Functional Morphology of the Enlarged Pharynx and Hyoid Bone of the Shoebill

The cavity of the pharynx and hyoid bone of the shoebill (Balaeniceps rex) were examined by using the three dimensional computed tomography image analysis. The pharynx and the cranial part of the esophagus were extraordinarily bilaterally enlarged. The unfixed flexible hyoid bone and degenerated tongue were discerned. We suggest that these morphological characteristics functionally enable the species to receive the large prey item peculiar to the feeding behavior of the shoebill. The structure of the pharynx region may totally act as a flexible pouch to pass the large food to the alimentary tract. The bilateral asymmetry was also confirmed in the hyoid bone, cavities of the pharynx and cranial esophagus. We think that these asymmetrical forms may also contribute to the deglutition of large prey fish in the shoebill.