The Tetrapodomorpha (also known as Choanata) are a

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English ter ...

vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with ...

s consisting of

tetrapod Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids ( pelycosaurs, extinct t ...

s (four-limbed vertebrates) and their closest

sarcopterygian Sarcopterygii (; ) — sometimes considered synonymous with Crossopterygii () — is a taxon (traditionally a class or subclass) of the bony fishes known as the lobe-finned fishes. The group Tetrapoda, a mostly terrestrial superclass includ ...

relatives that are more closely related to living tetrapods than to living

lungfish Lungfish are freshwater vertebrates belonging to the order Dipnoi. Lungfish are best known for retaining ancestral characteristics within the Osteichthyes, including the ability to breathe air, and ancestral structures within Sarcopterygii, i ...

. Advanced forms transitional between fish and the early

labyrinthodont "Labyrinthodontia" (Greek, 'maze-toothed') is an informal grouping of extinct predatory amphibians which were major components of ecosystems in the late Paleozoic and early Mesozoic eras (about 390 to 150 million years ago). Traditionally conside ...

s, 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 In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor ...

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 Tetrapodamorpha minus the

Tetrapoda are the Stem Tetrapoda, a

paraphyletic In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and most of its descendants, excluding a few monophyletic subgroups. The group is said to be paraphyletic ''with respect to'' the excluded subgroups. In ...

unit encompassing the fish to tetrapod transition. Among the characteristics defining tetrapodomorphs are modifications to the fins, notably a

humerus The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a r ...

with convex head articulating with the glenoid fossa (the socket of the

shoulder The human shoulder is made up of three bones: the clavicle (collarbone), the scapula (shoulder blade), and the humerus (upper arm bone) as well as associated muscles, ligaments and tendons. The articulations between the bones of the shoulder mak ...

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 The choanae (singular choana), posterior nasal apertures or internal nostrils are two openings found at the back of the nasal passage between the nasal cavity and the throat in tetrapods, including humans and other mammals (as well as crocodili ...

. Tetrapodomorph fossils are known from the early

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, wh ...

onwards, and include ''

Osteolepis ''Osteolepis'' (from el, ὀστέον 'bone' and el, λεπίς 'scale') is an extinct genus of lobe-finned fish from the Devonian period. It lived in the Lake Orcadie of northern Scotland. ''Osteolepis'' was about long, and covered with ...

'', '' Panderichthys'', '' Kenichthys'' and '' Tungsenia''.

Classification

Zachelmie tracks vs selected Devonian fossils

Taxonomy

After Benton, 2004; and Swartz, 2012. * Subclass

Sarcopterygii Sarcopterygii (; ) — sometimes considered synonymous with Crossopterygii () — is a taxon (traditionally a class or subclass) of the bony fishes known as the lobe-finned fishes. The group Tetrapoda, a mostly terrestrial superclass includi ...

:* Infraclass Tetrapodomorpha ::* Order † Rhizodontida ::::* Family † Sauripteridae ::::* Family † Rhizodontidae ::* Superorder † Osteolepidida (or Osteolepiformes) ::::* Family †

Canowindridae The Canowindridae are a family of prehistoric lobe-finned fishes which lived during the Devonian period (Famennian stage, about 374 to 359 million years ago). Fossils of fishes that belonged to this family have been found in Australia, Antarctic ...

::::* Family † Thysanolepidae ::::* Family † Tristichopteridae :::* Order † Osteolepiformes (or Megalichthyiformes) ::::* Family † Osteolepidae ::::* Family †

Megalichthyidae Megalichthyidae is an extinct family of tetrapodomorphs which lived from the Middle–Late Devonian to the Early Permian. They are known primarily from freshwater deposits, mostly in the Northern Hemisphere (Europe, the Middle East, North Africa ...

::* Clade Eotetrapodiformes :::* Clade Elpistostegalia (or Panderichthyida) ::::* Clade

Stegocephalia Stegocephali (often spelled Stegocephalia) is a group containing all four-limbed vertebrates. It is equivalent to a broad definition of Tetrapoda: under this broad definition, the term "tetrapod" applies to any animal descended from the first ve ...

:::::* Family † Elpistostegidae :::::* Family † Whatcheeriidae :::::* Family † Colosteidae :::::* Superfamily †

Baphetoidea Baphetoidea is a superfamily of early tetrapods. It includes the family Baphetidae and several more basal genera such as '' Eucritta'' and '' Spathicephalus'' (which has been given its own family Spathicephalidae). The superfamily has also been ...

:::::* Superclass Tetrapoda Other clades include the Eotetrapodiformes ('' Tinirau'', '' Platycephalichthys'', the Tristichopteridae and Elpistostegalia). Older taxa which include late stem tetrapods and early

s are the

Labyrinthodontia "Labyrinthodontia" ( Greek, 'maze-toothed') is an informal grouping of extinct predatory amphibians which were major components of ecosystems in the late Paleozoic and early Mesozoic eras (about 390 to 150 million years ago). Traditionally con ...

and Ichthyostegalia.

Relationships

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

References

* * * {{Taxonbar, from=Q1209254 Extant Early Devonian first appearances tl:Tetrapodomorpha