Section 1

Origin and Evolution of Birds

• Seven major characteristics of birds are feathers; wings; a lightweight, rigid flight skeleton; a respiratory system involving air sacs; endothermy; a beak instead of teeth; and oviparity.

• Three similarities between birds and dinosaurs include an S-shaped neck, a unique ankle joint, and hollow bones.

Vocabulary furcula (p. 842)

• Archaeopteryx had feathers covering its body, tail, and forelimbs. It had hollow bones and a fused collar bone, called a furcula.

• There are two hypotheses for the origin of flight in birds. One hypothesis is that flight evolved in tree-dwellers. The second hypothesis is that flight evolved in ground-dwellers.

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