This book presents our current knowledge of the early vertebrates, which were mainly fish, but included some land vertebrates, and lived 470 to 250 million years ago. It centres on anatomical and phylogenetic questions, but includes information about fossil discovery and preparation, as well as the analysis of the characteristics from which their relationships may be reconstructed. It addresses critically both old and new problems in the evolution of certain anatomical structures and deals briefly with the animals' way of life, extinction, and former distribution.

In addition, the author gives a potted history of the field of vertebrate palaentology and the rise of cladistics, a cmajor methodological revolution in comparative biology.

The book is the first in this field to use a cladistic approach. For each major vertebrate group, the reader will find a diagram or relationships, or cladogram, with a selection of characters at each node, and a succinct phlyogenetic classification.