concept

Pneumatic bone

Bone that is hollow and air-filled rather than solid with marrow — a key weight-saving trick for flight. Birds and pterosaurs both carry air-filled skeletons: air sacs from the lungs invade the inside of the bone, leaving thin bone walls braced by internal struts, light yet stiff. It is part of how a Quetzalcoatlus as tall as a giraffe stayed light enough to leave the ground. Pandora's giant fliers presumably lean on the same principle: maximise stiffness per gram, because for a flying machine every gram must be lifted.