Compare the characteristics of mammals and birds, noting the similarities and differences between the groups. Why don't we consider mammals and birds closely related with a common ancestor, since they are both "warm-blooded"?

Question

What will be an ideal response?

Answer 1

Answers may vary. Mammals and birds share some common traits, and are thought to have evolved from an ancestral stem reptile. Both birds and mammals have similar circulatory pathways and are endothermic. Birds have feathers, which are modified scales, to keep them warm, while mammals have hair. Many scientists think hair evolved from reptilian scales. There are also many differences between birds and mammals. Most modern mammals do not lay eggs, as birds do. They give birth to live young and have mammary glands which secrete milk as nourishment for their young. Birds do not have either of these characteristics. Although the brains of birds are well developed, mammalian brains are much more complex and larger. Birds and mammals differ structurally in a variety of ways, like teeth, bones, and respiratory systems. The fossil record clearly reveals that birds and mammals arise from different reptilian lineages. Scientists have discovered a sequence of transitional fossil forms between the dinosaurs and birds and between the dinosaurs and the thecodonts. Fossils evidence also supports the evolution of mammals from therapsids and therapsids from pelycosaurs.