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 term, ...

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, ...

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 theraps ...

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 includi ...

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 consid ...

s, such as ''

Tiktaalik ''Tiktaalik'' (; Inuktitut ) is a monospecific genus of extinct sarcopterygian (lobe-finned fish) from the Late Devonian Period, about 375 Mya (million years ago), having many features akin to those of tetrapods (four-legged animals). It may ha ...

'', 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

osteolepiform Osteolepiformes, also known as Osteolepidida, is a group of prehistoric lobe-finned fishes which first appeared during the Devonian period. The order contains the families Canowindridae, Megalichthyidae, Osteolepididae and Tristichopteridae. Th ...

s. The Tetrapodamorpha minus the

Tetrapoda are the Stem Tetrapoda, a

paraphyletic In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...

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 roun ...

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 ''Kenichthys'' is a genus of sarcopterygian fish from the Devonian period, and a member of the clade tetrapodomorpha. The only known species of the genus is ''Kenichthys campbelli'' (named for the Australian palaeontologist Ken Campbell), the fi ...

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 crocodilia ...

. 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, whe ...

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 ''Panderichthys'' is a genus of extinct sarcopterygian (lobe-finned fish) from the late Devonian period, about 380 Mya. ''Panderichthys'', which was recovered from Frasnian (early Late Devonian) deposits in Latvia, is represented by two species. ...

'', ''

'' and ''

Tungsenia ''Tungsenia'' is an extinct genus of basal tetrapodomorph bony fish known from the ~409 mya (Early Devonian) of northeastern Yunnan Province Yunnan , () is a landlocked province in the southwest of the People's Republic of China. The p ...

''.

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 Rhizodontida is an extinct group of predatory tetrapodomorphs known from many areas of the world from the Givetian through to the Pennsylvanian - the earliest known species is about 377 million years ago (Mya), the latest around 310 Mya. Rhizodo ...

::::* Family †

Sauripteridae Rhizodontida is an extinct group of predatory tetrapodomorphs known from many areas of the world from the Givetian through to the Pennsylvanian - the earliest known species is about 377 million years ago (Mya), the latest around 310 Mya. Rhizodo ...

::::* Family †

Rhizodontidae Rhizodontida is an extinct group of predatory tetrapodomorphs known from many areas of the world from the Givetian through to the Pennsylvanian - the earliest known species is about 377 million years ago (Mya), the latest around 310 Mya. Rhizodo ...

::* Superorder †

Osteolepidida Osteolepiformes, also known as Osteolepidida, is a group of prehistoric lobe-finned fishes which first appeared during the Devonian period. The order contains the families Canowindridae, Megalichthyidae, Osteolepididae and Tristichopteridae ...

(or Osteolepiformes) ::::* Family † Canowindridae ::::* Family †

Thysanolepidae Osteolepiformes, also known as Osteolepidida, is a group of prehistoric lobe-finned fishes which first appeared during the Devonian period. The order contains the families Canowindridae, Megalichthyidae, Osteolepididae and Tristichopterida ...

::::* Family †

Tristichopteridae Tristichopterids (Tristichopteridae) were a diverse and successful group of tetrapodomorph fishes living throughout the Middle and Late Devonian. They first appeared in the Eifelian stage of the Middle Devonian. Within the group sizes ranged fro ...

:::* Order †

Osteolepiformes Osteolepiformes, also known as Osteolepidida, is a group of prehistoric lobe-finned fishes which first appeared during the Devonian period. The order contains the families Canowindridae, Megalichthyidae, Osteolepididae and Tristichopterida ...

(or Megalichthyiformes) ::::* Family †

Osteolepidae Osteolepididae is an family (biology), family of primitive, fish-like tetrapodomorphs (the clade that contains modern tetrapods and their extinct relatives) that lived during the Devonian geological period, period. The family is generally thought ...

::::* 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 Afr ...

::* Clade

Eotetrapodiformes Eotetrapodiformes is a clade of tetrapodomorphs including the four-limbed vertebrates ("tetrapods" in the traditional sense) and their closest fish fin, finned relatives, two groups of stem tetrapods called tristichopterids and elpistostegalids. ...

:::* Clade

Elpistostegalia Elpistostegalia or Panderichthyida is an order of prehistoric lobe-finned fishes which lived during the Middle Devonian to Late Devonian period (about 385 to 374 million years ago). They represent the advanced tetrapodomorph stock, the fishes m ...

(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 Whatcheeriidae is an extinct family of tetrapods which lived in the Mississippian sub-period, a subdivision of the Carboniferous period. It contains the genera ''Pederpes'', '' Whatcheeria'', and possibly ''Ossinodus''. Fossils of a possible w ...

:::::* Family †

Colosteidae Colosteidae is a family of stegocephalians (tetrapod-like vertebrates) that lived in the Carboniferous period. They possessed a variety of characteristics from different tetrapod or stem-tetrapod groups, which made them historically difficult to ...

:::::* 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 c ...

:::::* Superclass Tetrapoda Other clades include the

(''

Tinirau In Polynesian mythology, stories about Tinirau are found throughout the islands of Polynesia. He is a guardian of fish. Many themes recur in the various versions. Often he travels to another land in search of his wife, or his wife travels to anot ...

'', ''

Platycephalichthys ''Platycephalichthys'' is a genus of tristichopterid lobe-finned fish which lived during the middle Devonian, upper Givetian stage. Phylogeny Below is a cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") ...

'', the

and

). 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 consid ...

and

Ichthyostegalia Ichthyostegalia is an order of extinct amphibians, representing the earliest landliving vertebrates. The group is thus an evolutionary grade rather than a clade. While the group are recognized as having feet rather than fins, most, if not all, ...

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