Endowed with colorful plumages and beautiful songs, birds in flight symbolize spirits released from the bondage of gravity. From the day that humans first looked up at the skies, birds have summoned a sense of wonder and mystery, enchanting our earthbound ancestors with their freedom and song. They fly where they please and when they please. The power of flight has opened up to birds a multilayered network of aerial highways and byways, enabling them to reach any place on our planet. They exhibit a wide variety of sizes, shapes, colors, and habits.

It is not much to document the origin of bird flight. Strictly speaking, these specimens are not the entire body of evidence. There are, of course, other fossil birds, not to mention bats, pterodactyls, and insects that have a few things to say about bird flight. And there are living creatures, mathematical models, and aerodynamic theories to help us understand this amazing evolutionary accomplishment. Nonetheless, these seven specimens are crucial. They lie at the heart of complex debates that began with the discovery of the first specimen of Archaeopteryx more than 130 years ago and continue up until today. These few, special fossils have served as the basis for brilliant deductions, wild speculations, penetrating analyses, and amazing insights. They have revealed—and continue to reveal—not only the pathway through which birds and bird flight may have originated, but they also tell us much about the strengths and weaknesses of science and scientists. <...>

Most palaeontologists will tell you they arrived in their job because, as a child, they loved prehistoric creatures, particularly dinosaurs. They just never grew up – or at least they never stopped seeing a world filled with wonder and excitement. In that sense, I never grew up either. I never stopped being the little kid staring up in awe at the 32-metre-long fossil of ‘Dippy’ the Diplodocus that fills the vaulted Central Hall of London’s Natural History Museum.

Having grown up reading that birds were at most only distantly related to dinosaurs, I was both startled and fascinated when a growing number of researchers began to argue that birds were the direct descendants of the terrible lizards. At the end of the 1970s, I was becoming involved in the ar¬ gument both as an artist and a scientist. Art and science could not be separated; the science deter¬ mined whether I should adorn the small predatory dinosaurs with scales or with feathers. Alas, there was no simple answer at the time, because there was no fossil evidence for either possibility. What I found disturbing was that many paleontologists were totally biased against illustrating dinosaurs with feathers, even though the available data was neutral on the subject. This bias only boosted my interest in researching bird origins. <...>