e world, but are just as diverse today in their habitats and breeding strategies as the 88 percent.
Two of the three surviving lineages that subsequently radiated widely came out of Africa, which remained intact as the continents shifted around over the ensuing eons, with the breakup of Pangea and then Gondwana to form the continents we see today. The African rift zone and mountain building in West Africa generated new habitats for the evolving frogs, Wake noted. The third, Hyloidea, radiated throughout what became South America.
Today's frogs, comprising more than 6,700 known species, as well as many other animal and plant species are under severe stress around the world because of habitat destruction, human population explosion and climate change, possibly heralding a new period of mass extinction. The new study provides one clear message for future generations.
"These frogs made it through on luck, perhaps because they were either underground or could stay underground for long periods of time," Wake said. "This certainly draws renewed attention to the positive aspects of mass extinctions: They provide ecological opportunity for new things. Just wait for the next grand extinction and life will take off again. In which direction it will take off, you don't know."
The paper's other co-authors are David Cannatella and David Hillis at UT Austin, Peng Zhang and Dan Liang of Sun Yat-Sen and David Blackburn of the Florida Museum. Cannatella, Zhang and Liang are all former UC Berkeley postdoctoral fellows.
Support for the research was provided by the U.S. National Science Foundation, the National Natural Science Foundation of China and the National Youth Talent Support Program and National Science Fund for Excellent Young Scholars of China.