Date Published: October 23, 2018
Publisher: Public Library of Science
Author(s): Eisuke Yamada, Mugino O. Kubo, Tai Kubo, Naoki Kohno, Alistair Robert Evans.
Categorizing the archaeological remains of Sus scrofa as domesticated “pigs” or wild “boars” is often difficult because of their morphological and genetic similarities. For this purpose, we tested whether feeding ecological change of S. scrofa that accompanied their domestication can be detected based on the three-dimensional texture created on the tooth enamel surface by mastication. We scanned the lower tooth surface of one wild and one stall-fed populations of modern S. s. leucomystax and one wild population of S. s. riukiuanus by using a confocal laser microscope. The average body weight of S. s. leucomystax is twice as heavier as that of S. s. riukiuanus. The textures were quantified using the industrial “roughness” standard, ISO 25178, to prevent inter-observer errors and to distinguish small differences that were difficult to detect by two dimensional image observation. The values of parameters related to height and volume were significantly larger in the stall-fed population. Twenty parameters differed significantly between the stall-fed and wild population of S. s. leucomystax, which indicated that the feeding ecological difference affected the ISO parameters of the two boar populations. Six parameters also differed between the wild populations of S. s. leucomystax and S. s. riukiuanus. Surprisingly, no parameter differed between the populations of stall-fed S. s. leucomystax and wild S. s. riukiuanus. Consumption of hard nuts and/or agricultural fruits and crops by the wild population of S. s. riukiuanus may have produced a tooth surface texture similar to that of the stall-fed population of S. s. leucomystax. Further analysis of S. s. riukiuanus with a known diet is necessary to conclude whether ISO parameters reflect the dietary transition accompanying the domestication of Sus (e.g., wild, semi-domestic, and domestic). Until then, caution is needed in discriminating domesticated populations from wild populations that mainly feed on hard objects.
Distinguishing domestic pig from wild boar is often difficult because they are the same species, Sus scrofa. Their body sizes and shapes vary corresponding to the climate and nutrition conditions. As a result, the morphology of pigs and boars often overlaps. Genetic characteristics are also unsuitable for distinguishing them because they can interbreed easily. Therefore, dichotomous approaches for the identification of zooarchaeological remains as pig or boar are insufficient to describe the complex domestication process of S. scrofa. Instead, the life style of each individual (i.e., whether they were reared, wild, or feral etc.) can be the key to understanding the continuous domestication process .
Among the 35 ISO 25178 parameters examined, Sda (average area of dales connected to the edge at a defined height; see S1 Table for basic statistics of the parameters) differed significantly between M1 and M2 (Table 2). Average scores of Sda were 317.93 μm2 for M1 and 559.04 μm2 for M2.
One surface roughness parameter (Sda) differed significantly between M1 and M2. The results suggested that some ISO parameters should not be applied in STA regardless of tooth position. Considering the small number of specimens used in the matched pairwise comparison, we expect ISO parameters to differ when we increase the sample size. When performing STA of archaeological remains, therefore, tooth position should be standardized if it can be identified. Considering the applicability for domesticated animals, which are often slaughtered before all permanent teeth have erupted, M1 is an ideal position for zooarchaeological studies because it erupts earlier than other permanent teeth.