Analysis of the Vertebral Morphology of Pacific Sand Lance, Ammodytes personatus

Abstract

Pacific sand lance (Ammodytes personatus) are small head-first burrowing fish distributed throughout the North Pacific Ocean. Despite lacking typical morphology of other burrowers, their elongate bodies allow for rapid burrowing through undulation. Vertebrae support full-body movements like swimming and bear the mechanical load for the axial skeleton. We hypothesize that structural changes in vertebrae, such as changes in mineralization and shape, enhance undulatory performance and help generate the forces needed for burial. We microCT scanned 22 sand lance (SL 33-95mm) to estimate the bone mineral density and used geometric morphometrics to characterize shape variation along the length of the fish and over ontogeny. We found sand lance vertebrae were 1.25 times denser near the head and tail regions compared to the middle. Additionally, the main drivers of vertebral shape variation were the prominence of the hemal spine and the angle of the neural and hemal spines relative to the centrum. These localized morphological increases in density and shifts in spine orientation may serve as additional support and points of force transmission for initiating and sustaining burial.