A recently discovered species with amniotic eggs, a four-chambered heart, and lightweight, honeycombed bones would most likely possess which additional characteristic?

• A. Mammary glands
• B. External fertilization
• C. Ectotherms
• D. Feathers for flying

Answer: (D)

Birds share amniotic eggs, a four-chambered heart, and lightweight, honeycombed bones that reduce weight for flight. This combination points to avian biology and a high metabolic rate. The characteristic that best fits is feathers for flying, since feathers are a defining feature of birds and enable the lift and control needed for flight. External fertilization is not typical for birds; fertilization occurs internally. Mammary glands belong to mammals, not birds. Ectothermy describes cold-blooded organisms, whereas birds are endothermic, maintaining body heat through metabolism. So the trait most likely present alongside those features is feathers for flying.