MORPHOMETRIC ANALYSIS OF SHAPES CHANGES IN A MIDDLE DEVONIAN PTERIOID BIVALVE LINEAGE

The Middle Devonian of the Appalachian was a period of widespread stability. Over 4.5-5 million years taxonomic richness and composition remained almost unchanged, and evidence of ecological stability supports the notion of stasis. One question that has remained largely unstudied for this time period is if morphological variation of organisms reflects this stability. In this study we examine the morphological variation of a single pterioid bivalve lineage from the Middle Devonian and test for an overall change in morphology.

Pterioids are cosmopolitan and abundant throughout the mid-Paleozoic and their variable shape is known to complicate the comparison of their morphologies by standard length and width measurements. We collected 118 well preserved specimens from 14 localities; majority of which represent shallow water environments, with the exception of a few specimens from slightly deeper water facies. Using geometric morphometric methods and multivariate statistical analyses, we quantified shell shapes and temporally and spatially compared pterioid shapes.

Our preliminary data suggests that there is no net change in pterioid morphology over the course of the Middle Devonian. Overall morphological fluctuations are apparent, but there seems to be no trend related to time or spatial distribution within an individual biofacies. Comparing conspecific samples from different water depth demonstrate a correlation of shape and environmental conditions. More samples from deeper water facies as well as the youngest units of the Middle Devonian are needed to further examine these differences. More specimens will provide a larger data set to further discern overall shape fluctuations from changes related to time and/or environment.