Reptiliomorpha

Reptiliomorpha (meaning reptile-shaped; in PhyloCode known as Pan-Amniota) is a clade containing the amniotes and those tetrapods that share a more recent common ancestor with amniotes than with living amphibians (lissamphibians). It was defined by Michel Laurin (2001) and Vallin and Laurin (2004) as the largest clade that includes Homo sapiens, but not Ascaphus truei (tailed frog). Laurin and Reisz (2020) defined Pan-Amniota as the largest total clade containing Homo sapiens, but not Pipa pipa, Caecilia tentaculata, and Siren lacertina. The informal variant of the name, "reptiliomorphs", is also occasionally used to refer to stem-amniotes, i.e. a grade of reptile-like tetrapods that are more closely related to amniotes than they are to lissamphibians, but are not amniotes themselves; the name is used in this meaning e.g. by Ruta, Coates and Quicke (2003). An alternative name, "Anthracosauria", is also commonly used for the group, but is confusingly also used for a more primitive grade of reptiliomorphs (Embolomeri) by Benton. While both anthracosaurs and embolomeres are suggested to be reptiliomorphs closer to amniotes, some recent studies either retain them as amphibians or argue that their relationships are still ambiguous and are more likely to be stem-tetrapods. As the exact phylogenetic position of Lissamphibia within Tetrapoda remains uncertain, it also remains controversial which fossil tetrapods are more closely related to amniotes than to lissamphibians, and thus, which ones of them were reptiliomorphs in any meaning of the word. The two major hypotheses for lissamphibian origins are that they are either descendants of dissorophoid temnospondyls or microsaurian "lepospondyls". If the former (the "temnospondyl hypothesis") is true, then Reptiliomorpha includes all tetrapod groups that are closer to amniotes than to temnospondyls. These include the diadectomorphs, seymouriamorphs, most or all "lepospondyls", gephyrostegids, and possibly the embolomeres and chroniosuchians. In addition, several "anthracosaur" genera of uncertain taxonomic...