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A new study from the University of Michigan has unveiled how the asteroid impact that ended the reign of dinosaurs 66 million years ago also sparked significant evolutionary changes in the early ancestors of birds.
This research provides new insights into how the mass extinction event influenced the genomic evolution of birds, contributing to the incredible diversity seen in modern avian species.
The study, published in the journal Science Advances, examined the evolutionary trajectory of all major bird groups.
Researchers identified "genomic fossils" in bird DNA that mark critical evolutionary steps, revealing how birds evolved into more than 10,000 living species.
"By studying the DNA of living birds, we can try to detect patterns of genetic sequences that changed just after one of the most important events in Earth's history," said lead author Jake Berv, who conducted the study as a Michigan Life Sciences Fellow.
A living organism's genome comprises four nucleotide molecules—A, T, G, and C. The order of these nucleotides defines the "blueprint" of life.
The DNA code can evolve, shifting the overall composition of nucleotides across the genome. These changes are crucial in determining genetic variation and evolutionary potential.
The researchers found that the mass extinction event caused shifts in nucleotide composition, which were linked to significant changes in bird biology.
Within 3 to 5 million years of the extinction event, surviving bird lineages tended to develop smaller body sizes and more altricial development patterns. Altricial birds hatch in a more embryonic state and require parental care, unlike precocial birds like chickens and turkeys, which are more self-sufficient at hatching.
"This study illustrates that we have probably been missing something by not considering changes in DNA composition across the tree of life," said Stephen Smith, U-M professor of ecology and evolutionary biology. The research team used a new software tool to track DNA composition changes over time, revealing that these shifts were concentrated within about 5 million years of the mass extinction event.
Daniel Field, professor of vertebrate paleontology at the University of Cambridge and co-author of the study, emphasized the profound impact of the mass extinction on bird evolution. "Our study emphasizes that these extinction events can actually influence organismal biology even more profoundly—by altering important aspects of how genomes evolve," he said.
The study's findings highlight the dramatic biological impacts of mass extinction events and provide a more nuanced understanding of the early evolutionary history of birds.
