New study refutes a 75-year-old belief in the evolution of reptiles

Challenging a 75-year-old idea of ​​how and when reptiles evolved over the past 300 million years involves a lot of imaging work, tomography loads, and most of all, thousands of miles of travel. Just check the stamps in Tiago R. Simões passport.

Simes is the Alexander Agassiz postdoctoral fellow in the laboratory of Harvard paleontologist Stephanie Pearce. From 2013 to 2018, he traveled to over 20 countries and over 50 different museums to take CT scans and images of nearly 1,000 reptile fossils, hundreds of millions of years old. It amounted to about 400 days of active aggregation, helping to shape what is believed to be the largest available development timeline of living and extinct reptile populations.

Now, statistical analysis of this huge database helps scientists better understand the evolution of these cold-blooded vertebrates through the contradiction of a widespread theory that major shifts in evolution always occur in large and rapid (geologically) bursts, caused by major environmental shifts. The results are described in a recently published paper in Nature Communications.

In it, the researchers showed that the evolution of extinct phyla of reptiles more than 250 million years ago occurred through many small flows of morphological changes, such as the development of armored body diagrams or slide wings, over 50 million years rather than through a single major evolutionary event, as It was previously thought. They also showed that the early development of most lineages of lizards was a consistently slower and more gradual process than was previously understood.

“It was not a sudden jump of this kind that validates the wide variety that we see today in reptiles,” said Simes. “There was an initial, but relatively small, jump, and then a steady increase over time in these rates [of evolution] And different diversity values. “

Evidence of this has been seen in other types of animals, but this is the first time that reptiles have been seen – one of the most diverse animals on the planet, with over 10,000 different species and an amazing variety of abilities and traits. Consider how some types of lizards can freeze overnight and then thaw the next morning, or how turtles grow their protective shields.

The results clash with the evolutionary theory of Adaptive radiation It was published by Harvard paleontologist George J. Simpson in the 1940s, who sought to explain the origins of the planet’s biodiversity. Adaptive radiation has been the focus of intense investigation for decades, but technology, methods, and data were not in place until recent years to accurately measure rapid rates of development in the fossil record in terms of different animal species, formations, and in the Molecular level Using DNA.

Researchers on this study include Pearce, Assistant Professor Thomas de Cabot in Organic and Evolutionary Biology and Curator of Vertebrate Paleontology at the Museum of Comparative Zoology. Oksana Vernegura, a graduate student from the University of Alberta in Canada; And Professor Michael Wayne Caldwell, Alberta.

Simões traveled to nearly all of the world’s major natural history museums to gather data for study, including the National Natural History Museums in London, Paris, Berlin, Ottawa, Beijing and Tokyo. In the United States, he visited the Smithsonian National Museum of Natural History, the Carnegie Museum of Natural History, and the Harvard Museum of Comparative Zoology.

Scientists believe that by understanding how animals evolved over longer periods of time, they can draw a number of lessons about the environment and how living things are affected by environmental changes. Using the database, researchers can determine when major reptile strains or polymorphs originated, find out how these changes affected reptile DNA, and learn important lessons about how the species was affected by historical events.

Reptiles, for example, survived three major mass extinction events. The largest of them was the mass extinction that occurred in the Permian and Triassic periods about 250 million years ago and that killed about 90% of the planet’s species, causing it to be called the “Great Death”. It is thought to be caused by an accumulation of natural greenhouse gases.

The researchers found in the timeline that the rates at which the reptiles were developing and the anatomical differences between them before the great death were nearly as high as they were after the event. However, reptiles became dominant in many ecosystems and were extremely diverse in terms of the number of different species only after the great death.

This finding reinforced that rapid rates of anatomical change did not need to coincide with genetic diversity or species abundance (called taxonomic diversity), and further disproved adaptive radiation as the only explanation for the origin of new animal populations and body plans. The researchers also noted that it took the reptiles nearly 10 million years to recover to previous levels of anatomical diversity.

“This kind of general scheme of things and on a global scale tells you just how surprisingly it can be throughout life’s history Environmental changes Samis said.

Other evidence that contradicted adaptive radiation included similar but surprising findings about the origins of snakes, which investigated key aspects of their slender and elongated body plans early in their evolution about 170 million years ago (but did not completely lose limbs for another 105 million years). They also underwent rapid changes in their skulls from about 170 to 165 million years ago, resulting in mouths so strong and flexible that today they can swallow whole prey larger than it is. But while snakes experienced the fastest rates of anatomical change in the evolutionary history of reptiles, these changes did not coincide with an increase in taxonomic diversity or higher rates of particles. has evolved The researchers also predicted the adaptive radiation.

Scientists were unable to determine why this mismatch occurred, and suggested that more research is needed. In particular, they want to understand how body blueprints evolve and how changes in DNA relate to them.

“We can now see better what the great changes are in the history of life, especially in the history of Reptiles We will continue digging, “Simes said.