Morphological conservatism of the Family Naticidae (Gastropoda) through time: potential causes and consequences

Taxonomic status of several members of the Family Naticidae is extremely vague because of its simple shell morphology. Conventional taxonomic classification schemes suggest that most of the morphological characters tend to be homoplastic and exhibit convergence. Such morphological convergence complicates naticid taxonomy and makes it difficult to understand the evolutionary history of this group; several unrelated taxa are often misidentified as naticids, thereby exaggerating the actual diversity of this group. Here, we employ a standard landmark–based approach to understand the pattern of morphological evolution of this family. Ordination methods such as Principal Components Analysis and Canonical Variate Analysis were used to create morphospaces, and disparity was quantified using variance and range. Our results reveal, when naticids are compared with their sister taxon, Ampullinidae, the two families show significant differences in their average shapes, despite their superficial resemblances. Among naticids, although the mean shapes of the individual subfamilies are different, overall, the family Naticidae has displayed extreme morphological conservatism from the Jurassic to the Holocene. Interestingly, this conservatism has been unaffected by taxonomic changes — neither the extinction of the subfamily Gyrodinae nor the appearance of the subfamily Sininae affected this morphological conservatism. Naticids have always shown strong ecological preference towards an infaunal mode of life, and strict behavioural selectivity in handling and preying upon infaunal organisms, and this ecological and behavioural conservatism could have enabled them to diversify, without undergoing a change in their basic bauplan.