The geographic, taxonomic and temporal distribution of determinate growth in marine gastropods

Abstract

Many marine gastropods are characterized by determinate growth, as inferred from the presence of unique terminal elaborations of the shell's aperture. Although determinate growth has evolved repeatedly in most major gastropod clades, it is especially frequent among siphonate caenogastropods. Analyses of shallow-water assemblages show that the incidence of species with determinate growth is far higher in the tropics (especially the tropical Pacific and Indian Oceans) than at higher latitudes. Compilations of fossil assemblages from warm-water environments indicate that, although determinate growth occurred in some Palaeozoic gastropods, it became widespread only in the Neogene. In some groups, terminal apertural elaborations arose in lineages whose growth was more or less continuous and indeterminate, but in others it was derived either from or was ancestral to episodic growth. The hypothesis that periodic or terminal apertural elaborations evolved as a means to dispose of calcium carbonate once growth in the spiral direction ceased is rejected in favour of functional interpretations. Among the latter, the roles of modified apertures in defence and in mate recognition are explored, but no firm conclusion regarding the latter possibility can be drawn owing to our ignorance of mate recognition in gastropods.