Paper No. 10
Presentation Time: 4:00 PM
USING ECOLOGICAL ORDINATION TO TEST FOR ECOPHENOTYPIC AND EVOLUTIONARY CHANGE IN THE BRACHIOPOD SOWERBYELLA RUGOSA FROM THE UPPER ORDOVICIAN KOPE FORMATION OF NORTHERN KENTUCKY
A recurring problem in studies of ecophenotypy has been the lack of a quantitative measure of environment, particularly troublesome for taxa that are confined to a single lithofacies. In a classic series of papers in the 1970's, Cisne demonstrated how paleoecological ordination techniques can be used to provide just such a measure of environment and for use in stratigraphic correlation, against which to test for clines and true evolutionary change. Here, we use Detrended Correspondence Analysis (DCA) scores of faunal samples to test for ecophenotypic variation and evolution in the brachiopod Sowerbyella rugosa from the Upper Ordovician Kope Formation (C1 sequence) of northern Kentucky. Haney et al. (2001; Palaios 16:115-125) recently documented several patterns of shape and size change in Sowerbyella from M5 through C3 strata of the Cincinnati Arch, including (1) a lack of allometry within samples, but allometry across samples, (2) a stepwise decrease in centroid size through time, and (3) the presence of onshore-offshore shape change, including more transverse shell shapes offshore. We tested these patterns within Kope S. rugosa with an analysis of over 300 shells from 38 horizons, using similar landmarks to Haney et al. (2001). DCA Axis 1 scores of beds from Holland et al. (1999) were used to test for depth-related changes in shape and centroid size, and to control for depth-related factors when testing for shape and centroid size through time. We find (1) no allometry between centroid size and shape, (2) centroid size remains constant through time and across environments, (3) landmark shape coordinates show no correlation with either time or environment. Thus, Sowerbyella rugosa in the Kope Formation appears to show morphological stasis in both size and shape through time, as well as a lack of clinal variation in size and shape. The differences in our results compared with those of Haney et al. (2001) suggest that size and shape change in Sowerbyella is punctuated in time and abrupt across environments.