Batrachomorpha

Taxobox
name = Batrachomorpha
regnum = Animalia
phylum = Chordata
subphylum = Vertebrata
unranked_classis = Sarcopterygii
superclassis = Tetrapoda
unranked_ordo = Batrachomorpha
unranked_ordo_authority = Säve-Söderbergh, 1934
subdivision_ranks = Groups
subdivision =
Temnospondyli
Lissamphibia

Batrachomorpha ("Frog form") is a name given to recent and extinct amphibians that are not related to reptiles.

Origin of the term: Are salamanders amphibians?

The name was coined by the Swedish palaeontologist Gunnar Säve-Söderbergh in 1934 to refer to the ichthyostegids, the labyrinthodonts, and the anurans. Säve-Söderbergh held the view that salamanders and caecilians are not related to the other tetrapods, but had developed independently from a different group of lobe-fined fish (the porolepiformes) [Säve-Söderbergh, G. (1934). Some points of view concerning the evolution of the vertebrates and the classification of this group. "Arkiv för Zoologi" 26A: pp 1-20] In this view amphibians would be a polyphyletic group, and Batrachomorpha was erected to form a natural group consisting of the "true amphibians" (i.e frogs in Säve-Söderberghs view) and their fossil relatives.

Friedrich von Huene adopted it as a superorder of his subclass "Eutetrapoda" (the lower tetrapods exclusive of the urodeles) and included the orders Stegocephalia (here includes a number of Labyrinthodontia and Anura. [von Huene, F. (1956): "Paläontologie und Phylogenie der niederen Tetrapoden", G. Fischer, Jena] . Erik Jarvik, who took over Säve-Söderberghs work and shared his view of the origin of the slamanders, used the term more informally, but in a wider sense, to include the ancestral osteolepiform fishes. [Jarvik, E. (1980). "Basic structure and evolution of vertebrates." Vol. 2. London: Academic Press.]

Though never a majority view, the notion that tetrapods had evolved twice, together with the usage of the term batrachomorpha, lingered until genetic analysis started conforming the monophyly of living amphibians in the 1990ies. [San Mauro & al (2005): Initial diversification of living amphibians predated the breakup of Pangaea. "American Naturalist" no 165: pp 590–599] . Jarviks classification is no longer followed.

Redefining Batrachomorpha, cladistic views

Michael Benton adopted the term Batrachomorpha in a cladistic sense to include all living amphibians, their common ancestor, and extinct relatives. This is suggested as a more precise term than "Amphibia", which is not diagnostic as it simply refers to all non-amniote tetrapods. However, the phylogenetic relationships of Paleozoic tetrapods have not yet been worked out with certainty, and the validity of the clade Batrachomorpha depends on where other amphibians and early amniotes fit on the evolutionary tree, and in some phylogenies the clade is redundant (e.g. Laurin 1996).

Anatomy of the Batrachomorps

Batrachomorphs are distinguished by a number of features in the skeleton, including a flat or shallow skull, a fused skull roof with no cranial kinesis, exoccipital-postparietal contact on the occiput, and four or fewer fingers on the hand. [Benton, M. J. (2000), Vertebrate Paleontology, 2nd Ed. Blackwell Science Ltd 3rd ed, pp.98-99]

Dr Benton contrasts Batrachomorphs with Reptiliomorphs; both are stem-based clades, but the former constitutes the "amphibian" evolutionary radiation, the later the contemporary proto-reptilian and early amniote evolution.

In the appendix to Benton 2004 (which combines cladistic and linnaean rankings) Batrachomorpha is given the taxonomic rank of Class.

References

General references and External links

* Benton, M. J. (2000), "Vertebrate Paleontology", 2nd Ed. Blackwell Science Ltd 3rd ed. 2004 - see also [http://palaeo.gly.bris.ac.uk/benton/vertclass.html taxonomic hierarchy of the vertebrates] , according to Benton 2004
* Laurin, Michel (1996) [http://tolweb.org/tree?group=Terrestrial_Vertebrates&contgroup=Sarcopterygii Terrestrial Vertebrates - Stegocephalians: Tetrapods and other digit-bearing vertebrates]
* Marjanović, David, (2002) [http://dml.cmnh.org/2002Jan/msg01091.html Re: thoughts on which nodes to name] Dinosaur Mailing List
* Jarvik, E. (1968). Aspects of vertebrate phylogeny. In: "Current Problems of Lower Vertebrate Phylogeny" (ed. T. Ørvig), Nobel Symposium 4, pp. 497-527. Stockholm, Almqvist & Wiksell.