The research presented in this PhD thesis explores the advantages of benchtop μXRF-element mapping as a tool for anatomical studies, and hence taxonomical implications related to the fossil fishes of the lowermost Eocene (Ypresian) Fur Formation, exposed in the western Limfjord area of northern Denmark. Amongst the fossil fishes of the Fur Formation and the underlying Stolleklint clay unit (Ølst Formation) are some of the earliest, and best preserved, articulated representatives of modern teleost lineages. The Fur Formation, which is considered a Konservat-Lagerstätte, consists of a fossil-rich marine diatomite succession interbedded with about 200 ash layers, resulting from the volcanic activity in response to the opening of the North Atlantic. The appearance of the distinct negative Carbon Isotope Excursion in the lowermost Ølst Formation identifies the Paleocene-Eocene boundary, and the fishes of the Ølst and Fur formations lived during and in the immediate aftermath of the Paleocene–Eocene Thermal Maximum.

The main goal of this project was to investigate whether or not μXRF-element mapping could be applied as a tool for alpha taxonomic studies on the Fur Formation ichthyofauna, in order to improve our understanding of the palaeobiodiversity in the formation, and early Cenozoic evolution of modern bony fish lineages. Particularly Sr, P, Ca, and Ti proved useful to expose various parts of the body anatomy in the fossil specimens originating from the carbonate concretions and silicified diatomite. Concerning the soft diatomite, there is typically little to no distinction in the element maps between the superficial residue imprints and enclosing matrix. Si-mapping of soft diatomite specimens, however, may be applied to make a sort of digital casts of the cavities to expose bones no longer present. Benchtop μXRF-element mapping was applied for anatomical and taxonomical studies of three new taxa of the Fur Formation, the polymixiid Polyspinatus fluere, the stromateiform Butyrumichthys henricii, and stem-argentiniform Surlykus longigracilis.

The results from this Industrial PhD project show that μXRF-element mapping, by applying a M4 Tornado benchtop spectrometer, can be directly used as a tool to expose and intensify intricate morphological details necessary for anatomical and taxonomical studies; details otherwise not visible. Furthermore, the results have increased our knowledge on selected fish taxa from the Fur Formation in relation to their modern counterparts, and finally, preliminary studies show that benchtop μXRF element mapping can be applied to other fossil fish assemblages from deposits from different environments, with similar results applicable for anatomical and taxonomical studies.