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Superregnum: Eukaryota
Regnum: Animalia
Subregnum: Eumetazoa
Cladus: Bilateria
Cladus: Nephrozoa
Superphylum: Deuterostomia
Phylum: Chordata
Cladus: Craniata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Superclassis: Tetrapoda
Cladus: Reptiliomorpha
Cladus: Amniota
Classis: Reptilia
Cladus: Eureptilia
Cladus: Romeriida
Subclassis: Diapsida
Cladus: Sauria
Cladus: Archelosauria
Division: Pan-Testudines
Superordo: †Sauropterygia
Ordines: Nothosauria - Placodontia - Plesiosauria
Name

Sauropterygia Owen, 1860
Vernacular names
English: Lizard flippers
日本語: 鰭竜類
ქართული: ზავროპტერიგიები
中文: 鰭龍超目

Sauropterygia ("lizard flippers") is an extinct taxon of diverse, aquatic reptiles that developed from terrestrial ancestors soon after the end-Permian extinction and flourished during the Triassic before all except for the Plesiosauria became extinct at the end of that period. The plesiosaurs would continue to diversify until the end of the Mesozoic. Sauropterygians are united by a radical adaptation of their pectoral girdle, adapted to support powerful flipper strokes. Some later sauropterygians, such as the pliosaurs, developed a similar mechanism in their pelvis. Uniquely among reptiles, sauropterygians moved their tail vertically like modern cetaceans and sirenians.[1]

Origins and evolution

The earliest sauropterygians appeared about 245 million years ago (Ma), at the start of the Triassic period: the first definite sauropterygian with exact stratigraphic datum lies within the Spathian division of the Olenekian era in South China.[2] Early examples were small (around 60 cm), semi-aquatic lizard-like animals with long limbs (pachypleurosaurs), but they quickly grew to be several metres long and spread into shallow waters (nothosaurs). The Triassic-Jurassic extinction event wiped them all out except for the plesiosaurs. During the Early Jurassic, these diversified quickly into both long-necked small-headed plesiosaurs proper, and short-necked large-headed pliosaurs. 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.
Classification

Classification of sauropterygians has been difficult. The demands of an aquatic environment caused the same features to evolve multiple times among reptiles, an example of convergent evolution. Sauropterygians are diapsids, and since the late 1990s, scientists have suggested that they may be closely related to turtles. The bulky-bodied, mollusc-eating placodonts may also be sauropterygians, or intermediate between the classic eosauropterygians and turtles. Several analyses of sauropterygian relationships since the beginning of the 2010s have suggested that they are more closely related to archosaurs (birds and crocodilians) than to lepidosaurs (lizards and snakes).[3]

The cladogram shown hereafter is the result of an analysis of sauropterygian relationships (using just fossil evidence) conducted by Neenan and colleagues, in 2013.[4]

Pantestudines Erpétologie générale, ou, Histoire naturelle complète des reptiles (Centrochelys sulcata).jpg

 Lepidosauromorpha 

Kuehneosauridae Icarosaurus white background.jpg

Lepidosauria Tylosaurus pembinensis 1DB flipped.jpg

 Archosauromorpha 

Prolacertiformes Megalancosaurus BW.jpg

Choristodera Champsosaurus BW flipped.jpg

Rhynchosauria Hyperodapedon BW2 white background.jpg

Trilophosaurus Trilophosaurus buettneri (flipped).jpg

Archosauriformes Barapasaurus DB.jpg

Ichthyopterygia Stenopterygius BW.jpg

Thalattosauria

Eusaurosphargis

Hanosaurus

Helveticosaurus

Sinosaurosphargis

 Sauropterygia 

Placodontiformes Placodus BW.jpg

 Eosauropterygia 
 Pistosauria 

Yunguisaurus

Plesiosauria Styxosaurus BW.jpg

Pistosaurus Pistosaurus BW.jpg

Augustasaurus

Corosaurus

Cymatosaurus

 Nothosauria 

Simosaurus

Germanosaurus

Nothosaurus Nothosaurus BW.jpg

Lariosaurus Lariosaurus BW.jpg

Diandongosaurus

 Pachypleurosauria 

Dianopachysaurus

Keichousaurus

Wumengosaurus

Anarosaurus-Dactylosaurus

Neusticosaurus-Serpianosaurus

The cladogram shown below follows the most likely result found by an analysis of turtle relationships using both fossil and genetic evidence by M.S. Lee, in 2013. This analysis resolved Sauropterygia as a paraphyletic assemblage of stem turtles.[3]

Crown Reptilia/

Pan-Lepidosauria / LepidosauromorphaBritish reptiles, amphibians, and fresh-water fishes (1920) (Lacerta agilis).jpg

Archelosauria/
Pan-Archosauria

ChoristoderaChampsosaurus BW flipped.jpg

Archosauromorpha s. s.

Prolacertiformes Prolacerta broomi.jpg

TrilophosaurusTrilophosaurus buettneri (flipped).jpg

RhynchosauriaHyperodapedon BW2 white background.jpg

ArchosauriformesDeinosuchus riograndensis.png

Pan-Testudines/

Eosauropterygia Dolichorhynchops BW flipped.jpg

Placodontia Psephoderma BW flipped.jpg

Sinosaurosphargis

Odontochelys

 Testudinata 

Proganochelys

TestudinesErpétologie générale, ou, Histoire naturelle complète des reptiles (Centrochelys sulcata).jpg

Pantestudines
Archosauromorpha s. l.
Sauria

Size and ecology

Each morphotype filled a specific ecological role. The large pliosaurs, such as Rhomaleosaurus, Liopleurodon, Pliosaurus, Kronosaurus and Brachauchenius, were the superpredators of the Mesozoic seas, measuring 7 to 12 meters in length, and filled a similar ecological role to that of killer whales today. The long-necked plesiosaurs included Plesiosauridae, Cryptoclididae, and Elasmosauridae. Some lineages of long-necked plesiosaurs evolved progressively longer and more flexible necks, reaching 13 meters in total length by the late Cretaceous. With their small heads in proportion to their neck length and body mass, long-necked plesiosaurs were limited to eating relatively small fish, which they probably snared in their tooth-lined jaws with rapid lunges of their long necks.
References

Sennikov, A. G. (2019). "Peculiarities of the Structure and Locomotor Function of the Tail in Sauropterygia". Biology Bulletin. 46 (7): 751–762. doi:10.1134/S1062359019070100. S2CID 211217453.
Ji Cheng, et al. 2013. "Highly diversified Chaohu fauna (Olenekian, Early Triassic) and sequence of Triassic marine reptile faunas from South China", in Reitner, Joachim et al., eds. Palaeobiology and Geobiology of Fossil Lagerstätten through Earth History p. 80
Lee, M. S. Y. (2013). "Turtle origins: Insights from phylogenetic retrofitting and molecular scaffolds". Journal of Evolutionary Biology. 26 (12): 2729–2738. doi:10.1111/jeb.12268. PMID 24256520. S2CID 2106400.

Neenan, J. M.; Klein, N.; Scheyer, T. M. (2013). "European origin of placodont marine reptiles and the evolution of crushing dentition in Placodontia". Nature Communications. 4: 1621. doi:10.1038/ncomms2633. PMID 23535642.

External links

Unit 220: 100: Lepidosauromorpha. Palaeos. July 15, 2003. Retrieved January 19, 2004.
A review of the Sauropterygia. Adam Stuart Smith. The Plesiosaur Directory. Retrieved April 17, 2006.
Paleofile taxalist - lists every species and synonyms. Retrieved February 26, 2006

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