SWIDERSKI, DL*; MILLER, DJ; SHEETS, HD; RAPHAEL, Y; Univ. of Michigan, Ann Arbor; Univ. of Michigan, Ann Arbor; Canisius College, Buffalo, NY; Univ. of Michigan, Ann Arbor: Comparing spirals: Geometric morphometrics with a twist

Coiled shapes occur in such disparate structures as flowers, snail shells and the cochlea in the mammalian inner ear. Variations in these shapes may have important functional consequences, such as resistance of shells to crushing, and in the case of the human cochlea, could have implications for the treatment of hearing loss. Mathematical models like the log spiral provide elegant approximations of an average shape, but offer few clues to understanding patterns of variation in populations. Empirical studies of variation in coiled shapes often are stymied by a paucity of landmarks. Recent studies have shown that semilandmarks (points defined in terms of their position along a curve or surface) can be used within the theoretical framework of geometric morphometrics to compare mean shapes of landmark-poor objects such as feathers. In this study, we explore the use of semilandmarks in geometric morphometric analyses of variation, focusing on the identification and characterization of localized shape differences (e.g., presence of a bell-shaped aperture). Such localized differences can be valuable for detecting regional shifts in developmental processes, and for the human cochlea, may be useful for targeting therapeutic treatments of hearing loss.