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Unformatted text preview: 1 Biological Sciences 1B Lecture 24 (Winter 2008) Phylum Chordata: Reptiles and (or) Birds I. Class Aves: birds distinctive, uniform, monophyletic group A. Two modern groups- palate structure 1. Paleognathae: primitive archosaurian palate; aka Ratites 2. Neognathae: flexible palate- all others B. Closest relatives- crocodilians (Archosauria) C. Diverse-8600 species D. Very widely distributed E. Well-known well-studied F. Flight constraints- conservative morphologically 1. Mostly confined to air and flight 2. Few semiaquatic 3. Very few flightless II. Shifts from reptile body plan A. Huge breast muscles, pectoralis ~50% of body weight 1. Ridged rib cage 2. Keel-like sternum 1. Air sacks, (diminish mass/volume) C. Light weight skeleton: 1. 4.4% of body weight-- 5.6% in rats 2. Hollow bones- sometimes air sacks 3. Extremely light skull D. Mass concentrated nr center of bird, efficient movement D....
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- Fall '09