Assertion: bird | /r/HasAspect | lightweight skeleton
Facets:
value: for flight
type: PURPOSE
Source sentences:
text: Birds have various adaptations for flight, including a lightweight skeleton, two large flight muscles, the pectoralis (which accounts for 15% of the total mass of the bird) and the supracoracoideus, as well as a modified forelimb (wing) that serves as an aerofoil.