Chapter 1 Shared Characters - Birds and Reptiles : Single Occipital Condyle Single Middle Ear Bone Lower Jaw Composed of Five Fused Bones Red Blood Cells Nucleated Egg Structure and Egg Tooth Chapter 2 Unique Avian Characters : Feathers Lack of Teeth Many Bones Fused or Reduced Bones Pneumatized, or Air-Filled Forelimbs Specialized for Flight Body Mass Highly Centralized Increased Ability to Withstand Metabolic Stress Unique Respiratory System