Cladistic classification of Sarcopterygii

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Cladistic classification of Sarcopterygii is the classication of Sarcopterygii as a clade containing not only the lobe-finned fishes (coelacanths and lungfish) but also the tetrapods, which are closely related to lungfish. The taxon Sarcopterygii was traditionally classified as a paraphyletic group considered either a class or a subclass of Osteichthyes (bony fish). Identification of the group is based on several characteristics, such as the presence of fleshy, lobed, paired fins, which are joined to the body by a single bone.[1]

Taxonomic and fossil history

The properties defining the sarcopterygians are in contrast to the other group of bony fish, the

lepidotrichia
. These two bony fish groups were classified together as Osteichthyes at one time, the whole combined group was seen as parallel to the tetrapods (mammals, birds, reptiles, and amphibians).

The extensive fossil record and numerous morphological and molecular studies have shown, however, that lungfish and some fossil lobe-finned fish ("rhipidistians") are more closely related to tetrapods than they are to coelacanths; as a result tetrapods are nested within Sarcopterygii.

cladistics in that in order for a group to be valid, it must have an ancestral species and all descendants of that common ancestor based on shared characteristics. As such mammals, sauropsids (birds and "reptiles"), and amphibians are highly derived sarcopterygians despite superficially looking nothing like the standard lobe-finned fish anatomically speaking. However, similarities can be noticed in their limb bones and tooth enamel.[4] Additionally, lungfish and tetrapods share a divided atrium.[5]

Classification

Multiple Linnean classifications have been proposed with the explicit intent to incorporate Sarcopterygii as a monophyletic taxon instead of maintaining its traditional paraphyletic definition.[6][7][8][9]

Ahlberg (1991)

Class Osteichthyes

Nelson et al. (2016)

Class Osteichthyes

Betancur-Rodrigues et al. (2017)

Superclass Sarcopterygii

Other classifications do not use Sarcopterygii as a ranked taxon but still nonetheless still reject traditional paraphyletic assemblages. In the scheme below, sarcopterygian groups are marked in bold letters.

Tedersoo (2017)

Phylum Craniata

See also

References

  1. ISBN 978-0-253-35675-8
    .
  2. ISBN 978-0-19-860426-6
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  3. ISBN 978-0-321-77336-4
    .
  4. OCLC 867852756
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  5. OCLC 1022979490
    .
  6. doi:10.1111/j.1096-3642.1991.tb00905.x
    .
  7. ISBN 978-1-118-34233-6
    .
  8. PMID 28683774
    .
  9. S2CID 90691603
    .
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