326-6 Exploring Stressors Leading to Increased Rates of Teratology Across the Mississippian Pella Formation of Iowa

Abstract:

Morphological abnormalities can provide an organism-level window into how extinct taxa responded to environmental stress. This work focuses on the Middle Mississippian (Visean) Pella Formation of Iowa, which has been referenced as having a large frequency of abnormal invertebrate fossils. Horowitz et al. (1986) describes teratological defects in the blastoid Pentremites pulchellus from the Pella Formation which occur at a rate of 2.7%. Hessler (1962) additionally references several trilobites belonging to the species Kaskia wilsoni (formerly Griffithides wilsoni) with abnormal segmentation from the same site. Horowitz et al. (1986) did not include any photographs of the observed abnormal blastoids and Hessler (1962) included only one photograph of an abnormal Pella Formation trilobite as an example. This study aims to describe and consider potential drivers leading to the abnormalities observed in the invertebrate paleocommunity of the Pella Formation. To do this, bulk samples have been collected from the portions of the Pella Formation exposed at Lacey-Keosauqua State Park in Keosauqua IA and the Russell Wildlife Area in Oskaloosa IA. Abnormal macrofossils collected from these site as well as from the Pella Formation museum collections at the University of Iowa have been photographed and their abnormalities have been classified. Ostracods were used to constrain salinity levels and wavelength dispersive XRF elemental analysis was performed on the fossil matrix to test for redox sensitive trace elements as a proxy for water column oxygenation. This work has yielded multiple abnormal blastoids, crinoids and trilobites, making this the first multi-phylum invertebrate community to be observed with high rates of abnormality. The ostracod community at the site yielded only normal marine taxa, indicating that salinity stress is likely not the main driver. Elevated trace metal concentrations can be observed in some Pella Formation samples, suggesting that local oceanographic conditions may play a role in the heightened frequency of abnormal growth. Further work is needed to elucidate the relative importance of environmental factors such as water column anoxia, heavy metal toxicity, or thermal stress on these communities.

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