This paper presents a reassessment of the archaeological record at Leang Burung 2, a key early human occupation site in the Late Pleistocene of Southeast Asia. Excavated originally by Ian Glover in 1975, this limestone rock-shelter in the Maros karsts of Sulawesi, Indonesia, has long held significance in our understanding of early human dispersals into ‘Wallacea’, the vast zone of oceanic islands between continental Asia and Australia. We present new stratigraphic information and dating evidence from Leang Burung 2 collected during the course of our excavations at this site in 2007 and 2011–13. Our findings suggest that the classic Late Pleistocene modern human occupation sequence identified previously at Leang Burung 2, and proposed to span around 31,000 to 19,000 conventional 14 C years BP (~35–24 ka cal BP), may actually represent an amalgam of reworked archaeological materials. Sources for cultural materials of mixed ages comprise breccias from the rear wall of the rock-shelter–remnants of older, eroded deposits dated to 35–23 ka cal BP–and cultural remains of early Holocene antiquity. Below the upper levels affected by the mass loss of Late Pleistocene deposits, our deep-trench excavations uncovered evidence for an earlier hominin presence at the site. These findings include fossils of now-extinct proboscideans and other ‘megafauna’ in stratified context, as well as a cobble-based stone artifact technology comparable to that produced by late Middle Pleistocene hominins elsewhere on Sulawesi.

Funding: The 2011-13 excavations at Leang Burung 2 and post-excavation work related to the research were supported by Australian Research Council fellowships awarded to A.B. (DP0879624 and Discovery Early Career Researcher Award DE130101560). B.L. and R.G.R. were supported by Future Fellowship FT140100384 and Laureate Fellowship FL130100116, respectively, while G.D.v.d.B.’s research was supported by Future Fellowship FT100100384. The 2011 excavations were also supported by a start-up grant from the University of Wollongong’s Centre for Archaeological Science, awarded to K.S. and A.B. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Data Availability: Archaeological and paleontological assemblages excavated from Leang Burung 2 in 2007 and between 2011 and 2013, and which form the basis of the current study, are under the permanent curation of Indonesian authorities at Pusat Penelitian Arkeologi Nasional (ARKENAS) in Jakarta and Makassar Balai Arkeologi. The data are not from a third party. Requests to access collections for study, including databases and catalogs of finds, should be directed in the first instance to the directors of ARKENAS ( http://arkenas.kemdikbud.go.id/#1 ) and Balai Arkeologi Makassar ( http://www.arkeologi-sulawesi.com//index.php ).

Copyright: © 2018 Brumm et al. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Glover [ 1 ] was unable to obtain any radiometric dates for the extensive high-level cemented breccias at Leang Burung 2. He claimed that samples of artifacts and faunal remains collected from these breccias were broadly similar to those excavated from the stratified floor deposits. No Toalean implements or ceramics were found. Noting that breccias were located at heights of up to 4 m above the shelter floor, Glover argued that they must represent the remnants of deposits that accumulated during the final phase of site occupation, and which had been almost completely scoured out by natural erosional processes–‘My expectation is that [the age of the breccias] should fall between 12000 and 8000 BP’ ([ 1 ], 17).

Similar high-level cemented breccias were noted at Ulu Leang 1 [ 36 ], where patches of cemented breccias are located 1–2 m above the present floor surface [ 20 ]. Glover [ 36 ] initially hypothesized that an earlier sedimentary deposit had been all but rinsed out from Ulu Leang 1, leaving only remnants in the form of the cemented wall breccias. A subsequent phase of deposition then led to the accumulation of the soft floor deposits. However, 14 C dating of charcoal from a patch of breccia located 70 cm above the present-day floor surface suggested to Glover [ 20 ] that the cemented deposit, and the upper part of the unconsolidated floor deposit below, were essentially the same age. Thus, he rejected the notion that there had been two separate phases of deposition [ 20 ], instead formulating the idea that erosion and undermining of the deposit from below, owing to karstic sink action, had led to subsidence. A similar process must have occurred at Leang Burung 2, Glover [ 1 ] argued. However, he inferred that the impact of karstic undermining on the Late Pleistocene strata at Leang Burung 2 had been more pronounced: ‘But, whereas at Ulu Leang 1 the deposits appear to have fallen evenly and parallel with the original surface, at Leang Burung 2 small sinks have formed in the cave floor, causing dramatic warping and local subsidence’ ([ 38 ], 311).

Glover [ 1 ] postulated that Pleistocene deposits at Leang Burung 2 had undergone major post-depositional disturbances. He observed that the upper Layer I boundary and upper and lower boundaries of Layers II and IV dip sharply downwards (45°) from the rear of the shelter towards the front, ‘an inclination quite opposed to the trend of the modern surface and upper layers’ ([ 1 ], 11). In other areas he noted ‘the erratic and often sudden dipping of layers… (e.g. unit IIa…)’ ([ 1 ], 11). Excavations in H10 adjacent to the shelter wall also revealed the presence of ‘a sink developing below the deposit’ ([ 1 ], 7) ( Fig 1 ). In addition, the presence of partly cemented archaeological deposits fixed to the rear wall of the shelter was interpreted to to indicate that a large portion of the uppermost stratigraphy had been scoured out.

Vertebrate fossil remains at the site were generally in highly fragmentary condition, the majority were unidentifiable, and most exhibited signs of burning [ 17 ]. Most identifiable elements were in Layer I. Compared with Layer I, the assemblages in Layers II, IV, and V layers are notable for their high proportions of diagnostic Sus celebensis (Celebes warty pig) remains and rodent elements, and the minimal representation of identifiable elements of babirusas (n = 4, Layer IV) and anoas (n = 3, Layer II) ( Fig 2 ).

Glover’s [ 1 ] report provides limited detail on the faunal assemblages from Leang Burung 2. An accompanying paper [ 43 ] describes the shell analysis. Of the four edible species of shellfish in the deposit, T. perfecta [ 44 ] was dominant [ 43 ]. No evidence for exploitation of marine/estuarine species was reported [ 1 , 43 ]. Layer I yielded negligible amounts of complete or even fragmentary shell [ 43 , 45 ].

Glover [ 1 ] recovered ochre fragments from Layers II, IV-V, and V, including two utilized (faceted/scored) pieces in Layer V. Edge-glossed flakes (n = 31) were found in Layers II and above [ 1 ]. Wear traces on these artifacts were attributed processing of silica-rich plants for craft activities ([ 1 ]; see also [ 42 ]).

The most common stone type (96.7%) in Layers II, IV and V was high quality chert [ 1 ]. Lithic assemblages in Layers III and IIIa/b were also dominated by chert (95.7%). By contrast, 59% of artifacts in Layer I were manufactured from chert, with the proportions of limestone (31%) and quartz (10%) much higher than in overlying layers [ 1 ].

Glover [ 1 ] claimed that ceramics and diagnostic Toalean tool types were absent below Layers IX, X, VIII and VII, and sterile Layer VI. Layers V, IV, II and III/IIIa yielded broadly similar lithic and faunal assemblages. Glover’s [ 1 ] analysis of the stone-flaking technology from these layers (see also [ 41 ]) indicates a relatively straightforward approach to lithic reduction based on hard-hammer knapping, and, less commonly, bipolar reduction. Small morphologically undifferentiated flakes dominated the assemblage. Very few flakes were retouched and only a small number of simple, intensively reduced cores (0.5%) were recovered. The most technologically and typologically distinctive implements in the assemblage were Levallois-like macroblades (n = 7) with facetted platforms, recovered in situ from Layers V, III and II [ 1 ]. Layer I yielded a total of 50 stone artifacts, only brief descriptions of which are published.

Charcoal from basal Layer VI ( Fig 1 ) yielded a 14 C age of 1708–1353 yr cal BP (I-9096) [ 1 ]. Glover obtained five 14 C determinations on shells of the freshwater gastropod Tylomelania (= Brotia) perfecta from underlying strata [ 1 ]. T. perfecta shells from Layers V, IV and II in the south wall of square G10 returned in-sequence ages (at 95% probability) of 27.7–27.3 ka cal BP (GrN-8293), 31.1–30.5 ka cal BP (GrN-8650), and 35.9–34.5 ka cal BP (GrN-8649), respectively [ 1 ]. Two additional 14 C ages on T. perfecta shells, one from the boundary between Layers IV and V (square H9), and another from Layer IIIa (square D10), yielded stratigraphically inconsistent ages of 32.6–31.4 ka cal BP (GrN-8292) and 24.9–23.6 ka cal BP (BM-1492), respectively [ 1 ]. No radiometric dates were obtained for Layer I owing to a lack of shell and other dateable materials.

Glover [ 1 ] traced Layer V across nearly the whole trench. However, underlying Layers IV, II and I were only identified adjacent to the rear wall, whereas Layers III and IIIa, also inferred to underlie Layer V, were only documented in square D10. The deepest excavations were in squares F10 (2.5 m depth) and D10 (3.6 m depth). Glover was unable to reconcile the Layers IV/II/I stratigraphy exposed below Layer V in F10 with the sediments (Layers III/IIIa) also seen to underlie Layer V in D10. A large roof-fall block in E10 prevented him from joining up these two squares and thus clarifying a key part of the stratigraphy. In squares F10-H10 and G8-G10, Layer I was exposed to a depth of about 30 cm and over a surface area of ~4 m 2 . The lower boundary of this deposit was not revealed.

From top to bottom, Glover’s [ 1 ] stratigraphic sequence ( Fig 5 ) is as follows–Layers X and IX and VIII: recent shallow pit fills and thin deposits; Layer VII: rubbish-filled sinkhole deposit (~80 x 40 cm, depth >2.9 m); Layer VI: a sterile red earth up to 1.5 m thick [ 1 ]; Layer V: a ~200 cm thick series of brown/grey-brown/red-brown lenses and discontinuous inter-fingering layers; Layer IV: a thin (<20 cm) deposit of loose shells in an ashy matrix; Layer II: a 20–30 cm thick chocolate brown deposit containing few shells; Layers III and IIIa: massive, poorly defined deposits of reddish brown to yellow sediment (III) and chocolate brown sediment (IIIa), both of which contained few shells; and Layer I: compact yellow-brown clay with negligible shell content.

Glover’s [ 1 ] work at Leang Burung 2 in 1975 involved the excavation of 1 m 2 units in a trench measuring 12 m in length by 1 m in width ( Fig 1 ). The trench (~15 m 2 ) extended southeast to northwest from near the rear wall to just past the dripline. The rearmost two squares adjacent to the wall were extended northeast, resulting in three additional 1 m 2 units.

( a ) Viewed from towards the front of the shelter, looking from west to east along the 2013 trench–the red arrow points to the main brecciated mass; the blue arrow points to the capping flowstone; ( b ) close-up view of the highlighted area shown in panel b .

A notable feature of Leang Burung 2 –and many cave and shelter sites in the Maros-Pangkep karsts–is the presence of cemented archaeological deposits, or breccias, attached to the rear wall of the shelter, as well as to speleothem columns and some large roof-fall boulders exposed on the surface (often at the dripline; [ 1 , 20 ]; see also [ 40 ]). On the rear wall of the shelter immediately adjacent to the excavated trench is a prominent bank of cemented breccias perched about 1.5 m above the present-day floor surface. This feature consists of a dense shell midden deposit capped by a thick layer of flowstone that slopes sharply downwards from the rear wall ( Fig 4 ). Nearby, remnants of midden-bearing breccias adhere to the rear wall of the shelter at heights of up to 4 m above the ground surface.

Leang Burung 2 is one of many sheltered areas at the foot of tall, precipitous limestone cliffs lining the western flanks of a ~270 m-high karst tower, part of the main hill mass forming the southern side of the Leang-Leang river valley where it abuts the coastal plain of Maros ( Fig 3 ). Located at the base of an 80 m high overhanging cliff face, the open, well-lighted site is 16 m long, 7 m wide, and about 20 m high, with a floor surface elevated 3 m above the level of the adjacent alluvial flats. The floor surface is marked by a large, shallow oval pit. According to Glover [ 1 ], this ‘robber’s hole’ was left by local people excavating phosphate-rich soil for sale as fertilizer, which took place in or around the year 1960.

The Dutch archaeologist, H.R. van Heekeren, visited Leang Burung 2 rock-shelter (called by him ‘Burung Cave’) in 1950, recording the presence of several hand stencils [ 31 ], and brecciated deposits on the rear wall that had been reported previously [ 38 ]. Thereafter, the karsts attracted little scientific interest until the Australian-Indonesian archaeological expedition to southern Sulawesi in 1969, led by J. Mulvaney and R.P. Soejono [ 35 , 39 ]. These researchers excavated Leang Burung 1, a cave site located 150 m from Leang Burung 2, revealing a 4-m-deep sequence of Holocene deposits. Glover, also a member of this expedition, conducted a single excavation season at Leang Burung 2 as part of his own Maros-based field research program [ 1 , 19 , 20 , 36 ], which concluded in the late 1970s.

The archaeological potential of the multitude of caves and shelters in the vicinity of the Leang-Leang valley in the Maros karsts had been noted since the early 1900s [ 29 ]. Subsequent work prior to the outbreak of WWII, and in the final years of the Dutch colonial period, led to small-scale excavations at several Leang-Leang sites and at other localities in nearby karst regions [ 30 – 32 ] (see [ 33 – 35 ] for reviews). These early investigations brought to light the first traces of the so-named ‘Toalean’ culture of Maros and surrounding districts [ 31 , 32 ]. The Toalean is a regionally unique industry of presumed middle to late Holocene antiquity that is characterized by backed blades, geometric microliths, and ‘Maros points’, small pressure-flaked projectiles with hollow bases and serrated margins [ 34 , 36 , 37 ].

The karst lies between 4°7'S and 5°1'S and is formed within the Early/Middle Eocene to Middle Miocene Tonasa Formation [ 27 ]. The topography of this extensive (~400 km 2 ) karst landscape is dominated by plateau-like hill masses formed by rivers cutting through intersecting joints in the limestone, and, in areas of advanced plateau dissection, classic steep-sided karst towers surrounded by alluvial plains that extend to the western coastline at an elevation of ~5 to 30 m a.s.l. [ 27 ]. The towers range from 1 to 10 km in diameter and 150 to 300 m in height. Extensive networks of footcaves developed around the bases as a result of subsurface weathering. These were exposed by lowering of the alluvial plains, or, alternatively, when uplift slowed or stopped long enough for laterally migrating rivers to undercut hillslopes [ 27 , 28 ].

The limestone tower karst region of Maros and the adjoining Pangkep district to the north are located on an alluvial plain close to the western shoreline of Sulawesi’s southwestern peninsula [ 27 ] ( Fig 1 ). Hereafter, we will refer to this karst landscape as a whole as Maros-Pangkep (or the Maros-Pangkep karsts), whereas individual karst valleys or regions (e.g., Maros) are named separately.

In 2007, in an initial effort to redress this issue, and as part of a wider program of research into the evolutionary origins and dispersal of the H. floresiensis lineage, the late Professor Michael ‘Mike’ Morwood’s team conducted the first excavations at Leang Burung 2 in over three decades. These pilot investigations were followed by three separate and larger scale excavation seasons at Leang Burung 2, carried out between 2011 and 2013. The objectives of this new research program at the rock-shelter were as follows:

Despite the potential of Leang Burung 2, however, and notwithstanding the enduring importance of this site in regional archaeological syntheses (e.g. [ 25 , 26 ]), most authorities have paid scant attention to the implications of the undated, culturally distinct occupation layer (Layer I) identified by Glover at the base of his 1975 trench (but see [ 18 ]).

The cultural horizon in Layer I, assumed by Glover [ 1 ] to pre-date 40 ka, could also provide the first clues for understanding what happened to Sulawesi’s ‘megafauna’ once modern humans were introduced to this insular island ecosystem, with its unbalanced and highly distinctive suite of Wallacean land mammals [ 2 , 3 ]. In the Walanae Depression, fossil-bearing strata of Early Pleistocene age have yielded remains of two distinct dwarfed or ‘pygmy’ proboscideans (Stegodon sompoensis and Stegoloxodon celebensis) and a large-sized Stegodon [ 22 , 23 ]. By the Middle Pleistocene, however, only two proboscideans seem to have existed on Sulawesi, a large to intermediate-sized Stegodon, and an advanced, high-crowned elephant [ 23 ]. No well-documented traces of these taxa had ever been found in the Maros karsts or in secure contexts outside the fossil record of the Walanae Depression, so it had remained unclear when and how these proboscideans–and the island’s other extinct endemic ‘megafauna’ taxa, such as the archaic suid Celebochoerus [ 24 ]–had met their demise.

Glover [ 1 ] did not recover any Pleistocene human skeletal remains from Leang Burung 2 –nor did his excavations reach bedrock or culturally-sterile archaeological deposits. Concerning the latter, his excavations clearly raised the possibility that deeper excavations at Leang Burung 2 might reveal important new insight into the early human settlement of Sulawesi. For instance, plumbing the depths of Layer I, and any intact Pleistocene strata below, could reveal not only whether pre-modern hominins had indeed reached Sulawesi, but whether this population persisted on the island for long enough to have encountered early modern humans, and when and why these hominins became extinct or locally extirpated.

It is also noteworthy that Glover’s [ 1 ] interpretation of the formation history of the site suggested that the Late Pleistocene deposit had been severely undermined by sink action, leading to significant slumping and deformation of archaeological layers across the excavated areas of the site. Glover’s work at Leang Burung 2, and wider research in Maros [ 19 , 20 ], led him to conclude that extensive disturbances of caves and shelters had rendered the karsts a very challenging, and perhaps unproductive, region from an archaeological perspective. This may be at least part of the reason for the long hiatus in research efforts by non-Indonesian archaeologists in the limestone karsts of Maros from the mid-1970s until the early 2000s [ 21 ].

Data source: Glover’s 1975 excavations [ 1 ], as reported by Clason [ 17 ]. Fauna codes: 1, Strigocuscus celebensis (ground cuscus); 2, Ailurops ursinus (bear cuscus); 3, flying fox; 4, Macaca sp. (macaque); 5, Homo sapiens; 6, Carnivora (unident.); 7, rodent; 8, Sus celebensis (Celebes warty pig); 9, Sus. sp; 10, Sus/Anoa; 11, Sus/babirusa; 12, Babirusa; 13, Anoa; 14, Sus/Babirusa/Anoa size (unidentified); 15, bear cuscus/macaque size (unidentified); 16, rodent size (unidentified); 17, bird (unidentified); 18, terrapin/tortoise; 19, reticulated python; 20, snake (unidentified); 21, fish (unidentified); 22, crayfish (unidentified). Clason’s [ 17 ] Table 1 lists Layer I and Layers IV-V as containing one and two Sus scrofa specimens, respectively. We follow Simons and Bulbeck [ 18 ] in regarding these identifications as implausible, and thus have included them in Clason’s [ 17 ] Sus celebensis tally for those layers. We also excluded Clason’s [ 17 ] "?" category, which dominates percentages for each layer. According to Table 1 in Clason’s [ 17 ] report, a single element attributed to Homo sapiens was identified in the Layer I faunal assemblage; however, this specimen is not described elsewhere in Clason’s [ 17 ] paper and there is no further reference in the literature to human skeletal material from Leang Burung 2.

Prior to these discoveries, the earliest record of a human presence on Sulawesi came from Ian Glover’s [ 1 ] excavations at the Maros rock-shelter Leang Burung 2 ( Fig 1 ). Over the course of a single field season at this site in 1975, Glover excavated a series of 1 x 1 m squares, with the deepest reaching a depth of ~3.6 m. Excavations were discontinued before bedrock or sterile deposits were reached. Glover’s [ 1 ] earliest radiometric determination– 35.9–34.5 thousand calibrated radiocarbon years before present (35.9–34.5 ka cal BP [GrN-8649])–came from a sedimentary unit overlying a deep and then-undated layer of compact, yellow-brown clay at the trench base, Layer I ( Fig 1 ). Immediately above Layer I, Glover [ 1 ] inferred the presence of a complex lithic technology (systematic macroblade manufacture) that, despite decades of subsequent research in Southeast Asia, remains unique in its temporal and regional context. Notably, excavations below this level in Layer I yielded cultural remains that contrasted sharply with those in overlying layers, inferred to span 31–19 thousand conventional 14 C years BP, which when calibrated is around 35–24 ka cal BP [ 1 ]. The stone technology was different, and the Layer I fauna was dominated by two endemic and still-extant large-bodied mammals that were rare to absent in overlying deposits: the dwarf bovid anoa (Bubalus sp.), and the babirusa (Babyrousa sp.) [ 17 , 18 ] ( Fig 2 ).

The antiquity of the Talepu artifacts implies that the first colonizers of Sulawesi were either Asian Homo erectus, members of the Homo floresiensis lineage, Denisovans, or an as-yet unknown group of archaic hominins [ 10 ]. Concerning H. floresiensis, it has been hypothesized that the founding population that gave rise to this endemic Late Pleistocene hominin of Flores originated on Sulawesi, and thus that hominin occupation of the latter island dates back at least several hundred millennia [ 11 ]. It follows that the Talepu tool-makers may have been close evolutionary cousins of H. floresiensis. Alternatively, recent work suggests our species had emerged in northern Africa by ~300 ka [ 12 ], while some archaeological and genomic data imply that H. sapiens was established in eastern Asia [ 13 ], and possibly Sunda (Java; [ 14 ]), by 120 ka (see also [ 15 , 16 ]. It is therefore at least conceivable, based on currently available evidence, that the early Middle Pleistocene inhabitants responsible for tool manufacture at Talepu were early members of our species that had dispersed from Africa and spread into Wallacea long before the Late Interglacial [ 10 ].

Two recent archaeological discoveries have brought the early human prehistory of Sulawesi to world attention. First, uranium-series (U-series) dating of coralloid speleothems overlying hand stencils and animal paintings in the limestone karsts of Maros, in the south of the island [ 7 ], demonstrated that Sulawesi’s rock art dates back to at least 40 ka [ 8 ], and is thus compatible in age with the world’s earliest dated cave paintings, at El Castillo in northern Spain [ 9 ]. Second, deep-trench excavations at the open site of Talepu in the Walanae Depression, a fault-bounded sedimentary valley in the interior of the southern peninsula ( Fig 1 ), revealed in situ stone artifacts in fossil-bearing strata dated to ~194–118 ka [ 10 ]).

Map of the Indonesian island of Sulawesi ( a ) showing the location of the Late Pleistocene rock-shelter site, Leang Burung 2 ( b ); the Holocene cave site, Ulu Leang 1, is located around 1.5 km to the north ( c ), plan view of Ian Glover’s 1975 excavations at Leang Burung 2; ( d ) stratigraphic profile of the south wall of the 1975 trench (redrawn from Fig 3 in [ 1 ]). Calibrated 14 C ages are reported at the 95% confidence interval.

Leang Burung 2 is a limestone rock-shelter site [ 1 ] on the Indonesian island of Sulawesi, the largest and oldest island within the oceanic archipelago (‘Wallacea’) separating continental Asia (Sunda) from the Pleistocene low-sea level landmass of Australia-New Guinea (Sahul) ( Fig 1 ). This Wallacean island, renowned for its unique biodiversity and particularly high rate of species endemism, for instance among mammals [ 2 , 3 ], is generally assumed to have been a key stepping-stone on one of the two most likely early human dispersal routes from the edge of Sunda to the northern fringes of Sahul [ 4 ]. Modern humans (Homo sapiens) may have made first landfall on Sulawesi by 50,000 years ago (50 ka) [ 5 ], and perhaps by as early as 65 ka [ 6 ], based on early colonization dates for Australia.

Results

Our pilot excavations at Leang Burung 2 in 2007 involved emptying backfill from squares E10 to G10 of the 1975 trench, where Glover [1] had obtained the oldest 14C date from the site and where he had traced Layer I to its deepest point ~2.6 m below the surface in the adjacent square F10. In 2011–13, our excavations below this level revealed the base of Layer I for the first time. Further deep-trench excavation over the course of these field seasons succeeded in extending Glover’s deepest excavated square (D10) from 3.6 m to 6.2 m depth (Fig 6). Excavations in 2011–13 also provided the opportunity to recover lithic and faunal assemblages from the uppermost strata and to evaluate Glover’s interpretation of the time depth of this distinctive occupation sequence. We will describe the results of the latter research first, then move to a discussion of our investigation of Layer I and underlying strata.

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larger image TIFF original image Download: Fig 6. South wall stratigraphic profile at Leang Burung 2 (2011–13 excavations). The South Wall section illustrated here comprises a composite of two separate stratigraphic exposures, the southern trench faces of excavation squares E10-I10 and A11-E11, respectively, which are situated a distance of 1 m apart. With regards to 14C ages, all of the dated samples comprise freshwater gastropod (Tylomelania perfecta) shells; only dated shells collected in situ from the deposit are shown projected onto the stratigraphic profiles. The sampling locations for pIRIR samples LB2-OSL12 (Layer A) and LB2-OSL13 (Layer B) are not illustrated on the south wall profiles because they were collected from different trench faces. https://doi.org/10.1371/journal.pone.0193025.g006

Archaeological and paleontological assemblages excavated from Leang Burung 2 in 2007 and between 2011 and 2013, and which form the basis of the current study, are under the permanent curation of Indonesian authorities at Pusat Penelitian Arkeologi Nasional (ARKENAS) in Jakarta and Makassar Balai Arkeologi. The material is available for analysis. Requests to access material for study, including databases and catalogs of finds, should be directed to the directors of ARKENAS and Balai Arkeologi Makassar.

Depth, age, and cultural contents of Layer I Based on our excavations in 2007 and 2011–13, it now evident that Glover’s Layer I is a massive weathered soil profile that is at least 3 m thick and which accumulated against the rear wall of the rock-shelter and atop a >2 m-high pile of limestone roof-fall slabs and angular blocks at the front of the shelter (Fig 6). Layer I directly abuts the rear wall of the rock-shelter from a depth of around 5 m to, essentially, the modern ground surface of the shelter. This deposit can be traced laterally from the shelter wall to the dripline. Near to the rear wall, this sedimentary unit is yellowish brown at the top and becomes conspicuously browner and more clayey with depth, with the former representing the weathered upper zone of the latter. The presence of clay-rich pockets or lenses within the upper zone is probably due to deposition in wetter conditions, leading to greater compaction of the sediments. Layer I contains large amounts of small, highly fragmentary bones and teeth, but very few stone artifacts. A sandy yellow interval at the base of Layer I adjacent to the rear wall contains a dense concentration of fossil fauna, including anoa molars and a near-complete babirusa upper incisor. Layer I yielded a small assemblage of minimally reduced limestone and volcanic flakes. Ochre and shells, furthermore, are absent, and the faunal assemblages, while dominated by bone fragments from vertebrate mammals equivalent in size to macaques and A. ursinus, features relatively high proportions of remains from larger-sized animals, including diagnostic elements from babirusas and anoas. Remains from the latter mammals, the largest of the existing Sulawesian endemics, were distinctly rare to absent in overlying deposits, where the only large animal represented in significant quantities is S. celebensis. Importantly, excavations in Layer I also yielded the first evidence for the presence of extinct ‘megafauna’ at Leang Burung 2. A number of proboscidean molar fragments were recovered in situ below Layer V in square B10 (spits 18–19). The Layer I specimens represent six molar plate fragments, and a single plate (Fig 9), all from milk molars, judging from the limited enamel thickness (1.4–2.5 mm). The enamel is double layered, with the inner enamel layer about two-thirds or more of the total enamel thickness. In longitudinal cross-section, the plates were clearly not wedge-shaped, and this characteristic, combined with the relatively thin outer enamel layer, suggests that the milk molars belong to a member of the genus Elephas or Palaeoloxodon, and not to Stegodon. The height of the largest fragment amounts to 32 mm, giving an indication of the minimum crown height. The base of the single plate is not preserved, so the degree of hypsodonty could not be established. To our knowledge, the proboscidean molar fragments from Layer I represent the only published evidence available thus far for the presence of proboscidean fauna in association with stone tools and other human occupation remains in an excavated cave or rock-shelter deposit on Sulawesi. PPT PowerPoint slide

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larger image TIFF original image Download: Fig 9. Elephantinae (genus and species indeterminate) molar plate fragment excavated from Layer I at Leang Burung 2. Scale bar is 10 mm. https://doi.org/10.1371/journal.pone.0193025.g009 Below, we report the results of our efforts to obtain a reliable chronology for the Layer I cultural horizon and associated findings.