A new study has found that majority of the extant, or existing frog species on our planet expanded after the catastrophic event that wiped out the dinosaurs 65 million years ago. Mass extinctions always mean that although a particular species will disappear, the void in the ecosystem will be filled up by other species. This new study was conducted by an international team of American and Chinese biologists. It suggested that the three main clades or group of frog species including Hyloidea, Microhylidae, and Natatanura, diversified in that period itself.
David Blackburn who co-authored the study said in an interview that frogs are known to have populated the Earth way more than 200 million years ago. What this study finds is that the explosion of more than 6,700 currently identified species of frogs occurred in the K-Pg boundary. Formerly known as the KT boundary, this is the timeline between the Cretaceous and Paleogene period when the planet was going through a major ecological shift.
What went on in the study?
Researchers went through a dataset that was seven times larger than the previous studies conducted on frog evolution. This ensured that they had a larger pool of data to work with and generate a new tree of life in the frog species. This data set mainly focused on 95 genes from 156 different species of frogs. To strengthen the research, an additional 145 species were added to the study based on already published studies. At the end, the team was able to combine a huge dataset of analysis that covered all the 55 known families of frogs.
This compilation took care of the basic dataset required for the study and now they moved on to determine where exactly did the species explode. So, the researchers analysed the fossil records of frogs across different branches to look for the occurrence of genetic differences between them. By observing the dates or time periods in which these genetic differences occurred, the research suggested a simultaneous change among the three main clades mentioned earlier. This sudden and simultaneous evolution occurred in the K-Pg boundary.
New conclusions in frog evolution
Contrary to previous research, even the team was confused with their own results. Blackburn said that they redid the entire process with different parameter settings just to be sure. But the result pointed to the same conclusion. By considering the results of this research along with the evolution of other animals based on climatic and geographic factors, it started to make sense. Factors such as mass extinction and the breakup of the continents have already played a huge role in diversifying and relocating several species of animals across the planet.
So why exactly did frogs flourish after the demise of dinosaurs?
One would wonder that the vigorous expansion of frog species could have simply coincided during that specific period. As mentioned earlier, mass extinction does favour the rise of other species. Although frogs were present when the killer asteroid hit Earth, they could have survived by staying underground, according to Blackburn. After the impact, most of the herbivorous giants had disappeared and the vegetation including trees and flowering plants evolved better in the late Cretaceous period. Since they had almost negligible predators, they were able to fully flower and host a potential habitat for new species. This is where the surviving frog species took advantage and evolved into arboreal beings. Having a rich ecosystem at their disposal abundant with food and very few predators to be afraid of, frogs were able to diversify.
Frogs also went through a major upgrade in their reproductive phase that enabled their proliferation in different conditions. Frogs conventionally laid eggs in water bodies and tadpoles developed from them, eventually growing into frogs. About half of the species today lay eggs in terrestrial conditions without the tadpole stage. This direct development from eggs along with their new arboreal living conditions also influenced their spread.
The entire study provides insight into a new timeline of the evolution of frogs through the millions of years they have occupied land and water. It also offers additional knowledge about evolution and how events like mass extinction can trigger and influence massive changes in the ecosystem.
You can read the entire study published in the journal Proceedings of the National Academy of Sciences here.
Source: Live Science