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

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

History

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

Classification

In Late Devonian vertebrate speciation, descendants of pelagic lobe-finned fish.
The exact shape of the phylogenetic tree is uncertain, with Zachelmie tetrapod tracks predating most tetrapodomorph fossils

Taxonomy

After Benton, 2004; and Swartz, 2012.

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 tetrapods and early tetrapods are the Labyrinthodontia and Ichthyostegalia.

Relationships

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

Tetrapodomorpha†Kenichthys †Rhizodontidae †Canowindridae †Marsdenichthys †Canowindra †Koharalepis †Beelarongia †Megalichthyiformes †Gogonasus †Gyroptychius †Osteolepis †Medoevia †Megalichthyidae Eotetrapodiformes †Tristichopteridae †Spodichthys †Tristichopterus †Eusthenopteron †Jarvikina †Cabonnichthys †Mandageria †Eusthenodon †Tinirau †Platycephalichthys Elpistostegalia †Panderichthys †Tiktaalik †Elpistostege †Elginerpeton †Ventastega †Acanthostega †Ichthyostega †Whatcheeriidae †Colosteidae †Crassigyrinus †Baphetidae Tetrapoda (crown group)
†Kenichthys
†Rhizodontidae †Canowindridae †Marsdenichthys †Canowindra †Koharalepis †Beelarongia †Megalichthyiformes †Gogonasus †Gyroptychius †Osteolepis †Medoevia †Megalichthyidae Eotetrapodiformes †Tristichopteridae †Spodichthys †Tristichopterus †Eusthenopteron †Jarvikina †Cabonnichthys †Mandageria †Eusthenodon †Tinirau †Platycephalichthys Elpistostegalia †Panderichthys †Tiktaalik †Elpistostege †Elginerpeton †Ventastega †Acanthostega †Ichthyostega †Whatcheeriidae †Colosteidae †Crassigyrinus †Baphetidae Tetrapoda (crown group)
†Rhizodontidae
†Canowindridae †Marsdenichthys †Canowindra †Koharalepis †Beelarongia †Megalichthyiformes †Gogonasus †Gyroptychius †Osteolepis †Medoevia †Megalichthyidae Eotetrapodiformes †Tristichopteridae †Spodichthys †Tristichopterus †Eusthenopteron †Jarvikina †Cabonnichthys †Mandageria †Eusthenodon †Tinirau †Platycephalichthys Elpistostegalia †Panderichthys †Tiktaalik †Elpistostege †Elginerpeton †Ventastega †Acanthostega †Ichthyostega †Whatcheeriidae †Colosteidae †Crassigyrinus †Baphetidae Tetrapoda (crown group)
†Canowindridae †Marsdenichthys †Canowindra †Koharalepis †Beelarongia
†Canowindridae†Marsdenichthys †Canowindra †Koharalepis †Beelarongia
†Marsdenichthys
†Canowindra †Koharalepis †Beelarongia
†Canowindra
†Koharalepis †Beelarongia
†Koharalepis
†Beelarongia
†Megalichthyiformes †Gogonasus †Gyroptychius †Osteolepis †Medoevia †Megalichthyidae Eotetrapodiformes †Tristichopteridae †Spodichthys †Tristichopterus †Eusthenopteron †Jarvikina †Cabonnichthys †Mandageria †Eusthenodon †Tinirau †Platycephalichthys Elpistostegalia †Panderichthys †Tiktaalik †Elpistostege †Elginerpeton †Ventastega †Acanthostega †Ichthyostega †Whatcheeriidae †Colosteidae †Crassigyrinus †Baphetidae Tetrapoda (crown group)
†Megalichthyiformes†Gogonasus †Gyroptychius †Osteolepis †Medoevia †Megalichthyidae
†Gogonasus
†Gyroptychius †Osteolepis †Medoevia †Megalichthyidae
†Gyroptychius
†Osteolepis †Medoevia †Megalichthyidae
†Osteolepis
†Medoevia †Megalichthyidae
†Medoevia
†Megalichthyidae
Eotetrapodiformes†Tristichopteridae †Spodichthys †Tristichopterus †Eusthenopteron †Jarvikina †Cabonnichthys †Mandageria †Eusthenodon †Tinirau †Platycephalichthys Elpistostegalia †Panderichthys †Tiktaalik †Elpistostege †Elginerpeton †Ventastega †Acanthostega †Ichthyostega †Whatcheeriidae †Colosteidae †Crassigyrinus †Baphetidae Tetrapoda (crown group)
†Tristichopteridae†Spodichthys †Tristichopterus †Eusthenopteron †Jarvikina †Cabonnichthys †Mandageria †Eusthenodon
†Spodichthys
†Tristichopterus †Eusthenopteron †Jarvikina †Cabonnichthys †Mandageria †Eusthenodon
†Tristichopterus
†Eusthenopteron †Jarvikina †Cabonnichthys †Mandageria †Eusthenodon
†Eusthenopteron
†Jarvikina †Cabonnichthys †Mandageria †Eusthenodon
†Jarvikina
†Cabonnichthys †Mandageria †Eusthenodon
†Cabonnichthys
†Mandageria †Eusthenodon
†Mandageria
†Eusthenodon
†Tinirau †Platycephalichthys Elpistostegalia †Panderichthys †Tiktaalik †Elpistostege †Elginerpeton †Ventastega †Acanthostega †Ichthyostega †Whatcheeriidae †Colosteidae †Crassigyrinus †Baphetidae Tetrapoda (crown group)
†Tinirau
†Platycephalichthys Elpistostegalia †Panderichthys †Tiktaalik †Elpistostege †Elginerpeton †Ventastega †Acanthostega †Ichthyostega †Whatcheeriidae †Colosteidae †Crassigyrinus †Baphetidae Tetrapoda (crown group)
†Platycephalichthys
Elpistostegalia†Panderichthys †Tiktaalik †Elpistostege †Elginerpeton †Ventastega †Acanthostega †Ichthyostega †Whatcheeriidae †Colosteidae †Crassigyrinus †Baphetidae Tetrapoda (crown group)
†Panderichthys
†Tiktaalik †Elpistostege †Elginerpeton †Ventastega †Acanthostega †Ichthyostega †Whatcheeriidae †Colosteidae †Crassigyrinus †Baphetidae Tetrapoda (crown group)
†Tiktaalik †Elpistostege
†Tiktaalik
†Elpistostege
†Elginerpeton †Ventastega †Acanthostega †Ichthyostega †Whatcheeriidae †Colosteidae †Crassigyrinus †Baphetidae Tetrapoda (crown group)
†Elginerpeton
†Ventastega †Acanthostega †Ichthyostega †Whatcheeriidae †Colosteidae †Crassigyrinus †Baphetidae Tetrapoda (crown group)
†Ventastega
†Acanthostega †Ichthyostega †Whatcheeriidae †Colosteidae †Crassigyrinus †Baphetidae Tetrapoda (crown group)
†Acanthostega
†Ichthyostega †Whatcheeriidae †Colosteidae †Crassigyrinus †Baphetidae Tetrapoda (crown group)
†Ichthyostega
†Whatcheeriidae †Colosteidae †Crassigyrinus †Baphetidae Tetrapoda (crown group)
†Whatcheeriidae
†Colosteidae †Crassigyrinus †Baphetidae Tetrapoda (crown group)
†Colosteidae
†Crassigyrinus †Baphetidae Tetrapoda (crown group)
†Crassigyrinus
†Baphetidae Tetrapoda (crown group)
†Baphetidae
Tetrapoda (crown group)

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

Dipnomorpha
TetrapodomorphaKenichthys Tungsenia Rhizodontida Hongyu Gooloogongia Sauripterus Barameda Screbinodus Rhizodus Strepsodus Osteolepidida Gyroptychius Osteolepis Gogonasus Medoevia Megalichthyidae Canowindridae Beelarongia Canowindra Koharalepis Marsdenichthys Spodichthys Tristichopterus Eusthenopteron Jarvikina Cabonnichthys Platycephalichthys Mandageria Eusthenodon Tinirau Bruehnopteron Panderichthys Tiktaalik Elpistostege Tetrapoda Ventastega Acanthostega Ichthyostega Tulerpeton
Kenichthys
Tungsenia Rhizodontida Hongyu Gooloogongia Sauripterus Barameda Screbinodus Rhizodus Strepsodus Osteolepidida Gyroptychius Osteolepis Gogonasus Medoevia Megalichthyidae Canowindridae Beelarongia Canowindra Koharalepis Marsdenichthys Spodichthys Tristichopterus Eusthenopteron Jarvikina Cabonnichthys Platycephalichthys Mandageria Eusthenodon Tinirau Bruehnopteron Panderichthys Tiktaalik Elpistostege Tetrapoda Ventastega Acanthostega Ichthyostega Tulerpeton
Tungsenia
Rhizodontida Hongyu Gooloogongia Sauripterus Barameda Screbinodus Rhizodus Strepsodus Osteolepidida Gyroptychius Osteolepis Gogonasus Medoevia Megalichthyidae Canowindridae Beelarongia Canowindra Koharalepis Marsdenichthys Spodichthys Tristichopterus Eusthenopteron Jarvikina Cabonnichthys Platycephalichthys Mandageria Eusthenodon Tinirau Bruehnopteron Panderichthys Tiktaalik Elpistostege Tetrapoda Ventastega Acanthostega Ichthyostega Tulerpeton
RhizodontidaHongyu Gooloogongia Sauripterus Barameda Screbinodus Rhizodus Strepsodus
Hongyu
Gooloogongia Sauripterus Barameda Screbinodus Rhizodus Strepsodus
Gooloogongia
Sauripterus Barameda Screbinodus Rhizodus Strepsodus
Sauripterus
Barameda
Screbinodus Rhizodus Strepsodus
Screbinodus
Rhizodus Strepsodus
Rhizodus
Strepsodus
Osteolepidida Gyroptychius Osteolepis Gogonasus Medoevia Megalichthyidae Canowindridae Beelarongia Canowindra Koharalepis Marsdenichthys Spodichthys Tristichopterus Eusthenopteron Jarvikina Cabonnichthys Platycephalichthys Mandageria Eusthenodon Tinirau Bruehnopteron Panderichthys Tiktaalik Elpistostege Tetrapoda Ventastega Acanthostega Ichthyostega Tulerpeton
OsteolepididaGyroptychius Osteolepis Gogonasus Medoevia Megalichthyidae Canowindridae Beelarongia Canowindra Koharalepis
Gyroptychius
Osteolepis
Gogonasus Medoevia Megalichthyidae Canowindridae Beelarongia Canowindra Koharalepis
Gogonasus
Medoevia
Megalichthyidae Canowindridae Beelarongia Canowindra Koharalepis
Megalichthyidae
CanowindridaeBeelarongia Canowindra Koharalepis
Beelarongia
Canowindra Koharalepis
Canowindra
Koharalepis
Marsdenichthys Spodichthys Tristichopterus Eusthenopteron Jarvikina Cabonnichthys Platycephalichthys Mandageria Eusthenodon Tinirau Bruehnopteron Panderichthys Tiktaalik Elpistostege Tetrapoda Ventastega Acanthostega Ichthyostega Tulerpeton
Marsdenichthys
Spodichthys Tristichopterus Eusthenopteron Jarvikina Cabonnichthys Platycephalichthys Mandageria Eusthenodon Tinirau Bruehnopteron Panderichthys Tiktaalik Elpistostege Tetrapoda Ventastega Acanthostega Ichthyostega Tulerpeton
Spodichthys
Tristichopterus Eusthenopteron Jarvikina Cabonnichthys Platycephalichthys Mandageria Eusthenodon Tinirau Bruehnopteron Panderichthys Tiktaalik Elpistostege Tetrapoda Ventastega Acanthostega Ichthyostega Tulerpeton
Tristichopterus
Eusthenopteron Jarvikina Cabonnichthys Platycephalichthys Mandageria Eusthenodon Tinirau Bruehnopteron Panderichthys Tiktaalik Elpistostege Tetrapoda Ventastega Acanthostega Ichthyostega Tulerpeton
Eusthenopteron
Jarvikina Cabonnichthys Platycephalichthys Mandageria Eusthenodon Tinirau Bruehnopteron Panderichthys Tiktaalik Elpistostege Tetrapoda Ventastega Acanthostega Ichthyostega Tulerpeton
Jarvikina
Cabonnichthys Platycephalichthys Mandageria Eusthenodon Tinirau Bruehnopteron Panderichthys Tiktaalik Elpistostege Tetrapoda Ventastega Acanthostega Ichthyostega Tulerpeton
Cabonnichthys Platycephalichthys Mandageria Eusthenodon
Cabonnichthys
Platycephalichthys Mandageria Eusthenodon
Platycephalichthys
Mandageria Eusthenodon
Mandageria
Eusthenodon
Tinirau Bruehnopteron Panderichthys Tiktaalik Elpistostege Tetrapoda Ventastega Acanthostega Ichthyostega Tulerpeton
Tinirau
Bruehnopteron Panderichthys Tiktaalik Elpistostege Tetrapoda Ventastega Acanthostega Ichthyostega Tulerpeton
Bruehnopteron
Panderichthys Tiktaalik Elpistostege Tetrapoda Ventastega Acanthostega Ichthyostega Tulerpeton
Panderichthys
Tiktaalik Elpistostege Tetrapoda Ventastega Acanthostega Ichthyostega Tulerpeton
Tiktaalik
Elpistostege Tetrapoda Ventastega Acanthostega Ichthyostega Tulerpeton
Elpistostege
TetrapodaVentastega Acanthostega Ichthyostega Tulerpeton
Ventastega
Acanthostega Ichthyostega Tulerpeton
Acanthostega
Ichthyostega Tulerpeton
Ichthyostega
Tulerpeton

Citations

  • Mikko Haaramo. . Archived from on 12 May 2006.
  • P. E. Ahlberg & Z. Johanson (1998). "Osteolepiforms and the ancestry of tetrapods". Nature. 395 (6704): 792–794. Bibcode:. doi:. S2CID .
  • Michel Laurin, Marc Girondot & Armand de Ricqlès (2000). (PDF). TREE. 15 (3). Archived from (PDF) on 2009-09-22.