Fast-evolving species more likely to go extinct, paleontologists say

“Slow and steady wins the race,” according to one new study of lepidosaurs (lizards, snakes, amphisbenes and tuatara) published in the journal Paleontology.

pleurosaurus, a remarkable long-bodied swimming rhynchocephalus who lived during the Late Jurassic period some 150 million years ago in what is now Germany. Image credit: Roberto Ochoa.

the Lepidosauria is a subclass or superorder of reptiles, containing the orders Squamata (snakes, lizards and amphisbenes) and Rhynchocephalia (tuatara).

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.

“Lepidoosaurs appeared 250 million years ago at the start of the Mesozoic era and they split into two main groups, the squamates on the one hand, leading to modern lizards and snakes, and the rhynchocephala of the ‘other, represented today by a single species, the tuatara (Sphenodon punctatus), ”Said Dr Jorge Herrera-Flores, researcher at the School of Earth Sciences at the University of Bristol.

“We expected to find slow evolution in rhynchocephali and rapid evolution in squamates. But we found the opposite.

“We looked at the rate of change in body size among these early reptiles,” said Dr Tom Stubbs, also from the University of Bristol’s School of Earth Sciences.

“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,” added Dr. Armin Elsler, also of the University’s School of Earth Sciences. from Bristol.

“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.”

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.  Image credit: Armin Elsler.

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. Image credit: Armin Elsler.

“After the extinction of the dinosaurs 66 million years ago, at the end of the Mesozoic, the rhynchocephali and squamates suffered a lot, but the squamates rebounded,” added Professor Mike Benton of the University of Bristol.

“But for most of the Mesozoic Era, the rhynchocephali were the innovators and the rapidly evolving.”

“They abated quite severely long before the end of the Mesozoic, and the whole dynamic changed after that.”

The new study confirms a difficult proposition made by famous paleontologist George Gaylord Simpson in his 1944 book “Tempo and Mode in Evolution.”

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.

“Slow and steady wins the race,” said Professor Benton.

“In Aesop’s classic fable, the fast hare loses the race, while the slow turtle crosses the finish line first.

“Since the time of Charles Darwin, 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.”

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JA Herrera-Flores et al. Slow and rapid rates of evolution in the history of Lepidosaurs. Paleontology, published online November 10, 2021; doi: 10.1111 / pala.12579

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