Tetrapodomorpha

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Tetrapodomorphs Fossil range: Early Devonian-Recent, 406–0 Ma PreЄ Є O S D C P T J K Pg N
The basal tetrapodomorph Tiktaalik
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Subphylum:	Vertebrata
Class:	Sarcopterygii
Infraclass:	Tetrapodomorpha Ahlberg, 1991
Subgroups
See text

Tetrapodomorpha is a clade of vertebrates, consisting of tetrapods (four-limbed vertebrates) and their closest sarcopterygian relatives. Primitive forms, like Tiktaalik, have been referred to as "fishapods" by their discoverers, since they were half-fish half-tetrapods, at least in appearance. Tetrapodomorpha contains the true tetrapods and several groups of related lobe-finned fishes, collectively known as the osteolepiforms.

Among the characters defining tetrapodomorphs are modifications to the fins, notably a humerus with convex head articulating with the glenoid fossa (the socket of the shoulder joint).

Tetrapodomorph fossils are known from the early Devonian onwards, and include Osteolepis and Panderichthys.

[edit] Classification

In Late Devonian vertebrate speciation, descendants of pelagic lobe-finned fish – like Eusthenopteron – exhibited a sequence of adaptations:

• Panderichthys, suited to muddy shallows;
• Tiktaalik with limb-like fins that could take it onto land;
• Early tetrapods in weed-filled swamps, such as:
  • Acanthostega which had feet with eight digits,
  • Ichthyostega with limbs.

Descendants also included pelagic lobe-finned fish such as coelacanth species.

[edit] Taxonomy

After Benton, 2004 [1]:

• Subclass Sarcopterygii
  • Infraclass Tetrapodomorpha
    • Kenichthys
    • Order Rhizodontida
    • Superorder Osteolepidida (or Osteolepiformes)
      • Order Osteolepiformes
      • Family Tristichopteridae
      • Order Panderichthyida
      • Superclass Tetrapoda

[edit] Phylogeny

Cladogram modified after Ruta, Jeffery, & Coates (2003)^[1]:

[edit] References

• Mikko Haaramo. "Tetrapodomorpha - Terrestrial vertebrate-like sarcopterygians". http://www.fmnh.helsinki.fi/users/haaramo/Metazoa/Deuterostoma/Chordata/sarcopterygii/tetrapodomorpha.htm. Retrieved 6 April 2006. 
• P. E. Ahlberg and Z. Johanson (1998). "Osteolepiforms and the ancestry of tetrapods". Nature 395 (6704): 792–794. doi:10.1038/27421. 
• Michel Laurin, Marc Girondot and Armand de Ricqlès (2000). "Early tetrapod evolution". TREE 15 (3). http://www.ese.u-psud.fr/epc/conservation/Publi/abstracta/AE_TREE2000.pdf.