Early feathers were very simple and apparently grown for warmth or for signaling. The prettier the feathers, the more likely the dinosaur was to attract a mate (patterns which certainly exist in birds today). Gradually, some dinosaurs began growing more complex feathers and began to learn how to fly. Then, their body shape changed and included lighter bones, less weight, and very strong chest muscles to power the wings. Suddenly, you have flying dinosaurs, which we now call birds.
One of Brusatte’s most interesting sections is on the lung systems that dinosaurs developed, which are so different from and much more powerful than mammal lung systems. Dinosaurs, like us, get oxygen out of incoming air that is inhaled, but they also have a system of air sacs that captures and momentarily stores some of the incoming air. When we exhale we send out carbon dioxide but get no new oxygen until we inhale again. Dinosaurs, on the other hand, get a second wave of oxygen to absorb when they release the stored fresh air from their air sacs. Essentially, they get two breaths of air each time they inhale. As the need for more air sacs grew, …Read the Rest