, S. P. 1952. A review of the North American Cretaceous elasmosaurs. University of California Publications in Geological Science 29:46-144, figs. 1-25.
• Welles, S. P. 1962. A new species of elasmosaur from the Aptian of Columbia and a review of the Cretaceous plesiosaurs. University of California Publications in Geological Science 46, 96 pp.
• White, T., 1935: in Occasional Papers Boston Soc. Nat. Hist. 8: 219-228
• Williston, S. W. 1890. A new plesiosaur from the Niobrara Cretaceous of Kansas. Transactions of the Kansas Academy of Science 12:174-178, 2 fig.
• Williston, S. W. (1902). "Restoration of Dolichorhynchops osborni, a new Cretaceous plesiosaur". Kansas University Science Bulletin. 1 (9): 241–244, 1 plate.
• Williston, S. W. 1903. North American plesiosaurs. Field Columbian Museum, Publication 73, Geology Series 2(1): 1-79, 29 pl.
• Williston, S. W. (1906). "North American plesiosaurs: Elasmosaurus, Cimoliasaurus, and Polycotylus". American Journal of Science. 21 (123): 221–234, 4 pl.
  doi:10.2475/ajs.s4-21.123.221
  .
• Williston, S. W. (1908). "North American plesiosaurs: Trinacromerum". Journal of Geology. 16 (8): 715–735.
  doi:10.1086/621573
  .
• Bardet, Nathalie; Cappetta, Henri; Pereda Suberbiola, Xabier (2000). "The marine vertebrate faunas from the Late Cretaceous phosphates of Syria". Geological Magazine. 137 (3). Cambridge University: 269–290.
  S2CID 129600143
  .

External links

Wikimedia Commons has media related to Plesiosauria.

Wikiquote has quotations related to Plesiosauria.

• The Plesiosaur Site. Richard Forrest.
• The Plesiosaur Directory. Adam Stuart Smith.
  • Plesiosauria technical definition at the Plesiosaur Directory
• Plesiosaur FAQ's. Raymond Thaddeus C. Ancog.
• Oceans of Kansas Paleontology. Mike Everhart.
• "Plesiosaur fossil found in Bridgwater Bay". Somersert Museums County Service. (best known fossil)
• "Fossil hunters turn up 50-ton monster of prehistoric deep". Allan Hall and Mark Henderson. Times Online, December 30, 2002. (Monster of Aramberri)
• Triassic reptiles had live young.
• Bridgwater Bay juvenile plesiosaur
• Just How Good Is the Plesiosaur Fossil Record? Laelaps Blog.