- Sauropterygia
Taxobox
name = Sauropterygians
fossil_range = EarlyTriassic -Late Cretaceous
image_caption = Reconstruction of theplesiosauria n "Thalassiodracon "
regnum =Animal ia
phylum = Chordata
classis = Sauropsida
superordo = Sauropterygia
superordo_authority = Owen,1860
subdivision_ranks = Orders
subdivision =
* ?Thalattosauriformes
*Placodont ia
*Nothosaur oidea
*Plesiosaur iaSauropterygia ("
lizard flipper s") is a group of very successful aquaticreptile s that flourished during the Age of the Dinosaurs before they becameextinct . They are united by a radical adaptation of theirshoulder , designed to support powerful flipper strokes. Some later sauropterygians like thepliosaur s developed a similar mechanism in theirpelvis .Origins and evolution
The earliest sauropterygians appeared about 245
million years ago (Ma), at the start of theTriassic period. Early examples were small (around 60 cm), semi-aquatic lizard-like animals with long limbs (pachypleurosaur s), but they quickly grew to be several meters long and spread into shallow waters (nothosaur s). TheTriassic-Jurassic extinction event wiped them all out except for theplesiosaur s. During theEarly Jurassic these diversified quickly into both long-necked small-headed plesiosaurs proper, and short-necked large-headedpliosaur s. Originally it was thought that Plesiosaurs and Pliosaurs were two distinct superfamilies that followed separate evolutionary paths. It now seems that these were simply morphotypes in that both types evolved a number of times, with some pliosaurs evolving from plesiosaur ancestors, and vice-versa.ize and ecology
Each morphotype filled a specific ecological role. The large pliosaurs, like the
Jurassic "Rhomaleosaurus ", "Liopleurodon " and "Pliosaurus ", and theCretaceous "Kronosaurus " and "Brachauchenius ", were thesuperpredator s of the Mesozoic seas, around 7 to 12 meters in length, and filled a similar ecological role to that ofkiller whale s today. The long-necked plesiosaurs, meanwhile, included both those with medium-long necks, like the 3 to 5 meter-longPlesiosauridae and theCryptoclididae , and the Jurassic and CretaceousElasmosauridae , which evolved progressively longer and more flexible necks, so that by the middle and late Cretaceous the entire animal was over 13 meters in length (e.g. "Elasmosaurus "), although as most of this was the neck, the actual body size was much smaller than that of the larger pliosaurs. These long-necked forms undoubtedly fed on fish, which they probably snared in their tooth-lined jaws with rapid lunges of the neck and head.Extinction
The sauropterygians thrived throughout the
Mesozoic . However, despite their success they becameextinct along with the non-avian dinosaurs, pterosaurs and mosasaurs during the end Cretaceousmass extinction .Taxonomy
Classification is difficult because the demands of the aquatic environment caused the same characteristics to evolve multiple times, illustrating
convergent evolution . While sauropterygians are considereddiapsid s, they are also sometimes classified withturtle s. The bulky-bodied, mollusc-eatingplacodont s may also be sauropterygians. In addition to the modifications of the shoulder, the group is also united by several modifications in theirskull s.* Class
Sauropsida (reptile s)
** InfraclassLepidosauromorpha (lizard s and relatives)
*** SUPERORDER SAUROPTERYGIA
**** OrderThalattosauriformes
***** SuborderThalattosauria
**** Order Placodontia
**** (unranked) Eusauropterygia
***** Order Nothosauroidea
****** Suborder Pachypleurosauria
****** Suborder Nothosauria
***** (unranked) Pistosauroidea
****** "Corosaurus "
****** "Chinchenia "
****** "Kwangsisaurus "
****** "Cymatosaurus "
****** Family Pistosauridae
****** OrderPlesiosauria
******* Suborder Plesiosauroidea (long-necked plesiosaurs)
******* Suborder Pliosauroidea (short-necked plesiosaurs)External links
* [http://www.palaeos.com/Vertebrates/Units/220Lepidosauromorpha/220.100.html Unit 220: 100: Lepidosauromorpha] . "Palaeos". July 15, 2003. Retrieved January 19, 2004.
* [http://www.plesiosauria.com/classification.html A review of the Sauropterygia] . Adam Stuart Smith. "The Plesiosaur Directory". Retrieved April 17, 2006.
* [http://www.paleofile.com/Demo/Mainpage/Taxalist/Sauropterygia.htm Paleofile taxalist] - lists every species and synonyms. Retrieved February 26, 2006
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