Figure 14.12 Landmark analysis of Aulacopleura. (a) Measurements, (b) landmarks, (c) plot of landmarks, (d) bivariate plot of occipital-glabellar length versus frontal area length, and (e) bivariate plot of occipital-glabellar length versus thoracic length. FAW, width of frontal area; PGW, OCW, width of occipital glabella; EGW, FAL, length of frontal area; PLL, GLL, THL, length of thorax; PYL, length of pygidium; PAW, PYW, width of pygidium; RMA, reduced major axis. (Courtesy of Nigel Hughes.)
In addition there are signs of predation that often show an asymmetric distribution. Predation scars are three times as likely to be present on the right-hand side of the exoskel-eton as the left. If predators preferred to attack from the right then perhaps there was already a lateralization of their nervous system and other organs (Babcock 1993). However, it can be argued that these specimens were the survivors and that predators preferred to attack on the left-hand side of the trilobite, and we never see those victims.
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