MARKEY, M. J.*; MAIN, R. P.; MARSHALL, C. R.; Harvard University; Harvard University; Harvard University: In vivo cranial suture function and suture morphology in the extant fish Polypterus

This study describes the mechanical role cranial sutures play in fish during feeding, and presents a quantification of fish suture morphology using microCT scanning. To measure suture deformation during feeding, strain gauges were surgically implanted across selected sutures in the skull roof of 4 individuals of Polypterus endlicheri. After surgery, sutural strains were measured during feeding along with high-speed videos of the feeding events. In each trial, suction feeding versus biting on prey was established, and head lifting, hyoid position, and gape were quantified. Suction feeding shows more stereotyped strain patterns than biting in Polypterus, and peak strains during suction exceed biting strains. In both feeding types the interfrontal suture (IF) is generally loaded in tension, the interparietal (IP) suture is loaded in compression, while the frontoparietal (FP) suture experiences compression or tension depending on feeding mode. MicroCT scans of the experimental animals indicate that the IP suture is interdigitated in cross section, while the IF suture is more flat-edged. These observations are consistent with published correlations of suture form and function (i.e., interdigitation indicates compression). In contrast, the highly overlapping FP suture may represent a compromise between varying tensile and compressive loads. Several metrics, some new to this study, were used to quantify suture shape in the CT scans, and test the hypothesis that shape variation within a suture is greater than variation among individuals. Further, we reject the hypothesis that the ectocranial trace of a suture predicts its 3D shape. These metrics and correlations between suture morphology and function may be used to help make inferences about feeding mode in living and extinct taxa.