EXPLORING DACRYOCONARID BODY SIZE TRENDS ACROSS THE LATE DEVONIAN PUNCTATA EVENT: INSIGHTS INTO THEIR ECOLOGICAL RESPONSES TO PALEOENVIRONMENTAL SHIFTS

Dacryoconarids are an extinct group of marine microorganisms that were abundant and globally distributed during the middle Paleozoic. The group experienced a rapid decline in diversity and geographic distribution entering the Late Devonian, followed by their extinction early in the Famennian (~371-359 Ma). In a previous study, dacryoconarids were found to have experienced concomitant reductions in body size and taxonomic diversity (Wei, 2019); however, it is not certain if this trend was due to environmental instability driving reduction in size within lineages, biological reorganization favoring smaller species, or a shift in ontogenetic growth strategies. In this study, we examine the diversity and size dynamics of dacryoconarids in the northern Appalachian Basin through the late Givetian to middle Frasnian. The adult conch and embryonic chamber volumes of dacryoconarids were measured from consecutive shale-bearing units representing the upper Hamilton (late Givetian) through West Falls (middle Frasnian) groups at Eighteen Mile Creek and Penn Dixie Fossil Park in western New York.

Two trends emerge from the data: a long-term decline in adult body volume and an apparently abrupt reduction in size at the onset of the globally recognized punctata positive carbon-isotope excursion (Lash, 2019). The gradual decline in the assemblage-scale adult body volume through the early Frasnian can be explained by warming trends at similar paleolatitudes inferred from previously published oxygen isotopic trends derived from conodont apatite (Joachimski et al., 2009). There is little change in species composition across the punctata event, but a substantial turnover occurs between the Givetian and Frasnian. An increase in the size of the juvenile stage of Striatostyliolina striata occurs in association with decreasing adult volumes, suggesting a change in life-history strategy. We speculate that warming during the punctata event, possibly in association with volcanic emissions (Pisarzowska et al. 2020), was the driver for the body-size evolution of dacryoconarids in the Appalachian Basin.