Avian evolution refers to the process by which birds, or Aves, developed from theropod dinosaurs during the late Jurassic period, around 150 million years ago. Key adaptations, such as feathers, lightweight bones, and a beak instead of teeth, allowed these creatures to thrive in various environments. The earliest known bird, Archaeopteryx, showcases both avian and reptilian features, highlighting this transition. Over millions of years, birds diversified into thousands of species, adapting to different ecological niches. Factors like natural selection and climate change played significant roles in shaping their evolution, leading to the wide variety of birds we see today, from sparrows to eagles.