Tetrapodomorpha

Tetrapodomorpha(also known asChoanata) is acladeofvertebratesconsisting oftetrapods(four-limbed vertebrates) and their closestsarcopterygianrelatives that are more closely related to living tetrapods than to livinglungfish.Advanced forms transitional between fish and the earlylabyrinthodonts,such asTiktaalik,have been referred to as "fishapods"by their discoverers, being half-fish, half-tetrapods, in appearance and limb morphology. The Tetrapodomorpha contains thecrown grouptetrapods (the last common ancestor of living tetrapods and all of its descendants) and several groups of earlystem tetrapods,which includes several groups of related lobe-finned fishes, collectively known as theosteolepiforms.The Tetrapodomorpha minus thecrown groupTetrapoda are thestem Tetrapoda,aparaphyleticunit encompassing the fish to tetrapod transition.

Tetrapodomorpha Temporal range: Early Devonian–Present,
Life restoration ofPanderichthys
Moderntetrapods
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Sarcopterygii
Clade:	Rhipidistia
Clade:	Tetrapodomorpha Ahlberg, 1991
Subgroups
†Kenichthys †Tungsenia Choanata †Rhizodontida †"Osteolepidida" †Tristichopteridae Elpistostegalia Stegocephali Tetrapoda See alsobelow.

Characteristics

Among the characteristics defining tetrapodomorphs are modifications to the fins, notably ahumeruswith convex head articulating with the glenoid fossa (the socket of theshoulderjoint). Another key trait is the internal nostril orchoana.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 likeKenichthys,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 thechoana.The nearly-equivalent clade Choanata often refers to these later forms specifically.

History

Tetrapodomorph fossils are known from the earlyDevonianonwards, and includeOsteolepis,Panderichthys,KenichthysandTungsenia.Tetrapodomorphaevolved from ancientlobe-finned fish(sarcopterygians) around390million years agoin theMiddle Devonian period.

Classification

InLate Devonianvertebratespeciation, descendants ofpelagiclobe-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.

• SubclassSarcopterygii

• 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

• CladeEotetrapodiformes

• CladeElpistostegalia(or Panderichthyida)

• CladeStegocephalia

• Family †Elpistostegidae
• Family †Whatcheeriidae
• Family †Colosteidae
• Superfamily †Baphetoidea
• SuperclassTetrapoda

Other clades include theEotetrapodiformes(Tinirau,Platycephalichthys,theTristichopteridaeandElpistostegalia).Older taxa which include latestem tetrapodsand earlytetrapodsare theLabyrinthodontiaandIchthyostegalia.

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)

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

	Dipnomorpha
Tetrapodomorpha	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

References

• Mikko Haaramo."Tetrapodomorpha – Terrestrial vertebrate-like sarcopterygians".Archived fromthe originalon 12 May 2006.Retrieved6 April2006.
• P. E. Ahlberg & Z. Johanson (1998). "Osteolepiforms and the ancestry of tetrapods".Nature.395(6704): 792–794.Bibcode:1998Natur.395..792A.doi:10.1038/27421.S2CID4430783.
• Michel Laurin, Marc Girondot & Armand de Ricqlès (2000)."Early tetrapod evolution"(PDF).TREE.15(3).