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Plesiosauroidea

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Plesiosaurs
Temporal range: Late Triassic - Late Cretaceous, 210–65 Ma
Reconstructed skeleton of Thalassomedon hanningtoni, an elasmosaurid
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Superorder: †Sauropterygia
Order: †Plesiosauria
Clade: †Neoplesiosauria
Superfamily: †Plesiosauroidea
Gray, 1825
Families

†Cimoliasauridae
†Cryptoclididae
†Elasmosauridae
†Plesiosauridae
†Polycotylidae

A plesiosaur (/[invalid input: 'icon']ˈpliːsiəsɔːr/; 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.

Plesiosaurs (sensu Plesiosauroidea) appeared at the end of the Triassic 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. Gastroliths are frequently found associated with plesiosaurs.[3]

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 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.[4] 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 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. 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 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.

It has been determined by teeth records that several sea-dwelling reptiles, including plesiosaurs, had a warm-blooded metabolism similar to that of mammals. They had the ability to generate endothermic heat to survive in colder habitats.[5]

Evolution

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.[6] 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}.[7] 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.

On 12 August 2011, researchers from the U.S. described a fossil of a pregnant plesiosaur found on a Kansas ranch in 1987.[8] The plesiosaur, Polycotylus latippinus, has confirmed that these predatory marine reptiles gave birth to single, large, live offspring - contrary to other marine reptile reproduction which typically involves a large number of small babies. Before this study, plesiosaurs had sometimes been portrayed crawling out of water to lay eggs in the manner of sea turtles, but experts had long suspected that their anatomy was not compatible to movement on land. The adult plesiosaur measures 4 m long and the baby is 1.5 m long.[9]

Taxonomy

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

Attenborosaurus
Mauisaurus
Muraenosaurus
Dolichorhynchops
Thililua
Libonectes
Styxosaurus

See also

References

  1. ^ Everhart, Mike (2005-10-14), "A Snake Drawn Through the Shell of a Turtle", Oceans of Kansas Paleontology, retrieved 2010-06-10 {{citation}}: External link in |work= (help)
  2. ^ "Fossils explained 54: plesiosaurs. Geology Today 24 (2): 71-75" by Adam S. Smith.
  3. ^ "Occurrence of Gastroliths in Mesozoic Taxa," in Sanders et al. (2001). Page 168.
  4. ^ p 339 Trewin, N. H.(ed)2002 The Geology of Scotland. The Geological Society, London
  5. ^ "Warm-blooded marine reptiles at the time of the dinosaurs". Sciencedaily.com. 2010-06-15. doi:10.1126/science.1187443. Retrieved 2011-08-15.
  6. ^ Massare, J. A. 1988. "Swimming capabilities of Mesozoic marine reptiles: Implications for method of predation". Paleobiology 14(2): 187-205.
  7. ^ Henderson, D. M. 2006. "Floating point: a computational study of buoyancy, equilibrium, and gastroliths in plesiosaurs", Lethaia, 39 pp. 227–244.
  8. ^ F. R. O’Keefe1,*, L. M. Chiappe2. "Viviparity and K-Selected Life History in a Mesozoic Marine Plesiosaur (Reptilia, Sauropterygia)". Sciencemag.org. Retrieved 2011-08-15.{{cite web}}: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link)
  9. ^ by Anthony King. "Ancient sea dragons had a caring side". Cosmosmagazine.com. Retrieved 2011-08-15.

Further reading

  • 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.
  • Everhart, M. J. "Marine Reptile References" and scans of "Early papers on North American plesiosaurs"
  • 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.
  • 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 document on the Plesiosaur Directory
  • 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.
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