Nothosaurs (order Nothosauroidea) were
Triassic
The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...
marine
sauropterygia
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 bec ...
n
reptiles that may have lived like
seals of today, catching food in water but coming ashore on rocks and beaches. They averaged about in length, with a long body and tail.
[F. v. Huene. 1956. Paläontologie und Phylogenie der Niederen Tetrapoden aleontology and Phylogeny of the Lower Tetrapods ''VEB Gustav Fischer Verlang, Jena'' 1-716] The feet were paddle-like, and are known to have been webbed in life, to help power the animal when swimming.
The neck was quite long, and the head was elongated and flattened, and relatively small in relation to the body. The margins of the long jaws were equipped with numerous sharp outward-pointing teeth, indicating a diet of
fish
Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% ...
and
squid
True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fitting ...
.
Taxonomy
The Nothosauroidea consist of two suborders:
*
Pachypleurosauria, small primitive forms, and
* Nothosauria (including two families
Nothosauridae and
Simosauridae), which evolved from pachypleurosaurs.
The placement of pachypleurosaurs within Nothosauroidea is uncertain, as several analyses recover it as
basal
Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''.
Science
* Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure
* Basal (medicine), a minimal level that is nec ...
to Eusauropterygia, e.i. the
clade formed by Nothosauria and Pistosauroidea, instead as the
sister taxon
In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree.
Definition
The expression is most easily illustrated by a cladogram:
Taxon A and ...
of Nothosauria.
However, most analyses still reinforce the traditional hypothesis of the sister taxon relationship between Pachypleurosauria and Nothosauria.
Nothosaur-like reptiles were in turn ancestral to the more completely marine
plesiosaurs, which replaced them at the end of the Triassic period.
image:Lariosaurus BW.jpg, '' Lariosaurus''.
image:Keichousaurus BW.jpg, '' Keichousaurus''.
image:Ceresiosaurus12.jpg, '' Ceresiosaurus''.
References
Sources
*
*
Benton, M. J. (2004), ''Vertebrate Paleontology'', 3rd ed.
Blackwell Science Ltdbr>
classification*
Colbert, E. H., (1969), ''Evolution of the Vertebrates'',
John Wiley & Sons Inc (2nd ed.)
*
Rieppel, O., (2000), Sauropterygia I, placodontia, pachypleurosauria, nothosauroidea, pistosauroidea: In: ''Handbuch der Palaoherpetologie'', part 12A, 134pp.
Verlag Dr. Friedrich Pfeilbr>
Table of contents
Triassic sauropterygians
Taxa named by Georg Baur
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