How Frogs Benefited From The Dinosaurs' Extinction

Enlarge this image toggle caption Peng Zhang, Sun Yat-Sen University Peng Zhang, Sun Yat-Sen University

The asteroid that hit Earth 66 million years ago spelled disaster for the dinosaurs.

But scientists say they've found one silver lining to the mass extinction — turns out, it was really good for frogs.

The resilient animals date back some 200 million years. And in the aftermath of the extinction event, they survived and thrived, taking advantage of an ecological vacuum other animals left behind.

About 9 in 10 frog species today evolved from three frog lineages that survived the event, which occurred at the boundary between the Cretaceous and Paleogene periods, according to research published Monday in Proceedings of the National Academy of Science.

The timing of this rapid diversification came as a surprise, University of California, Berkeley herpetologist and report co-author David Wake tells The Two-Way. It's about 35 million years later than previous research suggested.

As the Chinese and American researchers noted in a press release, the previous estimate was puzzling, "since Earth's environment was stable at that time. A changing environment typically drives evolution." They say that "analysis of molecular evolution in mitochondrial DNA [like in previous studies] often produces dates for lineage divergence that are too old."

The new research focuses on nuclear genes instead, which Wake says can provide a "much clearer picture of what's happening."

Frogs are "master survivors," Wake says, able to go underground and live through long periods of inactivity.

The scientists aren't sure why three main lineages ultimately outperformed all the others that were living at at the time of the asteroid strike.

There continue to be remnants of other pre-asteroid lineages around the world, the scientists say, and they're "just as diverse today in their habitats and breeding strategies" as those descended from the three dominant lineages.

But the primary ancestors of today's frogs seized the ecological opportunity after mass extinction, explosively evolving new species.

"It's these three lineages that were at the right place and the right time and they just took off like crazy," Wake says, adding that they also "rapidly increased in their use of habitats and their use of resources."

At the same time, seed-bearing trees and other flowering plants suddenly dominated the landscape. All three of the frog lineages contain species that started to dwell in trees, which was not previously seen in frogs. It was a sign, Wake says, of frogs "experimenting with new ways of life."

Many of the new frog species also started to lay their eggs on land, skipping the tadpole phase and growing directly into a small frog. There are currently about 6,775 known frog species, and Wake says this trait is now found in about half of them.

What this research shows, Wake says, is that frogs have the proven ability to "[take] advantage of opportunities — in this case [an] ecological vacuum that existed following the mass extinction."

Now, the scientists want to study what it was about these lineages that allowed them to perform so much better than the others that survived the extinction event.</s>The catastrophic mass extinction that wiped the dinosaurs off the face of the Earth set the stage for modern frog species to thrive, scientists have shown. Their findings suggest that this extinction 66 million years ago was crucial to shape the current wide diversity and geographic distribution of frogs seen on the planet.

Among the vertebrates that inhabit ponds and forests, frogs form part of a very large and diverse group. They comprise nearly 90% of all living amphibian species.

Biologists have long been fascinated by frogs' diverse biology and worldwide distribution, and thought that these little animals could help solve important evolution, ecology and conservation riddles.

However, to date, little is known about frogs' evolutionary history and about how fast they diversified due to sparse genetic data.

In a study now published in the Proceedings of the National Academy of Sciences, researchers present a new tree of life for frogs, clarifying the timeline for their evolution.

The international team of scientists sampled 95 genes of 156 frog species. They combined this data with previously published genetic data on an additional 145 species to produce the strongest-supported evolutionary tree of frogs to date. This method allowed them to come up with a robust hypothesis for how and when frogs evolved.

The scientists found that three major lineages of modern frogs - making up about 88% of them -appeared simultaneously, evolving right after the extinction event that marked the end of the Cretaceous Period and the beginning of the Paleogene 66 million years ago. This was the extinction event that led to the death of dinosaurs.

The results were surprising because past research had suggested a more ancient origin of many of these modern frog groups.

"Frogs have been around for well over 200 million years, but this study shows it wasn't until the extinction of the dinosaurs that we had this burst of frog diversity that resulted in the vast majority of frogs we see today. This finding was totally unexpected," said study co-author David Blackburn, associate curator of amphibians and reptiles at the Florida Museum of Natural History on the University of Florida campus.

Frogs appeared to diversify very quickly after the extinction event - which killed not only dinosaurs but also three quarters of all plants and animals on the planet. This suggests that the frogs that survived were probably filling up new niches on Earth. They emerged from this as one of the most diverse groups of vertebrates, with more than 6,700 known and described species to date.

"We think there were massive alterations of ecosystems at that time, including widespread destruction of forests. But frogs are pretty good at eking out a living in microhabitats, and as forests and tropical ecosystems rebounded, they quickly took advantage of those new ecological opportunities," Blackburn explained.

It's worth pointing out that despite many species of frogs survived the mass extinction event and thrived right after the age of dinosaurs, others did not make it. The extinction event was particularly hard on frog lineages in North America - most of the frogs seen today in this part of the world arose after the extinction.

"Except for a small handful of species, all other North American frogs are 'post-dinosaur' colonists," Blackburn concluded. "If you could travel back to the time of T. rex in North America, there would be frogs, but the chorus you would hear at night would have been nothing like you'd hear today. They're not even the same families."</s>WASHINGTON-A massive asteroid strike that wiped out the dinosaurs millions of years ago created room for frogs to colonize the Earth, said a study Monday that shows how frogs became among the most diverse vertebrates in the world.

As many as 10 types of frogs are believed to have survived the mass extinction some 66 million years ago, which erased three-quarters of life on Earth, said the report in the Proceedings of the National Academy of Sciences.

Of these survivors, just three major kinds of frogs went on to diversify and populate the planet. Some 6,700 known frog species exist today.

Nearly nine in 10 - 88 percent - of modern frogs can trace their roots back to these three lineages of hardy ancestors.

“Frogs have been around for well over 200 million years, but this study shows it wasn’t until the extinction of the dinosaurs that we had this burst of frog diversity that resulted in the vast majority of frogs we see today,” said study co-author David Blackburn, associate curator of amphibians and reptiles at the Florida Museum of Natural History.

Until now, scientists believed that most modern frog species emerged at a steady pace between 66 million and 150 million years ago.

But the latest research shows frogs burst onto the scene more like an “explosion,” as the tiny amphibians swept into habitats left vacant by other creatures. For the study, researchers in China and the United States compiled the largest set of frog genetic data ever evaluated. Genetic samples were taken from 156 frog species and combined with previously published data on 145 more species. Past studies looked at five to 12 genes, while the current one examined variations in 95 genes, offering a much more detailed look at how individual species relate to one another.

Researchers also studied fossil records to determine when different kinds of frogs likely diverged from one another.

Researchers found “evidence of not one but three explosions of new frog species, on different continents, and all concentrated in the aftermath of the mass die-off of most dinosaurs and many other species about 66 million years ago,” said the report.

Two of the three surviving lineages - Microhylidae and Natatanura - came out of Africa. The third, Hyloidea, spread throughout what became South America.

“These frogs made it through on luck, perhaps because they were either underground or could stay underground for long periods of time,” said co-author David Wake of the University of California.

“This certainly draws renewed attention to the positive aspects of mass extinctions: They provide ecological opportunity for new things.”

Similar evolutionary events happened with birds, said co-author David Hillis, professor of integrative biology at University of Texas, Austin.

“We know that the mass extinction event wiped out most of the dinosaurs, except for a few bird species, which then exploded in diversity and became one of the dominant groups of land animals,” he said.

“As we look at more and more groups of life, we see the same pattern, and that turns out to be the case for frogs as well.”

In particular, the demise of dinosaurs and most birds created new niches for frogs in the late Cretaceous Period.

Some climbed into trees for shelter, leading to the evolution of the now ubiquitous tree frogs.

“We think there were massive alterations of ecosystems at that time, including widespread destruction of forests,” said Blackburn.

“But frogs are pretty good at eking out a living in microhabitats, and as forests and tropical ecosystems rebounded, they quickly took advantage of those new ecological opportunities.”

Some frogs also adapted by producing young without a tadpole stage - today the standard for about half of all frog species.

Modern frogs face a host of threats to their survival, including habitat destruction, human encroachment and climate change.

“I think the most exciting thing about our study is that we show that frogs are such a strong animal group,” said lead author Peng Zhang, a researcher at Sun Yat-sen University in Guangzhou, China.

“They survived from the mass extinction that completely erased dinosaurs and boomed back quickly.”</s>In a paper published this week in the Proceedings of the National Academy of Sciences, an international team of researchers presented a new tree of life for frogs that helps solve longstanding riddles about relationships and sheds light on the history and pace of frog evolution.

Unexpectedly, their analyses showed three major lineages of modern frogs—about 88 percent of living species—appeared simultaneously, evolving on the heels of the extinction event that marked the end of the Cretaceous Period and the beginning of the Paleogene 66 million years ago. Previous research suggested a more ancient origin of many of these modern frog groups.

"Frogs have been around for well over 200 million years, but this study shows it wasn't until the extinction of the dinosaurs that we had this burst of frog diversity that resulted in the vast majority of frogs we see today," said study co-author David Blackburn, associate curator of amphibians and reptiles at the Florida Museum of Natural History on the University of Florida campus. "This finding was totally unexpected."

The speed at which frogs diversified after the asteroid or comet impact that triggered a massive die-off of most plant and animal life suggests that the survivors were probably filling up new niches on Earth, Blackburn said.

"We think there were massive alterations of ecosystems at that time, including widespread destruction of forests," he said. "But frogs are pretty good at eking out a living in microhabitats, and as forests and tropical ecosystems rebounded, they quickly took advantage of those new ecological opportunities."

Frogs rose to become one of the most diverse groups of vertebrates, with more than 6,700 described species. But sparse genetic data has hindered scientists from reliably tracing their evolutionary history and the links between frog families.

Blackburn joined researchers from Sun Yat-Sen University, the University of Texas at Austin and the University of California, Berkeley to tackle the mystery of frog evolution with a dataset seven times larger than that used in prior research. The team sampled a core set of 95 nuclear genes from 156 frog species, combining this with previously published genetic data on an additional 145 species to produce the strongest-supported evolutionary tree, or phylogeny, to date. The tree represents all 55 known families of frogs and generates a new timeline of frog evolution.

The researchers then used fossil records to translate genetic differences between frog lineages into dates at which they likely diverged from one another. When the analyses pointed to a simultaneous evolution of the three major frog clades—Hyloidea, Microhylidae and Natatanura—the researchers initially eyed the finding with skepticism, said Peng Zhang, a corresponding study author and professor in the department of biochemistry and molecular biology at Sun Yat-Sen University in China.

"Nobody had seen this result before," he said. "We redid the analysis using different parameter settings, but the result remained the same. I realized the signal was very strong in our data. What I saw could not be a false thing."

When examined in the context of the evolution of other animals, however, the finding makes sense, Blackburn said.

"Looking at bird or mammal phylogenies, we can see a reflection of Earth's history—its climatic and geologic events," he said. "You'd expect these major events—mass extinction and the breakup of continents—would have impact on frog evolution and that divergences between major lineages would relate to those in some respect. We see that in this phylogeny."

The close resemblance of distantly related frog species around the world, a factor of frog evolution and biology that has long confounded scientists, might be illuminated by the simultaneous evolution of major frog clades, Blackburn said. After the extinction event decimated ecosystems and stimulated a reset, modern frogs may have faced similar evolutionary paths.

"You could easily go to Central Africa, the Philippines and Ecuador and find what look like the same frogs that might have last shared a common ancestor 120 million years ago," he said. "These different lineages seem to have diversified in similar ways after the extinction."

While the extinction event opened new opportunities for frogs, notably leading to the evolution of tree frogs worldwide, it snuffed out many frog lineages, particularly in North America, Blackburn said.

"Except for a small handful of species, all other North American frogs are 'post-dinosaur' colonists," Blackburn said. "If you could travel back to the time of T. rex in North America, there would be frogs, but the chorus you would hear at night would have been nothing like you'd hear today. They're not even the same families."

The study also indicates that global frog distribution tracks the breakup of the supercontinents, beginning with Pangea about 200 million years ago and then, Gondwana, which split into South America and Africa. The data suggests frogs likely used Antarctica, not yet encased in ice sheets, as a stepping stone from South America to Australia.

Blackburn is eager to use the new phylogeny as a roadmap for the fossil record, particularly for frogs that occurred in the Cretaceous.

"This sets up expectations of what we should or shouldn't find," he said. "It's exciting to think about what discoveries could lay ahead in the frog fossil record."

While the survival and subsequent comeback of frogs testifies to their resilience, Zhang said, their current vulnerability to disease, habitat loss and degradation is cause for concern.

"I think the most exciting thing about our study is that we show that frogs are such a strong animal group. They survived from the mass extinction that completely erased dinosaurs and boomed back quickly," he said. "However, frog species are declining nowadays because humans are destroying their habitats. Does that mean humans are making a huge extinction event even stronger than this one? We need to think about it."

Explore further: Seven new species of night frogs from India including four miniature forms

More information: Yan-Jie Feng el al., "Phylogenomics reveals rapid, simultaneous diversification of three major clades of Gondwanan frogs at the Cretaceous–Paleogene boundary," PNAS (2017). www.pnas.org/cgi/doi/10.1073/pnas.1704632114</s>The asteroid that crashed into the planet about 66 million years might have been the end of the line for much of life on Earth, but for a few frogs it allowed a great leap forward.

Genetic analysis by an international team of researchers from the US and China indicates that 88% of existing frog species are descended from just three frog families that survived and prospered following the mass extinction event known as the Cretaceous-Paleogene (K–Pg) boundary, which wiped out an estimated three-quarters of animals including non-avian dinosaurs and most large mammals.

“Frogs have been around for well over 200 million years but this study shows it wasn't until the extinction of the dinosaurs that we had this burst of frog diversity that resulted in the vast majority of frogs we see today,” says study co-author David Blackburn, of the Florida Museum of Natural History. “This finding was totally unexpected.”

Quite a lot of frogs were also wiped out by the K–Pg extinction event or failed to adapt to its aftermath. Perhaps 10 frog groups survived the mass extinction, suggest Blackburn and his colleagues, but only three lineages – the Hyloidea, Microhylidae, and Natatanura – flourished in changed climates and habitats, and thrived by occupying vacant ecological niches.

Taking to the trees was particularly beneficial. As the planet’s vegetation recovered, flowering plants (or angiosperms) proliferated. “That’s when trees evolved to their full flowering,” says co-author David Wake, of the Museum of Vertebrate Zoology at the University of California, Berkeley. “Frogs started becoming arboreal.” Trees not only provided sanctuary from non-climbing predators but also ground cover via fallen leaves along with attracting food sources, such as insects.

Another important adaptation, Wake says, was to produce offspring without a tadpole stage, known as direct development, which is how about half of all frog species now reproduce: “The majority of the frogs that thrive now are thriving because of direct development of eggs in terrestrial situations.”

While the ability to stay underground for long periods probably enabled frogs to survive the K-Pa event, Wake credits the combination of direct development and use of arboreal habitat with “a great deal” of frog prosperity subsequently, with frog numbers exploding to become one of the most diverse and widely dispersed vertebrate groups on the planet.

The analysis, published in the Proceedings of the National Academy of Sciences, was based on gene sequencing data from 301 frog species. Though this is but a fraction of the 6,775 frog species so far identified, it covered all 55 frog families and importantly included a greatly expanded sequencing of 156 frog species from 44 of those families. That sequencing, led by Yan-Jie Feng of Sun Yat-Sen University in Guangzhou, used 95 nuclear protein-coding genes, rather than the five, six or 12 of previous studies.

Peng Zhang, also of Sun Yat-Sen University, says the most exciting thing about the team’s study is that it shows frogs are such a strong animal group. “They survived from the mass extinction that completely erased dinosaurs and boomed back quickly,” he says. “However, frog species are declining nowadays because humans are destroying their habitats. Does that mean humans are making a huge extinction event even stronger than this one? We need to think about it.”</s>The mass extinction that wiped out the dinosaurs paved the way for a totally different type of creature to take over — frogs.

The slimy amphibians exploded in numbers and diversified in the millions of years after a massive asteroid wiped out the dinosaurs, taking advantage of the huge holes in the ecosystem that extinct creatures left behind, a new study suggests.

"Frogs have been around for well over 200 million years, but this study shows it wasn't until the extinction of the dinosaurs that we had this burst of frog diversity that resulted in the vast majority of frogs we see today," study co-author David Blackburn, associate curator of amphibians and reptiles at the Florida Museum of Natural History on the University of Florida campus, said in a statement. "This finding was totally unexpected." [Wipe Out: History's Most Mysterious Mass Extinctions]

The dinosaurs reigned for about 175 million years, during a period known as the Mesozoic era. Then, about 65 million years ago, a massive asteroid wiped them out.

Frogs, meanwhile, have been around for about the past 200 million years, but how and exactly when species of frogs emerged and diversified has been murky. Some studies suggested that the major frog families — Hyloidea, Microhylidae and Natatanura — diverged sometime in the Mesozoic era.

To answer that question, Blackburn and his colleagues analyzed 95 genes from each of 156 different frog species alive today. They then combined this data with previously reported data from another 145 species. From this data, they created an evolutionary tree mapping out the history of all frog families.

Then, the team pored over frog fossils to anchor genetic changes in frogs to specific points in time. The team found that the three major families of frogs all diverged around the same time, the researchers reported today (July 3) in the journal Proceedings of the National Academy of Sciences. It turned out, this explosion in frog species, and the divergence of the major frog families, occurred right at the KT boundary (the boundary between the Cretaceous and the Paleogene periods), soon after the dinosaurs went extinct. Though the findings contradict previous research, they also make sense because there were so many holes in the ecological niches vacated by dinosaurs and other affected species, study co-author David Wake, an evolutionary biologist at the University of California, Berkeley, said in a statement.

"We think the world was quite impoverished as a result of the KT event, and when the vegetation came back, angiosperms dominated. That's when trees evolved to their full flowering," Wake said. "Frogs started becoming arboreal. It was the arboreality that led to the great radiation in South America in particular."</s>Most of the frogs alive today owe a big thank you to the asteroid or comet that delivered the coup de grace to the dinosaurs.

A new study by Chinese and American biologists shows that if the calamity had not wiped the planet clean of most terrestrial life 66 million years ago, 88 percent of today’s frog species wouldn’t be here. Nearly nine out of 10 species of frog today have descended from just three lineages that survived the mass extinction.

The results, published online today in the journal Proceedings of the National Academy of Sciences, are a surprise, because previous studies of frog evolution pinpointed the blossoming of the main frog lineages today to about 35 million years earlier, in the middle of the Mesozoic era.

The new analysis of 95 genes from frogs within 44 of 55 living families shows that these three lineages started to take off precisely at the boundary between the Cretaceous and Paleogene periods – the K-Pg boundary, formerly called the KT boundary – when the last mass extinction occurred, and not 100 million years ago.

According to herpetologist and co-author David Wake, a University of California, Berkeley professor of the graduate school and a curator of the Museum of Vertebrate Zoology, new frog species likely radiated rapidly throughout the world because so many environmental niches were available after the animals occupying them disappeared.

“We think the world was quite impoverished as a result of the KT event, and when the vegetation came back, angiosperms dominated. That’s when trees evolved to their full flowering,” Wake said. “Frogs started becoming arboreal. It was the arboreality that led to the great radiation in South America in particular.”

Trees are an ideal habitat for frogs not only because they allow them to escape from terrestrial predators, but also because their fallen leaves provide protection while the frogs are on the ground, breeding habitat and plenty of food, such as insects. Trees and other flowering plants took off in the late Cretaceous, and were ready for exploitation by frogs after they recovered from the extinction.

Another adaptation that became popular was direct development, that is, producing young without a tadpole stage, which is standard for about half of all frog species today.

“The majority of the frogs that thrive now are thriving because of direct development of eggs in terrestrial situations,” he said. “It is a combination of direct development and use of arboreal habitat that accounts for a great deal of the radiation.”

Previous genetic analyses of frog evolution focused on mitochondrial DNA and how long the molecular clock had been ticking for mitochrondrial genes. However, analysis of molecular evolution in mitochondrial DNA often produces dates for lineage divergence that are too old. In the case of frogs, such analysis pinpointed the radiation of most living frogs at about 100 million years ago, which was a puzzle, since Earth’s environment was stable at that time. A changing environment typically drives evolution.

The new analysis, based on data assembled primarily by graduate student Yan-Jie Feng at Sun Yat-Sen University in Guangzhou, China, focused on the sequences of 95 genes located on chromosomes in the nucleus and how they changed over time. He and his colleagues gathered genetic data from 156 frog species and combined this with earlier information about two genes from 145 different frogs, for a total of 301 distinct frog species from all 55 families of frogs. The data were calibrated using 20 dates derived from fossils and Earth historical events.

The team, which includes scientists from the Florida Museum of Natural History at the University of Florida and the University of Texas, Austin, concluded that perhaps 10 groups of frogs survived the extinction, but only three of them (Hyloidea, Microhylidae, and Natatanura) flourished and diversified to claim habitats and niches around the world.

The role of luck in mass extinctions

Nothing other than luck distinguishes the survivors, Wake said. Remnants of the other surviving lineages are scattered in isolated spots around the 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.

 

 RELATED INFORMATION
• Phylogenomics reveals rapid, simultaneous diversification of three major clades of Gondwanan frogs at the Cretaceous–Paleogene boundary (PNAS)</s>The mass extinction event 66 million years ago that wiped out three-fourths of the life on Earth, including dinosaurs, helped pave way for the swift rise of frogs, a study has found.

Researchers found a new tree of life for frogs that helps solve longstanding riddles about relationships and sheds light on the history and pace of frog evolution.

The analyses showed three major lineages of modern frogs - about 88 per cent of living species - appeared simultaneously, evolving on the heels of the extinction event that marked the end of the Cretaceous Period and the beginning of the Paleogene 66 million years ago.

Previous research suggested a more ancient origin of many of these modern frog groups.

"Frogs have been around for well over 200 million years, but this study shows it wasn't until the extinction of the dinosaurs that we had this burst of frog diversity that resulted in the vast majority of frogs we see today," said David Blackburn, from the Florida Museum of Natural History in the US.

The speed at which frogs diversified after the asteroid or comet impact that triggered a massive die-off of most plant and animal life suggests that the survivors were probably filling up new niches on Earth, Blackburn said.

"We think there were massive alterations of ecosystems at that time, including widespread destruction of forests," he said.

"But frogs are pretty good at eking out a living in microhabitats, and as forests and tropical ecosystems rebounded, they quickly took advantage of those new ecological opportunities," he added.

Frogs rose to become one of the most diverse groups of vertebrates, with more than 6,700 described species.

However, sparse genetic data has hindered scientists from reliably tracing their evolutionary history and the links between frog families.

Researchers tackled the mystery of frog evolution with a dataset seven times larger than that used in prior research.

The team sampled a core set of 95 nuclear genes from 156 frog species, combining this with previously published genetic data on an additional 145 species to produce the strongest- supported evolutionary tree, or phylogeny, to date.

The tree represents all 55 known families of frogs and generates a new timeline of frog evolution.

The researchers then used fossil records to translate genetic differences between frog lineages into dates at which they likely diverged from one another.

The analyses pointed to a simultaneous evolution of the three major frog clades - Hyloidea, Microhylidae and Natatanura.

The close resemblance of distantly related frog species around the world, a factor of frog evolution and biology that has long confounded scientists, might be illuminated by the simultaneous evolution of major frog clades, Blackburn said.

After the extinction event decimated ecosystems and stimulated a reset, modern frogs may have faced similar evolutionary paths.</s>Frogs leaped to take advantage of the global catastrophe that killed off the dinosaurs.

New research shows that 88 per cent of frog species alive today owe their existence to the meteor impact that wiped the planet clean of most terrestrial life 66 million years ago.

Nearly nine out of 10 of the amphibian species are descended from just three lineages that survived the mass extinction.

Each of them jumped forward precisely at the junction of the Cretaceous and Paleogene periods – formerly known as the KT boundary – when the disaster happened.

The first survivors may have ridden out the meteor strike by burrowing underground, the scientists believe. Thereafter, it was arboreal tree frogs that led the way by exploiting newly available habitat niches.

Previous research had suggested that frog evolution took off 35 million years earlier and had nothing to do with the dinosaur apocalypse.

“We know that the mass extinction event wiped out most of the dinosaurs, except for a few bird species, which then exploded in diversity and became one of the dominant groups of land animals,” says study co-author David Hillis, from the University of Texas at Austin, US.

“As we look at more and more groups of life, we see the same pattern, and that turns out to be the case for frogs as well.”

David Wake, from the University of California at Berkeley, says a key factor in early frog success was the way the creatures adapted to living in trees as flowering plants spread across the planet.

“Frogs started becoming arboreal,” he says. “It was the arboreality that led to the great radiation in South America in particular.”

Trees are an ideal habitat for frogs not only because they provide a refuge from terrestrial predators, leaf cover on the ground, and abundant insects for food, says the team.

American and Chinese scientists made the discovery after analysing genetic data from frogs within 44 living families.

Today’s frogs comprising more than 6,700 known species, are increasingly threatened by habitat destruction, increasing human population, and climate change.

“These frogs made it through on luck, perhaps because they were either underground or could stay underground for long periods of time,” Wake says. “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.”</s>Frogs have been around for nearly 200 million years, but it wasn’t until a 10-mile-wide asteroid struck our planet, wiping out three-quarters of all life on Earth — including the dinosaurs — that these crafty amphibians were able to make their big evolutionary move, according to new research.

A study published in Proceedings of the National Academy of Sciences this week shows that frog populations exploded after the Cretaceous-Paleogene extinction event some 66 million years ago. The sudden disappearance of the dinosaurs, followed by the re-emergence of abandoned ecosystems, allowed frogs to flourish and diversify, leading to the thousands of species that still inhabit our planet.

Mass extinction events are like giant reset buttons. When a large asteroid struck the Yucatan Peninsula some 66 million years ago, it set off a chain of geologic and atmospheric events that wiped out 75 percent of life on Earth, including nearly every animal larger than 55 pounds (except some turtles and crocodiles). With the giant lizards suddenly gone, and as the environment slowly healed itself, the survivors jockeyed for position within the re-emerging ecosystems. New research from the Florida Museum of Natural History and Sun Yat-Sen University in Guangzhou, China, shows that frogs were among the greatest beneficiaries of the transition from the Late Cretaceous to the post-dinosaur Paleogene.

In an effort to learn more about frog evolution, researchers David Blackburn and Peng Zhang put together a new phylogenetic tree of these amphibians (phylogenetic trees are like family trees, but at the species level, and driven by genetic data) . The researchers looked at 95 genes from the DNA of 156 frog species to establish genetic relationships and develop evolutionary timelines.

Contrary to conventional thinking, Blackburn and Zhang found that most modern frog families didn’t originate during the Mesozoic era—that vast expanse of time during which the dinosaurs reigned. Frogs first emerged hundreds of millions of years ago, but it wasn’t until after the demise of the dinosaurs that their populations really took off. With their lizard cousins gone, frogs became among the most diverse groups of vertebrates, accounting for more than 6,700 known species. As the new research shows, 88 percent of frog species are descended from three main lineages — hyloidea, microhylidae and the natatanura — that emerged during the transition from the Cretaceous to the Paleogene.

Repressed for millions of years, these wiley amphibians were suddenly able to occupy and thrive within vacant ecological niches. The asteroid that struck the Earth, and ensuing environmental changes, destroyed a significant fraction of our planet’s vegetation, but as forests recovered, frogs were one of the many animals groups (mammals included) that were able to take advantage of the new habitats.

Sadly, we are in the midst of another mass extinction event, one of our making. Frogs are threatened like never before, owing to habitat loss, pollution, disease, and other factors. According to the IUCN, nearly one-third of the world’s amphibians are now threatened or have recently become extinct. Frogs managed to survive the dinosaur era, but they’re having a hell of time dealing with us humans. [Proceedings of the National Academy of Sciences]
Researchers discover that the diversity of frogs is a direct result of the extinction of the dinosaurs.