The phylogeny of the 'higher' temnospondyls (Vertebrata : Choanata) and its implications for the monophyly and origins of the Stereospondyli

A parsimony analysis of 'higher' temnospondyls tall temnospondyls descended from the common ancestor of Eryops and Parotosuchus) was performed using 3 7 terminal taxa and 121 osteological characters. Bremer support values for each internal node were calculated as a measure of clade strength. Addition ally, the shortest trees that conformed to some alternative hypotheses were searched for. The following new taxa are established on the basis of the r esults: Euskelia (the clade containing the Eryopoidea and Dissorophoidea), Limnarchia (the clade containing Trimerorhachidae, Dvinosauroidea, Archegos auroidea and Stereospondyli), Dvinosauria (the clade containing Trimerorhac hidae and Dvinosauroidea), Stereospondylomorpha (the clade containing Arche gosauroidea and Stereospondyli), Capitosauria (the clade containing Lydekke rina and 'capitosauroids'), and Trematosauria (the clade containing Tremato sauroidea, Rhytidosteidae, Plagiosauroidea, Metoposauroidea and Brachyopoid ea). The monophyly of the assemblage of Mesozoic families called the Stereo spondyli by Romer is supported. The dominance of the Stereospondyli in the Mesozoic and its rarity in the Palaeozoic is discussed. It is suggested tha t the radiation of the diverse stereospondyl clades; the Capitosauria and T rematosauria, began in the Late Permian of Gondwana, in a 'safe haven' that was less severely affected by the Late Permian extinction event. It is fur ther speculated that the 'safe haven' was located in Antarctica, or possibl y Australia. (C) 2000 Academic Press.