Meeting Abstract
Nearly all syngnathiforms (seahorses, pipefishes, and their relatives) are characterized by a long snout, which they employ in an unusual motion called pivot feeding, or rapid dorsal rotation of the head to bring the mouth closer to prey. Previous research has shown that pivot feeding is further specialized in seahorses and pipefish by using power amplification to achieve head rotational velocities faster than should be possible by direct muscle activation. Among all ray-finned fishes, seahorses and pipefish possess the only known power-amplified mechanism, although it has not yet been tested for in other syngnathiforms. I collected high-speed video of feeding strikes from the snipefish, Macroramphosus scolopax , which prior studies have indicated may possess morphological traits thought to be important in power amplification. I used a combination of kinematics, biomechanics, and micro-CT to characterize snipefish feeding and ask whether snipefish have power-amplified head rotation. I find that they have extremely fast strikes (as fast as 2.5ms) with very little change in gape but near-simultaneous head elevation and hyoid depression. The anterior epaxial muscles appear to be specialized for feeding, while the underlying bones are apparently reinforced to resist bending. Measurements on micro-CT images show that lengths and orientations of the four-bar linkage coupling head elevation to hyoid-depression are consistent with a bistable-locking mechanism, although it is unclear what triggers the apparatus to unlock. Power calculations suggest that observed rotational velocities of the head and body would require power inputs physically impossible based on muscle mass. Kinematics, biomechanics, and morphology therefore support claims that snipefish use a “hyoid lock” and power-amplify their feeding strikes.
