Functional Morphology of Vertebrate Feeding Systems: New Insights from XROMM and Fluoromicrometry

Abstract

Investigations in the form–function relationships of vertebrate feeding systems have a long and illustrious history of inferring function from anatomical structure and specimen manipulation, and a shorter but highly successful history of measuring function directly in living animals with sophisticated methods such as electromyography, bone strain gauges, high-speed cinematography, and cineradiography. Two new methods, X-ray Reconstruction of Moving Morphology (XROMM) and fluoromicrometry show great promise for revealing the 3D form–function relationships of cranial and cervical musculoskeletal structures. XROMM has been applied to measure 3D jaw kinematics and tooth occlusion in mammalian mastication and 3D pharyngeal jaw mechanics in fishes. The form–function relationships of the temporomandibular and other cranial joints are being explored with XROMM, including cranial kinesis in squamates, birds, and fishes. Muscle strain can be measured with fluoromicrometry by implanting small radio-opaque beads and tracking them with biplanar fluoroscopy. Fluoromicrometry has been used to measure muscle strain in muscles with complex architectures, such as the axial muscles during suction feeding in fishes and tongue deformation during swallowing in mammals. XROMM, fluoromicrometry, and buccal pressure measurements together have been used to measure the instantaneous power required for suction feeding and relate required power to the available muscle power. In the future, some systems that may benefit greatly from XROMM and fluoromicrometry are tooth–food interactions during mastication, food transport and swallowing, and the form–function relationships of feeding muscles with complex muscle-tendon architecture, such as the mammalian muscles of mastication and the multi-part adductor mandibulae of fishes.