Micro-CT investigation of ostrich eggshell beads collected from Locality 12, the Shuidonggou site, China

Abstract

Ostrich eggshell (OES) beads are an important kind of human ornaments, because their production reflects the development of modern human behavior, thinking ability, and cognitive level. Although the manufacture procedure of OES beads has been reconstructed in some Later Stone Age sites and early Neolithic sites, little information is known about detailed drilling technologies. In this study, synchrotron radiation micro-CT (SR-μCT) was firstly used to scan OES beads to understand microstructure, drilling marks, and perforation shape in a non-destructive mode. In contrast to other method to research drilling technologies, SR-μCT has a unique advantage that it could eliminate the influence of the adhering soils in a perforation in case that they are not easily removed. The results indicate that (1) SR-μCT could differentiate the eggshell species between Struthio camelus and Struthio anderssoni in terms of pore distribution. Compared to other destructive methods, including the anatomical method, DNA and protein analysis, the species identification through SR-μCT is non-destructive and faster; (2) the outer and inner surface of OES could be non-destructively judged according to OES microstructure, which would help infer the drilling direction; and (3) the perforation shape and drilling marks are distinct between the discontinuous twisting drilling and the multi-rotary drilling methods on the basis of replication experiments. According to these criteria, SR-μCT was applied to examine OES beads found in Locality 12 of the Shuidonggou (SDG) site in China, which were probably discarded in 1.1 k yr BP. The results show that most of ancient beads were firstly drilled from inside. According to the perforation shape and drilling marks, both the twisting drilling and the multi-rotary drilling method with different kinds of drill bits were used in working beads. Therefore, the people in SDG site mastered a few drilling technologies in the early Holocene, and the use of the multi-rotary drilling method reflects the technical development of ancient people. Up to our knowledge, it is the earliest known evidence of the application of the multi-rotary drilling method in China. Furthermore, this study will provide a new approach and important reference to understand drilling technologies of much older OES beads in the Later Stone Age or Upper Paleolithic Age.