The adult leatherback turtle Dermochelys coriacea overlaps in body size (300–500 kg) with many marine
mammals, yet develops from a 50 g hatchling. Adults can dive deeper than 1200 m and have core body
temperatures of 25 °C; hatchlings are near-surface dwellers. Juvenile leatherbacks have rarely been studied;
here we present anatomical information for the upper respiratory tract of 3 turtles (66.7–83.0 cm straight
carapace length; 33.2–53.4 kg body mass) incidentally captured by long-line fisheries. Combined with existing
information from adults and hatchlings, our data show that there is an ontogenic shift in tracheal structure,
with cartilaginous rings becoming broader and eventually fusing anteriorly. This ontogenic shift during
independent existence is unique among extant deep-diving air breathing vertebrates. Tract wall thickness is
graded, becoming progressively thinner from larynx to bronchi. In addition, cross-sectional shape becomes
increasingly dorsoventrally flattened (more elliptical) from anterior to posterior. These characteristics ensure
that the tract will collapse fromposterior to anterior during dives. This study contains the first report of a double
(=internally bifurcated) posterior section of the trachea; it is suggested that this allows continuous food
movement along the esophagus without tracheal collapse. The whole upper respiratory tract (from larynx to
lungs) has a vascular lining (thicker anteriorly than posteriorly) that appears to be a simple analog of the complex
turbinates of birds and mammals. Our study confirmed that the leatherback tracheal structure represents a
distinctive way of dealing with the challenges of diving in deep, cold sea water.