Stegocephalia
| Stegocephalia* Temporal range: Devonian to Jurassic |
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| Classical 19th century interpretation of Stegocephalians from the Crystal Palace. | |
| 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 στεγοκεφαλια - "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).
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[edit] Systematic overview of Stegocephalians and relatives
Below is a suggested evolutionary tree of Labyrinthodontia, from Colbert 1969 and Caroll 1997.[3][4] Dashed lines indicate relationships that commonly vary between authors.
| From lobe-finned fish |
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[edit] Cladistic use of Stegocephalia
Paleontologist Michel Laurin has taken up the old term and defined stegocephalians cladistically as all vertebrates more closely related to temnospondyli than to Panderichthys (the closest relative of tetrapods known to have retained paired fins, see below) [5] 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.[6] As such, it encompasses all presently living land vertebrates as well as their early amphibious ancestors.
[edit] References
- ^ Cope E. D. 1868. Synopsis of the extinct Batrachia of North America. Proceedings of The Academy of Natural Sciences of Philadelphia: pp 208-221
- ^ Romer, A. S., (1947, revised ed. 1966) Vertebrate Paleontology, University of Chicago Press, Chicago
- ^ Colbert, E. H., (1969), Evolution of the Vertebrates, John Wiley & Sons Inc (2nd ed.)
- ^ Carroll, R. L. (1997): Patterns and Processes of Vertebrate Evolution. Cambridge University Press, Cambridge. 464 pages
- ^ Laurin M. (1998): The importance of global parsimony and historical bias in understanding tetrapod evolution. Part I-systematics, middle ear evolution, and jaw suspension. Annales des Sciences Naturelles, Zoologie, Paris, 13e Series 19: pp 1-42.
- ^ Laurin & al. Terrestrial Vertebrates. Stegocephalians: Tetrapods and other digit-bearing vertebrates. Tree of life
