Early modern birds evolved before the dinosaurs went extinct

Modern birds evolved earlier than previously thought—much earlier than the mass extinction of the dinosaurs—and seem to have had little impact on bird evolution.

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When did modern birds appear on earth? Scientists believe that modern birds appeared around the time that an asteroid hit the Earth 66 million years ago, when the dinosaurs became extinct. Although the conflict wiped out three of the four species alive on the planet at the time, birds did not die out as a group. In fact, paleontologists have long argued that the asteroid impact triggered a major spurt in bird evolution because it eliminated competition for birds, allowing them to evolve into the remarkable diversity of species we see today.

But a new study by an international team of researchers suggests that modern birds began diversifying millions of years ago. Before Asteroid strikes suggest that asteroid strikes did not have a major impact on bird evolution. The discovery, based on extensive mining and analysis of genetic data collected from 124 species of birds representing modern avian diversity, suggests that birds date back much further than previously thought.

The researchers came to this conclusion after analyzing bird DNA to reconstruct a high-resolution bird family tree that shows how the major groups of birds are related. The study's lead author is evolutionary biologist Shayuan Wu Georgia Institute of Technologyand collaborators The common ancestor of all modern birds lived approximately 130 million years ago (Figure 2).

Dr. Wu and collaborators collected and analyzed genome-wide data from 118 species, representing all 35 lineages, to estimate how long ago these lineages diverged based on the number of genetic mutations accumulated in each branch. . Dr. Wu and colleagues analyzed 25,460 genetic loci in four types of DNA, which they used to build their family tree.

Dr. Wu and collaborators then refined their findings by comparing the estimated ages of 19 bird fossils: if a branch was estimated to be younger than a particular fossil, the team adjusted their computer model so it estimated the bird's rate. Evolution consistent with fossil evidence.

Using these methods, Dr. Wu and collaborators mapped an ancient split in the bird tree into two lineages, one that gave rise to mice — today's ostriches and emus, the paleognaths — and the other, which includes all other modern birds, the neognaths. They found that two main branches of the neophytes split early in their evolutionary history, with one branch eventually containing land birds and the other waterfowl. Dr. Wu and collaborators found that the appearance of birds coincided with a global warming event that occurred about 55 million years ago, which appears to have triggered the evolution of modern seabirds. In fact, this report indicates that the radiation of modern birds occurred around the same time that flowering plants and other organisms first appeared and may have accelerated bird evolution.

Because it is based on a steady accumulation of mutations, this study raises a larger and more important question: Has the rate of mutations been constant? How can we be sure of this? This is a significant question when one considers that an asteroid would have wiped out larger birds but left smaller birds relatively untouched. Small birds produce more generations on a shorter timescale than larger birds, so mutations accumulate faster after an asteroid impact, and this can change the accuracy of our estimate of the rate of bird evolution. At the moment, scientists are developing techniques to more accurately estimate the rate at which genetic mutations occur, so they can better match genetic data with existing fossil evidence.


Shaoyuan Wu, Frank E. Rheindt, Jin Zhang, Jiajia Wang, Lei Zhang, Cheng Quan, Zhiheng Li, Min Wang, Feixiang Wu, Yanhua Qu, Scott V. Edwards, Zhonghe Zhou, and Liang Liu (2024). Genes, fossils, and the simultaneous rise of modern birds and flowering plants in the Late Cretaceous, Proceedings of the National Academy of Sciences 121(8):e2319696121 | doi:10.1073/pnas.2319696121

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