Investigating Rare Biomineralization Structures in Trilobites

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Trilobites, a diverse class of arthropods, inhabited a range of marine environments from Early Cambrian to Permian time, and their abundance and various morphologies are significant in the interpretation of evolution, paleoenvironments and biostratigraphy. Their preservation is due to their calcitic structures formed by biomineralization. Investigating biomineralization processes in trilobite can enhance our understanding of the evolution of trilobites. This thesis presents two rare biomineralization structures in trilobites; the Asaphus trilobites, displaying stalk eyes, varying in length and width, and the Eldredgeops rana trilobites, displaying patterns on their shells that may have served as an additional visual system or amorphous calcium carbonate reservoirs. The eyes of Asaphus kowalewski, Asaphus cornutus and Asaphus punctatus and the spots on the Eldredgeops rana were characterized using a scanning electron microscope for imaging, energy dispersive x-ray spectroscopy and electron backscattered diffraction mapping to obtain elemental composition and crystallographic orientation and to observe microstructural arrangements. Further analyses were done on the Eldredgeops rana trilobites using atomic force microscopy and Raman spectroscopy to study the surface of the spots and their chemical bonding, respectively. This study reveals the stalked eyes main features are lenses and fibers. Asaphus kowalewski has lenses shaped as a truncated prism. Asaphus cornutus and Asaphus punctatus have lenses that are shaped as either a cone or an elongated prism. The cone shaped lens resembles ommatidium in the compound eyes of modern arthropods. The variation in lens shape within a specie could be explained by sexual dimorphism, which has been reported in modern arthropods. These findings suggest a stronger evolutionary link between trilobites and modern arthropods. Analysis of the spots on the Eldredgeops rana trilobite show that they cannot be lenses; there is no pathway connecting the spots to the exterior of the trilobite and no uniform orientation in the crystalline structures. Atomic force microscopy and Raman analyses of the spots show inconsistency with amorphous calcium carbonate. Overall, the results of this study demonstrate that by applying new concepts from the study of modern organisms and using advanced analytical techniques, we can enhance our understanding of the diversification of trilobites.

Electronic Thesis or Dissertation
arthropods, Asaphus, Biomineralization, eyes, Trilobite