Batrachomorpha
Batrachomorpha ("frog form") is a name traditionally given to recent and extinct amphibians that are more closely related to modern amphibians than they are to reptiles. It most often includes the extinct groups Temnospondyli and Lepospondyli. The first tetrapods were all amphibians in the physiological sense that they laid their eggs in water, and are colloquially sometimes referred to as labyrinthodonts or stegocephalians. In this scheme, batrachomorphs composed one branch of these early amphibians, while the reptiliomorphs composed the other. While the actual phylogeny of the modern amphibians is not well understood, their ancestors are descended from one line of batrachomorphs.[1] All other living tetrapods (reptiles, birds and mammals) are descended from one branch of reptiliomorphs, the amniotes. Amniotes achieved dominance, while all other reptiliomorphs and most batrachomorphs have gone extinct.
The name Batrachomorpha was coined by the Swedish palaeontologist Gunnar Säve-Söderbergh in 1934 to refer to ichthyostegids, temnospondyls, anthracosaurs, and the frogs. 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-finned fish, the porolepiformes.[2] In this view amphibians would be a biphyletic 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. The salamanders and the Lepospondyli was consigned to "Urodelomorpha".
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 including a number of Labyrinthodonts and anurans).[3] Erik Jarvik, who took over Säve-Söderberghs work and shared his view of the origin of salamanders, used the term more informally, but in a wider sense, to include the ancestral osteolepiform fishes.[4]
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 confirming the monophyly of living amphibians in the 1990s.[5] Jarviks classification is no longer followed, all living amphibians and their fossil relatives now being classified together in the group Lissamphibia.
Michael Benton adopted the term Batrachomorpha to include all living amphibians and extinct relatives more closely related to amphibians than to amniotes. In his scheme, Batrachomorpha is a superorder of Amphibia, containing the following subgroups:[6]
The other groups of tetrapods considered more closely related to amniotes are put in the subclass Reptiliomorpha.
