Artist’s reconstruction of the adaptive radiation of reptiles in a terrestrial ecosystem during the warmest period in Earth’s history. The image depicts a massive, large-headed, carnivorous erythrosuchid (relative to crocodiles and dinosaurs) and a tiny slithering reptile from about 240 million years ago. The erythrosychid hunts the slithering and moving reptile using a fossilized skull of the extinct Dimetrodon (early mammal ancestor) in a hot and dry river valley. Credit: Image created by Henry Sharpe Harvard researchers found that the rapid evolution of reptiles was caused by nearly 60 million years of global warming and climate change. Researchers can investigate the impact of environmental crises on the evolution of organisms by studying mass extinctions caused by climate change in the deep geological past. A key example is the climate crises of the Permian-Triassic period. This series of climate changes was caused by global warming that occurred between the Middle Permian (265 million years ago) and the Middle Triassic (230 million years ago). These climate 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 second wiping out 86% of all animal species worldwide. In addition to their size, the end-Permian extinctions are also significant because they mark the beginning of a new era in the planet’s history, when reptiles became the dominant group of land-dwelling vertebrates. Synapsids, the ancestors of mammals, dominated the terrestrial vertebrate fauna throughout the Permian. In the Triassic period (252-200 million years ago), following the Permian extinctions, reptiles evolved at a rapid rate, creating an explosion of reptile diversity. This expansion was critical in building 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 conquer new habitats and food resources that had been dominated by several groups of synapsids before their extinction. However, in a new study published on August 19, 2022, in the journal Sciences Advances, researchers from the Department of Organizational and Evolutionary Biology and the Museum of Comparative Zoology at Harvard University and colleagues reveal that the rapid evolution and radiation of reptiles began much earlier. , before the end of the Permian. This occurred in relation to steadily increasing global temperature through a long series of climate changes spanning nearly 60 million years in the geologic record. Evolutionary response of reptiles to global warming and rapid climate change. Evolutionary rates (adaptive anatomical changes) in reptiles begin to increase early in the Permian (about 294 million years ago), which also marks the beginning of the longest period of successive rapid climate changes in the geologic record. From 261 to 235 million years ago, increased global warming from the massive volcanic eruption contributed to further climate change and led to the hottest period in Earth’s history. This resulted in two mass extinctions and the death of competing terrestrial reptiles (mammal ancestors). The most intense period of global warming coincided with the fastest rates of evolution in reptiles, marking the diversification of reptilian body plans and the origin of modern reptile groups. Creation: Figure by Tiago Simões “We found that these periods of rapid reptile evolution were closely linked to rising temperatures. Some groups changed very quickly and others less quickly, but almost all reptiles were evolving much faster than they ever had before,” said lead author postdoctoral fellow Tiago R Simões. Previous research on the effects of these changes has often neglected terrestrial vertebrates due to limited data availability, focusing mainly on the response of marine animals. In this study, Simões and senior author Professor Stephanie E. Pierce (both at Harvard) worked with collaborators Professor Michael Caldwell (University of Alberta, Canada) and Drs. Christian Kammerer (North Carolina Museum of Natural Sciences) to examine early amniotes. They represent the precursors of all modern mammals, reptiles, birds and their closest extinct relatives, in the initial phase of their evolution. At this point in time, the first groups of reptiles and ancestral mammals were separating from each other and evolving along their own separate 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 series of climate crises, including those that led to the largest extinction in the history of complex life, the Permian mass extinction- Three. Simões said. Reptiles were relatively rare during the Permian period compared to their mammalian ancestors. However, things changed significantly during the Triassic, when reptiles experienced a huge explosion in species number and morphological diversity. This led to the appearance of most of the major living groups of reptiles (crocodiles, lizards, turtles) and several groups that have now completely disappeared. The scientists created a dataset based on extensive first-hand data collection of more than 1,000 fossil specimens from 125 species of reptiles, synapsids and their closest relatives during the roughly 140 million years before and after the Permian-Triassic extinction. They then analyzed the data to detect when these species first arose and how quickly they evolved using modern analytical techniques such as Bayesian evolutionary analysis, which is also used to understand the evolution of viruses such as SARS-CoV-2 19. The researchers then combined the new dataset with global temperature data spanning several million years in the geologic record to provide a broad overview of the major adaptive response of animals to climate change. “Our results reveal that periods of rapid climate change and global warming are associated with extremely high rates of anatomical change in most groups of reptiles as they adapted to new environmental conditions,” Pierce said, “and this process began long before the Permian-Triassic extinction, at least 270 million years ago, indicating that the diversification of reptile body plans was not caused by the PT extinction event as previously thought, but actually began tens of millions of years before that.” “One lineage of reptiles, the lepidosaurs, which gave rise to the first lizards and tuataras, turned in the opposite direction from most groups of reptiles and underwent a phase of very slow rates of change in their overall anatomy,” Simões said, “essentially, The designs of body were limited by natural selection, rather than going rogue and changing radically like most other reptiles at the time.” The researchers suggest that this is due to pre-adaptations in their body size to better cope with high temperatures. “The physiology of organisms really depends on their body size,” said Simões, “smaller reptiles can better exchange heat with their environment. The first lizards and tuataras were much smaller than other groups of reptiles, not so different from their modern relatives, and thus were better adapted to cope with drastic temperature changes. The much larger ancestors of crocodiles, turtles and dinosaurs could not lose heat as easily and had to change their bodies quickly to adapt to new environmental conditions.” Simões, Pierce and colleagues also mapped how body size changed across geographic regions during this time frame. 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 spells of this era. “The large reptiles basically followed two ways to deal with these climate changes,” Pierce said, “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 to maintain its temperature is much better than air’. “This strong correlation between warming in the geological past and biological response by dramatically different groups of reptiles suggests that climate change was a key factor in explaining the origin and explosion of new reptile body plans during the late Permian and Triassic,” said Simões. . Citation: “Successive climatic shocks in the deep past drove the early evolution and radiation of reptiles” by Tiago R. Simões, Christian F. Kammerer, Michael W. Caldwell and Stephanie E. Pierce, 19 Aug 2022, Science Advances. DOI: 10.1126/sciadv.abq1898 The researchers would like to thank the Museum of Comparative Zoology (MCZ), Harvard University, vertebrate paleontology staff, and curators at 50+ natural history collections worldwide for their assistance in accessing specimens. Funding was provided by: Alexander Agassiz Postdoctoral Fellowship, MCZ; National Sciences and Engineering Research Council of Canada (NSERC) postdoctoral fellowship. Grant KA 4133/1-1 from the Deutsche Forschungsgemeinschaft. NSERC Discovery Grant #23458 and NSERC Accelerator Grant. Faculty of Science, Chairs Research Allowance, University of Alberta; Lemann Brazil Research Fund; Funds available through Harvard University.
