Global fluctuations of diversification in the history of modern amphibians

The fossil record of the class Amphibia (frogs, salamanders and caecilians) is notoriously poor, but has been interpreted as showing a gradual increase in taxonomic diversity, without any evidence for major extinction and diversification episodes since the End-Permian (250 Mya). This picture is difficult to reconcile with the sensitivity of present-day amphibian faunas to environmental change, the demonstrated incidence of similarly profound environmental perturbations in the past, and the congruence of high turnover rates in other vertebrate groups. We constructed a phylogenetic timetree based on a multi-gene data set of 3.75 kilobases for 171 amphibian species. Our analyses indicate a strong departure form gradual-diversification models and mark several episodes of accelerated net diversification. Global turning points of phylogenetic and ecological diversification are situated in the Early Triassic and Late Cretaceous. Approximately 86% of modern frog species an
d over 81% of salamander species descended from only five ancestors that started radiating in the Late Cretaceous and Early Tertiary. Fluctuations in amphibian diversification show strong temporal correlation with turnover rates in amniotes, the rise of angiosperm-dominated forests and related insect diversity. The proportionally late accumulation of extant lineage diversity contrasts with the long evolutionary history of amphibians, but is in line with the Tertiary increase in fossil abundance towards the present.