Mammals

Mammals are warm-blooded vertebrates distinguished by the presence of hair or fur at some stage of life, mammary glands that produce milk for offspring, and three middle ear bones. Most species give birth to live young rather than laying eggs. The lower jaw consists of a single bone on each side, and all possess a four-chambered heart. Found on every continent and in virtually all habitats from polar ice to tropical rainforests, deserts to oceans. The class exhibits extraordinary diversity in size, from the tiny Etruscan shrew weighing under two grammes to the blue whale exceeding 150 tonnes. Key identification features include the presence of hair, external ear pinnae in most species, and differentiated teeth adapted to varied diets. Young are typically dependent on parental care for extended periods compared to other vertebrate classes.