Trachea enables deep dives: leatherback sea turtle
 

The trachea of adult leatherback sea turtles enables deep dives via a compressible cartilaginous structure.

   
  "Functionally it appears that the deep diving mammals have a cartilaginous tracheal design that will facilitate progressive collapse with increasing depth, whereas shallow divers have rigid upper portions of the tracheae that remain patent during dives…the adult leatherback trachea has a structure markedly different from that of other living sea turtles. It consists of an elliptical tube of nearcontinuous uncalcified cartilage, rather than a sequence of circular, closely packed tracheal rings. The tube is easily compressible…We believe that the elasticity of tracheal cartilage (combined with expansion of the remaining tracheal air during ascents) will be sufficient to reinflate the trachea…"  (Davenport et al. 2009:3440, 3445-6)

  Learn more about this functional adaptation.