ASSESSING MECHANISMS FOR MORPHOLOGICAL CHANGE IN MARINE GASTROPODS THROUGH AN ECO-EVO-DEVO FRAMEWORK: COMBINING PHYLOGENETIC PALEOECOLOGY WITH ONTOGENETIC INFORMATION RECORDED IN FOSSIL AND EXTANT SHELLS (Invited Presentation)

Holistic understanding of evolution within a clade requires not only knowledge of the clade’s phylogenetic history and paleoecological context, but also the mechanisms generating morphological structures. Molluscan shells constructed through accretion preserve a highly informative ontogenetic record. Egg size and larval feeding mode may be inferred from protoconchs. Insights into growth rate, lifespan, and evolutionary development can be obtained through examination of physical shell construction (including microstructures) and isotopic sclerochronology. We use these ontogenetic data to distinguish among possible evolutionary mechanisms generating extreme callus development, shell septation, and unusual gross morphologies in gastropods within an eco-evo-devo framework.

Careful examination of the relationship between microstructure, gross morphology, and functional morphology led to the conclusion that extreme parietal callusing in several gastropod clades has arisen through both convergent and parallel processes. Analysis of the microstructure and distribution of septation in turritellid spires suggests that these septa arose as spandrels of shell thickening, which also generated similar septa in numerous other high spired gastropods. Isotopic sclerochronology clarified how peramorphic heterochronic changes have produced unusual morphologies in Turritellidae, including the heavy shelled Turritella abrupta (through hypermorphosis and acceleration in a high nutrient environmental context) and the uncoiled genus Vermicularia (through changes including hypermorphosis, acceleration, and pre-displacement). Isotopic data also indicates paedomorphic reversals in some Vermicularia lineages through progenesis and post-displacement, resulting in the re-evolution of more regularly coiled forms depending on environmental context (with more dramatic uncoiling associated with reef/hardground environments and more regular coiling associated with soft substrates).