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Feathers
Birds possess large flight feathers and smaller downy feathers for insulation. in the theropod lineage feathers would not have been used for flight, and more likely evolved for insulation, display or camouflage.
The Furcula
Also known as the wishbone, this acts as a biomechanical spring-spacer, which bends and recoils during flight. The pectoralis flight muscles are also partially attached to the furcula. These muscles power the downstroke of flight. A role in breathing has also been suggested for the furcula.
For diagram of the avian skeleton click here
The Elongated Forearm
This is a prerequisite for flight-worthy wings
Laterally Flexing Wrist
Lateral flexing of the wrist allows a thrust to generated which is essential for the wingbeat. In certain theropods, this action would have been for quick seizing of prey.
Lightly Constructed Bones
This is a weight-reducing strategy in birds. Marrow or marrow-like tissue in the cavities of bones is replaced by air, even in the skull.
Backwards-pointing Pubis
This may have been advantageous in the earliest tree-climbing birds. A reversed pubis would not be such a hindrance as a vertically-pointing one.
For diagram of the avian skeleton click here
Oviparous
All birds (and thir reptilian ancestors) lay eggs. There are no exceptions.
Author: Robert Davis
Last updated: 21/11/05
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