I've spent some time over the last few days generating some basic morphometric data from the 3D models of Kirk points that I've processed so far (n = about 50) . I'd like to have about double that for a formal analysis to publish, but I also would like to discuss some preliminary results as part of my presentation at the SEAC (Southeastern Archaeological Conference) meeting that's coming up in a few weeks. So you go to war with the Kirk assemblage you've got, not the Kirk assemblage you want.
Before I talk about the data, I'd like to congratulate myself on having the forethought to take a day last spring to write down the workflow right after I got it figured out. There were a few details that I neglected to mention in that blog post, but overall it was a huge time saver. Figuring out the steps was enough of a pain-in-the-ass the first time. Let us never do it again.
Before I talk about the data, I'd like to congratulate myself on having the forethought to take a day last spring to write down the workflow right after I got it figured out. There were a few details that I neglected to mention in that blog post, but overall it was a huge time saver. Figuring out the steps was enough of a pain-in-the-ass the first time. Let us never do it again.
 | I defined seven landmarks on each point (s0 through s6). To define these landmarks consistently, I first oriented the point to minimize the horizontal distance between s0 and s1. Generally, that resulted in s0 and s1 falling on roughly the same plane. I then defined s2 and s3 to mark the maximum deviation of the lateral haft edges proximal to maximum constriction of the haft (marked by s0 and s1). |
 | I used s0, s1, s2, and s3 to define the axial plane (in the "View" pulldown menu). This superimposes an asymmetrical grid on the point and defines a set of three planes: axial, coronal, and sagittal (named following conventions for anatomy, which is what this software was designed for). |
 | I turned on the sagittal plane to locate landmark s4. The sagittal plane splits the axial plane down the middle. Landmark s4 is defined as the location where the sagittal plane intersects with the basal edge of the point when the sagittal plane bisects the axial plane. If the point is symmetrical, s4 will fall in the center of the basal edge. Note: the sagittal plane is movable. When you initially turn it "on," it's automatically centered in reference to the axial plane. If it gets moved you can recenter it simply by turning it off and then on again. |
 | Finally, I turned on the coronal plane to locate landmarks s5 and s6. Landmarks s5 and s6 are defined as the locations were the coronal plane intersects the lateral edges of the haft when the coronal plane bisects the axial plane. |
For each point, you have to tell the software how the landmarks correspond to those on the "atlas" model. The simplest thing to do is to always place the landmarks in the same order. You still have to manually define the correspondence between each model and the atlas ("View Correspondences" in the "View" menu).
I followed the same steps I described in the previous post to export and edit the data so that I could import it into MorphoJ. I used MorphoJ to perform a principal components analysis (PCA), the purpose of which is take all the variability in the 3D data and boil it down to its most important components. PCA lets you flatten the variability in a dataset into scores that you can plot in two dimensions.
Here are the basic results of the PCA performed on the points currently in the sample:
I followed the same steps I described in the previous post to export and edit the data so that I could import it into MorphoJ. I used MorphoJ to perform a principal components analysis (PCA), the purpose of which is take all the variability in the 3D data and boil it down to its most important components. PCA lets you flatten the variability in a dataset into scores that you can plot in two dimensions.
Here are the basic results of the PCA performed on the points currently in the sample:
I haven't spent any significant time digging into the data yet, but my initial reaction is that the first principal component may well be measuring variability related to time. If you look at the examples of points that fall at the far left end of the plot, they look very Taylor- or Thebes-like, with relatively long hafts, deep notches, and small/shallow basal concavities/indentations separating broad convex basal edge segments. The points at the far right of the plot, conversely, have relatively short hafts, shallow notches, and broad basal concavities. If you squint a little, maybe, you can see how that end of the Kirk spectrum is trending toward a bifurcate/lobed haft morphology. In the center of the plot are points like 5947, which I think we can agree is a "modal" Kirk Corner Notched.
With the exception of the Nipper Creek cache points (shown in green), all the points in the sample are from Allendale County, South Carolina, and are made from Allendale chert. This all but eliminates the possibility that the variability is due to space or raw material.
My next step is to explore the possible "time" component of the PCA by gathering some data from the point forms that bracket Kirk: Taylor (on the earlier side) and lobed/bifurcate points (on the later side). If I'm correct that the first principal component shown above is telling us something about time, the Taylor points should plot to the left and the bifurcate/lobed points should plot to the right. It's notable that four of the five points from the Nipper Creek cache plot close together. Those points were almost certainly produced during a short period of time (but so was 5963 NC 4, so . . . something to think about).
With the exception of the Nipper Creek cache points (shown in green), all the points in the sample are from Allendale County, South Carolina, and are made from Allendale chert. This all but eliminates the possibility that the variability is due to space or raw material.
My next step is to explore the possible "time" component of the PCA by gathering some data from the point forms that bracket Kirk: Taylor (on the earlier side) and lobed/bifurcate points (on the later side). If I'm correct that the first principal component shown above is telling us something about time, the Taylor points should plot to the left and the bifurcate/lobed points should plot to the right. It's notable that four of the five points from the Nipper Creek cache plot close together. Those points were almost certainly produced during a short period of time (but so was 5963 NC 4, so . . . something to think about).
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