Stegocephalia* Fossil range: Devonian to Jurassic
Proterogyrinus, an Anthracosaur
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Amphibia sensu lato
Order:	Stegocephalia*

Stegocephalia is an old term for early (generally large) amphibians, comprising all pre-Jurassic and some later extinct large amphibians of more or less salamander-like build. The term was coined in 1868 by American palaentologist Edward Drinker Cope and comes from Greek stego cephalia - "roofed head", and refer to the copious amounts of dermal armour some of the larger forms evidently had.^[1]

Originally, the term was used as a systematic unit at the rank of order. Later, the term Labyrinthodontia was used, divided into three orders.^[2] However, the Stegocephalia (and the Labyrinthodontia) being paraphyletic, the name is now used in an informal way to denote the early non-piscine vertebrates, excluding amniotes (the first reptiles and their descendants) and modern lissamphibians).

Contents 1 Systematic overview of Stegocephalians 2 Cladistic use of Stegocephalia 3 References 4 External links

[edit] Systematic overview of Stegocephalians

Systematic based on Colbert (1969)^[3]

(from lobe-fined fish)

    `- Eusthenopteron (advanced lobe-fined fish)       `- Panderichthys (lobe-fined fish with limb-like fins)          `- Tiktaalik (transitional fish/amphibian)             `- Acanthostega (early amphibian with fishlike gills)                `- Ichthyostega (early amphibian)                   `- Crassigyrinus (early amphibian)                      |- Loxommatidae(eel-like primitive temnospondyles)                      |  `-Temnospondyls (large, flat-headed stegocephalians)                      `- Anthracosaurs (reptile-like amphibians)                          |- Seymouriamorphs (advanced repile-like amphibians)                          |  |- Westlothiana (small amphibian or possibly early reptile)                          |  `+ Diadectomorphs (earliest reptiles or sister groups of reptiles)                          |    `- amniotes (i.e. first reptiles)                          `- Lepospondyls (small stegocephalians)                               `?- Lissamphibia (modern amphibians) 

[edit] Cladistic use of Stegocephalia

Recent taxonomic work has redefined stegocephalians as all vertebrates more closely related to temnospondyli than to Panderichthys (the closest relative of tetrapods known to have retained paired fins, see below) ^[4] Therefore, stegocephalia includes all vertebrate groups that have toes rather than fins, and a few (Elginerpeton, Metaxygnathus, Ventastega and possibly Hynerpeton) that may have retained paired fins. Contrary to the old usage of this term, the Stegocephali refers to a clade in this scheme. This concept of the clade Stegocephalia was chosen to substitute for the name Tetrapoda by those who sought to restrict Tetrapoda to the crown group.^[5] As such, it encompasses all presently living land vertebrates as well as their early amphibious ancestors.

[edit] References

[edit] External links

• Tree of Life: Terrestrial Vertebrates