Birds utilize a unique structure, called a syrinx, for the production of their vocalizations. The origins of the syrinx are not well understood. New work, utilizing first principlesâbased models, suggests that a key element in selection for the early syrinx might be the position of this vocal structure: although the larynx sits at the cranial end of the airway, the avian syrinx is located at the base of the airway at the split of the trachea to the lungs. This position may make the syrinx intrinsically more efficient, which might have been critical in the origin of this anatomical feature.
Matthew J. Fogarty & Gary C. Sieck (2019)
Evolution and Functional Differentiation of the Diaphragm Muscle of Mammals.
Comprehensive Physiology (advance online publication)
Symmorphosis is a concept of economy of biological design, whereby structural properties are matched to functional demands. According to symmorphosis, biological structures are never over designed to exceed functional demands. Based on this concept, the evolution of the diaphragm muscle (DIAm) in mammals is a tale of two structures, a membrane that separates and partitions the primitive coelomic cavity into separate abdominal and thoracic cavities and a muscle that serves as a pump to generate intraâabdominal (Pab) and intrathoracic (Pth) pressures. The DIAm partition evolved in reptiles from folds of the pleural and peritoneal membranes that was driven by the biological advantage of separating organs in the larger coelomic cavity into separate thoracic and abdominal cavities, especially with the evolution of aspiration breathing. The DIAm pump evolved from the advantage afforded by more effective generation of both a negative Pth for ventilation of the lungs and a positive Pab for venous return of blood to the heart and expulsive behaviors such as airway clearance, defecation, micturition, and child birth.Â