Plesiosauria

From Palaeos

o Lepidosauromorpha
`--o Sauropterygia
   `--+?-Claudiosaurus 
      `--+?-Thalattosauriformes 
         |?-Placodontia
         `--o Eusauropterygia
            |--Pachypleurosauridae
            `--+--Nothosauridae
               `--+--Corosaurus 
                  `--+--Cymatosaurus 
                     `--+--Pistosauridae  
                        `--o Plesiosauria
                           |==Pliosauroidea
                           `--o Plesiosauroidea
                              |--Plesiosaurus
                              `--+--Elasmosauridae
                                 `--Cryptocleidoidea

[edit] Introduction

The Plesiosauria (the name means "near lizards,") were an important order of Mesozoic marine reptiles, members of the superorder Sauropterygia. The Plesiosauria include both short and long-necked forms. The largest short-necked forms reached enormous sizes (lengths of over 10 meters, weight of 20 tonnes or more), while some of the later long-necked forms, although only marginally longer and not as heavily built, developed the greatest number of neck vertebrae of any animal. Plesiosaurs evolved from animals related to pachypleurosaurs and nothosaurs during the Middle Triassic. They remained somewhat rare until the end of that period, when they underwent an amazing evolutionary radiation. These reptiles then dominated the seas throughout the Jurassic and Cretaceous periods, continuing to flourish right up until the end of the Mesozoic Era.

[edit] Information

Linnaean taxonomy

• class Reptilia/Sauropsida
  • subclass Diapsida
    • superorder Sauropterygia
      • unranked Eusauropterygia
        • order Plesiosauria

author de Blainville, 1835

Sratigraphic Range: Middle? or Late Triassic to Cretaceous

Environment: Pelagic Marine(several types freshwater)

Lifestyle: Large predatory Nekton

Geographic distribution: Cosmopolitan

[edit] History of Discovery

Plesiosaurs were among the earliest large prehistoric creatures to be described. Victorian British accounts are full of references to "antediluvian monsters". Most plesiosaur material was found and described in the Nineteenth Century, much of it located and prepared by an early paleontologist named Mary Anning (1799-1847). A life-long resident of Lyme Regis, England, Anning made a remarkable series of important discoveries in the Early Jurassic seaside cliffs and limestone quarries within walking distance of her home. Collectors quickly depleted these coastal exposures. Sadly, by about 1910 most limestone quarries had become mechanized, this severely limiting the collection of fossil material before it was destroyed. After this date very little new material was found, and paleontologists in this region were limited to re-classifying, redescribing, and reviewing old material.

Meanwhile, important discoveries were being made in North America, where sediments from the Late Cretaceous inland sea contain the remains of many large marine reptiles, including both long and short-necked plesiosaurs. This historical accident has led to the belief that plesiosaurs evolved and flourished in Europe during the Jurassic, and became rare there in the Cretaceous, spreading at that time to North America, and finally attaining world-wide distribution at the end of the period.

This opinion could not be more false. As with all large, ocean-going animals, there is no doubt that plesiosaurs had world-wide distribution virtually from the very start, even as early as the Triassic. Certainly Early Jurassic plesiosaurs are known from China, South America, and Australia as well as Europe. As with so much of paleobiology, it is misleading to make sweeping assumptions on the basis of patchy and incomplete geological preservation. MAK

[edit] Characteristics

[edit] General Description

This section from Wikipedia:

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.

[edit] Characters

Characters: Up to 13m; nostrils high, just preorbital; $ nasals absent; large eyes located on sides of head; palate less specialized than nothosaurs; palate consists mainly of vomers, large palatines & pterygoids; interpterygoid vacuities retained, sharp, jagged teeth set in sockets at the edge of the jaw; heavy, rigid trunks; $ presence of nutritive foramina in vertebral centra, on underside of cervical and caudal, on sides of dorsal centra, and on base of neural canal (either tubes joining neural canal to underside of spinal column, or openings into a space filled with some specialized tissue within the body of the centrum); single-headed ribs; $ relatively short tail; $ gastralia present and well-developed (ballast?); $ both girdles elaborated ventrally, with massive ventral plates; space between girdles filled with thick gastralia, giving them almost continuous ventral bone surface; anterior and posterior limbs similar, $ hyperphalangy; $ illium does not contact pubis; presumed rowing or "flying" locomotion; propulsive stroke, but no dorsoventral control? ATW030515.

[edit] Behaviour

This section from Wikipedia:

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).

[edit] Taxonomy

This section from Wikipedia:

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
      • Thalassiodracon
      • Attenborosaurus
      • Eurycleidus
      • Family Rhomaleosauridae
      • Family Pliosauridae
    • Suborder Plesiosauroidea
      • Family Plesiosauridae
      • (Unranked) Euplesiosauria
        • Family Elasmosauridae
        • Superfamily Cryptoclidoidea
          • Family Cryptoclididae
          • (Unranked) Tricleidia
            • Tricleidus
            • Family Cimoliasauridae
            • Family Polycotylidae (= "Dolichorhynchopidae")

See also List of plesiosaur genera.

[edit] References

This section from Wikipedia:

• Lingham-Soliar, T., 1995: in Phil. Trans. Roy. Soc. Lond. 347: 155-180
• Cicimurri, D., and M. Everhart, 2001: in Trans. Kansas. Acad. Sci. 104: 129-143
• O'Keefe, F. R., 2001: A cladistic analysis and taxonomic revision of the Plesiosauria (Reptilia: Sauropterygia); Acta Zool. Fennica 213: 1-63
• White, T., 1935: in Occasional Papers Boston Soc. Nat. Hist. 8: 219-228
• Hampe, O., 1992: Courier Forsch.-Inst. Senckenberg 145: 1-32
• Ellis, R. 2003: Sea Dragons' (Kansas University Press)
• ( ), 1997: in Reports of the National Center for Science Education, 17.3 (May/June 1997) pp 16–28.
• 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)

[edit] Links

<a href="http://www.dinosauria.com/dml/names/plesi.html">Plesiosauria Translation and Pronunciation Guide Introduction</a>; <a href="http://www.pvisuals.com/dinosaur_museum/assorted/plesiosaur.html">Plesiosaur Skeleton</a>; <a href="http://www.alphalink.com.au/~dannj/marine.htm">Marine Reptiles (NOT Dinosaurs)</a>; <a href="http://www.enchantedlearning.com/subjects/dinosaurs/dinos/Plesiosaur.shtml">Plesiosaurs- Enchanted Learning Software</a>; <a href="http://www.ucmp.berkeley.edu/history/plesio.html">plesiosaurs</a>; <a href="http://unmuseum.mus.pa.us/searepti.htm">The UnMuseum - Sea Reptiles</a>; <a href="http://www.toyen.uio.no/palmus/galleri/montre/english/m_marineogler_liste_e.htm">List of fossils</a>; <a href="http://www.suite101.com/article.cfm/4003/30361">Marine Reptiles II: Plesiosaurs - Suite101.com</a>; <a href="http://www.isgs.uiuc.edu/dinos/de_4/5c5d3fa.htm">PLESIOSAURIA</a>; <a href="http://www.vertpaleo.org/jvp/16-403-420.html">Untitled Document</a>; <a href="http://www.geocities.com/sea_saur/plesiosauria.html">plesiosauria</a> (excellent, but rather incomplete site); <a href="http://www.fmnh.helsinki.fi/users/haaramo/Metazoa/Deuterostoma/Chordata/Reptilia/Sauropterygia/Plesiosauria.htm">Plesiosauria after O'Keefe, 2001</a> (Mikko's Phylogeny); <a href="http://www.plesiosaur.com/">The Plesiosaur Site</a> (Best on the Web -- Richard has finally fixed up this site so that it really works, and the result is a very complete database); <a href="http://www.nathis.nl/fauna/marreptielen.htm">Nathis Fauna Reptilelen Mariene Reptielen</a>; <a href="http://www.courtenaymuseum.ca/paleo/paleo/elasmo.html">The CDM's Earth Sciences Resource Site- Elasmosauridae</a>; <a href="http://www.heritagenet.unesco.kz/kz/hn-english/csmrk/engl/fauna_en.htm">Fauna</a> (detailed image of vertebrae); <a href="http://www.vertpaleo.org/jvp/16-403-420.html">The Journal of Vertebrate Paleontology</a> (abstract). ATW030515.

[edit] Credits

From Palaeos com; Addirional material from wikipedia. This page MAK061214