CRYSTALLOGRAPHIC CHARACTERIZATION OF CALCITE MICROSTRUCTURES IN FOSSIL BRACHIOPOD SHELLS IN RELATION TO LIFESTYLES

Brachiopod shells are one of the most abundant and diverse representatives of invertebrate faunas in the Phanerozoic fossil record. Modern representative taxa usually attach to a hard substrate by a pedicle and have simple morphologies optimized to withstand stresses specific to their environment by precisely controlling the crystallographic orientation of calcite biomineral structures. On the contrary, fossil species are shown to have inhabited diverse modes of life, including cementation to the substrate or partial burial, and possessed more varied morphologies. This research studies the possibility that brachiopods similarly exerted a precise control on their crystallographic arrangement of calcite microstructures, such as prism and fiber growth, for better ecological adaptation, to the point of influencing shell growth that resulted in a higher morphological disparity in the fossil record.

Up to now, studies have focused on comparing the shapes of fossil brachiopods to paleoenvironmental parameters, showing that the environment plays a large role in shell shape, size, and other features such as ornamentation. Recently, researchers have been analyzing how shell microstructures and biological control in mineral formation influence ecological adaptation in modern taxa. Similar studies are rare for fossil species, although they present a much greater morphological disparity and arrangement of shell microstructures. The focus of this research project compares EBSD microstructural data across 16 different species of fossil brachiopods and attempts to correlate this data with previously determined modes of life. By studying these shell structures in fossil brachiopods, we are increasing our understanding of environmental influence on marine organisms and their ecological adaptation. This research also provides detailed analyses of structural features in genera of brachiopods that are understudied and increase our knowledge of functional morphology and shell growth in ancient organisms. These analyses can always be applied on an even broader scale in understanding biological strengthening mechanisms within materials science and novel engineering strategies against environmental stressors, such as variations in hydrostatic pressure.