Dates, nodes and character conflict: addressing the Lissamphibian origin problem

<p>Extant amphibians consist of Salientia (frogs), Caudata (salamanders), and Gymnophiona(caecilians). The mutual relationships of these groups are controversial, with either Batrachia(Salientia + Caudata) or Procera (Gymnophiona + Caudata) as emerging clades in recent molecularand morphological analyses. The monophyly of amphibians as a whole is supported by independentdata, but their origins and affinities with early tetrapods are debated. A new cladistic analysisof early tetrapods retrieves Temnospondyli (the most species-rich group of early tetrapods) as theclosest relatives of crown group amphibians. One temnospondyl group, the Dissorophoidea, forms aseries of consecutive outgroups to crown amphibians. In particular, the Lower Permian amphibamidDoleserpeton is the most derived plesion on the amphibian stem. The Albanerpetontidae, a groupof salamander-like tetrapods ranging from the Jurassic to the Pliocene, are placed as stem Gymnophiona.The shortest trees support the Batrachia hypothesis. However, the Procera hypothesisis not a significantly worse fit for the whole character set. Exhaustive treatment of characters andtaxa is the most appropriate way to disentangle contrasting phylogenetic signals in large matrices.Tests of different crown topologies show that placement of amphibians within lepospondyls (e.g.as sister taxon to Lysorophia) is not a significantly worse fit for the whole character set than aclose temnospondyl-lissamphibian relationship. However, the latter phylogenetic hypothesis bestcaptures the most coherent assembly of derived lissamphibian apomorphies.</p>