Tetrapodomorpha

 ( Extant Early Devonian First Appearances ) 

Tetrapodomorpha (also known as Choanata

) is a clade of consisting of (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 , 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 , which includes several groups of related lobe-finned fishes, collectively known as the . The Tetrapodomorpha minus the crown group Tetrapoda are the stem Tetrapoda, a paraphyletic unit encompassing the fish to tetrapod transition.

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Characteristics Among the characteristics 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). In early tetrapodomorphs like Kenichthys, the excurrent nostrils had shifted towards the mouth's perimeter. In later tetrapodomorphs, including tetrapods, the excurrent nostril is positioned inside the mouth, where it is known as the choana.

Jennifer A. Clack (2025). 9780253356758, Indiana University Press. . ISBN 9780253356758

The nearly-equivalent clade Choanata often refers to these later forms specifically.

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History

Tetrapodomorph fossils are known from the early Devonian onwards, and include Osteolepis, Panderichthys, Kenichthys and Tungsenia. Tetrapodomorpha evolved from ancient lobe-finned fish () around in the Middle Devonian.

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Classification

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Taxonomy

After Benton, 2004; and Swartz, 2012.

• Subclass Sarcopterygii

* Infraclass Tetrapodomorpha

:* Order †Rhizodontida

:::* Family †Sauripteridae

:::* Family †Rhizodontidae

:* Superorder †Osteolepidida (or Osteolepiformes)

:::* Family †Canowindridae

:::* Family †Thysanolepidae

:::* Family †Tristichopteridae

::* Order †Osteolepiformes (or Megalichthyiformes)

:::* Family †Osteolepidae

:::* Family †Megalichthyidae

:* Clade Eotetrapodiformes

::* Clade Elpistostegalia (or Panderichthyida)

:::* Clade Stegocephalia

::::* Family †Elpistostegidae

::::* Family †Whatcheeriidae

::::* Family †Colosteidae

::::* Superfamily †Baphetoidea

::::* Superclass Tetrapoda

Other clades include the Eotetrapodiformes ( Tinirau, Platycephalichthys, the Tristichopteridae and Elpistostegalia). Older taxa which include late Stem tetrapoda and early are the Labyrinthodontia and Ichthyostegalia.

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Relationships

The cladogram is based on a phylogenetic analysis of 46 taxa using 204 characters by B. Swartz in 2012.

The following cladogram follows the results found by Clement et al. (2021).

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Citations

Categories: Extant Early Devonian First Appearances

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