Reptiloform - Changing Definitions

Changing Definitions

The name Reptiliomorpha was coined by Professor Gunnar Säve-Söderbergh in 1934 to designate various types of late Paleozoic reptile-like labyrinthodont "amphibians". In his view, the amphibians had evolved from fish twice, with one group composed of the ancestors of modern salamanders and caecilians and the other, which Säve-Söderbergh referred to as Reptiliomorpha, consisting of the ancestors of anurans (frogs) and amniotes.

Alfred Sherwood Romer rejected Säve-Söderbergh's theory of a biphyletic amphibia and used the name Anthracosauria to describe the labyrithodont lineage from which amniotes evolved. In 1970, the German paleontologist Alec Panchen took up Säve-Söderberghs name for this group as having priority, but Romer's terminology is still in use, e.g. by Carroll (1988 and 2002) and by Hildebrand & Goslow (2001). Some writers preferring phylogenetic nomenclature use Anthracosauria.

In 1956, Friedrich von Huene included both amphibians and anapsid reptiles in the Reptiliomorpha. This included the following orders: Anthracosauria, Seymouriamorpha, Microsauria, Diadectomorpha, Procolophonia, Pareiasauria, Captorhinidia, Testudinata.

In 1997, Michel Laurin and Robert Reisz (1997) adapted the term in a sense compatible with the Phylocode. Michael Benton (2000, 2004) made it the sister-clade to Lepospondyli. However, when considered in a Linnean framework, Reptiliomorpha is given the rank of superorder and includes only reptile-like amphibians, not their amniote descendants. More recently, in accordance with the Phylocode, Reptiliomorpha has been adopted as the term for the largest clade that includes Homo sapiens but not Ascaphus truei (a primitive frog) or is, as Toby White (Palaeos website) puts it, more like dogs than frogs (i.e. more like mammals than like amphibians). However, given the lack of consensus of the phylogeny of the labyrinthodonts in general, and the origin of modern amphibians in particular, the actual content of the Reptiliomorpha under the latter definition is uncertain.