It was a Global Warming that started the Age of Reptiles!

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When we dig deep into the geological past, it is possible that we will encounter many mass extinctions due to climate change. Conducting research on these mass extinctions allows researchers to examine the impact of environmental crises on organism evolution. A prime example of mass extinctions is the Permian-Triassic climate crisis. This climate crisis, which took place during the Permian and Middle Triassic periods, 265 and 230 million years ago, respectively, is a series of climate shifts caused by global warming. These climate shifts led to the two largest mass extinctions in history at the end of the Permian period. The former took place 261 million years ago and the latter 252 million years ago, while the latter wiped out 86% of all animal species from Earth.

The extinctions during the Permian period were not only significant in terms of size. They also marked the beginning of a new era in planetary history in which reptiles were the most dominant group of vertebral animals living on land. During the Permian period, synapsites, the ancestors of mammals, dominated the vertebral fauna on land. After the Triassic-Permian extinctions, which took place 252-200 million years ago, reptiles began to evolve at a high rate. Not only did this bring a rapid increase in reptilian diversity, but it also played a key role in the formation of today's ecosystems and many extinct ecosystems. After the extinction of some species of synapsites, reptiles seized habitats and food sources that they had previously occupied. Accordingly, paleontologists concluded that the acceleration of evolution and diversification in reptiles was a result of the extinction of competing species.

But a new study in the journal Sciences Advances reveals a different situation. Researchers from Harvard University's Department of Organism and Evolutionary Biology and the Museum of Comparative Zoology have discovered that reptiles' sudden evolution and spread began much earlier. The process, which began even before the late Permian periods, was found to be due to increasing global temperatures, with a series of climatic changes in the geological record spanning 60 million years. Lead author Tiago R. Simões explains his discovery:

We discovered that these periods of sudden evolution of reptiles were closely linked to rising temperatures. Some groups changed faster, others slower; but almost all reptiles evolved much faster than before.

Previous studies on the effects of these changes have focused much on land vertebrates, with a focus on marine life and limited access to data.

In this study, Simões and expert author Prof. Stephanie E. Pierce worked with Prof. Michael Caldwell and Dr. Christian Kammerer. They studied the first phase of the evolution of amniote, the ancestor of all modern mammals, reptiles, birds and their closest extinct relatives. In this early phase, the first groups of reptiles and mammals diverged from each other and evolved in their own evolutionary path. Simões says:

Reptiles offer us a unique land system that is more ideal for us to study this issue. Because reptiles have relatively better fossil evidence. They also survived some climatic changes, including those that caused the greatest extinction of wildlife, such as the Permian-Triassic.

Compared to mammalian ancestors, reptiles were quite rare in the Permian period. But things changed drastically during the Triassic period. There was a great increase in the species numbers and formal diversity of reptiles. As a result of this situation; Many of today's important reptile groups, such as crocodiles, lizards and turtles, and some other groups that are now extinct have emerged.

The researchers uncovered a dataset on top of a large-scale collection of first-hand sources. The sources collected included 1,000 fossil specimens from 125 species: lizards, synapses, and close relatives who lived almost 140 million years ago and after the Permian-Triassic extinction. After this stage, they analyzed when these species first appeared and how quickly they evolved. They used advanced analytical techniques such as Bayesian evolution analysis, which is also used in the analysis to understand the evolution of SARS viruses. The researchers then combined global temperature data covering several million years in the geological record with the new dataset. With this, they aimed to provide a broad perspective on the adaptive response of animals to climate shifts. Pierce explains his work:

Our results show that sudden climate shifts and global warming are associated with the extremely high rates of anatomical changes observed in many of the reptilian groups adapting to their new environmental conditions. This process began at least 270 million years ago, long before the Permian-Triassic extinction. That is, the Permian-Triassic extinction did not lead to the diversification of reptiles' body structures, as is supposed. In fact, this diversification began millions of years before the extinction.

Simões explains an exceptional case they encountered in their research:

We could not observe the same situation in the Lepidosauiria group, which included the first lizards and tuataras. Unlike many groups of reptiles, they went through a rather slow phase of change relative to their overall anatomy. In fact, their body structures were constrained by natural selection, rather than changing completely in an instant, like other reptiles.

The researchers think this is due to pre-adaptations in body sizes to cope with high temperatures. Simões explains:

The physiology of organisms depends on their body size. Small-sized reptiles can exchange heat better with their environment. The first lizards and tuataras were not much different from their present relatives and were smaller compared to other groups of reptiles. So they were better able to adapt to large changes in temperature. The much larger ancestors of crocodiles, turtles and dinosaurs could not lose heat so easily. So they had to quickly change their bodies to adapt to their new environmental conditions.

Simões, Pierce and other participants also detailed how body sizes varied over time by geographic region. They discovered that there was a maximum body size for reptiles so that they could survive in the tropics during periods of lethal heat. Accordingly, they concluded that the climatic pressure in body size was quite high.Pierce explains:

Large reptiles basically had two options for dealing with climate shifts. They would either migrate to temperate regions or invade the realm of waters, where there would be no worries of overheating; because water can absorb heat and maintain its current temperature better than air.

Simões concluded:

We now know that there is a strong correlation between rising temperatures in the geological past and the sudden biological responses of different groups of reptiles. This relationship shows us that climate change was a key element in explaining the origin and increase of reptilian body structures during the last Permian-Triassic period.

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