Using elliptical fourier analysis to compare size of morphospace occupation between modern edentulous freshwater unionoid mussels and the fossils at L6516 (Slope County, North Dakota, USA), with remarks on preservation
Date of Award
Master of Science (MS)
The purpose of this project was to use outline morphometric techniques to determine the number of freshwater mussel taxa present at locality L6516 (“Das Goods”),which is located in Cretaceous strata in the basal Ludlow Member of the Fort Union Formation in Slope County, North Dakota, U.S.A. Secondary goals were to improve the outline morphometric procedures that have been previously used to characterize fossil and extant freshwater mussels, and to describe in more detail the preservation of the edentulous unionoid specimens from the Das Goods area.
Outlines of individual mussel valves were used for morphometric analyses due to lack of preserved taxonomic characters. Outlines were digitized as a series of (x,y)coordinates, after which elliptical Fourier analysis was used to standardize the valves according to position, size, and rotation. A series of coeﬃcients was produced for each valve that was used to characterize the freshwater mussels from L6516 as well as a selection of modern edentulous genera and species. The size of morphospace occupation was calculated and compared between the fossil and modern groups to determine the probability of multiple taxa at L6516. Diﬀerent regions of preservation on the best-preserved specimens from locality L6516 were mapped to characterize preservation trends at this site. Traces attributed to epizoic organisms were also examined for position, size, and relief.
The fossil edentulous freshwater mussel assemblage from locality L6516 does not possess statistically signiﬁcantly more or less morphological variation than the modern genera and species with which it was compared, suggesting a single taxon is preserved. Some of the eﬀects of procedural changes on the outcome of the statistical tests were described in order to enhance the eﬃcacy of the morphometric techniques: standardization of both digitization size and increased smoothing during elliptical Fourier analysis lead to a reduction in size of morph space occupation. Detailed descriptions of the specimens led to new insight into the epifaunal association of other organisms with the unionoid assemblage. Suggestions were made for the improvement of morphometric methods in the natural sciences, including making standardized datasets and detailed documentation more available to new researchers.
Burton-Kelly, Mathew E., "Using elliptical fourier analysis to compare size of morphospace occupation between modern edentulous freshwater unionoid mussels and the fossils at L6516 (Slope County, North Dakota, USA), with remarks on preservation" (2008). Theses and Dissertations. 42.