Skeletal remains of a Pleistocene modern human (Homo sapiens) from Sulawesi

Abstract

Major gaps remain in our knowledge of the early history of Homo sapiens in Wallacea. By 70-60 thousand years ago (ka), modern humans appear to have entered this distinct biogeographical zone between continental Asia and Australia. Despite this, there are relatively few Late Pleistocene sites attributed to our species in Wallacea. H. sapiens fossil remains are also rare. Previously, only one island in Wallacea (Alor in the southeastern part of the archipelago) had yielded skeletal evidence for pre-Holocene modern humans. Here we report on the first Pleistocene human skeletal remains from the largest Wallacean island, Sulawesi. The recovered elements consist of a nearly complete palate and frontal process of a modern human right maxilla excavated from Leang Bulu Bettue in the southwestern peninsula of the island. Dated by several different methods to between 25 and 16 ka, the maxilla belongs to an elderly individual of unknown age and sex, with small teeth (only M1 to M3 are extant) that exhibit severe occlusal wear and related dental pathologies. The dental wear pattern is unusual. This fragmentary specimen, though largely undiagnostic with regards to morphological affinity, provides the only direct insight we currently have from the fossil record into the identity of the Late Pleistocene people of Sulawesi.

Fig 1. Map of Wallacea showing the location of Sulawesi.

The Late Pleistocene cave site Leang Bulu Bettue is located in the island’s southwestern peninsula, known as South Sulawesi. Wallacea comprises an extensive zone of oceanic islands located east of a significant biogeographical boundary, the Wallace Line. This archipelago is positioned between the continental regions of Asia (Sunda) and Australia-New Guinea (Sahul). The Malayan-Papuan Line delineates a major east-west division in the genetic diversity of modern human populations in Wallacea. Map source, Shuttle Radar Topography Mission 1 Arc-Second Global by NASA/NGS/USGS; GEBCO_2014 Grid, version 20150318 (http://gebco.net). Base map generated using ArcGIS by M. Kottermair and A. Jalandoni.

Fig 2. Excavations at Leang Bulu Bettue.

(a-b) overview of the trench in the rock-shelter area (2017); (a) viewed from south to north; (b) viewed from northwest to southeast. (c) site plan showing the layout of the excavated squares in the rock-shelter and cave (2013–15, 2017–18).

Fig 3. Stratigraphy and archaeological findings at Leang Bulu Bettue (2017).

Top: East wall profile of the 2017 rock-shelter excavations, showing the stratigraphic sequence (note: Layers 4c-f are not visible here). Bottom: Spatial distribution of stone artefacts, faunal remains, and other findings recovered during the 2015–17 excavations, color-coded by stratigraphic layer (prepared using ArcScene). The location of the modern human right maxilla (Maros-LBB-1a) in relation to Stalagmite 437 is indicated by a white star.

Fig 4. Stalagmites dated using U-series analysis at Leang Bulu Bettue.

(a) Stalagmite 485 (scale is in 10 cm increments). The in situ speleothem comprises distinct lower and upper sections. We only dated the lower section (highlighted by a broken red line). This part of the stalagmite has a diameter of 13.5 cm. It grew to a height of 18 cm on a 10 cm-thick pedestal of cemented sediment and archaeological detritus, which includes shell, bone, ochre fragments and stone artefacts. During excavation the lower section of the stalagmite was left in situ on a plinth of Layer 4a sediments; (b) Stalagmites 485 (lower section) and 605 in situ. Stalagmite 485, the base of which is highlighted by a broken red line, grew atop Layer 4a. The broken blue line shows the boundary between Layer 4a and overlying Layer 3f. Stalagmite 485 grew between 13.7 to 10.3 ka, providing a minimum age for Layer 4a. Stalagmite 605 formed on top of Layer 4b between 26 to 24.5 ka; (c) cross-sections of Stalagmites 485 and 605 showing U-series sub-sample locations and dating results (scale is in 10 mm increments).

Fig 5. Stalagmite dated using U-series analysis at Leang Bulu Bettue.

(a) Stalagmite 437 in situ within the trench under excavation–during the excavation the stalagmite was left in situ on a plinth of unexcavated Layer 4a sediments. The blue dashed line shows the boundary between Layer 4a and overlying Layer 3; (b) cross-section of Stalagmite 437 showing the locations of U-series sub-samples LBB17-Stal_3d and LBB17-Stal_3e, which were used to determine the growth age of the speleothem; (c) human maxilla fragments (Maros-LBB-1a) in situ in Layer 4a below the base of Stalagmite 437.

Fig 6. Right maxilla and frontal process (Maros-LBB-1a) from Layer 4a at Leang Bulu Bettue.

(a-b) right and left lateral views of the right maxilla (after reconstruction). The small point of contact between the dental portion and nasal pillar is obscured by glue and plasticine; (c) inferior view of the right palate; (d) detail of the lingual sides of the extant first to third right upper molars (M¹ to M³), showing the extreme degree of occlusal attrition on the M¹ and M³. The M¹ had lost its crown by extreme wear and there are abscess cavities around the root tips, owing to the exposure of dental pulp cavities. The M³ retains its enamel only at the mesiobuccal corner. Only the M² has a normal occlusal plane. The M² still retains much of its occlusal enamel but is considerably over-erupted, suggesting that its opposing tooth (M₂) had been lost while the individual was alive; (e) anterior view of the reconstruction of the right maxilla and frontal process. The scale in (a-c) is in 10 mm increments; in (e) the scale bar is 10 mm. Photo credits: Ratno Sardi (a-d); David Bulbeck (e).

Fig 7. M² crown size and shape in Maros-LBB-1a, other H. sapiens, Javanese H. erectus, and H. floresiensis.

Crown size = SQRT (BL diam. x MD diam.); crown shape index = (MD diam./BL diam.) x 100. Red cross: Maros-LBB-1a (measurement by Y. Kaifu); orange crosses: Prehistoric Indonesian H. sapiens (Java and Flores) (N = 11); grey crosses: Global H. sapiens (Asia, Australia/Melanesia, Africa, Europe) (N = 363); green “S” and “s”: Sangiran H. erectus (S, older subgroup; s, younger subgroup) (N = 9); blue “L”: H. floresiensis (LB1). Y. Kaifu carried out all measurements. For data sources for comparative H. sapiens sample, see Table 2.

Fig 8. Comparative data for Island Southeast Asian upper molar diameters at the cemento-enamel junction.

Sources: [40,53]; Table 4 (this paper).

Fig 9. Dental pathologies in Maros-LBB-1a.

(a) Inferior view of the right palate. Note the inflammation of the interproximal septa at all tooth sites, particularly marked at the sites of the premolar sockets, including the resorbed first premolar; (b) close-up of the inflammation of the interproximal septa at the second premolar site, showing also the rough interior surface of the socket. Note also the mesio-lingual to bucco-distal striation on the third molar; (c) close-up of the inflammation of the alveolar bone at the second premolar site, and slighter inflammation of the interproximal septa between the first and second molars. Scale bars are 10 mm.