Tetrapodomorpha

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Tetrapodomorphs
Fossil range: late Early Devonian - Recent

Image:Tiktaalik.png

The basal tetrapodomorph Tiktaalik.

Scientific classification

Kingdom:	Animalia
Phylum:	Chordata
Subphylum:	Vertebrata
Class:	Sarcopterygii
Subclass:	Tetrapodomorpha Ahlberg, 1991

Subgroups

See text

Image:Fishapods.jpg

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.

Tetrapodomorpha is a clade of vertebrates, consisting of sarcopterygians with a number of features of tetrapods. 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 the 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] Taxonomy and Phylogeny

Class Sarcopterygii
- Subclass TETRAPODOMORPHA
  - Kenichthys
  - Order Rhizodontida
  - Superorder Osteolepidida (or Osteolepiformes)
    - Family Osteolepididae
      - Osteolepis
    - Family Tristichopteridae
      - Eusthenopteron
    - Family Megalichthyidae
    - Family Canowindridae
    - (unranked) Elpistostegalia
      - Order Panderichthyida
      - Tiktaalik
      - Livoniana
      - Metaxygnathus
      - Ventastega
      - Superclass Tetrapoda

After Benton, 2004 [1]:

[edit] References

Mikko Haaramo. Tetrapodomorpha - Terrestrial vertebrate-like sarcopterygians. Retrieved on 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).ca:Tetrapodomorf