Plesiosaur

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Plesiosaur
Conservation status: Fossil
Plesiosaur-illustration.png
Plesiosaur illustration
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Superorder: Sauropterygia
Order: Plesiosauria}}
de Blainville, 1835
Suborders

Plesiosauroidea
Pliosauroidea


Plesiosaurs (Greek: plesios meaning 'near' or 'close to' and sauros meaning 'lizard') were carnivorous, aquatic (mostly marine) reptiles that lived from the Triassic to the Cretaceous periods.

The common name "plesiosaur" is generally applied both to the "true" plesiosaurs, belonging to the Suborder Plesiosauroidea, and to the larger taxonomic rank, the Order Plesiosauria. Plesiosauria includes both long-necked and short-necked forms. Short-necked, elongated-headed plesiosaurs (for the large part) belong to the second suborder of Plesiosauria, the Suborder Pliosauroidea, and are more properly called pliosaurs.

True plesiosaurs" (sensu Plesiosauroidea) first appeared at the very start of the Jurassic period, while the Order Plesiosauria appeared earlier, in the Middle Triassic. Plesiosaurs (including pliosaurs) thrived until the K-T extinction, at the end of the Cretaceous period. Plesiosaurs were Mesozoic reptiles that lived at the same time as dinosaurs, but they were not dinosaurs.

There were many species of plesiosaurs and not all of them were as large as Liopleurodon, Kronosaurus, or Elasmosaurus.

Mesozoic era (251 - 65 mya)
Triassic Jurassic Cretaceous

Description of the Order Plesiosauria

The first plesiosaur fossil, discovered by Mary Anning, 1821

After the discovery of plesiosaur fossils, they were somewhat fancifully said to have resembled "a snake threaded through the shell of a turtle".


The typical plesiosaur had a broad body and a short tail. They retained their ancestral two pairs of limbs, which evolved into large flippers. Plesiosaurs evolved from the earlier nothosaurs, who had a more crocodile-like body; major types of plesiosaur are primarily distinguished by head and neck size. The Plesiosauroidea such as Cryptoclididae, Elasmosauridae and Plesiosauridae had long necks and may have been 'bottom-feeders', in shallow waters. The Pliosauridae (Pliosaurs), however, had a short neck with large, elongated head and may have been at home in deeper waters.

All plesiosaurs had four paddle-shaped 'flipper' limbs. This is an unusual arrangement in aquatic animals and it is thought that they were used to propel the animal through the water by a combination of rowing movements and up-and-down movements. There appears to have been no tail fin and the tail was most likely used for helping in directional control. This arrangement is in contrast to that of the later mosasaurs and the earlier ichthyosaurs. There may be similarities with the method of swimming used by penguins and turtles, which respectively have two and four flipper-like limbs.

As a group, the plesiosaurs were the largest aquatic animals of their time, and even the smallest were about 2 m (6.5 ft) long. They grew to be considerably larger than the largest giant crocodiles, and were bigger than their successors, the mosasaurs. However, their predecessors as rulers of the sea, the dolphin-like ichthyosaurs, are known to have reached 23 m in length, and the modern whale shark (18 m), sperm whale (20 m), and especially the blue whale (30 m) are known from considerably larger specimens.

The anteriorly placed internal nostrils have palatal grooves to channel water, the flow of which would be maintained by hydrodynamic pressure over the posteriorly placed external nares during locomotion. During its passage through the nasal ducts, the water would have been 'tasted' by olfactory epithelia.


Description of "true plesiosaurs

combine with above

Plesiosaurs evolved from earlier, similar forms such as pistosaurs or very early, longer-necked pliosaurs. There are a number of families of plesiosaurs, which retain the same general appearance and are distinguished by various specific details. These include the Plesiosauridae, unspecialised types which are limited to the Early Jurassic period; Cryptoclididae, (e.g. Cryptoclidus), with a medium-long neck and somewhat stocky build; Elasmosauridae, with very long, inflexible necks and tiny heads; and the Cimoliasauridae, a poorly known group of small Cretaceous forms. According to traditional classifications, all plesiosaurs have a small head and long neck but, in recent classifications, one short-necked and large-headed Cretaceous group, the Polycotylidae, are included under the Plesiosauroidea, rather than under the traditional Pliosauroidea.

Behaviour of the order

Plesiosaurs have been discovered with fossils of belemnites (squid-like animals), and ammonites (giant nautilus-like molluscs) associated with their stomachs. They had powerful jaws, probably strong enough to bite through the hard shells of their prey. The bony fish (Osteichthyes), started to spread in the Jurassic, and were likely prey as well. Recent evidence seems to indicate that some plesiosaurs may have, in fact, been bottom feeders.[1]

It had been theorized that smaller plesiosaurs may have crawled up on a beach to lay their eggs, like the modern leatherback turtle, but it is now clear plesiosaurs gave birth to live young.

Another curiosity is their four-flippered design. No modern animals have this swimming adaptation, so there is considerable speculation about what kind of stroke they used. While the short-necked pliosaurs (e.g. Liopleurodon) may have been fast swimmers, the long-necked varieties were built more for maneuverability than for speed. Skeletons have also been discovered with gastroliths in their stomachs, though whether to help break down food in a muscular gizzard, or to help with buoyancy has not been established (Everhart).

Behaviour of the suborder: combine with above

Plesiosaur paddle in the Charmouth Heritage Coast Centre.

Unlike their Pliosaurian cousins, Plesiosaurs (with the exception of the Polycotylidae) were probably relatively slow swimmers. It is likely that they cruised slowly below the surface of the water, using their long flexible neck to move their head into position to snap up unwary fish or cephalopods. Their unique, four-flippered swimming adaptation may have given them exceptional maneuverability, so that they could swiftly rotate their bodies as an aid to catching their prey.

Contrary to many reconstructions of plesiosaurs, it would have been impossible for them to lift their head and long neck above the surface, in the 'swan-like' pose that is often shown. Even if they had been able to bend their necks upward, to that degree (they could not), gravity would have tipped their body forward and kept most of the heavy neck in the water.


Taxonomy

The classification of the Plesiosauria has varied over time; the following represents one current version (mostly following O'Keefe 2001)

  • Superorder SAUROPTERYGIA
    • Order PLESIOSAURIA
      • Suborder Pliosauroidea (pliosaurs)
        • Thalassiodracon
        • Attenborosaurus
        • Eurycleidus
        • Family Rhomaleosauridae
        • Family Pliosauridae
      • Suborder Plesiosauroidea (true plesiosaurs)
        • Family Plesiosauridae
        • (Unranked) Euplesiosauria
          • Family Elasmosauridae
          • Superfamily Cryptoclidoidea
            • Family Cryptoclididae
            • (Unranked) Tricleidia
              • Tricleidus
              • Family Cimoliasauridae
              • Family Polycotylidae (= "Dolichorhynchopidae")

Discovery

The first plesiosaur skeletons were found in England by Mary Anning, in the early 1800s, and were amongst the first fossil vertebrates to be described by science. Many have been found, some of them virtually complete, and new discoveries are made frequently. One of the finest specimens was found in 2002 on the coast of Somerset (UK) by someone fishing from the shore. This specimen, called the Collard specimen after its finder, will be on display in Taunton museum in 2007. Another, less complete skeleton was found in 2002, in the cliffs at Filey, Yorkshire, England, by an amateur palaeontologist. The preserved skeleton will be displayed at Scarborough's new Rotunda Museum, from 2007.

Many museums all over the world contain plesiosaur specimens. Notable among them is the collection of plesiosaurs in the Natural History Museum, London, which are on display in the marine reptiles gallery. Several historically important specimens can be found there, including the partial skeleton from Nottinghamshire reported by Stukely in 1719 which is the earliest written record of any marine reptile. Others specimens include those purchased from Thomas Hawkins in the early 19th century.

Historic specimens such as these are on display in several museums in the UK, including New Walk Museum, Leicester, The Yorkshire Museum, The Sedgwick Museum in Cambridge, Manchester Museum, Warwick Museum, Bristol Museum and the Dorset Museum. An historic specimen which has recently been prepared as part of a scientific study was put on display in Lincoln Museum in 2005. Peterborough Museum holds an excellent collection of plesiosaur material from the Oxford Clay brick pits in the surrounding area, most of which has been collected relatively recently. The most complete knows specimen of the long-necked plesiosaur Cryptoclidus, excavated in the 1980's can be seen there.

In Europe, notable specimens can be found in the following collections: The National Museum of Wales, Cardiff The Hunterian Collection, Glasgow Stuttgart Naturaliensammlung, Stuttgart Hauff Museum, Holzmaden, Baden-Wuerttemberg Humbolt Museum, Berlin Teylers Museum, Haarlem, The Netherlands

The National Museums of Ireland in Dublin holds several important historic specimens, including the holotype of Rhomaleosaurus cramptoni, an impressive specimen seven meters long which is currently being prepared for scientific study and display.

North America is home to several extensive collections of plesiosaur material. Signifiant displays are found in the following collections: Royal Saskatchewan Museum Manitoba Museum of Man and Nature Courtney District Museum, BC Yale Peabody Museum of Natural History The Academy of Natural Sciences, Philadelphia American Museum of Natural History, New York Museum of Comparitive Zoology, Harvard National Museum of Natural History, Washington DC Sternberg Museum of Natural History Field Museum of Natural History, Chicago Dallas Museum of Natural History Museum of Texas Tech University Museum of Paleontology, University of California at Berkeley

In Australia: Western Australian Museum Queensland Museum South Australian Museum Northern Territory Museum of Arts and Sciences, Darwin, Australian Museum, Sydney

New Zealand: Auckland Museum Canterbury Museum, New Zealand

It is occasionally claimed that plesiosaurs are not extinct, although the evidence for this belief is generally not accepted in the scientific world. The modern 'sightings' that are occasionally reported are usually explained either as basking shark carcasses or as hoaxes.


In fiction

The plesiosaur is popular among children and cryptozoologists, appearing in a number of children's books and several films. It fought an icthyosaur in Jules Verne's novel Journey to the Center of the Earth. In the bizarre 1899 short story "The Monster of Lake LaMetrie", a man's brain was put into the body of a plesiosaur.

It has appeared in films about lake monsters, including Magic in the Water (1995), and movies about the Loch Ness Monster, such as Loch Ness (1996). In both films, the creature primarily serves as a symbol of a lost, child-like sense of wonder. The plesiosaur is also present in the Japanese Jaws-inspired movie Legend of the Dinosaurs (1983). There are also unsubstantiated rumors across the Internet that a plesiosaur may be featured in the upcoming film Jurassic Park IV.

Contrary to reports, the long-necked, sharp-toothed creature in the classic film King Kong (1933), which flips a raft full of rescuers on their way to save Fay Wray and then munches on the swimmers, is not a plesiosaur. Despite striking a profile in the mist very similar to the famous 'Surgeon's Photo' of the Loch Ness Monster, it then chases the routed heroes onto dry land, where it is clearly intended to be a sauropod, like the Brontosaurus (now Apatosaurus). However, Kong later battles a serpent-like creature in a cave, which possesses four flippers and resembles a plesiosaur but acts more like some kind of giant snake.

In Steve Alten's novel The Trench, a climatic scene at the end has a Megalodon fighting with several deep sea reptiles, similar to Pliosaurs, identified as Kronosaurs.

Alleged living plesiosaurs

File:Lochnessmonster.jpg
The "Surgeon's Photo" of the Loch Ness Monster. In November 1993, Christian Spurling confessed on his deathbed that he made it from a toy submarine and putty.

Lake or sea monster sightings are occasionally explained as plesiosaurs. While the survival of a small, unrecorded breeding colony of plesiosaurs for the 65,000,000 years since their apparent extinction is unlikely, the discovery of real and even more ancient living fossils such as the Coelacanth and of previously unknown but enormous deep-sea animals such as the giant squid, have fuelled imaginations.

The 1977 discovery of a carcass with flippers and what appeared to be a long neck and head, by the Japanese fishing trawler Zuiyo Maru, off New Zealand, created a plesiosaur craze in Japan. Members of a blue-ribbon panel of eminent marine scientists in Japan reviewed the discovery. Professor Yoshinori Imaizumi, of the Japanese National Science Museum, said, "It's not a fish, whale, or any other mammal." However, the general consensus amongst scientists today is that it was a decayed basking shark.[2]

The Loch Ness Monster is reported to resemble a plesiosaur. Arguments against the plesiosaur theory include the fact that the lake is too cold for a cold-blooded animal to survive easily, that air-breathing animals like plesiosaurs would be easily spotted when they surface to breathe, that the lake is too small to support a breeding colony and that the loch itself formed only 10,000 years ago during the last ice age.

However, these arguments have all been opposed by Robert Rines, who said that "animals can adapt" and that "some reptiles can stay in water for a long time". "Many sightings tell of "horns" or "ears", which may be nostrils. If it(the monster) breathes regularly, it could breathe without being noticed".

While no definitive claims have been made about the biology of the plesiosaurs, most scientific evidence points to the fact that dinosuars (which were contemporaries and distant relatives of plesiosaurs) were warm-blooded [3]. This should not be an indication of the thermophysiology of the plesiosaurs, however — modern reptiles, which are also "distant relatives" of dinosaurs, are most assuredly cold-blooded.

There are some theories of how plesiosaurs may have surfaced to breathe but supporters of the notion of surviving plesiosaurs say that plesiosaurs may have lifted only their nostrils above the surface to breathe. Some artist's impressions of plesiosaurs support this.

The National Museums of Scotland confirmed that vertebrae discovered on the shores of Loch Ness, in 2003, belong to a plesiosaur, although there are some questions about whether the fossils were planted (BBC News, July 16, 2003).

It was reported in The Star (Malaysia) on April 8th, 2006, that fishermen discovered bones resembling that of a Plesiosaur near Sabah, Malaysia. The creature was speculated to have died only a month before. A team of researchers from Universiti Malaysia Sabah investigated the specimen but the bones were later determined to be those of a whale.

On November 2nd, 2006, Leslie Noè of the Sedgwick Museum in Cambridge, UK, announced research which casts further doubt on a plesiosaur inhabiting Loch Ness. While many sightings of the monster include reports of it lifting its head out of the water, including the Spurling photo, Noè's study of fossilized vertebrae of a Muraenosaurus concluded this articulation would not be possible. Instead, he found that the neck evolved to point downwards allowing the plesiosaur to feed on soft-shelled animals living on the sea floor. [4]

Trivia

  • The Transformers character Magmatron turns into a Plesiosaur.
  • Plesiosaurus is one of the prehistoric creatures mentioned in Jules Verne's "Journey to the Center of the Earth", in which it fights an Ichthyosaur in the Central Sea. See also this webpage regarding the early descriptions of plesiosaurs in science and literature.
  • The first elasmosaur was found in Kansas

External links

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References
ISBN links support NWE through referral fees

  • Carpenter, K. 1996. A review of short-necked plesiosaurs from the Cretaceous of the western interior, North America. Neues Jahrbuch fuer Geologie und Palaeontologie Abhandlungen (Stuttgart) 201(2):259-287.
  • 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., and M. Everhart, 2001: in Trans. Kansas. Acad. Sci. 104: 129-143
  • 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., 2000. Gastroliths associated with plesiosaur remains in the Sharon Springs Member of the Pierre Shale (Late Cretaceous), western Kansas. Kansas Acad. Sci. Trans. 103(1-2):58-69.
  • Everhart, M. J. 2002. Where the elasmosaurs roam… Prehistoric Times 53: 24-27.
  • Everhart, M. J. 2004. Plesiosaurs as the food of mosasaurs; new data on the stomach contents of a Tylosaurus proriger (Squamata; Mosasauridae) from the Niobrara Formation of western Kansas. The Mosasaur 7:41-46.
  • Everhart, M. J. 2005. Bite marks on an elasmosaur (Sauropterygia; Plesiosauria) paddle from the Niobrara Chalk (Upper Cretaceous) as probable evidence of feeding by the lamniform shark, Cretoxyrhina mantelli. PalArch, Vertebrate paleontology 2(2): 14-24.
  • 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. "Gastroliths associated with plesiosaur remains in the Sharon Springs Member (Late Cretaceous) of the Pierre Shale, Western Kansas" (on-line, updated from article in Kansas Acad. Sci. Trans. 103(1-2):58-69)
  • Hampe, O., 1992: Courier Forsch.-Inst. Senckenberg 145: 1-32
  • Lingham-Soliar, T., 1995: in Phil. Trans. Roy. 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
  • 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. Kansas Academy of Science, Transactions 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, Series 4, 21(123): 221-234, 4 pl.
  • Williston, S. W. 1908. North American plesiosaurs: Trinacromerum. Journal of Geology 16: 715-735.
  • ( ), 1997: in Reports of the National Center for Science Education, 17.3 (May/June 1997) pp 16–28.

See also Mike Everhart's "Marine Reptile References" and scans of "Early papers on North American plesiosaurs" on the Oceans of Kansas Paleontology website.

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