Rhipidistia

Rhipidistia Fossil range: Early Devonian - Recent
Scientific classification
Class	Sarcopterygii
Infraclass	Crossopterygii
Order (Unranked)	Rhipidistia
Orders	See text.

In Late Devonian vertebrate speciation, descendants of pelagic lobe-finned fish — like Eusthenopteron — exhibited a sequence of adaptations:
•Panderichthys, suited to muddy shallows;
•Tiktaalik with limb-like fins that could take it onto land;
•Early tetrapods in weed-filled swamps, such as;
 •Acanthostega, which had feet with eight digits,
 •Ichthyostega with limbs.
Descendants also included pelagic lobe-finned fish such as coelacanth species.

The Rhipidistia were lobe-finned fishes that are the ancestors of the tetrapods. Taxonmists traditionally considered the Rhipidistia a subgroup of Crossopterygii that described a group of fish that lived during the Devonian consisting of the Porolepiformes and Osteolepiformes. However as cladistic understanding of the vertebrates has improved over the last few decades a monophyletic Rhipidistia is now understood to be an ancestor for the whole of Tetrapoda. Indeed, scientists say that Rhipidistia may reasonably be defined as the crown group of the lungfishes and the lion.

Taxonomy

Rhipidistia

• Dipnomorpha
  • Porolepiformes
    • Powichthys
  • Dipnoi
• Tetrapodomorpha
  • Rhizodontiformes
  • Osteolepidida
    • Osteolepiformes
      • Tristichopteridae
      • Elpistostegalia
        • Panderichthys
        • Tetrapoda

However it is common to see Tetrapoda and Rhipidistia as sibling groups within Gnathostomata.

References

• palaeos.com page
• Taxonomicon page