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Uncertainties in the vertebrate phylogeny examined in this study. (A) The five alternative hypotheses for the placement of turtles within amniotes 1) turtles as basal amniotes, 2) turtles as basal sauropsids, 3) turtle-lepidosaur sister group, 4) turtle-archosaur sister group, and 5) turtle-crocodilian sister group. (B) monophyletic and (C) paraphyletic alternative hypotheses for lissamphibian (extant amphibians) relationships.
