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Plesiosaur
Fossil range: 190–65 Ma
Early Jurassic - Late Cretaceous
Reconstructed skeleton of Futabasaurus, an elasmosaur
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Superorder: Sauropterygia
Order: Plesiosauria
Suborder: Plesiosauroidea
Gray, 1825
Families

Cimoliasauridae
Cryptoclididae
Elasmosauridae
Plesiosauridae
Polycotylidae

A plesiosaur (pronounced /ˈpliːsiəˌsɔər/; Greek: plēsios/πλησιος 'near' or 'close to' and sauros/σαυρος 'lizard') was a type of carnivorous aquatic (mostly marine) reptile. After their discovery, plesiosaurs were somewhat fancifully said to have resembled "a snake threaded through the shell of a turtle",[1] although they had no shell. The common name "plesiosaur" is applied both to the "true" plesiosaurs (Superfamily Plesiosauroidea), which include both long-necked (elasmosaurs) and short-necked (polycotylid) forms, and to the larger taxonomic rank of Plesiosauria, which includes the pliosaurs.[2] The pliosaurs were the short-necked, large-headed plesiosaurians that were the apex predators for much of the Mesozoic. There were many species of plesiosaurs, while most of them were not as large as Elasmosaurus.

Plesiosaurs (sensu Plesiosauroidea) appeared at the start of the Jurassic Period and thrived until the K-T extinction, at the end of the Cretaceous Period. While they were Mesozoic diapsid reptiles that lived at the same time as dinosaurs, they were neither dinosaurs nor archosaurs.

Contents

History of discovery

Cast of Plesiosaurus macrocephalus found by Mary Anning, Muséum national d'histoire naturelle, Paris

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 (England) by someone fishing from the shore. This specimen, called the Collard specimen after its finder, was on display in Taunton Museum in 2007. Another, less complete skeleton was also found in 2002, in the cliffs at Filey, Yorkshire, England, by an amateur palaeontologist. The preserved skeleton is displayed at Rotunda Museum in Scarborough.

Well preserved Nichollssaura at the Royal Tyrrell Museum

Many museums have 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.

Specimens are on display in 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. A specimen was put on display in Lincoln Museum (now The Collection) in 2005. Peterborough Museum holds an excellent collection of plesiosaur material from the Oxford Clay brick pits in the area. The most complete known specimen of the long-necked plesiosaur Cryptoclidus, excavated in the 1980s can be seen there.

Description

Dolichorhynchops, a short-necked, long-jawed plesiosaur, National Museum of Natural History, Washington D.C.

Plesiosaurs had a broad body and a short tail. They retained their ancestral two pairs of limbs, which evolved into large flippers. 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, unspecialized 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. Size of different plesiosaurs varied significantly, with an estimated length of Trinacromerum being three meters and Mauisaurus growing to twenty meters.

Behavior

Restoration of a Plesiosaurus dolichodeirus pair, one catching a fish.

Unlike their pliosaurian cousins, plesiosaurs (with the exception of the Polycotylidae) were probably slow swimmers {Massare, 1988}. 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 four-flippered swimming adaptation may have given them exceptional maneuverability, so that they could swiftly rotate their bodies as an aid to catching 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 {Everhart, 2005; Henderson, 2006}. Even if they had been able to bend their necks upward to that degree (which they could not), gravity would have tipped their body forward and kept most of the heavy neck in the water.

Taxonomy

The classification of plesiosaurs has varied; the following represents one version (see O'Keefe 2001)

See also

Literature

  • 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. J. and Everhart, M. J. 2001. An elasmosaur with stomach contents and gastroliths form the Pierre Shale (Late Cretaceous) of Kansas. Kansas Academy of Science, Transactions 104(3-4): 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)
  • Everhart, M.J. 2005. Probable plesiosaur gastroliths from the basal Kiowa Shale (Early Cretaceous) of Kiowa County, Kansas. Kansas Academy of Science, Transactions 108 (3/4): 109-115.
  • Everhart, M. J. 2005. Elasmosaurid remains from the Pierre Shale (Upper Cretaceous) of western Kansas. Possible missing elements of the type specimen of Elasmosaurus platyurus Cope 1868? PalArch 4(3): 19-32.
  • Everhart, M. J. 2006. The occurrence of elasmosaurids (Reptilia: Plesiosauria) in the Niobrara Chalk of Western Kansas. Paludicola 5(4):170-183.
  • Everhart, M. J. 2007. Use of archival photographs to rediscover the locality of the Holyrood elasmosaur (Ellsworth County, Kansas). Kansas Academy of Science, Transactions 110(1/2): 135-143.
  • Everhart, M. J. 2007. Sea Monsters: Prehistoric Creatures of the Deep. National Geographic, 192 p. ISBN 978-1426200854.
  • 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.
  • Henderson, D. M. 2006. Floating point: a computational study of buoyancy, equilibrium, and gastroliths in plesiosaurs; Lethaia; 39 pp. 227–244.
  • Massare, J. A. 1988. Swimming capabilities of Mesozoic marine reptiles: Implications for method of predation. Paleobiology 14(2): 187-205.
  • Massare, J. A. 1994. Swimming capabilities of Mesozoic marine reptiles: a review. pp. 133–149 In Maddock, L., Bone, Q., and Rayner, J. M. V. (eds.), Mechanics and Physiology of Animal Swimming, Cambridge University Press.
  • Smith, A. S. 2008. Fossils explained 54: plesiosaurs. Geology Today. 24, (2), 71-75 PDF on Plesiosauria.com
  • Storrs, G. W., 1999. An examination of Plesiosauria (Diapsida: Sauropterygia) from the Niobrara Chalk (Upper Cretaceous) of central North America, University of Kansas Paleontological 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.

References

External links

Notes

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Simple English

Plesiosaur
Fossil range: Upper Triassic to Upper Cretaceous
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Superorder: Sauropterygia
Order: Plesiosauria
Families

Pliosauridae
Plesiosauridae
Cryptoclididae
Elasmosauridae

Plesiosaurs were large, meat-eating marine reptiles, first discovered by Mary Anning. She discovered a plesiosaur on the 'Jurassic Coast' of Lyme Regis, England in the winter of 1820-21. The fossil was missing its skull, but in 1823 she found another one, this time complete with its skull. The name Plesiosaurus was given by the Rev. William Conybeare.

The earliest plesiosaur remains are from the Upper Triassic period,[1]p128 and the group was important through the Jurassic and Cretaceous. They had two large pairs of paddles, short tails, short or long necks, and broad bodies. They died out at the K/T extinction event, 65 million years ago.[2]

Contents

Description

Plesiosaurs had many bones in their flippers, making them flexible. No modern animal has this four-paddle anatomy.[3] They were mainly piscivorous (fish-eaters).

Pliosaurs

The pliosaurs were a group of mostly large submarine predators with short necks and large heads. Their sizes ranged from two to 15 metres, and they were predators of large fish and other reptiles. Their streamlined body shape suggests they swam and ate under water.

Long-necked plesiosaurs

File:Rhomaleosaurus & Mary Anning plaque
One of Mary Anning's finds: Rhomaleosaurus in the Natural History Museum, London.

There were three families of long-necked plesiosaurs,[4] who evidently had a different life-style from the pliosaurs. It was suggested by D.M.S. Watson that their method was as surface swimmers, mostly eating with their head above water, darting down to snatch smaller fish which were feeding on plankton.[5][6][7] It is hard to see the benefit of a long neck under water; aquatic mammals operating under water all have a streamlined torpedo-shape, as did pliosaurs and ichthyosaurs. All the longer-necked familiers were, from the setting of the teeth and jaws, eaters of small fish. However, some at least were bottom-feeders, consuming various prey. Digestion of shellfish was aided by gastroliths.

  • Plesiosaurids: neck not so long as the other two families, and not so flexible: a more general all-round plesiosaur. Head of medium size, neck fairly thick and strong, up to 30 vertebrae.
  • Cryptoclidids: longer necks, with more than 30 vertebrae.
  • Elasmosaurids: very long necks; some later forms have as many as 76 cervical (neck) vertebrae and quite small skulls.[8]p30 Watson and Alexander's ideas apply especially to this group.

Gastroliths

[[File:|thumb|Plesiosaur gastroliths]] Plesiosaurs have been found with fossils of belemnites (squid-like animals), and ammonites (giant nautilus-like molluscs) associated with their stomachs. But plesiosaurs could not crack shells. Instead, they probably swallowed them whole. In the belly of a plesiosaur were "stomach stones", which are called gastroliths. These stones moved around in the plesiosaur's stomach and cracked or crushed the shells of the animals it ate. One plesiosaur fossil found in South Dakota had 253 gatroliths weighing a total of 29 pounds.[10]

Live birth?

Live birth has been proved for ichthyosaurs, but is uncertain for plesiosaurs.

References

Look up Plesiosauria in Wikispecies, a directory of species
  1. Benton M.J. 1990. The reign of the reptiles. Quarto N.Y.
  2. Carroll R.L. 1988. Vertebrate paleontology and evolution. Freeman N.Y.
  3. Modern turtles use their forelimbs for swimming.
  4. Other classifications are possible: O'Keefe F.R. 2001. A cladistic analysis and taxonomic revision of the Plesiosauria (Reptilia: Sauropterygia); Acta Zool. Fennica 213: 1-63.
  5. Watson D.M.S. 1951. Palaeontology and modern biology. Yale, CT.
  6. Watson D.M.S. 1958. Studies on fossil vertebrates. London.
  7. Alexander, R. McNeill 1989. Dynamics of dinosaurs and other extinct giants. Columbia N.Y. p137
  8. Benton M.J. 2004. Vertebrate palaeontology. 3rd ed, Blackwell, Oxford.
  9. Hiller N. Mannering A.A. Jones C.M. Cruickshank A.R.I. 2005. The nature of Mauisaurus haasti Hector, 1874 (Reptilia: Plesiosauria). Journal of Vertebrate Paleontology 25:588-601.
  10. 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


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