The start of The land before time sees our dinosaur – and a pterosaur – cast of characters endure a climate change that pushes them away from their current home and into the Great Valley. Similar environmental changes were not unusual during prehistory. Mass extinction events have occurred at least five times in our planet’s history, and although the most famous is the result of an asteroid impact, more often they are the consequence of dramatic climate changes.
While these events were devastating to huge portions of extant species, they also presented an opportunity for those that survived. The elimination of competitors and the reduction of predators have opened up niches that were previously occupied, allowing the process of evolution to spread in new directions.
Tracing the branches of the tree of life to its major breaking points illustrates how certain groups of animals have taken advantage of these environmental disasters for their own benefit. Mammals certainly benefited from the Cretaceous-Paleogene extinction event 66 million years ago, at least once the dust settled. Before that, however, reptiles ruled the Earth, and their success story is a bit more complicated.
Tiago R. Simões of the Museum of Comparative Zoology and the Department of Organism and Evolutionary Biology at Harvard University, and his colleagues, studied the fossilized remains of hundreds of species in 23 groups of reptiles to reconstruct their historical diversification. While the Permian-Triassic extinctions played a role in their evolutionary explosion, new research suggests they were already on the rise when they occurred, driven by rising global temperatures. The results of the study have been published in the journal Scientists progress.
“At the end of the Permian, about 252 million years ago, there was a massive eruption that occurred in what is now Siberia. It was a huge continuous flow of lava that erupted. released huge amounts of greenhouse gases into the atmosphere and lasted for nearly 400,000 years This created a cascading effect that released even more greenhouse gases like methane from the deep ocean and raised the temperature,” Simões told SYFY WIRE.
Simões and his colleagues spent eight years visiting museum collections in countries around the world, collecting data. They took photos and CT scans, examining hundreds of different morphological variables to build a phylogenetic tree tracing the history of reptiles over 300 million years ago.
They expected drastic climatic changes as a result of the volcanic extinction event and corresponding speciation radiation, but were surprised to see that the rapid expansion of reptile species began considerably earlier than intended.
“People usually focused their attention on the Permian-Triassic boundary because that’s when you get the most volcanic activity and the temperature rise. Indeed, that’s when we see the highest rates of change in reptiles, but it all actually starts millions of years before that,” Simões said.
As temperatures rose, rates of desertification increased with higher levels of wildfires. Around the world, environments were changing and species had to adapt or die. The reptiles, it seems, took the challenge to heart. The fossil record paints a picture of rising temperatures giving reptiles some sort of evolutionary head start before mass extinction events looming on the horizon. The increased diversification meant that when extinctions occurred, they were ready to fill many newly available niches.
“As mass extinctions occur at the end of the Permian, a large number of ecological possibilities open up for surviving species. They can explore resources that were previously inaccessible to them,” Simões said.
Over the course of approximately 60 million years, between 290 and 230 million years ago, nearly all major reptile groups were evolving at rates considerably higher than the background rate. At its peak, just after the Permian extinctions, researchers estimate that the rate of reptile evolution was about three times higher than normal.
“It’s not just one group or part of their body that has changed. We tested different parts of their bodies in 23 different groups of reptiles and virtually all responded the same way. They changed at different rates, but all increased their rates of evolution, matching the line of temperature change,” Simões said.
Understanding how prehistoric animals responded to dramatic climate change provides a roadmap for our own time. Although these environmental changes occur on time scales far longer than a human lifetime, they illustrate the ease with which climate change upsets the ecological landscape. Preventing or mitigating these types of climate change is probably in our interest. Every time you see a lizard, it’s proof that when times start to change, you either change with them or die.
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