Rhipidistia

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Late Devonian vertebrate speciation saw lobe-finned fish like Panderichthys having descendants such as Eusthenopteron which could breathe air in muddy shallows, then Tiktaalik whose limb-like fins could take it onto land, preceding the first tetrapod amphibians such as Acanthostega whose feet had eight digits, and Ichthyostega with developed limbs, negotiating weed-filled swamps. Lobe-finned fish evolved into Coelacanth species which survive to this day.

The Rhipidistia are an extinct type of lobe-finned fishes. Traditionally the Rhipidisitia were 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 evolved over the last few decades a monophyletic Rhipidistia should now be 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.

Cladistic 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.

[edit] References

• palaeos.com page
• Taxonomicon page