Tetrapodomorpha is a clade

Clade

A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...

 of vertebrate

Vertebrate

Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...

s, consisting of tetrapod

Tetrapod

Tetrapods are vertebrate animals having four limbs. Amphibians, reptiles, birds and mammals are all tetrapods; even snakes and other limbless reptiles and amphibians are tetrapods by descent. The earliest tetrapods evolved from the lobe-finned fishes in the Devonian...

s (four-limbed vertebrates) and their closest sarcopterygian

Sarcopterygii

The Sarcopterygii or lobe-finned fishes – sometimes considered synonymous with Crossopterygii constitute a clade of the bony fishes, though a strict classification would include the terrestrial vertebrates...

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

Lungfish

Lungfish are freshwater fish belonging to the Subclass Dipnoi. Lungfish are best known for retaining characteristics primitive within the Osteichthyes, including the ability to breathe air, and structures primitive within Sarcopterygii, including the presence of lobed fins with a well-developed...

. Advanced forms transitional between fish and the early labyrinthodonts, like Tiktaalik

Tiktaalik

Tiktaalik is a genus of extinct sarcopterygian from the late Devonian period, with many features akin to those of tetrapods . It is an example from several lines of ancient sarcopterygian "fish" developing adaptations to the oxygen-poor shallow-water habitats of its time, which led to the...

, have been referred to as "fishapods" by their discoverers, being half-fish half-tetrapods, in appearance and limb morphology. Tetrapodomorpha contains the crown group

Crown group

A crown group is a group consisting of living representatives, their ancestors back to the most recent common ancestor of that group, and all of that ancestor's descendants. The name was given by Willi Hennig, the formulator of phylogenetic systematics, as a way of classifying living organisms...

 tetrapods (the last common ancestor of living tetrapods and all of its descendants) and several groups of early stem tetrapods. Tetrapodomorpha contains several groups of related lobe-finned fishes, collectively known as the osteolepiforms. The Tetrapodamorpha minus the crown group

Crown group

A crown group is a group consisting of living representatives, their ancestors back to the most recent common ancestor of that group, and all of that ancestor's descendants. The name was given by Willi Hennig, the formulator of phylogenetic systematics, as a way of classifying living organisms...

 Tetrapoda is the Stem Tetrapoda

Stem Tetrapoda

Stem Tetrapoda is a cladistically defined group, consisting of all animals more closely related to extant four legged vertebrates than to their closest extant relatives , but excluding the crown group Tetrapoda...

, a paraphyletic unit encompassing the fish to tetrapod transition.

Among the characters defining tetrapodomorphs are modifications to the fins, notably a humerus

Humerus

The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....

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

Shoulder

The human shoulder is made up of three bones: the clavicle , the scapula , and the humerus as well as associated muscles, ligaments and tendons. The articulations between the bones of the shoulder make up the shoulder joints. The major joint of the shoulder is the glenohumeral joint, which...

 joint).

Tetrapodomorph fossils are known from the early Devonian

Devonian

The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...

 onwards, and include Osteolepis

Osteolepis

Osteolepis is an extinct genus of lobe-finned fish from the Devonian period. It lived in the Orcadian Lakes of northern Scotland....

, Panderichthys

Panderichthys

Panderichthys is a 90–130 cm long fish from the Devonian period 397 million years ago, of Latvia. It is named after the german-baltic palaeontologist Christian Heinrich Pander. It has a large tetrapod-like head...

and Kenichthys

Kenichthys

Kenichthys was an ancient tetrapodomorph, a lineage that included tetrapods. It was one of the most primitive tetrapodomorphs. This specific genus is important because it contains a primitive choana on its upper lip, giving it a cleft palate-like structure...

.

Classification

Taxonomy

After Benton, 2004 http://palaeo.gly.bris.ac.uk/benton/vertclass.html:

• Subclass Sarcopterygii
  Sarcopterygii
  The Sarcopterygii or lobe-finned fishes – sometimes considered synonymous with Crossopterygii constitute a clade of the bony fishes, though a strict classification would include the terrestrial vertebrates...
  
  
  • Infraclass Tetrapodomorpha
    • • Order Rhizodont
        Rhizodont
        Rhizodonts are an extinct group of predatory lobe-finned fishes. They are known from many areas of the world from the Givetian through to the Pennsylvanian - the earliest known species is about 377 Ma, the latest around 310 Ma. Rhizodonts lived in tropical rivers and freshwater lakes and were the...
        
        ida
    • Superorder Osteolepidida (or Osteolepiformes)
      • Order Osteolepiformes
        Osteolepiformes
        Osteolepiformes are a group of prehistoric lobe-finned fishes which appears first time during the Devonian period. The order contains five families: Canowindridae, Elpistostegidae, Megalichthyidae, Osteolepidae and Tristichopteridae...
        
        
        • Family Tristichopteridae
          Tristichopteridae
          Tristichopterids , were a diverse and successful group of tetrapodomorph fishes throughout the Late Devonian stage. They first appeared in the Givetian epoch of the Middle Devonian stage...
          
          
      • Order Panderichthyida

Phylogeny

Cladogram

Cladogram

A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...

 modified after Ruta, Jeffery, & Coates (2003):