Sims, Eileah Renee (2020-07). Morphometric Analysis of Biostratigraphically Significant Fusulinid Foraminiferan Genus Triticites across the Pennsylvanian-Permian Boundary in the Central and Southwestern United States. Master's Thesis.
Thesis
Fusulinid foraminifera are commonly used for Late Paleozoic biostratigraphic correlations in the Central and Southwestern United States instead of conodonts due to the high abundance of fusulinids in Late Paleozoic carbonates. These correlations rely on consistent identification of biostratigraphically significant species using morphological characters. However, these characters are often translated into qualitative descriptors such as, "inflated", "elongated" and "more fluted", which can lead to discrepancies among taxonomists and cause biostratigraphic disagreements. Quantitative morphometric studies can help make taxonomy replicable among workers. Here, we use 14 linear measurements to define the morphology of 18 species within the biostratigraphically important genus Triticites. A canonical variates analysis (CVA) shows that while specimens of a given species occupy similar morphospace, congenerics overlap considerably in morphospace, and thus cross-validation showed that species prediction based on these measurements was poor (~27%). However, a linear discriminant analysis (LDA) of specimen measurements correctly predicted whether specimens were from the Virgilian (latest Pennsylvanian) or Newwellian-Nealian (earliest Permian) in ~77% of cases. This indicates that incorrect predictions most often occurred among specimens of similar age. The LDA further revealed morphological differences between specimens of different stratigraphic age, which are primarily driven by proloculus size relative to the overall size of the organism at the 4th volution. This may reflect a change within Triticites from an r-selected reproductive strategy in the latest Pennsylvanian to a K-selected reproductive strategy in the earliest Permian in response to changing environmental conditions. This morphological change is replicated in all four tested North American basins and could indicate that the environmental changes across the Pennsylvanian-Permian boundary were at the continent-scale. This morphological shift is potentially useful for biostratigraphy because it does not depend on species identification and is recognizable in analyses blind to stratigraphic age association.
