You know what they say: Life finds a way. In this case, we're talking about frog life. Scientists say the mass extinction event that killed off so many dinosaurs may have paved the way for "explosive radiations of frogs," including the nearly 90 percent of species alive on Earth today. They published their report in the journal Proceedings of the National Academy of Sciences.
Previous research has suggested that the frog family party started about 100 million years ago. These studies based their conclusions on analysis of modern frogs' mitochondrial DNA, which can provide a sort of road map to an organism's evolutionary past. But sometimes that map is hard to read or even outdated.
To get a clearer picture, researchers from China and the U.S. decided to look at genes inside the nuclei, rather than the mitochondria, of frogs' cells. They compared nuclear (nucleus-based) genes among 301 different frog species, including one from each of the 55 major branches of the frog family tree.
Oddly enough, branches and trees may have been the key to the frogs' success. Analysis of the frogs' genetic histories suggests that the party really only started about 66 million years ago—just after so many of the dinosaurs were wiped out. It also reveals that nearly 90 percent of frog species today trace their genetic roots to just three frog lineages that survived the mass extinction.
But the researchers say it wasn't necessarily the dinosaurs' disappearance that made our planet a more frog-friendly place. The catastrophe that killed the thunder lizards also killed a lot of other things, including primitive prehistoric plants.
"We think the world was quite impoverished as a result of the [extinction event]," co-author David Wake of UC-Berkeley said in a statement, "and when the vegetation came back, angiosperms dominated. That's when trees evolved to their full flowering."
Seeing their opportunity, frogs began moving into the trees. And up there, they thrived.
Around the same time, Wake says, frog species that stayed on the ground learned their own neat trick: direct development, or skipping the tadpole stage, which requires access to water.
"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."