Summary

A phylogenetic analysis based on a data matrix of 38 taxa and 157 osteological characters has produced a dramatically new hypothesis of tetrapod phylogeny. Amniota and diadectomorphs are closely related, as previously reported, but this clade is closely related to a monophyletic Lepospondyli that includes Lissamphibia. In contrast to previous hypotheses, diadectomorphs, amniotes, and Lepospondyli include all extant tetrapods and constitute the crown group of terrestrial choanates. This crown group is much smaller that previously suggested. Seymouriamorpha, long considered closely related to diadectomorphs and amniotes, is the sister group of tetrapods according to this analysis. Gephyrostegids, embolomeres, temnospondyls, loxommatids, and Crassigyrinus are more distant relatives of the crown group.

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