60 million years of climate change drove the evolution of reptiles

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Just over 250 million years ago, at the end of the Permian and the beginning of the Triassic, the reptiles had a hell of a party.

Their rates of evolution and diversity began to explode, leading to a dizzying variety of abilities, body plans, and traits, and helping to firmly establish both their extinct bloodlines and those that still exist today like the one of the most successful and diverse groups of animals in the world. has never seen. For a very long time, this bloom was explained by the fact that their competition was wiped out by two of the greatest mass extinction events (about 261 and 252 million years ago) in the history of the planet. .

A new study conducted by Harvard rewrote this explanation by reconstructing how the bodies of ancient reptiles changed and comparing it to millions of years of climate change.

Harvard paleontologist Stephanie Pierce’s lab shows that the morphological evolution and diversification seen in early reptiles not only began years before these mass extinction events, but was instead directly driven by what caused them. first – rising global temperatures due to climate change.

“We suggest that we have two major factors at play – not just this open ecological opportunity that has always been thought of by several scientists – but also something that no one had imagined before, namely that climate change has in fact directly triggered the adaptive response of reptiles to help build this vast range of new body plans and the explosion of groups that we see in the Triassic,” said Tiago R. Simões, postdoctoral fellow at Pierce Lab and lead author of the study. .

“Fundamentally, [rising global temperatures] triggered all these different morphological experiments – some that worked quite well and survived for millions of years to this day, and others that all but disappeared a few million years later,” Simões added.

In the newspaper published in Scientists progressthe researchers expose the vast anatomical changes that took place in many groups of reptiles, including the precursors to crocodiles and dinosaurs, in direct response to major climate changes concentrated between 260 and 230 million years ago.

The study takes a close look at how a large group of organisms are changing due to climate change, which is particularly relevant today as temperatures continually rise. In fact, the rate of carbon dioxide released into the atmosphere today is about nine times greater than it was during the period that culminated in the greatest mass extinction due to climate change of all. time 252 million years ago: the Permian-Triassic mass extinction.

“Major changes in global temperature can have dramatic and variable impacts on biodiversity,” said Pierce, Thomas D. Cabot Associate Professor of Organismal and Evolutionary Biology and Curator of Vertebrate Paleontology at the Museum. of Comparative Zoology. “We show here that rising temperatures during the Permian-Triassic led to the extinction of many animals, including many mammalian ancestors, but also triggered the explosive evolution of others, especially reptiles that dominated the Triassic period.”

The study involved almost eight years of data collection and required a heavy dose of camera work, CT scans and tons of passport stamps as Simões traveled to over 20 countries and over 50 different museums to take scans and snapshots of over 1,000 reptilians. fossils.

With all the information, the researchers created a large dataset that was analyzed with state-of-the-art statistical methods to produce a diagram called an evolutionary time tree. Time trees reveal how closely the earliest reptiles were related to each other, when their lineages first appeared, and how quickly they evolved. They then combined it with global temperature data from millions of years ago.

The diversification of reptile body plans began about 30 million years before the Permian-Triassic extinction event, making it clear that these changes were not event-triggered as previously thought. Extinction events, however, helped set them in motion.

The dataset also showed that the increase in global temperatures, which began around 270 million years ago and lasted until at least 240 million years ago, was followed by changes fast bodily in most reptile lineages. For example, some of the larger cold-blooded animals have evolved to become smaller so that they can cool themselves more easily. others have evolved to live in water for the same effect. This latter group included some of the most bizarre forms of reptiles that were about to go extinct, such as a giant, long-necked marine reptile once believed to be the Loch Ness Monster, a tiny chameleon-like creature with a bird-like skull. and beak, and a gliding gecko-like reptile with wings. It also includes the ancestors of reptiles that still exist today such as turtles and crocodiles.

The small reptiles, which gave rise to the first lizards and tuataras, followed a different path than their bigger reptile brothers. Their rates of evolution have slowed and stabilized in response to rising temperatures. Researchers believe this is because small-sized reptiles were already better adapted to the rising heat since they can more easily shed heat from their bodies compared to large reptiles when temperatures rose very quickly all around. Earth.

The researchers say they plan to extend this work by studying the impact of environmental disasters on the evolution of organisms with abundant modern diversity, such as major groups of lizards and snakes.

– This press release was provided by Harvard University

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