The classification of animals frequently seems confusing. This is a book about mammals and their structural relationships to each other. Following an explanation of the basic attributes of mammals and how they originated, each genus is described in terms of its characteristics and historical development. Family trees assist in demonstrating the evolution of the species and help to explain why they have been classified together. The text is detailed, informative, and clear. So are the illustrations, which show the reconstructions of the ancient animals superimposed upon drawings of the existing skeletal remains.