Feathers and flight

3. One side of the feather is thin and hard, while the other side is long and ________.
5. Modern birds use the same bone to pull their wings toward their ________ as they fly.
6. Scientists believe feathers evolved because they provided certain ________.
8. Anchiornis had feathers on both its arms and ________.
11. These feathers were similar to ________ bird feathers but had the same shape on both sides.
13. Paleontologists study theropod dinosaurs to find ________ about the origin of flight.

1. The difference in air ________ allows birds to fly.
2. Anchiornis is a 150-million-year-old ________.
4. Birds lift themselves by turning their ________ at a particular angle.
5. A small movable ________ was found in Anchiornis fossils.
7. A bird’s feathers are not the same ________ on each side.
9. This bone helped Anchiornis fold its arms to its ________.
10. Feathered dinosaurs may have evolved flight by jumping from tree to ________.
11. Feathers helped animals stay warm, attract ________, and eventually fly.
12. Because of this, Anchiornis probably couldn’t ________.