RUTA, M. *; COATES, M.I.; QUICKE, D.L.J.: Early Tetrapod Relationships Revisited

A cladistic analysis of early tetrapods (90 taxa; 307 characters) yields 60 most parsimonious cladograms. These differ only in the internal relationships of aistopods and embolomeres, in the relative position of Balanerpeton, trimerorhachoids and more derived temnospondyls, and in the relative position of derived diplocaulid nectrideans. The results support the occurrence of a deep phylogenetic split between lissamphibian-related and amniote-related groups in the Palaeozoic. Crown lissamphibians join a clade of amphibamids, micromelerpetontids and branchiosaurids. Westlothiana is sister group to a monophyletic Lepospondyli on the amniote stem, but evidence for such monophyly is tenuous. The placement of lepospondyls other than microsaurs on the tetrapod stem is not found to be a significantly worse fit for the total data set than the original cladogram topology. A mid to late Visean age for the origin of crown tetrapods is in agreement with divergence time data based on recent molecular studies.