Modern bird genomes still carry echoes of the asteroid that ended the age of dinosaurs. “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. That global cascade of extinctions marked the end of non-avian dinosaurs and opened ecological space for other groups to evolve and thrive. Shortly after the asteroid’s impact, the early ancestors of modern birds began to appear. Now American and British scientists have found traces of that catastrophe in bird genomes — dramatic shifts that helped birds diversify into a hugely successful group of animals.
The asteroid that struck what is now the Yucatán Peninsula in Mexico left an ecological vacuum that was quickly filled with new life. Avian dinosaurs underwent radical transformations and eventually gave rise to the roughly 10,000 bird species that live on Earth today. When animals evolve, their genomic DNA composition can shift. The fundamental building blocks of DNA—nucleotides—are made up of four bases represented by the letters A, C, G, and T. The relative frequencies of those bases can change, and that can influence how an organism develops. Previous studies of bird evolution largely assumed DNA composition was fixed. Using new software, researchers challenged that assumption by allowing nucleotide composition to vary across lineages. Jake Berv and his colleagues used this software to analyze genomic differences across all major groups of birds. They identified shifts in genomic composition dating back to the Cretaceous–Paleogene extinction, according to ScienceAlert.
The team focused on the roughly five million years following the asteroid’s impact. They found that the extinction triggered several pronounced shifts in bird genomes over the next three to five million years. Those changes were linked to traits such as adult body size, metabolism, and patterns of development during the chick stage. For example, adult birds later became much smaller than their avian dinosaur ancestors. There was also a move toward smaller, weaker hatchlings that emerged featherless and required intensive parental care. Today, some birds—like ducks—hatch relatively independent young, a trait called precociality that was common in 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,” Berv said. Compositional changes in DNA had not been thoroughly studied in the context of mass extinction. Mass extinctions can dramatically reshape ecosystems and the relationships among species. “This work expands our understanding of the biological consequences of mass extinctions and shows that the event that wiped out the giant dinosaurs was one of the most biologically significant in Earth’s history,” said Daniel Field, a paleontologist at the University of Cambridge. The study’s findings were published in the journal Science Advances.
