plesiosaur

Plesiosaur Fossil range: 190–65 Ma PreЄ Є O S D C P T J K Pg N Early Jurassic - Late Cretaceous
Plesiosaurus
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 reptiles that lived at the same time as dinosaurs, they were not dinosaurs.

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 Scarborough Rotunda 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.

Thalassiodracon hawkinsi cast in Bristol City Museum, Bristol, England. Found in the Lower Lias strata, Street, Somerset, England.

Description

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, 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. Size of different plesiosaurs varied significantly, with an estimated length of Trinacromerum being 3 meters and Mauisaurus growing to 20 meters.

Behaviour

Plesiosaur paddle in the Charmouth Heritage Coast Centre.

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)

Attenborosaurus

Cryptocleidus

Muraenosaurus

Dolichorhynchops

Thililua

Thalassomedon

Libonectes

Styxosaurus

• Superorder SAUROPTERYGIA
  • Order PLESIOSAURIA
    • Suborder Pliosauroidea
    • Suborder Plesiosauroidea (Gray, 1825) Welles, 1943 sensu O'Keefe, 2001
      • Plesiopterys O'Keefe, 2004
      • Family Plesiosauridae Gray, 1825 sensu O'Keefe, 2001
        • Attenborosaurus Bakker, 1993
        • Plesiosaurus De la Beche & Conybeare, 1821
      • (Unranked) Euplesiosauria O'Keefe, 2001
        •  ? Sthenarosaurus Watson, 1911 (nomen dubium)
        •  ? Eretmosaurus Seeley, 1874
        •  ? Leurospondylus Brown, 1913
        •  ? Nichollssaura Druckenmiller & Russell, 2008
        • Superfamily Cryptoclidoidea Williston, 1925 sensu O'Keefe, 2001
          • Family Cryptoclididae Williston, 1925 sensu O'Keefe, 2001
            •  ? Tatenectes O’Keefe & Wahl, 2003
            •  ? Colymbosaurus Seeley, 1874
            • Cryptocleidus Seeley, 1892
            • Muraenosaurus Seeley, 1874
            • Pantosaurus Marsh, 1891
            • Vinialesaurus Gasparini, Bardet & Iturralde-Vinent, 2002
          • (Unranked) Tricleidia O'Keefe, 2001
            • Family Tricledidae Nova
              • Tricleidus Andrews, 1909
            • Family Cimoliasauridae Delair, 1959 sensu O'Keefe, 2001
              •  ? Aristonectes Cabrea, 1941
              • Kaiwhekea Cruickshank & Fordyce, 2002
              • Kimmerosaurus Brown, 1981
              • Cimoliasaurus Leidy, 1851 (nomen dubium)
            • Family Polycotylidae Williston, 1909 sensu O'Keefe, 2001
              • Dolichorhynchops Willison, 1903
              •  ? Edgarosaurus Druckenmiller, 2002
              •  ? Georgiasaurus Otschev, 1978
              • Manemergus Buchy, Metayer, & Frey, 2005
              • Polycotylus Cope, 1869
              • Sulcusuchus Gasparini & Spalletti, 1990
              • Thililua Bardet, Pereda Suberbiola & Jalil, 2003
              • Trinacromerum Cragin, 1888
            • Family Elasmosauridae Cope, 1869 sensu Bardet, Godefroit & Sciau, 1999
              • Microcleidus Watson, 1911
              •  ? Morenosaurus Welles, 1943
              • Occitanosaurus Bardet, Godefroit & Sciau, 1999
            • Family Elasmosauridae Cope, 1869 sensu O'Keefe, 2001
              •  ? Aphrosaurus Welles, 1943
              • Brancasaurus Wegner, 1914
              • Callawayasaurus Carpenter, 1999
              • Elasmosaurus Cope, 1869
              •  ? Fresnosaurus Welles, 1943
              •  ? Futabasaurus Sato, Hasegawa & Manabe, 2006
              •  ? Goniosaurus Meyer, 1860
              •  ? Hydrotherosaurus Welles, 1943
              •  ? Hydralmosaurus Welles, 1943
              • Libonectes Carpenter, 1997
              •  ? Mauisaurus Hector, 1874
              •  ? Ogmodirus Williston & Moodie, 1913 (nomen dubium)
              •  ? Orophosaurus Cope, 1887 (nomen dubium)
              •  ? Piptomerus Cope, 1887 (nomen vanum)
              • Styxosaurus Welles, 1943
              •  ? Terminonatator Sato, 2003
              •  ? Thalassomedon Welles, 1943
              •  ? Tuarangisaurus Wiffen & Moisley, 1986
              •  ? Woolungasaurus Persson, 1960

Alleged living plesiosaurs

Reconstruction of Ogopogo, a supposed lake monster said to resemble a plesiosaur

This section does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (February 2007)

Modern legends of aquatic monsters, such as the Loch Ness Monster, are sometimes explained as sightings of extant relict populations of plesiosaurs.^{[citation needed]} While knowledgeable researchers consider^[who?] this to be unlikely or impossible, it has become a popular concept in cryptozoology.

Beached carcasses that prove controversial or hard to identify, a phenomenon known as globsters, sometimes fuel speculation about living plesiosaurs. 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 the coast of New Zealand, created a plesiosaur craze in Japan. However, the consensus amongst scientists is that it was the decayed remains of a basking shark.^[3]

See also

• Australian plesiosaurs

Literature

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

This article includes a list of references, related reading or external links, but its sources remain unclear because it lacks inline citations. Please improve this article by introducing more precise citations where appropriate. (November 2007)

External links

Wikibooks has a book on the topic of Wikijunior Dinosaurs/Plesiosaurs

Wikimedia Commons has media related to: Plesiosauria

• Fox News: Possibly Complete Plesiosaur Skeleton Found in Arctic
• The Plesiosaur Site. Richard Forrest.
• The Plesiosaur Directory. Dr Adam Stuart Smith.
• Oceans of Kansas Paleontology. Mike Everhart.
• Where the elasmosaurs roam: Separating fact from fiction. Mike Everhart.
• The history of the description of a plesiosaur as a "snake drawn through the shell of a turtle. Mike Everhart and other contributors.
• "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.
• The Filey (Yorkshire) Plesiosaur 2002 (part 1)
• The Filey (Yorkshire) Plesiosaur 2002 (part 2)
• Antarctic Researchers to Discuss Difficult Recovery of Unique Juvenile Plesiosaur Fossil, from the National Science Foundation, December 6, 2006.

Notes