WESTNEAT, M. W.; Field Museum of Natural History: Biomechanical Models of Feeding in Fishes: New Applications of Lever and Linkage Theory

Fishes use a sensational diversity of jaw mechanisms to capture and ingest their food. One of the hallmarks of this diversity is the complexity of the kinetic fish skull, which can have more than 20 mobile skeletal elements driven by numerous muscles. This study expands previous lever and linkage modeling to include a broader set of musculoskeletal couplings and develop more comprehensive models for analysis of fish feeding. New models connect the lever mechanism of the lower jaw to mechanisms that operate elsewhere in the skull including the maxilla, opercle, and pectoral girdle. Software for analysis of cranial levers and linkages allows for simulation of structure-function relationships in a wide range of taxa. Simulations show that structural changes in four-bar linkages map to unique sets of primary functional variables with little redundancy when multiple variables are examined. A survey of skull mechanical designs throughout the phylogeny of fishes reveals that evolutionary changes in feeding mechanisms of fishes are accompanied by a wide range of strategies for transferring force and motion. For example, mechanisms for premaxillary protrusion have evolved independently at least 5 times in ray-finned fishes. The lower jaw closing lever has a variable mechanical advantage ranging from 0.04 to 0.68. Linkage modeling leads to several recommendations for morphometric protocols and the use of lever and linkage theory: (1) Coordinate based shape analyses can yield functional insight using mechanically relevant landmarks; (2) The geometric positions and contraction physiology of muscles are critical to accurate estimations of lever and linkage function in real behaviors.