DEVELOPMENTAL ASPECTS OF MORPHOLOGICAL DISPARITY DYNAMICS: A SIMPLE ANALYTICAL EXPLORATION

I present a simple model for assessing the role of development in shaping the evolution of morphological disparity. Disparity of a clade at any given time is expressed in terms of the developmental dynamics that leads to the variety of adult morphotypes observed. Assumed phenotypic manifestations of developmental processes, as they could be detected from allometric characterizations, are used to distinguish a few, non-exclusive types of evolutionary changes in ontogeny. Based on this formaliza`tion, diversification of hypothetical clades is described using the standard curve of adult morphological disparity, the curve of juvenile disparity, and the curve of allometric disparity, the latter quantifying the diversification of clades in allometric space. Contrasts of these curves reflect the underlying developmental scheme which drives temporal changes in disparity. The parameters of the model are then varied to assess the expected signature of each metric under specific conditions: changes in the relative frequencies of the types of evolutionary developmental changes, changes in the transition magnitude attached to each of them, and effects of temporal variation in average adult size on disparity curves and patterns of morphospace occupation. Results emphasize the potential contribution of these proxies for developmental dynamics – juvenile morphological disparity, allometric disparity, and average adult size – in enriching the interpretation of standard disparity curves and the description of clade histories, with possible process-oriented inferences.