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AVES - BIRDS 2 main groups Paleognatha – Flightless birds which include ostriches, emus, rheas, cassowaries Neognatha – Flying birds Adaptations For Flight 1. Body shape -Body long and spindle shaped (aerodynamic). Neck long for balance and food gathering 2. Limbs - Forelimbs usually modified for flying. (Hindlimbs for perching, walking, swimming, etc.) Wing shape: Called an airfoil Upper surface of wing is longer than lower surface. Air travels faster above than below, so air pressure above wing is decreased causing the wing to lift. Lower air pressure Higher air pressure 3. Body Covering - Body covered with feathers. (Legs covered with scales.) 4. Skeleton - Bony skeleton with air cavities hollow for reduced weight. Sternum with keel. (Jaws cornified to form beak.) 5. Nervous system Hearing and vision very keen. 6. Circulation - 4 chambered heart with double circulation. 7. Temperature control – Endothermic for a high activity level 8. Respiration - Slightly expansible lungs and air sacs among organs and skeleton. (Syrinx (voice box) near junction of trachea and bronchi.) 9. Excretory system Semi-solid uric acid waste. No bladder. 10. Reproduction Sexes separate. In females only the left ovary develops (to reduce weight). 11. Fertilization internal. Amniote egg with hard shell.