SCALE-DEPENDENT PATTERNS OF MORPHOLOGICAL VARIABILITY IN FLEXICALYMENE GRANULOSA FROM THE CINCINNATIAN SERIES (UPPER ORDOVICIAN) OF OHIO AND KENTUCKY

The documentation of morphological variability in the fossil record is scale dependent, where patterns of interspecific variation are built upon patterns of intraspecific variation. As spatio-temporal scale increases, at what resolution is it possible to begin to detect significant patterns in intraspecific variability that may contribute to larger-scale trends? The goal of this project is to measure the outcome that increasing scale has on the stratigraphic and geographic patterns of morphological variability for Flexicalymene granulosa from the Kope Formation of the type Cincinnatian Series. Strata of the Kope are ideal for addressing this issue because the stratigraphic architecture is resolved enough to provide a large range of hierarchical scales across time and space.This is part of a larger project examining the relationship between morphology and quantified environmental signals to interpret stratophenetic patterns in this trilobite species throughout the Kope Formation. Establishing a baseline at which morphological variation becomes significant can streamline sampling protocol.

Previous morphometric analyses have shown that: 1) landmark positions within the cranidia of F. granulosa shift temporally through the Kope as a whole (10⁶ years), and 2) morphological patterns consistently vary with geography at the scale of limestone bedsets (10³ years), specifically in up-ramp to down-ramp directions. Current analyses focus on identifying the amount of morphological variability within individual beds that can be successively stacked according to bedsets, small-scale sedimentary cycles, and larger-scale cycles for multiple outcrops across a wide geographic region (~100 km). Results show that morphology varies little within beds and bedsets. Stratigraphic trends become apparent when looking within submembers, which are composed of several meter-scale cycles (10⁴ to 10⁵ years). Interestingly, stratigraphic trends are not uniform among outcrops even though geographic patterns remain. Each locality follows unique temporal trajectories while maintaining an overall up-ramp to down-ramp morphological gradient. This indicates a decoupling of the spatio-temporal pattern where local effects dominate temporal trends and regional effects dominate spatial trends within this interval.