Tetrapodomorpha

Tetrapodomorpha Temporal range: Early Devonian-Recent, 409–0 Ma PreЄ Є O S D C P T J K Pg N
The advanced tetrapodomorph Tiktaalik
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Craniata
Subphylum:	Vertebrata
Subclass:	Rhipidistia
Clade:	Tetrapodomorpha Ahlberg, 1991
Subgroups
See below

The Tetrapodomorpha (also known as Choanata^[1]) are a clade of vertebrates consisting of tetrapods (four-limbed vertebrates) and their closest sarcopterygian relatives that are more closely related to living tetrapods than to living lungfish. Advanced forms transitional between fish and the early labyrinthodonts, such as Tiktaalik, have been referred to as "fishapods" by their discoverers, being half-fish, half-tetrapods, in appearance and limb morphology. The Tetrapodomorpha contains the crown group tetrapods (the last common ancestor of living tetrapods and all of its descendants) and several groups of early stem tetrapods, and several groups of related lobe-finned fishes, collectively known as the osteolepiforms. The Tetrapodamorpha minus the crown group Tetrapoda are the Stem Tetrapoda, a paraphyletic unit encompassing the fish to tetrapod transition.

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). Another key trait is the internal nostril or choana. Most fish have two pairs of nostrils, one on either side of the head for incoming water (incurrent nostrils) and another pair for outgoing water (excurrent nostrils). Early tetrapodomorphs such as Kenichthys had excurrent nostrils that had migrated to the edge of the mouth. In later tetrapodomorphs, including tetrapods, the excurrent nostril is positioned inside the mouth, where it is known as the choana.^[2]

Tetrapodomorph fossils are known from the early Devonian onwards, and include Osteolepis, Panderichthys, Kenichthys and Tungsenia.^[3]

Classification

In Late Devonian vertebrate speciation, descendants of pelagic lobe-finned fish.

Taxonomy

After Benton, 2004 :

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

Relationships

The exact shape of the phylogenetic tree is uncertain with Zachelmie tetrapod tracks predating most tetrapodomorph fossils^[4]

Cladogram from Swartz, 2012:^[5]

References

• Mikko Haaramo. "Tetrapodomorpha - Terrestrial vertebrate-like sarcopterygians". Retrieved 6 April 2006. 
• P. E. Ahlberg and Z. Johanson (1998). "Osteolepiforms and the ancestry of tetrapods". Nature 395 (6704): 792–794. Bibcode:1998Natur.395..792A. doi:10.1038/27421. 
• Michel Laurin, Marc Girondot and Armand de Ricqlès (2000). "Early tetrapod evolution" (PDF). TREE 15 (3).