Climate change caused massive waves of evolution in reptiles – study

Ancient reptiles evolved faster due to climate change, which caused mass extinctions in multiple species, a new study by researchers at Harvard University, University of Alberta and North Carolina Museum of Natural History revealed.

The peer-reviewed study, published in Sciences Advances, found that numerous climate crises led to the rapid evolution of a number of reptiles, shaping their mode of selection, size and numerous other factors. There is therefore an inherent connection between waves of climate change and reptilian evolution.

Prehistoric mass extinctions

Between the Middle Permian (265 million years ago) and Middle Triassic (230 million years ago) periods, two of the largest mass extinctions in history struck the Earth at the end of the Permian period.

The first of these two extinctions was 261 million years ago, while the second was 252 million years ago. That second one wipes out 86% of all animal species worldwide. These marked the beginning of reptiles’ dominance as the largest group of vertebrate animals living on land.

Prior to that, they were dominated by synapsids, often described as mammal-like reptiles, though more accurately, they are made up largely of mammals and other animals more closely related to mammals than to reptiles.

After the aforementioned mass extinctions, reptiles multiplied at an incredible rate, shaping the ecosystem and therefore having a massive impact on how the world evolved altogether. Many scientists believe that this was made possible due to the mass extinctions, during which perhaps many of reptiles’ competitors died out.

‘We were here first!’

The shifts studied in this particular paper, however, occurred far earlier, supposedly prior to the end of the Permian period. According to the study, the extreme increases in temperatures on the planet directly correlated with the rapid evolution of reptilian creatures of the time. This allowed them to survive the mass extinctions much more than the other animals, therefore allowing them to multiply rapidly after the fact.

“Some groups changed really fast and some less fast, but nearly all reptiles were evolving much faster than they ever had before,” said lead author postdoctoral fellow Tiago R Simões.

The researchers looked at over “1,000 fossil specimens from 125 species of reptiles, synapsids, and their closest relatives during approximately 140 million years before and after the Permian-Triassic extinction,” according to a Harvard University statement. They managed to find the earliest appearances of the different species and watch as they evolved during the subsequent fossils to track how fast they were changing.

The data set was 40% larger than the previous largest one, according to the study. 

This, combined with data about global temperatures during the same time, gave the researchers a unique overview of how the changes in temperatures went hand-in-hand with reptilian evolution.

According to the researchers, most studies up until this point have focused on marine animals when looking at the particular period and mass extinction. Reptiles, however, have excellent fossil records, making them relatively suitable to track and study evolutionarily.

Evolution: Then and now

The explosion of reptilian multiplication following the mass extinctions led to the appearance of some major reptilian creatures we still know to this day such as lizards, turtles and crocodiles, as well as several others that have since gone extinct.

“One reptile lineage, the lepidosaurs, which gave rise to the first lizards and tuataras, veered in the opposite direction of most reptile groups and underwent a phase of very slow rates of change to their overall anatomy,” said Simões. “Essentially, their body plans were constrained by natural selection, instead of going rogue and radically changing like most other reptiles at the time.”

“Their body plans were constrained by natural selection, instead of going rogue and radically changing like most other reptiles at the time.”

Lead author, postdoctoral fellow Tiago R Simões

This is an example of the adaptations the species had made prior to having been suited to the climate changes that came about years and years later.

Changes in size are the most noticeable change in these different species, and the causation can be easily traced. According to Simões, “small-bodied reptiles can better exchange heat with their surrounding environment,” while large-bodied reptiles could not do so just as well. Larger species such as crocodiles and dinosaurs, therefore, could not lose heat as well, forcing them to “quickly change their bodies in order to adapt to the new environmental conditions.”

Another change reptiles made due to the changes in temperatures was geographical; they would move to more temperate areas or the globe or submerge themselves in the marine world to cool themselves down.

Every good thing must come to an end

Reptiles aren’t so lucky today, however. Recent studies have found that 21% of reptiles today are at risk of extinction, according to an April study published in Nature. 

“The analysis of the first global reptile assessment enables us to pinpoint where reptiles need the most help and serve as a major step to countering the global extinction crisis,” said Dr. Sean T. O’Brien, President and CEO of NatureServe.