Sauropterygia

From Palaeos

Jump to: navigation, search
Parent taxa:
(check the following menu and phylogeny - the taxon in bold refers to the topic on this page)


LEPIDOSAUROMORPHA
Taxonomy Phylogeny 
o Sauria
|?-Thalattosauriformes
`--o LEPIDOSAUROMORPHA
   |--Acerosodontosaurus [Acerosodontosauridae]
   |--+--Sauropterygia
   |  `?-Testudinata (Rieppel & deBraga)
   `--Lepidosauriformes


Sauropterygia


Plesiosaurus drawing CC-by-sa Adam Stuart Smith
Plesiosaurus drawing CC-by-sa Adam Stuart Smith


Contents

[edit] Introduction and Description

The following section of this page needs to be wikified. At its simplest, wikifying can just mean adding links to other pages via the edit tab. For help in editing Palaeos org pages, see the edit help page

The Sauropterygia or "lizard flippers" are an important group which includes a wide range of aquatic lizard-like, crocodile-like, long-necked "Loch Ness monster"-like, and large-headed killer whale-like aquatic reptiles. Among the great prehistoric success stories, they first appeared at (or just before) the very start of the Mesozoic and flourished right until the end of the era. Yet as with the Ichthyosauria, they are so specialized their evolutionary relationships are still somewhat obscure.

Earlier forms (pachypleurosaurs) were mostly small amphibious lizard-like animals with slender, elongated limbs and small heads, that lived in estuarine and near-shore environments. They quickly increased to several meters in size and ventured further out to sea, although still retaining amphibious traits and sinuous lizard-like form (nothosaurs). By the Middle Triassic there were a number of divergent lineages. In addition to the line leading to the successful Jurassic plesiosaurs, there were several divergent branches of early sauropterygians, including pachypleurosaurs, several lines of nothosaurs, and the transitional pistosaurs. These early divergent branches show successive stages in adaptation to oceanic life.

The Carnian extinction took out most of these early Sauropterygia, but the one surviving group, the plesiosaurs, underwent a tremendous evolutionary radiation around the very end of the Triassic period and the very start of the Jurassic, diverging rapidly into variously lineages in a typical example of a macroevolutionary adaptive radiation. It is not yet clear whether this event coincided with and was caused by the full development of the plesiosaur locomotor plan, or whether it was simply opportunistic factors, such as the mass extinction of potential competitors in the Rhaetian turnover, that allowed the plesiosaurs to exploit the potential of a previously evolved locomotor plan (see below). In any case by the early Jurassic there were a diverse range of long- medium- and short-necked forms, some with small heads others with large. These were all open ocean types, completely adapted for marine life, and usually 3 metres or more in length. The two principal morphs were the plesiosaurs (long necked "Loch Ness monster" types) and pliosaurs (reptilian killer whales). However, the evolutionary relationships of the Plesiosauria are complex, and it appears that long-necked and short-necked types occurred in a number of lineages.

The Sauropterygia are united by unique derived features features of the skull and shoulder girdle. As Carroll & Gaskill (1985) note, the fundamental relations of the shoulder girdle elements are altered in the Sauropterygia. The figure illustrates the differences in shoulder structure between a basal amniote (adapted from Carroll, 1988) and the basal sauropterygian, Neusticosaurus (adapted from Carroll & Gaskill 1985). In the terrestrial amniote, force is directed by the humerus against the plate-like scapulocoracoid, which dissipates the force over a wide area and is, in turn, supported by extensive contact with the dermal bones of the clavicle and interclavicle. In the sauropterygian shoulder, a direct, medially directed force would probably cause the shoulder girdle to collapse. However, the anterior and posterior strains caused by paddling and steering simply bind the girdle more strongly together by forcing the interclavicles and coracoids against their opposite numbers. The fundamental re-engineering of the shoulder girdles suggests that the strains involved were considerable, i.e., that the sauropterygians were fast, agile swimmers.

A remarkably similar arrangement was evolved in the pelvic girdle of derived sauropterygians, e.g. plesiosaurs, and both girdles were connected by a net of gastralia (stomach ribs) probably reinforced by stout ligaments. This arrangement and the problems of plesiosaur locomotion, will be covered on a subsequent page. MAK991206, ATW061220.


(The following menu and phylogeny refers to subtopics of this page)


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


[edit] Information

Range: Late Permian to Late Cretaceous.

Phylogeny: Lepidosauromorpha: Lepidosauriformes + Sauropterygia : Placodontia + Nothosauria

[edit] Characters

Characters: Postorbital skull elongated; upper fenestra enlarged; "euryapsid" (lower temporal arch lost) [CG85]; quadrate rigid (primitive) [CG85]; elongate neck (>7 cervicals); limbs relatively large [CG85]; curved humerus; radius equal length to ulna.

References:

  • Carroll, RL & Gaskill, P (1985), The nothosaur Pachypleurosaurus and the origin of plesiosaurs. Phil. Trans. Roy. Soc. Lond. B 309: 343-393.

[edit] Taxonomy

This section from Wikipedia:

[edit] Links

The following section is in html (web page) format and needs to be converted to wiki markup. This involves removing the html tags and replacing them with wiki tags. For help in editing Palaeos org pages, see the edit help page

<a href="http://dinosauricon.com/taxa/sauropterygia.html">Sauropterygia -- The Dinosauricon</a>; <a href="http://www.fmnh.helsinki.fi/users/haaramo/Metazoa/Deuterostoma/Chordata/Reptilia/Sauropterygia/Sauropterygia.htm">Sauropterygia</a>; <a href="http://cas.bellarmine.edu/tietjen/Diversity/turtle_origins.htm">Turtle Origins</a>; <a href="http://www.uni-mainz.de/~fastm000/Literatur/Sauropterygia.html">Literature - Sauropterygia</a>; <a href="http://www.lippisches-landesmuseum.de/bericht/detmoldsaurier.html">muschelkalk lipperland</a> (German: never saw this site before. Very nice.); <a href="http://homepage1.nifty.com/sizensi/repoot/971225/971225.htm">????????</a> (Japanese); <a href="http://www.vertpaleo.org/jvp/19-321-337.html">Untitled Document</a>; <a href="http://www.geocities.com/sea_saur/classification.html">classification</a>; <a href="http://www.uni-mainz.de/~fastm000/Literatur/Sauropterygia.html">Literature - Sauropterygia</a>; <a href="http://www.fmnh.helsinki.fi/users/haaramo/Metazoa/Deuterostoma/Chordata/Reptilia/Sauropterygia/Sauropterygia.htm">Sauropterygia after Rieppel, 1997, 1998ab and Rieppel & Hagdorn, 1997</a>; <a href="http://www.ethicalatheist.com/img/fossils/106-0649_img.htm">Fossil Room</a>; <a href="http://www.cmnh.org/dinoarch/1997Jun/msg00305.html">some additions to Re: MOSASAURS AND PLIOSAURS</a>; <a href="http://www.cmnh.org/dinoarch/1997Jun/msg00263.html">MOSASAURS AND PLIOSAURS</a>; <a href="http://www.lippisches-landesmuseum.de/bericht/detmoldsaurier.html">muschelkalk lipperland</a> (German).

[edit] Credits

MAK991206, ATW061216, ATW061220 Palaeos com

Retrieved from "http://www.palaeos.org/Sauropterygia"
Personal tools