Dissertation Research: Growth and Evolution of the Shell in Turtles: Patterns, Processes, and Consequences of Morphological Variation

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LaBarbera 9701119 The authors will study patterns of dermal shell growth, function and evolution in turtles. The turtle shell represents a unique skeletal system which is particularly amenable to growth studies because most ossification and development occurs post-hatching. As one of few sutured vertebrate skeletal systems other than the skull, the turtle shell is a useful comparative model for exploring the growth of sutured structures. The functional consequences of growth patterns will be evaluated in the context of morphological integration, mechanical integrity and relative shell mass. Patterns of shell growth will be characterized for various species of cryptodiran turtles and compared in a phylogenetic context. Growth trajectories will be quantified and compared using landmark-based morphometric methods. The role that sutures play in shell growth, and the relationship of that role to shell geometry, will be assessed in a study using fluorochrome bone markers to quantify skeletal growth. Functional hypotheses of morphological integration, shell strength, and relative shell mass will be evaluated using a combination of statistical models and mechanical testing. This study contributes to an understanding of the relationship between ontogenetic change and morphological evolution, examines tissue level processes which contribute to the gross development of form, and places these findings in a functional context.