Plot showing the interaction between bifacial point stratigraphic layer and bifacial point centroid size, as well as their combined effect on PC1 shape change.

<p>Importantly, the “stratigraphic layer” variable has been specifically transformed for usage in the plot: the individual cells along this axis cannot be equated with individual layers, however, the axis represents the spectrum of variation in the stratigraphic layer variable. In the older layers there is little to no relationship between bifacial point size and shape change along PC1. However, in the younger layers point elongation and refinement are correlated with overall point size. Data points on the plot reflect the average response per cell and are scaled according to their size in accordance with the number of data per cell. Data points are depicted as filled when their average is above the fitted model and empty if they fall below.