Comparative Functional Morphology of the Skeletal Forelimb, Pectoral Girdle, and Sternum in Japanese Native Domestic Fowls

This study aims to understand the relationships among morphological characteristics, their functional roles, and breeder preferences in Japanese native fowls. We analyzed and compared the shapes and sizes of the skeletal forelimb, pectoral girdle, and sternum among six breeds: Chabo, Oh-Shamo, Onagadori, Shokoku, Tosajidori, and Totenko. Because skeletal forelimb, pectoral girdle, and sternum are one of the bases for composing body appearance and for movement of birds such as flapping, we treated those skeletons. All measurements of size were smaller in Chabo than those in other breeds except Tosajidori. The largest measurement values of all parameters were observed in Oh-Shamo. The largest measurement values were observed in all measurements of Oh-Shamo. Short and wide forelimb bones and a short coracoid were observed in Chabo. Oh-Shamo was equipped with a wide sternum and a widely articulated coracoid. Shokoku and Totenko possessed longer bones that constitute the thoracic cavity. We suggest that the small bone size in ornamental fowls contributes toward a cute appearance and that the large bone size of fighting fowls is correlated with their masculinity and aggressiveness. The short forelimb bones, wide articulation, and corpus of forelimb bones in Chabo create a round and soft body silhouette. The observed short coracoid prevents Chabo from dragging its body on the ground while walking. The wide sternum and articulation of the coracoid observed in Oh-Shamo are considered to contribute to the ability to pounce on an opponent by flapping during a fight. The wide sternum of Oh-Shamo is considered to affect its body outline, producing a strong, masculine physical appearance. We also suggest that the characteristics observed in Shokoku and Totenko create a space for the vocal organs, such as clavicle air sacs. We suggest that the observed morphological characteristics underlie the function and breeder preferences of each breed.