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Quickly evolving species face greater threat of extinction

New research from the University of Bristol looks closely at the dangers of rapid evolution. A team of researchers led by Dr. Jorge Hererra-Flores looked at lepidosauria, a group which includes lizards, snakes and their relatives. Modern lepidosaurs contain 10,000 extant species, and recent success among this group is due to quick evolutionary change. Historically though, lepidosaurs have been slow to change. 

“Lepidosaurs originated 250 million years ago in the early Mesozoic Era, and they split into two major groups, the squamates on the one hand, leading to modern lizards and snakes, and the rhynchocephalians on the other, represented today by a single species, the tuatara of New Zealand. We expected to find slow evolution in rhynchocephalians, and fast evolution in squamates. But we found the opposite,” said Dr. Herrera-Flores.

The research confirms ideas first put forward by paleontologist George Gaylord Simpson in his 1944 book Tempo and Mode in Evolution, where he suggested that fast evolving groups were generally unstable and prone to extinction from quickly changing conditions. 

“We looked at the rate of change in body size among these early reptiles,” said study co-author Dr. Tom Stubbs. “We found that some groups of squamates evolved fast in the Mesozoic, especially those with specialised lifestyles like the marine mosasaurs. But rhynchocephalians were much more consistently fast-evolving.”

“In fact, their average rates of evolution were significantly faster than those for squamates, about twice the background rate of evolution, and we really did not expect this,” noted study co-author Dr. Armin Elsler.

“In the later part of the Mesozoic all the modern groups of lizards and snakes originated and began to diversify, living side-by-side with the dinosaurs, but probably not engaging with them ecologically. These early lizards were feeding on bugs, worms, and plants, but they were mainly quite small.”

Professor Mike Benton emphasized the downside to quick evolution. “In some cases, they can stabilize and survive well, but in many cases the species go extinct as fast as new ones emerge, and they can go extinct, just like the napping hare. On the other hand, Simpson predicted that slowly evolving species might also be slow to go extinct, and could in the end be successful in the longer term, just like the slow-moving but persistent tortoise in the fable.”

The study is published in the journal Paleontology.

By Zach Fitzner, Staff Writer

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