A massive asteroid impact 66 million years ago wiped out most of the dinosaurs, which had dominated Earth for millions of years. The extinction of non-avian dinosaurs created opportunities for other life forms to thrive and diversify. The ancestors of modern birds emerged shortly thereafter, and by analyzing bird genomes, scientists have uncovered genetic traces of this catastrophic event. Comparisons of genomes among major bird groups revealed multiple significant changes within 3 to 5 million years following the impact. These changes are associated with adult bird size, metabolism, and the development of chicks. For example, adult birds are much smaller than avian dinosaurs, and chicks are smaller, weaker, and born without feathers, requiring parental care for a period of time. Some birds today, such as chickens and ducks, are precocial, meaning they can move and feed themselves shortly after hatching, a trait also found in avian dinosaurs. The study suggests that the extinction event had a profound impact on organismal biology by altering genomes.
