PHYLOGENETIC-RELATIONSHIPS OF AMPHIBIAN FAMILIES INFERRED FROM DNA-SEQUENCES OF MITOCHONDRIAL 12S AND 16S RIBOSOMAL-RNA GENES

Nucleotide sequence comparisons were used to investigate ordinal and f amilial relationships within the class Amphibia. Approximately 850 bas e pairs of the mitochondrial 16S ribosomal RNA (rRNA) gene from repres entatives of 28 of the 40 families of extant amphibians were sequenced . Phylogenetic analyses of these data together with published data of the 12S rRNA gene for the same families and both genes for three more taxa (approximately 1,300 base pairs total for 35 taxa) support the mo nophyly of each of the three amphibian orders: Anura (confidence value with the interior-branch test: P-c = 99%), Caudata (P-c = 100%), and Gymnophiona (P-c = 99%). An analysis using the four-cluster method can not discriminate significantly between all three possible unrooted tre es involving the three orders of amphibians and an outgroup. Within th e Anura, there is support for the monophyly of the two suborders: Neob atrachia (P-c = 100%) and Archaeobatrachia (P-c = 97%); the latter was believed to be paraphyletic on the basis of morphology. Within the Ar chaeobatrachia, the following pairs of taxa cluster: Pelobatidae + Pel odytidae (P-c = 99%), Pipidae + Rhinophrynidae (P-c = 99%), Ascaphus Leiopelmatidae (P-c = 89%), and Bombina + Discoglossidae (P-c = 99%). The latter six taxa cluster (P-c = 94%) such that Pelobatidae + Pelod ytidae forms a basal lineage within the Archaeobatrachia. Three major lineages are distinguished within the Neobatrachia: the superfamily Bu fonoidea sensu Duellman (P-c = 86%), the superfamily Ranoidea sensu Ly nch (P-c = 99%), and the Sooglossidae. Basal within the Bufonoidea, My obatrachidae + Heleophrynidae cluster at P-c = 96%. The enigmatic Dend robatidae clusters with the bufonoid families (P-c = 92%) and is exclu ded from the ranoid families (P-c = 99%). The Microhylidae, considered by some to form a separate superfamily, clusters within the Ranoidea (P-c = 99%). Within the Caudata, familial relationships are not resolv ed at significant confidence levels. We suggest that short divergence times among amphibian orders and among salamander families have contri buted to the difficulty in fully resolving these relationships.