A plesiosaur (; 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", 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. The pliosaurs were the short-necked, large-headed plesiosaurians that were the apex predators for much of the Mesozoic.
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 not dinosaurs.
History of discovery
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The first plesiosaur skeletons were found in England by
Mary Anning, in the early 19th century, and were amongst the first fossil vertebrates to be described by science. Plesiosaur remains were found by the Scottish geologist
Hugh Miller in 1844 in the rocks of the
Great Estuarine Group (then known as 'Series') of western Scotland. Many others 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 in 2007. Another, less complete skeleton was also found in 2002, in the cliffs at , Yorkshire, England, by an amateur palaeontologist. The preserved skeleton is displayed at
Rotunda Museum in Scarborough.
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. Other 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 . 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
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
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.
The series Walking with Dinosaurs shows the plesiosaur Cryptoclidus hauling out on land like a sea lion.
Taxonomy
The classification of plesiosaurs has varied; the following represents one version (see O'Keefe 2001)
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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
**** Seeleysaurus
*** (Unranked) Euplesiosauria O'Keefe, 2001
**** ? Eretmosaurus Seeley, 1874
**** ? Leurospondylus Brown, 1913
**** ? Nichollssaura Druckenmiller & Russell, 2008
**** ? Sthenarosaurus Watson, 1911 (nomen dubium)
**** Superfamily Cryptoclidoidea Williston, 1925 sensu O'Keefe, 2001
***** Family Cryptoclididae Williston, 1925 sensu O'Keefe, 2001
****** ? Colymbosaurus Seeley, 1874
****** Cryptoclidus Seeley, 1892
****** Muraenosaurus Seeley, 1874
****** Pantosaurus Marsh, 1891
****** ? Tatenectes O’Keefe & Wahl, 2003
****** 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
******* Cimoliasaurus Leidy, 1851 (nomen dubium)
******* Kaiwhekea Cruickshank & Fordyce, 2002
******* Kimmerosaurus Brown, 1981
****** 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
See also
List of 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
External links
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
Category:Plesiosaurs
