MICROPALEONTOLOGICAL AND GEOCHEMICAL INSIGHTS INTO THE AGE OF FOSSIL CETACEANS MAIABALAENA NESBITTAE AND SIMOCETUS RAYI

Cetaceans (whales, dolphins, and porpoises) first evolved in the Eocene Period (~56 Ma). Since their evolution from land back into aquatic environments, two key groups have evolved: mysticetes (baleen whales) and odontocetes (toothed whales). The most common ancestor to modern mysticetes is thought to be Maiabalaena nesbittae, and the most common ancestor to modern odontocetes is thought to be Simocetus rayi. Both fossil cetacean specimens are the only known occurrences of their species globally and were recovered less than half a mile from each other in Toledo, Oregon. However, the exact timing of evolution for these specimens relative to each other and the geologic time scale is unconstrained, causing uncertainty in reconstructing the evolutionary history of these two groups. Here we use foraminiferal abundance, species composition, and bulk rock geochemistry to investigate differences between the fossil cetacean outcrops as a means to assess age and paleoenvironment. Previously these outcrops were thought to be exposures of the same rock formation (Alsea Fm.), recording the same stage (Rupelian). However, preliminary results using multivariate statistical analyses of bulk geochemistry (e.g., cluster analysis, principal component analysis) indicate that the fossil cetacean outcrops are geochemically different. The S. rayi outcrop shows high Fe abundance, likely due to higher amounts of mafic-sourced sediments. Conversely, M. nesbittae outcrops show high Ca and Si abundance. Microfossil assemblages are dominated by benthic foraminifera across all sampled outcrops indicating a shallow marine environment, with overall foraminiferal abundance in the M. nesbittae outcrops far exceeding that of the S. rayi outcrop. Initial geochemical and micropaleontological evidence suggests that these outcrops and their associated cetacean fossils are not likely to be the same age. Further analysis will illuminate the evolutionary history of these two unique cetaceans and possibly reveal which group first evolved (mysticetes or odontocetes), contributing to current understandings of modern cetacean evolution.