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American scientists, using mathematical methods of Bayesian modeling, restored the dynamics of the evolution of the first quadrupeds, which descended from fish 400-360 million years ago and gave rise to all vertebrate inhabitants of the land.

One of the most important evolutionary events in the history of life on Earth is the transition from fish to quadrupeds — vertebrates with limbs. It happened somewhere between the Middle and Late Devonian, but it is not known exactly when.

Researchers from Harvard University used the recently developed statistical method of Bayesian evolutionary analysis, which is used in epidemiology to study the evolution of viruses such as the COVID-19 coronavirus, to accurately estimate the time of origin of quadrupeds, and only recently became a tool of paleontologists.

Using this method, the authors were able to very accurately establish the exact age of the origin of quadrupeds-390 million years ago, which is 15 million years earlier than the oldest known fossil fossils of quadrupeds.

"Usually traces appear after the bodies of their creators," the head of the study, Professor Stephanie Pierce (Stephanie Pierce) from the Faculty of Organic and Evolutionary Biology, is quoted in a press release from the university. — In this case, we have traces of quadrupeds that are several million years older than the first fossils, which is extremely unusual."

The researchers also found that the ancestors of quadrupeds had exceptionally low rates of anatomical evolution. The fish were well adapted to the aquatic environment and they did not need to change. But the first quadrupeds that came to land evolved very quickly.

"We found that the evolutionary lines that led to the appearance of the first quadrupeds acquired the main new adaptive features at an incredibly fast pace, which were preserved for about 30 million years," says the second author of the article, Dr. Tiago Simoes (Tiago R. Simush).

The authors used molecular methods to study how quickly various parts of the body of early quadrupeds, such as the skull, jaws and limbs, evolved, as well as the force of natural selection acting on each of them, and found that the skull and jaws developed faster than the rest of the body, including the limbs.

"This suggests that changes in the skull played a more important role in the initial stages of the transition from fish to quadrupeds than changes in the rest of the skeleton. The evolution of limbs for life on land was important, but mainly in the later stages of the evolution of quadrupeds, when they became completely terrestrial, " explains Pierce.

"We see several anatomical innovations in their skulls related to feeding and foraging, which allowed the transition from a fish-like prey capture based on sucking to biting, as well as an increase in the size and location of the eye orbit. These changes have prepared the quadrupeds for searching for food on land and exploring new food resources that are inaccessible to their fish relatives," adds Simoes.

The authors contrast the classical hypothesis that new groups of animals appeared at high rates of anatomical changes and diversity of species with a new view. In their opinion, at such critical moments, anatomical changes first developed rapidly, and the expansion of species diversity occurs only a few million years later.

PHOTO: This could look like tiktaaliki-fossil fish from the Late Devonian, which had many common features with quadrupeds © University of Chicago, Neil Shubin

The article was published in the journal Ecology of Nature and Evolution
Source: RIA Novostisci-dig.ru

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