Phylogenetic relationships of Pelobatoidea re-examined using mtDNA.

Pelobatoidea is a clade of ancient anurans with obscure relationships to the remaining clades of frogs. We used partial sequences of two mitochondrial genes (cytochrome b and 16S RNA) from all Pelobatoidea subclades, including all species of Pelobatidae and Pelodytidae and four outgroup taxa (Xenopus, Ascaphus, Discoglossus, and Rana), to propose a phylogenetic hypothesis for relationships within Pelobatoidea. Maximum likelihood and Bayesian analyses support the monophyly of Pelobatoidea, but our hypothesis of internal relationships differs substantially from all previous hypotheses. Megophryidae is sister to Pelobates, and this clade is sister to Pelodytes. The most basal clade within Pelobatoidea is formed by Scaphiopus and Spea. The family Pelobatidae, as previously defined is not monophyletic, and it is split into Eurasian spadefoot toads Pelobates which retain the name Pelobatidae and North American spadefoot toads Scaphiopus and Spea which comprise the revived taxon Scaphiopodidae. Our analysis uncovers the existence of morphologically cryptic taxa within previously recognized species of the genus Spea and reveals marked genetic differentiation within Iberian Pelodytes. We discuss biogeographic implications and the evolution of fossoriality in the light of the new phylogenetic hypothesis.