The evolution of Birds
The Origin of Birds
1. Which of the sentences below best expresses the information in the highlighted statement in the passage? The other choices change the meaning or leave out important information.
2. The word modifications in the passage is closest in meaning to
3. According to paragraph 2, how did birds adapt to achieve efficient flight?
P3 A bird’s most obvious adaptations for flight are its wings and feathers. Feathers are made of the protein B-keratin, which is also found in the scales of other reptiles. The shape and arrangement of the feathers form the wings into airfoils, and they illustrate some of the same principles of aerodynamics as the wings of an airplane. Power for flapping the wings comes from contractions of large pectoral (breast) muscles anchored to a keel on the sternum (breastbone). Some birds, such as eagles and hawks, have wings adapted for soaring on air currents and flap their wings only occasionally; other birds, including hummingbirds, must flap their wings continuously to stay aloft. Among the fastest birds are the appropriately named swifts, which can fly up to 170 km/hr.
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