Almost 60 million years of global warming and climate change gave rise to the age of reptiles

Aug. 22 () –

Researchers from the Department of Evolutionary and Organismic Biology at Harvard University (United States) and their collaborators have revealed that the rapid evolution and radiation of reptiles actually began before the end of the Permian in relation to the constant increase in temperatures, which caused successive climatic changes for 60 million years, as published in the journal ‘Science Advances’.

Studying climate change-induced mass extinctions in the deep geological past allows researchers to explore the impact of environmental shocks on the evolution of organisms. These climatic changes caused two of the largest mass extinctions in the history of life at the end of the Permian, the first 261 million years ago and the other 252 million years ago, the latter eliminating 86% of all animal species in the world.

The extinctions at the end of the Permian are important not only because of their magnitude, but also because they mark the beginning of a new era in the planet’s history.when reptiles became the dominant group of vertebrate animals living on land.

After the Permian extinction, in the Triassic Period (252-200 million years ago), reptiles evolved at a rapid rate, creating an explosion of reptile diversity. This expansion was key to the construction of modern ecosystems and many extinct ecosystems. Most paleontologists believed that these rapid rates of evolution and diversification were due to the extinction of competitors that allowed the reptiles to gain new habitats and food resources. that various groups of synapsids had dominated before their extinction.

But the new study researchers have found that the rapid evolution and radiation of reptiles began much earlier, before the end of the Permian. “We found that these periods of rapid reptilian evolution were closely related to rising temperatures. Some groups changed very quickly and others less so, but almost all reptiles evolved much faster than they had before,” says Dr. lead author, postdoctoral fellow Tiago R Simões. “Previous studies on the impact of these changes have often neglected terrestrial vertebrates due to poor data availability, focusing mostly on the response of marine animals.”

On this study, Simões and lead author Professor Stephanie E. Pierce, both from Harvard, worked with collaborators Professor Michael Caldwell of the University of Alberta, Canada, and Dr. Christian Kammerer of the Science Museum. Natives of North Carolina, to examine the earliest amniotes, which represent the forerunners of all modern mammals, reptiles, and birds, as well as their closest extinct relatives, in the early stages of their evolution. At that time, the earliest groups of reptiles and mammalian ancestors diverged from each other and evolved along their own evolutionary paths.

“Reptiles represent an ideal and rare terrestrial system to study this question, as they have a relatively good fossil record and survived a number of climatic shocks, including those that led to the greatest extinction in the history of complex life, the massive Permian-Triassic period,” explains Simões.

Reptiles were relatively rare during the Permian compared to mammalian ancestors. However, things took a major turn during the Triassic, when reptiles experienced a massive explosion in species number and morphological variety. This led to the appearance of most of the major groups of living reptiles (crocodiles, lizards, turtles) and several groups that are now totally extinct.

The researchers created a dataset based on an extensive collection of first-hand data from more than 1,000 fossil specimens from 125 species of reptiles, synapsids, and their closest relatives for approximately 140 million years before and after the Permian extinction- Triassic. They then analyzed the data to detect when these species first originated and how fast they were evolving using state-of-the-art analytical techniques such as Bayesian evolutionary analysis, which is also used to understand the evolution of viruses such as SARS-COVID 19. They then combined the new dataset with global temperature data spanning several million years in the geological record to provide a broad view of the main adaptive response of animals to climate changes.

“Our results reveal that periods of rapid climate change and global warming are associated with exceptionally high rates of anatomical change in most reptile groups.since they adapted to the new environmental conditions – Pierce emphasizes -, and this process began long before the Permian-Triassic extinction event, at least 270 million years ago, which indicates that the diversification of body plans of reptiles was not triggered by the PT extinction event, as previously thought, but actually began tens of millions of years earlier.”

“One lineage of reptiles, the lepidosaurs, which gave rise to the first lizards and tuataras, veered in the opposite direction from most reptile groups and went through a phase of very slow rates of change in their overall anatomy,” he said. Simões–.Essentially, their body plans were constrained by natural selection, rather than going free and radically changing like most other reptiles at the time.” The researchers suggest that this is due to their body size pre-adapting to better cope with high temperatures.

“The physiology of organisms really depends on their body size – explains Simões -, small-bodied reptiles are better able to exchange heat with the environment around them“. The first lizards and tuataras were much smaller than other groups of reptiles, not so different from their modern relatives, and thus better adapted to cope with drastic changes in temperature. The much larger ancestors of crocodiles, Turtles and dinosaurs couldn’t lose heat as easily and had to quickly change their bodies to adapt to new environmental conditions.”

They also mapped how body size changed in different geographic regions during this time period. They revealed that climatic pressures on body size were so high that there was a maximum body size for reptiles to survive in tropical regions during the deadly hot periods of this time.

Large reptiles basically took two routes to cope with these climate changes, Pierce says, either they migrated closer to temperate regions or they invaded the aquatic world where they didn’t have to worry about overheating because water can absorb heat and maintain its temperature much better than air.”

“This strong association between rising temperatures in the geologic past and a biological response by dramatically different reptilian groups suggests that climate change was a key factor in explaining the origin and explosion of new reptilian body plans during the late Permian and Triassic,” concludes Simões.