“By studying the DNA of modern birds, we can uncover patterns in genetic sequences that changed immediately after one of the most significant events in Earth’s history,” said ornithologist Jake Berv from the University of Michigan, the lead author of a new study. A massive asteroid struck our planet around 66 million years ago, altering the course of life on Earth. The impact, which triggered the Cretaceous-Paleogene extinction event, wiped out an estimated 76 percent of all animal life on the planet. This chain reaction of changes worldwide marked the end of non-avian dinosaurs. However, their extinction opened the door for other forms of life that would eventually evolve and thrive. Shortly after the asteroid’s impact, the early ancestors of modern birds emerged. Now, American and British scientists have discovered traces of this catastrophe in the genomes of birds—dramatic changes brought about by the mass extinction that allowed birds to diversify and become an incredibly successful class of fauna.
So, the impact of the enormous rock that struck what is now the Yucatán Peninsula in Mexico left a certain vacuum. However, it was quickly filled with new life that evolved, diversified, and ultimately took its place in the rejuvenated world. Avian dinosaurs underwent radical transformations, evolving into the approximately 10,000 species of birds that inhabit the Earth today. When an animal evolves, shifts can occur in the DNA composition of its genome. The fundamental building blocks of DNA—nucleotides—are made up of four different bases, represented by the letters A, C, G, and T. The ratios of these nucleotide bases in the genome can vary, leading to changes in the development of the organism. Previous studies on bird evolution had assumed a fixed DNA composition that could change. Using cutting-edge software, researchers challenged this assumption by working within a paradigm that allowed for shifts in the ratios of nucleotides and bases. Jake Berv and his colleagues utilized this software to analyze genomic differences among all major groups of birds. As a result, they identified shifts in genomic composition dating back to the time of the Cretaceous-Permian extinction, as reported by Science Alert.
The team focused on a period of 5 million years immediately following the asteroid’s impact. Scientists discovered that this extinction led to several significant shifts in bird genomes over the next 3 to 5 million years. These changes were linked to factors such as adult bird size, metabolism, and how they developed during the chick stage. For instance, adult birds eventually became significantly smaller than their avian dinosaur counterparts. There was also a shift towards smaller, weaker chicks that hatched featherless and required a period of intensive parental care. Today, some birds, like ducklings and chicks, do not need such care. This trait, known as precociality, was characteristic of avian dinosaurs.
“The size of the adult organism and the patterns of development leading up to hatching are two important features of bird biology that we can link to the genetic changes we’ve identified,” noted Berv. Previously, compositional changes in DNA had not been thoroughly studied in the context of mass extinction. However, scientists know that mass extinctions can have dramatic consequences for the world. They alter entire ecosystems and the relationships between organisms within them. “This work has expanded our understanding of the dramatic biological consequences of mass extinctions and demonstrated that the mass extinction that wiped out the giant dinosaurs was one of the most biologically significant events in the history of our planet,” remarked paleontologist Daniel Field from the University of Cambridge in the UK. The findings of the study were published in the journal Science Advances.