For around 100 million years before the end of the Age of Dinosaurs, the temperate forests of what is now northeastern China, the arid landscapes of Mongolia, and the open woodlands surrounding the lakes of modern-day Germany—among countless other ecosystems around the world—were host to an array of feathered dinosaurs out of which arose the modern birds. These animals occupied every niche in the habitats they lived in—from terrestrial predators to flighted seedeaters, kingfisher-like piscivores, and tree-dwelling gliders—and displayed many of the behavioral and anatomical characteristics that we attribute exclusively to birds today.

Some, like the formidable and flightless dromaeosaurids and the slender, large-eyed troodontids marked the last branches on the tree of life before the divergence of birds and their immediate ancestors—bearers of a standard dinosaurian body plan that was subsequently adapted and modified to meet the rigors of flight and the dizzying variety of habits and habitat that birds would come to occupy. Other members of this chimeric assortment of species include groups such as the Pygostylia and the Ornithothoraces that contain transitional forms illustrating a stepwise evolution continued by the birds of the present day. Others still such as the Enantiornithes—or “opposite-birds”—and the bizarre, membrane-winged Scansoriopterygidae are evidence of radiations that were eminently well-suited to the environments in which they arose but which left no modern descendants in the wake of the disappearance of those worlds.

The evolutionary episode that saw the dinosaurs take to the air and forge arguably their most enduring legacy left behind an extensive record of the specialized and exploratory morphological adaptations that birds and their closest relatives underwent during the Mesozoic Era. This remarkable radiation is brought to life in Juan Benito and Roc Olivé’s Birds of the Mesozoic: An Illustrated Field Guide. Often exquisitely preserved in fine grained sediments of ash or silt, the fossil record of Mesozoic birds offers an increasingly expansive window into these prehistoric birds’ appearances, such as skin impressions, pigmentation, and skeletal structure, their paleoecology, and even their behavior. This fossil record provides a solid foundation for paleontological research. With detailed and accessible overviews of important anatomical transitions, fossil-bearing localities, and paleobiology, Birds of the Mesozoic traces the descent of birds from their earliest origins through the end of the Cretaceous.

The loss of teeth and the development of the keratinous beak, the fusing of key bones in the avian hand that anchor flight feathers, and the aerodynamic tradeoffs between fused and unfused tail vertebrae are all among the important chapters in the story of bird evolution that are outlined in the book in a way compelling to both casual enthusiasts and technical specialists. The authors fully describe classification systems and terminologies, which makes this work an invaluable reference for readers interested in cladistic phylogeny and systematics. The geologic time scale included in the early chapters provides elucidatory chronological context for the biological events discussed.

Olivé’s full-color illustrations are arranged in an imaginative and familiar field guide format, which complements individual accounts of nearly every species known from the Mesozoic. These illustrations make this indispensable volume not only the most current and comprehensive reference on the subject, but also a powerful stimulant for the imagination. Birders accustomed to spending time in the pursuit and presence of feathered reptiles will find Birds of the Mesozoic to be a vivid look into the primeval forests of deep time and an opportunity to reflect on what an encounter with these ancient birds might have signified for a careful observer in a time unseen by human eyes.