Figure 1.
Manufacturing the experimental spears.
A. Using disc sander to shape distal end of spear. B. L-notch used for hafting stone tools to half of the spears. C. Two sets of spears were manufactured, 5 tipped, 5 untipped. D. The shape of the distal end was constant between all 10 spears; a contour gauge was used to ensure consistency. E. Commercial epoxy was used as the binding agent to attach the quartzite stone tips.
Figure 2.
The calibrated crossbow and gelatin targets.
A. The calibrated crossbow consists of two commercial bows mounted crosswise. A digital scale was used to draw the bow with a consistent 20 kg draw force. B. Fifty gelatin targets were manufactured using published ballistic standards. Plastic pictures were used as the molds. C. During shooting, the molds were secured in place with a foam target.
Figure 3.
Wound track profiles in gelatin targets after being shot.
A. Tipped spear gelatin half showing wound track details. B. Same gelatin in A with traced outlines of wound track features. C. Untipped gelatin half, spear 13-U5, shot 1. D. Same gelatin in C with traced outlines of wound track features. The inner cavity is represented by the red line and the outer cavity is represented by the blue line. E. Tipped gelatin half, spear 13-T5, shot 4. F. Same gelatin in E with traced outlines of wound track features.
Figure 4.
Box plot comparison of tipped and untipped performance characteristics.
A. Penetration depth (cm). B. Inner cavity area (cm2). C. Outer cavity area (cm2). Each of these variables is significantly different between tipped and untipped spears based on t-tests (see text).
Figure 5.
Consensus shape of gelatin wound track profiles based on geometric morphometrics for A) tipped and B) untipped spears.
Scale represents relative percentage of total wound track length. Red arrow highlights location at about 80% of wound length where there is a widening of the inner cavity in tipped spears. That same relative location is narrow in tipped spears.
Figure 6.
Scatter plots of the first two principal components from the geometric morphometric relative warps analysis of the tipped and untipped wound track shape.
A) The tipped inner wound track shape is significantly different from the untipped inner wound track shape (PC1 explains 35% and PC2 explains 27% of variance). B) The outer wound track shapes are not significantly different between tipped and untipped spears (PC1 explains 52% and PC2 explains 23% of variance).