A study led by researchers from the University of Michigan has unveiled the relationship between bird genomes and the mass extinction event that wiped out dinosaurs. This research reveals that the genetic markers within bird genomes, referred to as genomic fossils, hold insights into how birds evolved and adapted following the catastrophic event 66 million years ago. This study is published in the journal Science Advances.
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Around 66 million years ago, a massive asteroid collided with Earth in what is now the Yucatán Peninsula in Mexico.
This event triggered a global chain reaction causing environmental changes including massive wildfires, tsunamis and a nuclear winter effect due to the dust and aerosols ejected into the atmosphere.
The impact led to the Cretaceous-Paleogene (K-Pg) extinction, one of the most mass extinction events in Earth’s history. Approximately 76% of all species including non-avian dinosaurs, were wiped out.
While non-avian dinosaurs perished, some small, feathered dinosaurs managed to survive. These survivors are the ancestors of modern birds.
In the aftermath of the extinction event, these early birds underwent evolutionary changes leading to the incredible diversity of bird species we see today.
The study reveals that the genetic makeup of these early birds was influenced by the mass extinction allowing them to adapt to the new world.
The DNA of modern birds contains remnants of the genetic changes that occurred after the K-Pg extinction.
Scientists led by ornithologist Jake Berv from the University of Michigan, have used advanced genomic analysis techniques to detect these changes.
The study focused on shifts in the composition of nucleotides, the building blocks of DNA, which are labeled as A, C, G and T.
These shifts were found to be associated with aspects of bird biology such as body size, metabolism and development patterns.
The study identifies the presence of genomic fossils within the DNA of living birds. These genomic fossils represent genetic markers that changed in response to the mass extinction event.
Lead author Jake Berv addressed the importance of examining bird DNA to uncover Earth’s historical events. By analyzing the DNA of contemporary birds, researchers were able to detect patterns in genetic sequences that shifted following the asteroid strike.
This asteroid strike, which occurred 66 million years ago is believed to be the catalyst for the dinosaur extinction.
The research team discovered that the mass extinction event triggered shifts in nucleotide composition within bird genomes. Nucleotides, the building blocks of DNA include molecules represented by the letters A, T, G and C.
The study found that the shifts in nucleotide composition were linked to how birds develop as babies, their adult size and their metabolism.
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Post-extinction, bird lineages that survived tended to develop smaller body sizes. There was also a shift toward an altricial pattern of development, where hatchlings are born in a more embryonic state, requiring parental care to survive.
Birds with altricial development are born needing parental care and take weeks to fledge. Precocial birds, like chickens and turkeys, hatch ready to fend for themselves.
The study links the shift towards altricial development to the genetic changes detected in bird DNA.
Mapping the tree of life for birds is complicated due to the complexity of evolutionary changes over time.
Over the past 15 years, researchers have utilized large genomic datasets to tackle this issue, but traditional methods have limitations.
Scientists relied on statistical models that assumed the composition of DNA remains constant throughout evolutionary history.
These models allowed for the reconstruction of genetic changes but missed nuances in DNA composition shifts.
The new research employed advanced genomic modeling techniques that allowed for a more accurate tracking of DNA composition over time.
Berv collaborated with Stephen Smith, a U-M professor, to develop a software tool that could more closely track DNA composition changes over time.
This tool relaxed the assumption that DNA composition remains constant, allowing for a more nuanced understanding of evolutionary changes.
The software helped identify critical shifts in DNA composition within a specific timeframe after the mass extinction event.
The study found that the shifts in DNA composition were concentrated within 3 to 5 million years of the end-Cretaceous mass extinction.
The researchers describe the changes detected in bird DNA as genomic fossils. These are essentially remnants of the ancient genetic adaptations that allowed birds to survive and thrive in a post-dinosaur world.
The study was made possible by newly developed software that allows scientists to relax the assumption of a fixed DNA composition.
This software enabled the researchers to detect shifts in the nucleotide base ratios across different bird species, providing new insights into the evolutionary processes that occurred in the aftermath of the K-Pg extinction.
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