A new analysis using an unprecedented dataset reveals that major changes in frog diversity are linked to mass extinctions
Although Kermit the Frog has always struggled with body image, in evolutionary terms, the frog body plan is a rather successful one. With a short, stout body, protruding eyes and strong, flexible limbs with webbed feet, the world can be your swamp. The frog body plan has remained rather similar for almost 200m years, and with only limited tweaks in anatomy, frogs (Anura) have managed to occupy a range of different habitats, from muddy pools in Alaska to tree tops in the tropics. Currently, over 6700 species are known from all continents except Antarctica, which makes frogs one of the most diverse and species-rich groups of tetrapods. Never change a good thing. However, this limited variation in the frog body plan over time and space has made it difficult for biologists to reconstruct the evolutionary history of frogs and to sort out who is related to who.
Frogs are amphibians, and the oldest member of the frog lineage – the stem-frog Triadobatrachus massinoti which lived during the Early Triassic (~250m years ago) in what is now Madagascar – still retained primitive features, such as a tail and the likely inability to jump, that distinguish it from modern frogs. By the Early Cretaceous (131-120m years ago), the first members of the modern frogs have evolved, such as the three-dimensionally preserved Liaobatrachus zhaoi from the Yixian Formation in China (Dong et al., 2013).