Figures
Abstract
A number of functions have been proposed for cached Clovis points. The least complicated hypothesis is that they were intended to arm hunting weapons. It has also been argued that they were produced for use in rituals or in connection with costly signaling displays. Lastly, it has been suggested that some cached Clovis points may have been used as saws. Here we report a study in which we morphometrically compared Clovis points from caches with Clovis points recovered from kill and camp sites to test two predictions of the hypothesis that cached Clovis points were intended to arm hunting weapons: 1) cached points should be the same shape as, but generally larger than, points from kill/camp sites, and 2) cached points and points from kill/camp sites should follow the same allometric trajectory. The results of the analyses are consistent with both predictions and therefore support the hypothesis. A follow-up review of the fit between the results of the analyses and the predictions of the other hypotheses indicates that the analyses support only the hunting equipment hypothesis. We conclude from this that cached Clovis points were likely produced with the intention of using them to arm hunting weapons.
Citation: Buchanan B, Kilby JD, Huckell BB, O'Brien MJ, Collard M (2012) A Morphometric Assessment of the Intended Function of Cached Clovis Points. PLoS ONE 7(2): e30530. https://doi.org/10.1371/journal.pone.0030530
Editor: Stephen Shennan, University College London, United Kingdom
Received: December 7, 2011; Accepted: December 23, 2011; Published: February 10, 2012
Copyright: © 2012 Buchanan et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: BB's work on this study was supported by a National Science Foundation Doctoral Dissertation Improvement Grant and postdoctoral fellowship grants from the National Science Foundation and the Social Sciences and Humanities Research Council. JDK's work on the study was supported by a National Science Foundation Doctoral Dissertation Improvement Grant and the University of New Mexico. MC's work on this study was supported by the Canada Research Chairs Program, the Social Sciences and Humanities Research Council, the Canada Foundation for Innovation, the British Columbia Knowledge Development Fund and Simon Fraser University was supported by a National Science Foundation Doctoral Dissertation Improvement Grant and the University of New Mexico. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
Introduction
Caches—tightly clustered deposits of artifacts that contain little or no manufacturing and maintenance debris and that appear to have been deposited at the same time [1]—are a striking feature of the Clovis archaeological record. To date, 17 Clovis caches from the western United States have been published [1], [2]. Two assemblages from farther east—Rummells-Maske (Iowa; [3], [4]) and Lamb (New York; [5])—are often described as Clovis caches, but it is unclear whether they meet the established criteria for assignment to Clovis or whether they are in fact caches [1]. At the moment, the temporal range of Clovis caches is poorly understood. This is because only two of them—the Anzick cache (Montana) and the East Wenatchee, or Richey-Roberts, cache (Washington)—have been dated radiometrically. The usual practice is to treat caching as a part of the Clovis behavioral repertoire for the entire span of Clovis, which is widely accepted to be 13,600–13,000 calBP [6], [7].
Currently, opinions differ regarding the intended function of points found in Clovis caches. Some researchers argue that the resemblance of cached Clovis points to smaller Clovis points that have clearly been used for hunting suggests that the former were created to be used as parts of hunting weapons and were simply stored for future use [8]–[11]. Other researchers contend that points in some of the caches were produced for use in rituals rather than for hunting [12]–[17]. Additional functions for cached points have been proposed on the basis of the points included in the East Wenatchee cache. For example, Buchanan [18] and Kilby [1] have suggested that the East Wenatchee points may have been used in costly signaling displays, whereas Lyman et al. [19] have argued that the points from the East Wenatchee cache are too large to have been used for hunting and were actually designed to be used as saws.
Here we report a study in which we used a sample of points from Clovis caches and points from Clovis kill and camp sites (hereinafter “kill/camp points”) to test the hypothesis that cached Clovis points were intended to be used as parts of hunting weapons. We focused on the hunting equipment hypothesis because it is the least complicated of the hypotheses that have been put forward to explain cached Clovis points, and because it makes straightforward predictions regarding the morphological similarities and differences between cached points and kill/camp points.
In the study we compared the size and shape of the cached points and kill/camp points. We did so because the usual ways of determining the function of stone tools—use-wear analysis and residue analysis—were not an option. The reason for this is that most cached points are unused and therefore have neither use-wear nor residues. Our research protocol was further influenced by the fact that the size of cached Clovis points is within the range of variation of the size of historically- and ethnographically-documented hunting weapon points [20]. This is important because it means that size alone cannot be used to determine whether or not cached Clovis points were used for hunting.
In the study we tested two of the predictions of the hunting equipment hypothesis. One concerns point size and shape. If cached points and kill/camp points were produced to arm hunting weapons but the former were mostly unused when they were deposited whereas the latter were mostly used before they were deposited, then cached points should be the same shape as, but generally larger than, kill/camp points. The reason for this is that kill/camp points are likely to be damaged and/or resharpened, and both damage and resharpening inevitably reduce the size of a lithic artifact.
The other prediction involves “allometry,” or size-related shape change. Allometric analysis is commonplace in biology but it has not been used often in archaeology. To date, stone tools have been analyzed allometrically in less than a dozen studies [21]–[30]. The reason for the limited use of allometric analysis in archaeology appears to be that many archaeologists believe that allometry only applies to living things. This is not correct, however. The laws of physics are such that we often have to change the shape of artifacts as we increase or decrease their size. For example, due to the fact that the ratio between the surface area and volume of an object changes as its volume increases, the wings of a large aircraft have to be proportionately larger relative to the fuselage than the wings of a small aircraft. For the same reason, a large sailing ship requires more sail surface area than a small sailing ship to travel at the same rate. In biology, statistically indistinguishable allometric trajectories are taken to be evidence of the same function whereas statistically significant differences in allometric trajectories are taken to be evidence of differences in function [31], [32]. This line of reasoning was also employed in two of the allometry-focused stone tool studies mentioned earlier [23], [26]. Thus, if cached points and kill/camp points were intended for the same purpose, they should follow the same allometric trajectory.
Materials and Methods
Sample
Our sample comprised 122 Clovis points. We focused on complete points and specimens missing at most a basal ear because it is difficult to implement the methods we employed with incomplete artifacts. Fifty-four points are from caches. We measured six points from the Anzick cache [11], [33]–[37], 13 from the Drake cache (Colorado; [38]), 14 from the East Wenatchee cache [9], [19], [39], 16 from the Fenn cache (Wyoming; [15]), and five from the Simon cache (Idaho; [8], [40], [41]). It has been suggested that the Anzick points may be burial goods rather than part of a cache, because human skeletal remains have also been recovered at the site [33]–[35]. We do not find this argument convincing for two reasons. First, the artifacts and skeleton were recovered with a front-end loader, so there is no stratigraphic evidence that they are associated [36]. Second, radiocarbon dates derived from some of the artifacts recovered at the site do not overlap with radiocarbon dates derived from some of the human bones, which suggests that they are not contemporaneous [36], [42].
We used epoxy casts in place of five of the points from the Drake cache and one of the points from the East Wenatchee cache. For another three points from the East Wenatchee cache we scanned and digitized technical drawings because neither the actual artifacts nor casts were available for analysis. The locations of the caches are shown in Fig. 1.
Triangles = kill sites/camp sites. Circles = caches.
The other 68 points in our sample are from kill sites and camps sites. We measured 24 points from Blackwater Draw (New Mexico; [43]–[46]), four from Colby (Wyoming; [47]), two from Dent (Colorado; [48], [49]), four from Domebo (Oklahoma; [50]), and four from Jake Bluff (Oklahoma; [51], [52]). We also measured 10 points from Lehner (Arizona; [53]), three from Miami (Texas; [54], [55]), six from Murray Springs (Arizona; [56], [57]), and eight from Naco (Arizona; [58]). We used epoxy casts in place of three of the points from Blackwater Draw, four from Colby, two from Dent, three from Miami, and two from Naco.
Digitization
The digitizing method we used was the same as that employed by Buchanan [18], Buchanan and Collard [59], and Buchanan and Hamilton [60]. Digital images of the points were imported into version 2.02 of F.J. Rohlf's Thin Plate Spline Digitizing Program [61] and 32 landmarks placed along the edges and base of each point. The resulting coordinate data were imported into Matlab 6.0 and used to compute 12 characters. The characters are described in Table 1 and illustrated in Fig. 2. Eleven of the characters are interlandmark distances. These were designed to capture the main elements of point form and include traditional linear measurements as well as measurements that cannot be taken easily with calipers but are useful in describing point variation. Four characters relate to the base (BB, LB, BW, and LT), three to the blade length (BL, MW, and TW), and four to overall point length (ML, OL, EL, and TB). The twelfth character is point area (PA). In addition to the 12 characters derived from digitizing the points, thickness was measured directly using calipers or taken from published sources.
Character abbreviations follow Table 1.
The precision of the 12 characters derived from digitizing was estimated on a sample of points from Naco and Lehner. Measurement error—the percentage of the total variance attributable to within-individual variance resulting from imprecision of measurements—was calculated for each character using Model II ANOVA [62]–[64]. Points were chosen randomly and digitized in three non-consecutive sessions, and the variance components were calculated from the resulting dataset. Measurement error associated with the characters ranges from 0.002 to 0.031 percent, which compares favorably to measurement errors reported in biological morphological studies (e.g., [62], [64]). Further, there is no relationship between percent measurement error and the coefficient of variation of a character (r = −0.072, p = 0.623), which suggests measurement error does not drive variation.
Because the multivariate statistical methods we use require complete data matrices, we estimated missing values for nearly complete points. This was accomplished with the expectation-maximization missing-data replacement method, which uses information about covariation among characters to predict missing values [65]. A simulation-based study has demonstrated that this method is more precise and reliable than principal-component estimation when using a moderate number of characters (6–12) and large sample sizes [65].
As noted, epoxy casts were used in lieu of some of the original points. Buchanan [18] compared epoxy casts of Clovis points from the Lehner site to the actual points and found that there was no statistical difference between the casts and the real artifacts. The paired t-tests he carried out gave p values ranging between 0.841 and 0.962. Consequently, the inclusion of epoxy casts in the sample is not expected to have affected the study.
Analyses
To test the prediction that cached points should be the same shape as, but generally larger than, kill/camp points, we used histograms and principal components analysis (PCA). The histogram analysis focused on the second part of the prediction, namely that cached points should be generally larger than kill/camp points. To test this part of the prediction, we plotted point area (PA) and overall length (OL) separately for the kill/camp points and the cached points, and then compared the histograms on the same scale.
The PCA was designed to test both parts of the prediction. We opted for PCA because it is generally accepted to be capable of decomposing form into size and shape by researchers who work with morphometric data (e.g., [66]). In studies in which PCA is applied to morphometric data, it is usual for the first principal component (PC1) to be assumed to reflect size variation among the taxa and for the other components, which are orthogonal to and therefore uncorrelated with PC1, to be taken to reflect shape variation among the taxa.
We began by log-transforming the data to make them more closely approximate a normal distribution [67]. We then tested the 13 characters for normality with the Kolmogorov-Smirnov test. Having found that the characters did not depart significantly from normality, we subjected them to PCA. We retained the principal components that constituted more than 1% of the variation in the dataset. We then used the t-test to evaluate the significance of the differences between the cached points' and kill/camp points' scores on the retained principal components. In line with the standard interpretation of morphometrics-derived PCs discussed above, the test prediction was that the scores for the cached points and kill/camp points should differ significantly on PC1 but not on any other PC.
To test the prediction that cached points and kill/camp points should follow the same allometric trajectory, we conducted bivariate analyses of allometry using point area as a proxy for point size. We used point area instead of the more traditional measure of point size—overall length—because the latter character is more susceptible to disproportionate reduction as a result of resharpening [22]. We used a simple model of allometric shape change, y = bXk, where X and Y are the sizes of two forms and k (the allometric coefficient) is an exponential factor that relates the sizes. The allometric equation y = bXk is commonly used in the logarithmically transformed form that translates to a simple linear relationship, logeY = logeb+k logeX, where Y is the character examined in relation to size, k is the slope, or allometric coefficient, and b is the y-intercept [68]. Using a linear-regression model, the regression coefficient of logged Y on logged X is an estimate of k, the allometric coefficient [69]. We used least squares regression because it is the most conservative of the estimation procedures that have been advocated for bivariate allometry analysis [70].
Allometric coefficients (k) indicate the manner in which given characters change in relation to point size. Values greater than unity (k>1) indicate positive allometry (characters disproportionately larger relative to size), and values less than unity (k<1) indicate negative allometry (characters disproportionately smaller relative to size). Isometry is a property of characters that increase at the same relative rate with proportions remaining constant (k = 1) [71]. For the allometric analyses, we tested for homogeneity in the allometric coefficients (k) and the y-intercepts (b) associated with cached points and kill/camp points. We used Benjamini and Yekutieli's [72] method of significance-level correction for multiple comparison tests. Narum [73] has shown that Benjamini and Yekutieli's [72] method optimizes the reduction of both Type-I and Type-II error rates.
We conducted the histogram analysis, Kolmogorov-Smirnov tests, and the t-tests in PASW (SPSS) 18. All other analyses were conducted in MATLAB 6.0 (release 12), using statistical functions written by R. E. Strauss [74].
Results
Test of the prediction that cached points should be the same shape as, but generally larger than, kill/camp points
The histograms generated to test the size part of the prediction are shown in Figure 3. The histograms are consistent with the prediction. For both characters, there is some overlap between the cached points and the kill/camp points but all the large points are from caches and all the small points are from kill/camp sites.
A) point area. B) overall length.
The results of the PCA conducted to test the prediction that cached points should be the same shape as, but generally larger than, the kill/camp points are summarized in Figure 4 and Table 2. Four principal components met the criterion for retention. As expected, PC1 accounts for the majority of variation in the dataset (93.5%). The large magnitude and consistent direction of the loadings of the 13 characters on PC1 is consistent with the idea that it represents size variation (Fig. 4a). The other three principal components capture aspects of shape variation, as expected. The loadings on PC2 (3.75% of the variation) indicate a changing relationship between width (TW, MW, and BW) and base characters (BB and LB) on the one hand and length characters (EL, TB, ML, and OL) on the other, such that in Fig. 4a points become shorter and wider as one moves up the PC2 axis. The loadings on PC3 (1.41% of the variation) indicate a changing relationship between base characters (BB and LB) and width characters (TW and MW). As shown in Fig. 4b, points become more triangular (wider bases, narrow tips) as one moves from left to right along the PC3 axis. Lastly, the loadings on PC4 (1.04% of the variation) contrast BL with TW such that points become narrower with long blades as one moves up the PC4 axis (Fig. 4b).
A) PC1 versus PC2. B) PC3 versus PC4. Triangles = kill/camp points. Circles = cached points.
The distribution of points in Fig. 4a suggests that cached points tend to be larger than kill/camp points. In this figure only cached points have PC scores above 14 on the PC1 axis, which represents size, whereas both cached and kill/camp points overlap below 14 on the PC1 axis. This is supported by the results of the t-test of the PC1 scores for the two groups of points. According to this t-test, the difference between the PC1 scores for the cached points and the kill/camp points is highly significant (t = −10.82, df = 120, p<0.000). In contrast, there is no difference between cached points and kill/camp points on the other PCs. Along the PC2 axis, cached points and kill/camp points exhibit considerable overlap, and the t-test confirms that there is no statistical difference in PC2 scores between the two groups of points (t = 0.79, df = 120, p = 0.429). Overlap of cached points and kill/camp points is also evident in the plot of the PC3 and PC4 scores (Fig. 4b). In line with this, scores from PC3 and PC4 are not different between the two groups of points, according to the t-test (t = −0.01, df = 120, p = 0.989 and t = 0.03, df = 120, p = 0.977, respectively). Thus, the results of the PCA are consistent with the prediction that cached points should be the same shape as, but generally larger than, kill/camp points.
Test of the prediction that cached points and kill/camp points should follow the same allometric trajectory
Table 3 and Figure 5 summarize the results of the analyses carried out to test the prediction that cached points and kill/camp points should follow the same allometric trajectory. Points from caches have positive allometric coefficients for the characters EL, TB, TW, BL, ML, and OL and have negative allometric coefficients for the characters MW, BB, LB, BW, and thickness. Thus, all the length characters (EL, TB, BL, ML, and OL) and one width character (TW) tend to be larger relative to point area in large points than in small points. In contrast, another width character (MW), the three basal characters (BB, LB, and BW), and thickness tend to be smaller relative to point area in large points than in small points. The third width character (LT) is very close to isometry in the cached points, indicating that it increases more or less proportionally with overall size.
Character abbreviations follow Table 1. Triangles = kill/camp points. Circles = cached points. Solid line = best-fit line for kill/camp points. Dashed line = best-fit line for cached points.
Kill/camp points have positive allometric coefficients for length characters (EL, TB, ML, and OL), indicating that these characters tend to be longer relative to point area in large points than in smaller points. Conversely, kill/camp points have negative allometric coefficients for the characters TW, BL, MW, BB, LB, BW, and thickness. Therefore, width (MW and TW), blade length (BL), basal characters (BB, LB, and BW), and thickness tend to be smaller relative to point area in larger points than in smaller points. The character LT also is very close to isometry in the cached points. Again, this indicates that LT basically increases proportionally with overall size.
Visual inspection of the allometry plots suggests that there are no allometric trajectory differences between the cached points and kill/camp points (Fig. 5). Results of the statistical comparisons of the y-intercepts and slopes for cached points and kill/camp points are consistent with this for 11 of the 12 characters (Table 3). For the remaining character, LT, the slope for cached points is significantly closer to 1 than the slope for kill/camp points, and the y-intercept for cached points is significantly lower than the y-intercept for kill/camp points (Table 3). Given that cached points and kill/camp points follow the same allometric relationship in all but one of the characters examined, we consider the results of the allometric analyses to be consistent with the prediction that cached Clovis points and Clovis points from kill and camp sites should follow the same allometric trajectory.
Discussion
Do the results support the hunting equipment hypothesis?
We compared morphometric data from cached Clovis points and Clovis points from kill and camp sites to test the following predictions of the hunting equipment hypothesis: 1) cached points should be the same shape as, but generally larger than, kill/camp points, and 2) cached points should follow the same allometric trajectories as kill/camp points. The results of the analysis carried out to test the first prediction were entirely consistent with it. The results of the analysis carried out to test the second prediction showed that cached points and kill/camp points follow the same allometric relationship in all but one of the characters examined. Together, these results support the idea that cached Clovis points were intended to arm hunting weapons.
Do the results support any of the other hypotheses?
Earlier we outlined a number of other hypotheses that have been offered to explain the function of cached Clovis points. To reiterate, one of these contends that points from a number of Clovis caches were produced for use in rituals rather than for hunting [12]–[17]. The other two hypotheses were put forward to account for the large points from the East Wenatchee cache. One holds that the points in question were the focus of costly signaling displays [1], [18]. The other contends that they were too big to have been used for hunting and were intended to be used as saws instead [19].
Although we did not directly test these other hypotheses, our results have a bearing on them. To begin with, our results suggest that the costly signaling hypothesis can be discounted as an explanation not only for cached Clovis points in general but also for the points that gave rise to the hypothesis in the first place—the points from the East Wenatchee cache. The general version of the costly signaling hypothesis predicts that there should be differences in the allometric trajectories of the characters between cached Clovis points and Clovis points from kill and camp sites. The reason for this is that the hypothesis holds that Clovis point makers who engaged in costly signaling would have attempted to produce points with exaggerated length and width dimensions because it is difficult to create long and wide points without increasing thickness. This in turn would lead length and width characters to have a different relationship to point area in cached points versus kill/camp points without any difference between the two groups of points in the relationship between thickness and point area. Crucially with respect to this hypothesis, our analyses indicate that the allometric trajectories of blade length, maximum width, and thickness do not differ between the cached Clovis points and the kill/camp Clovis points. Thus, our analyses suggest that the costly signaling hypothesis can be discounted as a general explanation for the function of cached Clovis points, at least in the form proposed by Buchanan [18] and Kilby [1].
If the costly signaling hypothesis is restricted to points from the East Wenatchee cache, the prediction is that there should be differences in the allometric trajectories of the blade length characters between the points from the East Wenatchee cache and all the other Clovis points in the sample. Our analyses are not consistent with this prediction either. The East Wenatchee points do not differ significantly from the other cached Clovis points or the Clovis kill/camp points in terms of the allometric coefficients of the characters examined (Table 4). The y-intercepts for the characters EL and LT are different between the East Wenatchee cache and all the other Clovis points in the sample, but the difference is the reverse of what the costly signaling hypothesis predicts. Specifically, the y-intercept for the East Wenatchee cache is lower, not higher, than the y-intercept for the other Clovis points. Thus, our analyses also suggest that in its current form the costly signaling hypothesis can be discounted as an explanation for the function of the points recovered from the East Wenatchee cache.
We think the results of our analyses also shed light on the saws-not-hunting-weapons hypothesis. As with the costly signaling hypothesis, it is possible to treat the saws-not-hunting-weapons hypothesis as a general explanation for cached Clovis points and as a specific explanation for the points from the East Wenatchee cache. And as with the costly signaling hypothesis, we believe our results allow both versions of the hypothesis to be discounted. Given that the allometric trajectories of the majority of the characters we examined do not differ between the cached Clovis points and kill/camp Clovis points, there is no reason to believe that the function of the two groups of points differed. When this is taken together with the fact that some of the kill/camp points were clearly used for hunting, it suggests that the cached Clovis points were not intended to be saws. It is more parsimonious to assume that they were intended to be the tips of hunting weapons.
The same logic holds for the East Wenatchee points. As noted in the previous paragraph, they do not differ from the other points in the sample with respect to the allometric trajectories of the characters examined. Hence, in view of the fact that we know that some of the other points were used for hunting, there is no reason to believe that they were intended to be used as saws. Of course, we cannot rule out the possibility that the East Wenatchee points might have been used as saws, but our results suggest that any such use would have been incidental to their intended function.
Three hypotheses with a ritual element can be identified in the literature on Clovis caches [1], [11]–[17]. However, two of these hypotheses are not relevant for present purposes. The two hypotheses in question were put forward by Wilke et al. [11] and Kilby [1], respectively. Wilke et al. [11] speculated that caches that are associated with burials include tools that were intended to be functional and were included in the burial to help the deceased reproduce the technological system in the afterlife. Kilby [1] argued that some caches consist of items that were being used by the interred individual and/or other members of their group. The reason these hypotheses are not relevant for present purposes is that they both assume that cached points were intended to be parts of hunting weapons and that it was only the deposition of the points that was ritual. Thus, they do not represent real alternatives to the hunting equipment hypothesis.
The third hypothesis with a ritual element was first proposed by Frison and Bradley in the late 1990 s [15]. Since then it has been offered as an explanation for certain cached points by Bradley and Stanford [13], Gillespie [16], Bamforth [12], Ellis [14] and Speth et al. [17]. According to this hypothesis, the large points in some Clovis caches were produced specifically for ritual purposes. Critically, then, this hypothesis views ritual as the intended goal of production rather than as something that is incidental to the production of the points, as is the case with Wilkes et al.'s [11] and Kilby's [1] hypotheses. This makes it a direct competitor to the hunting equipment hypothesis when it comes to explaining the form of cached Clovis points.
Do our results support this hypothesis? We think not. Again, given that for the vast majority of the characters we examined there is no significant difference between the allometric trajectories of the cached points and the kill/camp points, there is no reason to invoke a different intended purpose for the cached points compared to the kill/camp points. Since the kill/camp points are known, or can reasonably be inferred, to have been used for hunting, the simplest hypothesis is that both groups of points were intended to be used as parts of hunting weapons.
In sum, then, the results of our analyses do not support any of the other hypotheses that have been put forward to account for the function of cached Clovis points. They only support the hunting equipment hypothesis.
On the principles that guided the production and maintenance of Clovis points
If we assume for the sake of argument that the results of our study are conclusive and that the primary function of Clovis points was to arm hunting weapons, the data presented here can be used to shed some light on the principles that guided the production and maintenance of Clovis points. Given that many of the cached points appear to be unused whereas many of the kill/camp points clearly have been used, allometric analyses of the combined sample can provide a use-life trajectory for Clovis points.
When allometric analyses are run with the two groups of points combined, 11 of the 12 characters return slopes that are significantly different from 1 when they were regressed on point area (Table 5). The length characters (EL, TB, ML, and OL) are positively allometric, whereas the width and basal characters (TW, MW, BB, LB, LT, and BW) are negatively allometric. Thickness is also negatively allometric. The only character that returns a slope that does not differ from 1.0 is BL (F = 1.45, df = 1,107, p = 0.239).
We suspect that the positive allometry of characters EL, TB, ML, and OL is driven primarily by resharpening, which during the early Paleoindian period appears to have focused on the tips of points that were damaged or dulled through use. The shape of Clovis points is such that removing flakes from the tip of a point would have altered the length of the point more dramatically than it altered the area of the point. Hence, in a sample comprising unused and retouched Clovis points, characters that reflect length should decrease more rapidly than point area. The corollary of this is that the relationship between the length characters and point area should be positively allometric.
We can think of two factors that may have—singly or collectively—produced the negative allometry of the width and basal characters, and of thickness. The first is resharpening. Because resharpening focused on point tips, it will have reduced the length of a point as well as its area, but may not have decreased the width of the point, the dimensions of its base, or its maximum thickness. One consequence of this is that when width and basal characters and thickness are subjected to allometric analyses in which point area is used as the proxy for size, the resulting relationships are likely to be negatively allometric. The other factor that may have produced negative allometry in the width, basal, and thickness characters is the functional constraint of hafting. It seems likely that the width and thickness of larger points would have been kept relatively narrow and thin to facilitate hafting to a foreshaft. This too can be expected to result in negative allometry when width and basal characters and thickness are subjected to allometric analyses in which point area is used as the proxy for size, because larger points will have relatively smaller widths and thicknesses than smaller points.
The character that returns a slope that does not differ from 1.0, BL, measures the leading edge of the point. This is the section of the point that penetrates the hide and flesh of prey. The isometry of BL (Fig. 5) suggests that for any given size of point, Clovis hunters aimed to maintain a particular proportion of blade length. This was true even with the smallest of Clovis points in the sample, suggesting that even after point tips were resharpened or reworked, blade length was kept proportional. Interestingly, Buchanan [22] found similar allometric trajectories in a sample of Folsom points from the Southern Plains. We suspect that this property may have been optimal for the tip's penetration into the hide and flesh of prey. It also might have minimized the likelihood of catastrophic breakage when a point was in use.
Light is potentially also shed on the construction and maintenance of Clovis hunting weapons by the fact that character LT had a different allometric trajectory in cached points than in kill/camp points. To reiterate, both groups of points returned negative slopes for LT, but the slope returned by the kill/camp points was more negatively allometric than the slope for the cached points. Given that LT runs from the basal ears to one-third up the edge means that the lower third of the edges of cached points is slightly but consistently more convex than the equivalent part of kill/camp points.
The allometric coefficients for LT in the cached point and kill/camp point samples are both very close to 1, and the difference between the slopes for the two groups of points cannot be seen in the relevant scatter plot (Fig. 5). As such, we do not want to make too much of this finding. However, there is one possibility that is worth considering. Given that the allometric trajectories of the basal, thickness, and non-LT width characters do not differ between the cache points and kill/camp points, the difference between the cached points and kill/camp points in the allometric coefficients for LT must be due to differences in the shape of the distal two-thirds of the edges of the points. More specifically, it must be due to the kill/camp points having straighter or more concave edges between LT's distal landmark and the tip than the cached points. One way in which this could have come about is if Clovis points were hafted in such a way that about a third of their length was embedded in the spear shaft and covered with binding, and used points were resharpened while they were hafted. Thus, the difference between the cached points and kill/camp points in the allometric coefficients for LT may tell us something important about the construction of Clovis hunting spears and about how such weapons were maintained.
Possibilities for future research
With regard to further research, there are two obvious next steps. The first is to use experiments to shed light on the design aspects of Clovis points discussed in the previous section. One set of experiments could focus on the resharpening hypothesis. Using the combined sample of Clovis points, we found that length characters exhibited positive allometry, whereas the width and basal characters, and maximum thickness showed negative allometry. We proposed that these allometric relationships were produced primarily through resharpening. This hypothesis can be tested by repeatedly resharpening replica Clovis points, measuring them after each resharpening event, and then carrying out allometric analyses in which the length, width, base, and thickness characters are regressed on point area. If the hypothesis is correct, then the point length characters should exhibit positive allometry and the width, base, and thickness characters should display negative allometry. Shott et al. [30] conducted a similar type of experimental analysis using replica Folsom points.
Another set of experiments could focus on blade length. Our results indicate that Clovis point blade length displays an isometric trajectory, and we suggested that this was the result of blade length needing to be a certain proportion of point size for optimal functioning. An experiment using a set of replica Clovis points of varying sizes and blade lengths could be used to test the performance characteristics associated with blade lengths with negative, positive, and isometric allometric trajectories. Point performance could be assessed by firing them into carcasses following the procedures of Frison [75] and Cheshier and Kelly [76] and then determining which set of points experience the least amount of breakage. Point performance could also be assessed using Waguespack et al.'s [77] experimental launching procedure using the replica points. Their experiment used a remotely triggered compound bow from a specified distance to assess the accuracy, precision, and depth of penetration of different points being fired at a target. Our hypothesis predicts that replica points with isometric blade lengths should outperform points with blade lengths that have negative or positive allometric trajectories.
Given that our results suggest cached points were intended to be used as parts of hunting weapons, the other obvious next step is to determine how caches fitted into the food procurement and land use strategies of Clovis groups. Currently, there are two competing models. The first, suggested by Collins [78], is that caching of hunting equipment was the result of the predictable use of the landscape. In this model, Clovis hunters deposited caches of tools because they expected to return to particular spots on the landscape and the caching of hunting equipment would have allowed them to replenish their toolkits without having to return to a raw material source location. The other model was proposed by Meltzer [10]. He suggested that caches were used by Clovis groups to help them explore new territories by establishing supply depots between known and unknown landscapes. In this model, Clovis hunters exploring a new landscape would have cached hunting equipment as they moved away from known sources. This behavior would have reduced the risk of moving into unknown landscapes. One way of testing between these models is to obtain radiocarbon dates from more caches, and then compare the cache dates to the earliest dates from non-cache Clovis sites. Meltzer's aides-to-exploration hypothesis clearly predicts that the caches should not only be indistinguishable from the earliest non-cache Clovis sites in terms of their temporal distribution, but also exhibit a similar geographic pattern to the earliest non-cache Clovis sites, which Hamilton and Buchanan [79] have shown are consistent with a population diffusion from the Ice-Free Corridor. In contrast, Collins' [78] hypothesis predicts that caches will occur throughout the entire Clovis period and will not be significantly correlated with distance from any of the points of entry into North America that have been proposed for the Clovis Paleoindians.
Summary
In the study reported here we tested two predictions of the hypothesis that cached Clovis points were intended to be used as parts of hunting weapons. The two predictions are: 1) cached points should be the same shape as, but generally larger than, points from kill/camp sites, and 2) cached points and kill/camp points should follow the same allometric trajectory. The results of the analyses are consistent with both predictions and therefore support the hunting equipment hypothesis. Significantly, the results of the analyses are not consistent with the predictions of the other hypotheses. Thus, we contend that cached Clovis points were likely produced with a view to them being used to arm hunting weapons.
Acknowledgments
For access to specimens we thank Eastern New Mexico University, University of Arizona, Arizona State Museum, Smithsonian Institution, Washington State Historical Society, Burke Museum of Natural History and Culture, Montana Historical Society, and Herrett Center for Arts and Sciences. We are also grateful to the reviewers and academic editor for their comments on our paper.
Author Contributions
Conceived and designed the experiments: BB JDK BBH MJO MC. Performed the experiments: BB. Analyzed the data: BB JDK BBH MJO MC. Contributed reagents/materials/analysis tools: BB JDK MC. Wrote the paper: BB JDK BBH MJO MC.
References
- 1.
Kilby JD (2008) An Investigation of Clovis Caches: Content, Function, and Technological Organization. PhD Dissertation, Department of Anthropology, University of New Mexico, Albuquerque.
- 2. Huckell BB, Kilby JD, Boulanger MT, Glascock MD (2011) Sentinel Butte: neutron activation analysis of White River Group chert from a primary source and artifacts from a Clovis cache in North Dakota, USA. J Archaeol Sci 38: 965–976.
- 3. Anderson AD, Tiffany JA (1972) Rummells-Maske: a Clovis find spot in Iowa. Plains Anthropol 17: 55–59.
- 4. Morrow JE, Morrow TA (2002) Rummells-Maske revisited: a fluted point cache from east central Iowa. Plains Anthropol 47: 307–321.
- 5.
Gramly RM (1999) The Lamb Site: A Pioneering Clovis Encampment. Buffalo: Persimmon Press.
- 6.
Haynes G (2002) The Early Settlement of North America: The Clovis Era. Cambridge: Cambridge University Press.
- 7. Haynes G, Anderson DG, Ferring CR, Fiedel SJ, Grayson DK, et al. (2007) Comment on “redefining the age of Clovis: implications for the peopling of the Americas”. Science 317: 320b.
- 8. Butler BR (1963) An early man site at Big Camas Prairie, south-central Idaho. Tebiwa 6: 22–33.
- 9.
Gramly RM (1993) The Richey Clovis Cache. New York: Persimmon.
- 10.
Meltzer DJ (2002) What do you do when no one's been there before? thoughts on the exploration and colonization of new lands. In: Jablonski NJ, editor. The First Americans: The Pleistocene Colonization of the New World. Memoirs of the California Academy of Sciences No. 27. pp. 27–58.
- 11. Wilke PJ, Flenniken JJ, Ozbun TL (1991) Clovis technology at the Anzick site, Montana. J Calif Great Basin Anthropol 13: 242–272.
- 12. Bamforth DB (2009) Projectile points, people, and Plains Paleoindian perambulations. J Anthropol Archaeol 28: 142–157.
- 13. Bradley BA, Stanford DJ (2004) The North Atlantic ice-edge corridor: a possible Palaeolithic route to the New World. World Archaeol 36: 459–478.
- 14.
Ellis C (2009) The Crowfield and Caradoc sites, Ontario: glimpses of Palaeo-Indian sacred ritual and world view. In: Keenlyside DL, Pilon JL, editors. Painting the Past with a Broad Brush: Papers in Honour of James Valliere Wright. Mercury Series Archaeology Paper 170. Gatineau: Canadian Museum of Civilization. pp. 319–352.
- 15.
Frison GC, Bradley BA (1999) The Fenn Cache: Clovis Weapons and Tools. Santa Fe: One Horse Land and Cattle Company.
- 16. Gillespie JD (2007) Enculturing an unknown world: caches and Clovis landscape ideology. Canadian J Archaeol 31: 171–189.
- 17. Speth JD, Newlander K, White AA, Lemke AK, Anderson LE (in press) Early Paleoindian big-game hunting in North America: provisioning or politics? Quatern Int.
- 18.
Buchanan B (2005) Cultural Transmission and Stone Tools: A Study of Early Paleoindian Technology in North America. PhD Dissertation, Department of Anthropology, University of New Mexico, Albuquerque.
- 19. Lyman RL, O'Brien MJ, Hayes V (1998) A mechanical and functional study of bone rods from the Richey-Roberts Clovis cache, Washington, U.S.A. J Archaeol Sci 25: 887–906.
- 20.
Blackmore HL (2000) Hunting Weapons from the Middle Ages to the Twentieth Century. Mineola: Dover.
- 21. Archer W, Braun DR (2010) Variability in bifacial technology at Elandsfontein, Western cape, South Africa: a geometric morphometric approach. J Archaeol Sci 37: 201–209.
- 22. Buchanan B (2006) An analysis of Folsom projectile point resharpening using quantitative comparisons of form and allometry. J Archaeol Sci 33: 185–199.
- 23. Crompton RH, Gowlett JAJ (1993) Allometry and multidimensional form in Acheulean bifaces from Kilombe, Kenya. J Hum Evol 25: 175–199.
- 24. Gowlett JAJ, Crompton RH (1994) Kariandusi: Acheulean morphology and the question of allometry. The African Archaeol Rev 12: 3–42.
- 25.
Iovita R (2010) Comparing stone tool resharpening trajectories with the aid of elliptical Fourier analysis. In: Lycett SJ, Chauhan PR, editors. New Perspectives on Old Stones: Analytical Approaches to Paleolithic Technologies. Springer: New York. pp. 235–253.
- 26. Iovita R, McPherron SP (2011) The handaxe reloaded: A morphometric reassessment of Acheulian and Middle Palaeolithic handaxes. J Hum Evol 61: 61–74.
- 27. McPherron SP (1999) Ovate and pointed handaxe assemblages: two points make a line. Préhistoire Européenne 14: 9–32.
- 28.
McPherron SP (2003) Typological and technological variability in the bifaces from Tabun Cave, Israel. In: Soressi M, Dibble H, editors. Prehistoric Bifaces to Human Behavior: Multiple Approaches to the study of Bifacial Technology. Philadelphia: University of Pennsylvania Museum Press. pp. 55–75.
- 29.
McPherron SP (2006) Variability in Acheulian handaxe morphology and its implications for typology. In: Goren-Inbar N, Sharon G, editors. Axe Age: Acheulian Toolmaking, from Quarry to Discard. Equinox: London. pp. 267–285.
- 30. Shott MJ, Hunzicker DA, Patten B (2007) Pattern and allometric measurement of reduction in experimental Folsom bifaces. Lithic Technol 32: 203–217.
- 31. Bonduriansky R, Day T (2003) The evolution of static allometry in sexually selected traits. Evolution 57: 2450–2458.
- 32.
Harvey PH, Pagel MD (1991) The Comparative Method in Evolutionary Biology. Oxford: Oxford University Press.
- 33.
Jones JS (1996) The Anzick Site: Analysis of a Clovis Burial Assemblage. Master's thesis, Department of Anthropology, Oregon State University, Corvallis.
- 34. Jones JS, Bonnichsen R (1994) The Anzick Clovis burial. Curr Res Pleist 11: 42–43.
- 35. Lahren L, Bonnichsen R (1974) Bone foreshafts from a Clovis burial in southwestern Montana. Science 186: 147–150.
- 36. Owsley DW, Hunt DR (2001) Clovis and Early Archaic period crania from the Anzick site (24PA506), Park County, Montana. Plains Anthropol 46: 115–121.
- 37. Taylor DC (1969) The Wilsall excavations: an exercise in frustration. Proc Mont Academy Sci 29: 147–150.
- 38. Stanford DJ, Jodry MA (1988) The Drake Clovis cache. Curr Res Pleist 5: 21–22.
- 39.
Huckell BB, Bradley BA, Mehringer P (2006) Flaked stone artifacts from the East Wenatchee Clovis cache. Manuscript on file, Maxwell Museum of Anthropology, University of New Mexico, Albuquerque.
- 40. Butler BR, Fitzwater RJ (1965) A further note on the Clovis site at Big Camas Prairie, south-central Idaho. Tebiwa 8: 38–39.
- 41. Woods JC, Titmus GL (1985) A review of the Simon Clovis collection. Idaho Archaeol 8: 3–8.
- 42.
Morrow JE, Fiedel SJ (2006) New radiocarbon dates for the Clovis component of the Anzick site, Park County, Montana. In: Morrow JE, Gnecco C, editors. Paleoindian Archaeology: A Hemispheric Perspective. Gainesville: University of Florida Press. pp. 123–138.
- 43.
Boldurian AT, Cotter JL (1999) Clovis Revisited: New Perspectives on Paleoindian Adaptations from Blackwater Draw, New Mexico. Philadelphia: University Museum, University of Pennsylvania.
- 44. Cotter JL (1937) The occurrence of flints and extinct animals in pluvial deposits near Clovis, New Mexico: Part IV, Report on excavation at the gravel pit, 1936. Proc Academy Nat Sci Phil 89: 1–16.
- 45.
Hester JJ (1972) Blackwater Draw Locality No. 1: A Stratified Early Man Site in Eastern New Mexico. 8 p. Ranchos de Taos: Fort Burgwin Research Center Publication No 8.
- 46. Warnica JM (1966) New discoveries at the Clovis site. Am Antiq 31: 345–357.
- 47.
Frison GC, Todd LC (1986) The Colby Mammoth Site: Taphonomy and Archaeology of a Clovis Kill in Northern Wyoming. Albuquerque: University of New Mexico Press.
- 48. Figgins JD (1933) A further contribution to the antiquity of man in America. Colo Mus Nat Hist Proc 12: 4–8.
- 49. Haynes CV , McFaul M, Brunswig RH, Hopkins KD (1998) Kersey–Kuner terrace investigations at the Dent and Bernhardt sites, Colorado. Geoarchaeol 13: 201–218.
- 50.
Leonhardy FC, editor. (1966) Domebo: A Paleo-Indian Mammoth Kill in the Prairie–Plains. Lawton: Contributions of the Museum of the Great Plains No. 1. 1 p.
- 51. Bement LC, Carter BJ (2003) Clovis bison hunting at the Jake Bluff site, NW Oklahoma. Curr Res Pleist 20: 5–7.
- 52. Bement LC, Carter BJ (2010) Jake Bluff: Clovis bison hunting on the southern Plains of North America. Am Antiq 75: 907–933.
- 53. Haury EW, Sayles EB, Wasley WW (1959) The Lehner mammoth site, southeastern Arizona. Am Antiq 25: 2–30.
- 54. Holliday VT, Haynes CV Jr, Hofman JL, Meltzer DJ (1994) Geoarchaeology and geochronology of the Miami (Clovis) site, Southern High Plains of Texas. Quat Res 41: 234–244.
- 55. Sellards EH (1938) Artifacts associated with fossil elephant. B Geol Soc Am 49: 999–1010.
- 56.
Haynes CV Jr, Huckell BB, editors. (2007) Murray Springs: A Clovis Site with Multiple Activity Areas in the San Pedro Valley, Arizona. Anthropological Papers of the University of Arizona No. 71. Tucson: University of Arizona Press.
- 57.
Hemmings ET (1970) Early Man in the San Pedro Valley, Arizona. PhD Dissertation, Department of Anthropology, University of Arizona, Tucson.
- 58. Haury EW, Antevs E, Lance JF (1953) Artifacts with mammoth remains, Naco, Arizona. Am Antiq 19: 1–24.
- 59. Buchanan B, Collard MC (2007) Investigating the peopling of North America through cladistic analyses of early Paleoindian projectile points. J Anthropol Archaeol 26: 366–393.
- 60. Buchanan B, Hamilton MJ (2009) A formal test of the origin of variation in North American early Paleoindian projectile points. Am Antiq 74: 279–298.
- 61.
Morphometrics at SUNY Stony Brook website Available: http://life.bio.sunysb.edu/morph. Accessed 2011 August.
- 62. Bailey RC, Byrnes J (1990) A new, old method for assessing measurement error in both univariate and multivariate morphometric studies. Syst Zool 39: 124–130.
- 63.
Sokal RR, Rohlf FJ (1995) Biometry: The Principles and Practice of Statistics in Biological Research. 3rd ed. New York: Freeman.
- 64. Yezerinac SM, Lougheed SC, Handford P (1992) Measurement error and morphometric studies: statistical power and observer experience. Syst Biol 41: 471–482.
- 65. Strauss RE, Atanassov MN, de Oliveira JA (2003) Evaluation of the principal-component and expectation-maximization methods for estimating missing data in morphometric studies. J Vert Paleontol 23: 284–296.
- 66.
Strauss RE (2010) Discriminating groups of organisms. In: Elewa AMT, editor. Morphometrics for Nonmorphometricians. Berlin: Springer-Verlag. pp. 73–91.
- 67. Keene ON (1995) The log transform is special. Stat Med 14: 811–819.
- 68. Kuhry B, Marcus LF (1977) Bivariate linear models in biometry. Syst Zool 26: 201–209.
- 69. Leamy L, Bradley D (1982) Static and growth allometry of morphometric traits in randomized house mice. Evolution 36: 1200–1212.
- 70. Gould SJ (1974) The origin and function of “bizarre” structures: antler size and skull size in the “Irish Elk,” Megaloceros giganteus. Evolution 28: 191–220.
- 71. Jolicoeur P (1984) Principal components, factor analysis, and multivariate allometry: a small-sample direction test. Biometrics 40: 685–690.
- 72. Benjamini Y, Yekutieli D (2001) The control of the false discovery rate in multiple testing under dependency. Annals of Statistics 29: 1165–1188.
- 73. Narum SR (2006) Beyond Bonferroni: less conservative analyses for conservation genetics. Conserv Genet 7: 783–787.
- 74.
Richard Strauss's Matlab Page website Available: http://www.faculty.biol.ttu.edu/Strauss/Matlab/matlab.htm. Accessed 2011 August.
- 75. Frison GC (1989) Experimental use of Clovis weaponry and tools on African elephants. Am Antiq 54: 766–784.
- 76. Cheshier J, Kelly RL (2006) Projectile point shape and durability: the effect of thickness: length. Am Antiq 71: 353–363.
- 77. Waguespack NM, Surovell TA, Denoyer A, Dallow A, Savage A, et al. (2009) Making a point: wood- versus stone-tipped projectiles. Antiquity 83: 786–800.
- 78.
Collins MB (1999) Clovis Blade Technology. Austin: University of Texas Press.
- 79. Hamilton MJ, Buchanan B (2007) Spatial gradients in Clovis-age radiocarbon dates across North America suggest rapid colonization from the north. Proc Natl Acad Sci 104: 15629–15634.