Stone tool technological innovations from 5050 to 4200 years ago

A large fragment of carved stone depicting the brow ridge of a human or animal face provides the earliest evidence for the figurative expression of body form in Oceania (Fig. 4A). The carved stone is a gabbro sourced from discrete outcrops 5 to 15 km from Waim and was produced by hammer dressing (fig. S4). A complete stone carving depicting a human face with a bird on top of the head was also recovered by Waim residents before our investigations (Fig. 4B). It was found 20 to 30 cm below the surface while cutting back the hill slope immediately adjacent to where squares B/D were placed. The find location equates to layers 2a and 2b, and therefore securely within the upper cultural horizon.

Fig. 4 Formally manufactured stone carvings and pestles from Waim. (A) Excavated fragment of carved stone face with image above and three-dimensional (3D) photogrammetry textured model below showing brow ridges and eye socket. Comparative carvings from undated contexts are provided in fig. S5. (B) Complete carved face with bird above the head showing front and top, found during groundworks in the same location where excavations were undertaken. (C) Large excavated pestle base fragment (pestle 1) with natural mineral lens indicated by arrow. (D) Small excavated pestle base fragment (pestle 2). (E) Complete pestle (local surface find) with similar base morphology as the excavated example (D). Photo and figure credits: Ben Shaw, UNSW.

Figurative stone carvings are part of a regional cultural complex, which spans the highlands and parts of the northern lowlands, as indicated by the distribution of similar objects from undated surface contexts (fig. S5). The distribution of bird carvings is also centered in the highlands where the Waim site is situated, with centers also in the Sepik-Ramu basin and Huon Gulf (Fig. 1). Few isolated bird carvings have been found outside of this range, suggesting that these lowland areas were conduits for interaction with coastal and island populations (9). Many carved stone objects have no recognized function other than having probable social significance, although figurative carvings sometimes feature on stone pestles and mortars. Animal and human forms have been argued to represent spirit figures, consistent with known customary practices in New Guinea and elsewhere in the world (10). Their distribution suggests that they were also part of regionally networked symbolic social system that facilitated communication between a number of dispersed populations. The excavated carved stone described here establishes a minimum antiquity for the symbolic depiction of anthropomorphic/zoomorphic forms in New Guinea.

Two ground stone pestle fragments were recovered in close proximity to each other (adjoining squares C and F) and are the first formally manufactured pestles recovered from a secure archaeological context in Oceania (Fig. 4, C and D). The tools, made from diorite and gabbro-diorite, were manufactured using a combination of hammer dressing and grinding (Supplementary Materials). The pestle fragments were of differing morphologies but similar to numerous undated surface collected examples found in the highlands (e.g., Fig. 4E). The Waim pestles contrast with earlier unmodified cobble pounders (~10 ka ago) and demonstrate a shift in social behaviors associated with food processing (11).

Yam, fruit, and tree nut starches were identified on the distal ground pestle surfaces using the geometric morphometric method (12). Phytoliths associated with tree nut–producing species (e.g., Castanopsis and Flacourtia) were also present, with tissue fragments supporting the interpretation of soft tissue plant processing (see the Supplementary Materials for starch and phytolith results). Starchy plant taxa included Dioscorea pentaphylla (Five leaf yam), D. alata (Greater yam), Pueraria lobata (Kudzu tuber), Musa cf. ingens (Banana), Castanopsis acuminatissima (tree nut), Hydriastele spp. (palm), and Saccharum officinarum (sugar cane). Yam and banana, also identified in the Kuk sequence, are modern staple crops in the highlands, but wild variants are also available (11). C. acuminatissima, the most common taxon on both pestles, is an endemic tree species and common throughout the highlands, with small edible starchy nuts available from July to December (13). Kudzu, also endemic, grows wild and is now considered a famine food perhaps falling into disuse following the introduction of sweet potato ~300 years ago, but has traditional medicinal uses (14, 15). It is uncertain whether yams were harvested locally. However, Waim is near the modern maximum altitudinal growing limit for D. alata (2100 m asl) and well above the known limit for D. pentaphylla (1550 to 1600 m asl) (16). If mid-Holocene climatic conditions were in the same range or even slightly warmer than the modern day (6), then it is likely that D. pentaphylla was harvested at lower elevations and transported up to Waim.

A large ground planilateral axe-adze preform (10 kg) and associated manufacturing debris at Waim indicate a New Guinea highland origin for this technology (Fig. 5A). These finds predate the earliest evidence for planilateral axe-adzes in New Guinea by at least 1000 years, a technology previously thought to have been introduced with agricultural groups (Lapita cultural complex) from Southeast Asia (17, 18). A block of argillite with evidence of sawing is consistent with historically documented techniques of sawing and splitting for axe-adze manufacture (Fig. 5B) (19). A small ground lenticular axe-adze (31 g) was also found, further confirming the mid-Holocene presence of this tool morphology in the highlands (Fig. 6C).

Fig. 5 Components of planilateral axe-adze manufacture from Waim excavations. (A) Large siliceous argillite preform prepared by grinding all surfaces of a naturally occurring tabular slab, with the distal ends heavily ground to obtain an acute angle. (B) Siliceous argillite with deeply incised cut marks, perhaps delineating the distal end of an axe-adze, demonstrating the use of cutting as a manufacturing technique at Waim. Photo credit: Judith Field, UNSW. Figure credit: Ben Shaw, UNSW.

Fig. 6 Ground and cut stone artefacts from Waim excavations. (A) Incised volcanic stone with ochre residue, (B) pyroxenite fragment with striations, (C) siliceous argillite lenticular axe-adze, and (D to F) siliceous argillite tool fragments with ground surfaces. Photo and figure credits: Ben Shaw, UNSW.

On-site manufacture of ground stone axe-adzes is indicated by preforms and flakes (n = 10) exhibiting evidence of hammer dressing and grinding (Fig. 6, D to F). Both the lenticular axe-adze and the planilateral preform were made of siliceous argillite. The preform is parallelogram in profile, and all surfaces have evidence of grinding, with well-defined asymmetrical bevels at each end. A large lightly ground slab of the same lithology was also found immediately adjacent to the planilateral preform, indicating that they were deliberately cached together (fig. S6). Splitting and sawing is a well-documented method for the manufacture of large planilateral axe-adzes in the highlands, which are recorded as having both functional and ceremonial uses. Known quarries are located in the Jimi and Wahgi valleys where tabloid blocks of raw stone were sourced (Fig. 1) (19). Quarried stone could be readily split along naturally occurring fracture lines and subsequently ground and sawn to produce several axe-adzes (20). Planilateral axe-adze technology in the highlands has therefore been in use for more than four millennia.

Fibercraft and the coloring of string are well-known traditional practices in societies across modern-day New Guinea, and an ochre-stained incised volcanic stone from Waim implies a mid-Holocene antiquity for this technology. The incised stone and a pyroxenite fragment, both recovered from the upper cultural horizon, were recognized by local informants, the former used to stain organic fibers in the production of woven bags (bilums) and the latter as a fire lighting tool (Fig. 6, A and B). These artefacts were examined for microwear traces to determine function (Supplementary Materials). The incised stone was weathered with ochre residues and had two worked surfaces. Deep grooves had been cut into the surface, probably from sawing, and two are U-shaped in cross section, which is characteristic of wear from pulling soft plant fibers through the cut grooves. The pyroxenite fragment had grinding wear consistent with stone-on-stone use. Pyroxenite has high concentrations of iron-rich minerals, which create sparks for lighting fires (c.f. “strike-a-light”) (21).

The lithic assemblage (n = 486) derives from sources no more than 15 km from Waim and includes a range of flakes, angular fragments, and cores, demonstrating on-site reduction and tool manufacture (table S2). Flakes (n = 214, 44%) and angular fragments (n = 181, 37%), some with retouch and use wear, were the most common artefact classes. Seventeen raw materials were identified, predominated by argillite/siltstone (81.3%), shale (6.2%), and greywacke (6%), with minor contributions of intrusive plutonic and volcanic tuff (fig. S4). Collectively, the lithic assemblage provides evidence for a range of domestic and social activities, specifically complex food processing, axe-adze manufacture, fibercraft, on-site lithic reduction, and symbolic expression.