Fast-moving species more likely to go extinct

The first lizards and snakes evolved slowly, but eventually became much more diverse than their close relatives, the rhynchocephali, which initially showed rapid evolution. Today there are 10,000 species of squamates, but only 1 of rhynchocephali. Credit: Dr Tom Stubbs

Researchers from Bristol University have discovered that rapid change leads nowhere.

In a new study on lizards and their relatives, Dr Jorge Herrera-Flores of the Bristol School of Earth Sciences and his colleagues have found that “is winning the race slowly and steadily”.

The team studied lizards, snakes and their relatives, a group called lepidosauria. Today there are over 10,000 species of Lepidosaurs, and much of their recent success has been the result of rapid change under favorable circumstances. But this has not always been the case.

Mr. Herrera-Flores explained: “Lepidosaurs were born 250 million years ago at the beginning Mesozoic Era, and they split into two large groups, the squamates on the one hand, leading to modern lizards and snakes, and the rhynchocephali on the other hand, represented today by a single species, the New Zealand tuatara. We expected to find slow evolution in rhynchocephali and rapid evolution in squamates. But we found the opposite.

Evolution rate of lizards and snakes

The evolution rates of lizards and snakes (Squamata, blue line) have been much lower than those of Rhynchocephalia (green line) for about 200 million years, and they have only tilted in the last 50 million about years. Credit: Armin Elsler

“We looked at the rate of change in body size among these early reptiles,” said Dr. Tom Stubbs, a collaborator. “We found that certain groups of squamates evolved rapidly in the Mesozoic, especially those with specialized lifestyles like marine mosasaurs. But rhynchocephali evolved much faster.

“In fact, their average evolution rates were significantly faster than those of squamates, about double the background evolution rate, and we really weren’t expecting that,” said Dr. Armin Elsler, another. collaborater. “In the latter part of the Mesozoic, all modern groups of lizards and snakes were born and began to diversify, living side by side with the dinosaurs, but probably without engaging with them in an ecological way. These early lizards fed on insects, worms, and plants, but they were mostly quite small.


Pleurosaurus from the Late Jurassic, some 150 million years ago, from southern Germany, a remarkable long-bodied swimming rhynchocephalus. Credit: Roberto Ochoa

Professor Mike Benton added: “After the dinosaurs died out 66 million years ago, at the end of the Mesozoic, the rhynchocephali and squamates suffered a lot, but the squamates rebounded. But for most of the Mesozoic Era, the rhynchocephali were the innovators and the rapidly evolving ones. They abated quite severely long before the end of the Mesozoic, and the whole dynamic changed after that. “

This work confirms a stimulating proposition made by the famous paleontologist George Gaylord Simpson in his 1944 book Changing tempo and mode. He examined the fundamental models of evolution within the framework of Darwinian evolution and observed that many rapidly evolving species belonged to unstable groups, which potentially adapted to rapidly changing environments.

Professor Benton continued, “Slow and steady wins the race. In Aesop’s classic fable, the fast hare loses the race, while the slow turtle crosses the finish line first. Since Darwin’s time, biologists have questioned whether evolution is more like the hare or the tortoise. Is it true that large groups of many species are the result of rapid evolution over a short period or of slow evolution over a long period?

“In some cases, they can stabilize and survive well, but in many cases, species disappear as quickly as new ones emerge, and they can disappear, just like the hare that naps. On the flip side, Simpson predicted that slow-evolving species might also be slow to disappear and might ultimately be successful in the longer term, much like the slow but persistent turtle in the fable.

Reference: “Slow and fast evolutionary rates in the history of lepidosaurs” by Jorge A. Herrera-Flores, Armin Elsler, Thomas L. Stubbs and Michael J. Benton, November 10, 2021, Paleontology.
DOI: 10.1111 / pala.12579

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