MORPHOMETRIC ANALYSIS OF BIOSTRATIGRAPHICALLY SIGNIFICANT FUSULINID FORAMINIFERAN GENUS TRITICITES ACROSS THE PENNSYLVANIAN-PERMIAN BOUNDARY IN THE CENTRAL AND SOUTHWESTERN UNITED STATES

Fusulinid foraminifera are commonly used for Late Paleozoic biostratigraphic correlations in the Central and Southwestern United States instead of conodonts due to their abundance. 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 genus Triticites. These 195 specimens are from museum collections at the Yale Peabody Museum and the New Mexico Museum of Natural History and Science and are previously identified specimens referred to in publications. To determine if these measurements can distinguish among species, we used a Canonical Variates Analysis (CVA). The 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, we found that placement of specimens into either the Virgilian (latest Pennsylvanian) or Newwellian-Nealian (earliest Permian), based upon the stratigraphic context of the specimens, yield more accurate predictions (~77%). This indicates that misidentifications most often occurred among specimens of similar age. The Linear Discriminant Analysis (LDA) revealed significant morphological differences between specimens of different age, which are primarily driven by proloculus size relative to the overall size of the organism. This may reflect a change within Triticites from an r-selected (small offspring) reproductive strategy in the latest Pennsylvanian to a K-selected (large offspring) reproductive strategy in the earliest Permian. This morphological change is replicated in all four tested North American basins and could indicate a response to continent-scale environmental changes across the Pennsylvanian-Permian boundary.