Definitions

Batrachomorpha

Batrachomorpha

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) 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.. 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.

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.. 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.

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

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