Introduction

Abstract

The story of the vertebrates is one of continuing biological improvement from primitive jawless fish-like animals, represented today by the lampreys, through the true fishes, amphibians and reptiles to the birds and mammals. Each class of vertebrate tends to demonstrate particular biological concepts better than others. The fishes have sustained their dominance in aquatic environments for some 500 million years from the Ordovician Period to the present and have evolved into a group of enormous complexity with large numbers of families and species, especially in the teleosts. The amphibians were the vertebrate pioneers in terrestrial environments, but, although they proved successful with experiment and improvisation, they have never fully severed their link with aquatic life. The reptiles dominated the land during the Permian Period and the succeeding Mesozoic and, although they then declined with the ascendancy of more efficient competitors, chiefly the mammals, their descendants still form a significant component of the fauna, particularly in warmer parts.