Going round the twist—an empirical analysis of shell coiling in helicospiral gastropods

• DOI: 10.1017/pab.2021.8
• Publication Date: 2021-03-23T13:41:40Z
• Authors: Katie S. Collins; Roman Klapaukh; James S. Crampton; Michael F. Gazley; C. Ian Schipper; Anton Maksimenko; Benjamin R. Hines
• Keywords: Whorl (mollusc)

Abstract The logarithmic helicospiral has been the most widely accepted model of regularly coiled molluscan form since it was proposed by Moseley and popularized Thompson Raup. It is based on an explicit assumption that shells are isometric grow exponentially, implicit external shell follows internal shape, which implies parameters spiral could be reconstructed from whorl profile. In this contribution, we show these assumptions fail all 25 gastropod species examine. Using a dataset 176 fossil modern shells, construct empirical morphospace coiling using expansion rate, translation rate increasing distance axis, plus aperture shape change, their best-fit models. We present case study change in through geologic time austral family Struthiolariidae to demonstrate utility our approach for evolutionary paleobiology. fit various functions shell-coiling best morphological not same each parameter. set R routines will calculate sagittal sections allow workers compare models choose appropriate sets own datasets. Shell-form highlight hitherto neglected hypothesis relationship between Antarctic Perissodonta enigmatic Australian genus Tylospira fits biogeographic stratigraphic distribution both genera.