The shell game, who's under what? : morphological evolution and trajectories through morphospace exemplified with species of lambis

grantor: University of TorontoMorphological space provides a means of analysing the physical forms of organisms. Mathematical modeling allows patterns generated by biological processes to be analysed. And cladistic methodology permits the formulation of phylogenetic hypotheses concerning groups of organisms. In this dissertation, a synthesis of analytical techniques is developed, in which morphological space, mathematical modeling, and cladistic methodology are combined to reconstruct evolutionary history. In particular, new methods for tracking changes in shape during ontogeny and for positioning cladogram nodes in three dimensions extend the concept of morphological space to accommodate results of ontogenic and cladistic analyses. This approach to the study of morphological evolution integrates developmental and phylogenetic information and permits the formulation of hypotheses of ancestral forms. Species of the genus Lambis (Mollusca: Gastropoda) are analysed to exemplify the approach. In the development of the synthesis, current generic classification of the family Strombidae is unsupportable and current subgeneric classification within the genus Lambis is untenable. During evolution of members within a clade containing all species currently classified in Lambis and some in the genus Strombus, morphological change consisted predominantly of an increase in vertical dimensions of whorls. The change was greatest early in the history of the group and diminished thereafter.Ph.D