There’s nothing like a major mass extinction to open up ecological niches and eliminate competition, accelerating the evolution of a few lucky survivors. Or is there? A new study suggests that the rate of climate change may play an equally important role in speeding up evolution.
The study focuses on the evolution of reptiles over 57 million years, before, during and after. mass extinction at the end of the Permian Period (Serial number: 6/12/18). That extinction event, triggered by carbon dioxide pumped into the atmosphere and oceans through increased volcanic activity about 252 million years ago, wiped out 86 percent of Earth’s species. However, the reptiles recovered relatively well from the chaos. Their explosive species diversity at that time has been widely considered to be a result of their slippage into newly available niches.
But rapid climate fluctuations were already happening much earlier in the Permian, as were waves of reptile diversification, the researchers say. Fossil analysis of 125 reptile species shows that bursts of evolutionary diversity in reptiles were closely correlated with relatively rapid fluctuations in climate throughout the Permian and millions of years into the next geological period, the Triassic, researchers report August 19 in Progress of science.
Scientists’ understanding of evolution is expanding as they become more attuned to the connection between it and environmental change, says Jessica Whiteside, a geologist at the University of Southampton in England who works on mass extinctions but was not involved in the new study. worked. “This study is sure to become an important part of that conversation.”
To investigate the evolution of reptiles, evolutionary biologist Tiago Simões of Harvard University and colleagues accurately measured and scanned reptile fossils that are between 294 and 237 million years old. In all, the researchers examined 1,000 specimens at 50 research institutions in 20 countries. For climate data, the team used a large existing database of sea surface temperatures based on oxygen isotope data, going back 450 million years, published in 2021.
By closely tracking changes in body and head size and shape in so many species, along with climate data, the researchers found that the faster climate change, the faster reptiles evolved. The fastest rate of reptile diversification did not occur at the end of the Permian extinction, the team found, but several million years later in the Triassic, when climate change was at its fastest and global temperatures were extremely high. . Ocean surface temperatures during this time soared to 40° Celsius, or 104⁰ Fahrenheit, about the temperature of a hot tub, Simões says.
Some species evolved less quickly than their relatives, says Simões. The difference? Size. For example, reptiles with smaller bodies are already preadapted to living in rapidly warming climates, he says. Due to their higher surface-to-body area ratio, “small-bodied reptiles are better able to exchange heat with their surrounding environment,” so stay relatively cooler than larger animals.
“Essentially, natural selection was forcing the smaller reptiles to stay the same, while during that same time period, natural selection was telling the larger reptiles, ‘You have to change immediately or you’re going to go extinct.’ Simões says.
This phenomenon, called the Lilliput effect, is not a new proposition, says Simões, adding that it is well established in marine organisms. “But it’s the first time it’s been quantified in limbed vertebrates during this critical period in Earth’s history.”
The detailed work of Simões and his colleagues has refined the complex evolutionary tree of reptiles and their ancestors. But for now, it’s unclear which played a bigger role in reptilian evolution long ago: all those ecological niches opened up after the end-Permian mass extinction, or the dramatic climatic fluctuations outside of the extinction event.
“We can’t say which was more important,” says Simões. “Without either, the course of evolution in the Triassic and the rise of reptiles to global dominance in terrestrial ecosystems would have been quite different.”