MicroCT reveals domesticated rice (Oryza sativa) within pottery sherds from early Neolithic sites (4150-3265 cal BP) in Southeast Asia

Abstract

Rice (Oryza sativa) was domesticated in the Yangtze Valley region at least 6000-8000 years ago, yet the timing of dispersal of domesticated rice to Southeast Asia is contentious. Often rice is not well-preserved in archaeobotanical assemblages at early Neolithic sites in the wet tropics of Southeast Asia and consequently rice impressions in pottery have been used as a proxy for rice cultivation despite their uncertain taxonomic and domestication status. In this research, we use microCT technology to determine the 3D microscale morphology of rice husk and spikelet base inclusions within pottery sherds from early Neolithic sites in Vietnam. In contrast to surface impressions, microCT provides images of the entire husk and spikelet base preserved within the pottery, including the abscission scar characteristic of domesticated rice. This research demonstrates the potential of microCT to be a new, non-destructive method for the identification of domesticated plant remains within pottery sherds, especially in contexts where archaeobotanical preservation is poor and chaff-tempered sherds are rare and unavailable for destructive analysis. The method has the potential to greatly advance the understanding of crop domestication and agricultural dispersal for ceramic cultures in different parts of the world.

Figure 1

Map of Vietnam (right) with inset showing location of sites (left). Map created by Bellwood, P. & Piper, P. using Adobe Illustrator version CS5.

Figure 2

(A) – Photograph of Sherd 1 (An Son) showing offcut used for tomographic imaging. (B) – Optical microscope image of rice impression on surface of Sherd 1. (C) – SEM image of rice impression on exposed cut surface of Sherd 1. (D) – Tomograph showing high-density, highly attenuated, clay fraction within offcut of Sherd 1. (E) – Tomograph showing mineral fraction within offcut of Sherd 1. (F) – Tomograph of low-density organic inclusions within offcut of Sherd 1. (G) – Tomograph of targeted rice husk fragment in offcut of Sherd 1, showing distinctive checkboard patterning of epidermis. (H) – Tomograph of rice spikelet base in offcut of Sherd 1, identified by positional relationship with husk fragments and recessed, irregular abscission scar. See Animations S1–S5 for detail of Fig. 2D–G.

Figure 3

(A) – Tomograph of offcut from Sherd 5, Loc Giang, showing organic component in green and position of rice husk (B) and attached spikelet base (C) in red (Animation S6). (B) – Front and side view of tomograph of rice husk and attached spikelet base in offcut of Sherd 5. (C) – Closeup of tomograph of spikelet base in Sherd 5, showing irregular, and recessed, abscission scar at base of near complete husk, as well as evidence of rachis pore (Animation S7). Recessed nature of scar shows that force was used to remove seed husk from plant rather than naturally occurring wind dispersal.

Figure 4

(A) – SEM image of domesticated-type rice spikelet base (from Fuller et al. Fig. 3G). (B) – Tomographic image of domesticated-type spikelet base in Sherd 3 from Loc Giang (Animation S8). (C) – Tomographic image of domesticated-type rice spikelet base in Sherd 1 from An Son (Animation S9).