Supplementary Information for

Title: When did Homo sapiens first reach Southeast Asia and Sahul?

Authors: James F O’Connell, Jim Allen, Martin AJ Williams, Alan N Williams, Chris SM Turney, Nigel A Spooner, Johan Kamminga, Graham Brown, Alan Cooper

Corresponding author: James F O’Connell Email: [email protected]

This PDF file includes: Supplementary text Figs. S1 to S4 Table S1 References for SI reference citations

Supplementary Information

SI.1 Hominin fossils

SI.1.1 – Background notes

Four species of Homo are identified on the South -Sahul arc (1). Defining characteristics include aspects of body size, skeletal robusticity, and cranial anatomy.

H. erectus (2,3). This is a widespread taxon, known from parts of Africa, Europe, North China, and Java, and dated from 1.8 Ma to the late Middle Pleistocene (<200 ka). Postcranial anatomy is relatively robust; estimated height and weight are within the modern human range. Crania are defined by a low vault, receding frontal, prominent brow ridges, moderate post-orbital constriction, and occipital angulation. Brain sizes are estimated at 700-1200 cc. Examples from Java are well represented in deposits dating 500-1000 ka. Some may have been present there as early as 1.6 Ma (4,5). Terminal dates as recent as 143 ka are cited for Javanese populations (6). Persistence to the time of anatomically modern human (AMH) arrival is possible but disputed (7,8). Skeletal and archaeological evidence indicates a presence on Flores >1.0 Ma (9,10); archaeological evidence suggests the same on Sulawesi >200 ka (11). Other interpretations, one involving Denisovans on Sulawesi, are also plausible (12).

H. floresiensis (13). This is an insular dwarf known from deposits on Flores dated 60-100 ka (13,14). Brain size is estimated at c. 425 cc.; height 100-109 cm; weight 30-41 kg. Appendicular proportions differ significantly from those of H. erectus and later humans. Homo sp. teeth from c. 0.7 Ma, also on Flores, are similar in form and size to those of H. floresiensis, suggesting long- term taxonomic and locational continuity (10). Derivation is attributed to early H. erectus (10,15) or H. habilis (16,17), the former being more parsimonious. The >66 ka metatarsal from Callao, assigned to Homo sp. and widely referenced as a small-bodied H. sapiens, might represent H. floresiensis or a similarly dwarfed insular collateral (18).

Archaic H. sapiens (19-21). Fossils assigned to this category are also called Late H. erectus, H. heidelbergensis, or pre-modern H. sapiens. They combine H. erectus-like features, including a

1 www .pnas.org/cgi/doi/10.1073/pnas.1808385115

massive, forwardly projecting supraorbital torus, thick cranial walls, and great basal breadth, with derived traits, including an endocranial capacity of >1200 cc, a relatively steep (non- receding) frontal, and a relatively rounded occipital. Dated East Asian specimens are Late Middle Pleistocene in age, roughly 100-400 ka. It is uncertain whether they reflect an in situ evolution of Asian H. erectus or are the product of Middle Pleistocene (>400 ka) introgression with African or European H. heidelbergensis (22). They may represent Denisovans (23). Examples are reported from China and SE Asia (e.g. Dali, Jinniushan, Maba [19]; more recently Xuchang [22]) but are so far not known from Sunda or areas further east.

H. sapiens (24). Also called anatomically modern humans (AMH). Some characteristic attributes are known from Africa by 160-195 ka (25,26) and are recently reported there as early as 300 ka (27). A broader list of attributes are known from Southwest Asia at 100-130 ka (28,29) and are recently reported there as early as 177-194 ka (30). Strictly defined, AMH are identified in Africa before 50 ka, are widespread across the Eastern Hemisphere after 50 ka, and present in the Americas after 15 ka (31). They are identified by a high, rounded neurocranium, basicranial flexion, small face retracted under the frontal bone, true chin, and small, discontinuous brow ridges. Early East and Southeast Asian and Australasian examples include Tam Pà Ling (TPL 1, ), Niah Deep Skull (Borneo), and WLH 1, 3 (). They may date earlier in South China and Southeast Asia but that is uncertain (see below).

SI.1.2 - SCS arc fossils, dated 40-120 ka, said by some to represent H. sapiens

SI.1.2.1 China

Bailian (32). Published in Chinese, with English abstract. Two hominin teeth identified as H. sapiens; overlain by flowstone dated 160 ka via U-series. Dennell (1) is skeptical of both the identification as H. sapiens and the estimated age.

Fuyan (33,34). Forty-seven teeth, dated 80-120 ka, said to be “more derived than any other anatomically modern humans, resembling middle-to-late specimens and even contemporary humans” (33).

Specimens were recovered from a sandy clay (Layer 2) associated with remains of a Late Pleistocene fauna, some elements of which are extinct. U-series dates on eight speleothem fragments in the same layer range from 120-557 ka. One non-human bone from the same layer yielded a calibrated radiocarbon date of 42-43 ka. A stalagmite purportedly rooted in overlying Layer 1 yielded two U-series dates, said to indicate a minimum age of 80 ka for the underlying component and its contents. Liu et al. (33) reject the 14C date, citing technical limits of the laboratory that provided it. They favor the 120 ka U-series speleothem determination over the seven others and conclude that the human teeth in Layer 2 fall in the range 80-120 ka.

Michel et al. (34) observe that the Layer 2 sediments are “suggestive of extensive fluvial activity … which raises the possibility that the deposits are reworked and actually comprise materials from different time periods.” The 42-43 ka radiocarbon date, the wide range of associated speleothem dates, and the derived quality of the teeth are consistent with this possibility. Michel et al. question whether the stalagmite from Layer 1 actually pertains to that component, rather than to underlying Layer 2. They also note that it is at least 15m away from any of the teeth, raising further questions about its relationship with the latter. They regard as inadequate

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the appeal to faunal correlations as an additional basis for the 80-120 ka age-estimate. They conclude that the teeth may date from “the latter half of the Late Pleistocene or even more recently.”

Ganquian (Tubo) (35). Published in Chinese, with English abstract. Seventeen hominin teeth identified as H. sapiens; bracketed by flowstone layers dated 94-220 ka via U-series. Dennell (1) accepts an age estimate of c. 100 ka but is skeptical of assignment of the teeth to H. sapiens.

Huanglong (36,37). Sample includes seven human teeth from multiple individuals. Comparative analysis (36) shows that most of their morphological and metric features resemble those of modern H. sapiens: “Generally speaking, the Huanglong human teeth look gracile and lack the archaic features usually identified on Middle and Late Pleistocene humans. [This] study also indicates that the Huanglong Cave human teeth already possess some dental features of modern East Asian populations.”

The teeth were recovered from the lower portion of a red silty clay (Layer 3) in association with stone artifacts, non-human faunal remains, and dark, carbon-rich patches read as the remains of anthropogenic fires. Liu et al. (36) appeal to sediment clast size, lack of evidence of bone or artifact rounding, and the presence of the carbon patches as evidence that Layer 3 contents including human teeth are in primary context, not re-deposited from another location.

Layer 3 dates originally reported from rhinoceros teeth (U-series 79.4 ± 6.3 ka, 94.7 ± 12.5 ka; ESR 34-44 ka) and a stalagmite (U-series, c. 103 ka) were seen as potentially unreliable (36,37), the former for methodological reasons, the latter because of uncertainty about sample provenience relative to the human teeth. Subsequent U-series analyses of the thin, patchily distributed flowstone capping Layer 3 yielded a date of 28 ka. Flowstones in the upper part of Layer 3 were pegged at 32-45 ka; those in the mid-lower part of Layer 3 at a composite 81.4 ± 1.1 ka. The latter estimate is seen by Liu et al. (36) as a minimum date for the human teeth. The weighted mean of three samples underlying the teeth is 101 ± 1, indicating a maximum age for the teeth; hence, the bracketing age estimate of 81-101 ka. Bae (38) is cautious about whether teeth are in primary context, citing possible fluvial or rodent disturbance. Dennell (1) expresses similar concerns. As at Fuyan, the derived quality of the teeth encourages this skepticism.

Laibin (Gaitou) (39,40). The term Laibin applies to a set of hominin remains collected from Gaitou Cave in 1956. They consist of three disconnected pieces, probably once part of the same individual, including “a nearly complete hard palate with several teeth and the adjoining lower part of the body of the maxilla, a large part of the right zygomatic, and an occipital fragment” (40). They were identified by Jia and Wu (39) as H. sapiens based on a “lack of distinct archaic features.” Dennell (1) favors a date of 39-44 ka.

All skeletal parts were recovered from a sandy clay layer, capped by a thick flowstone. Two U- series dates on that flowstone have a weighted mean of 38.5 ± 1.0 ka. Two dates on thinner, less extensive flowstones within the sandy clay, said to underlie sediments where the fossils were located, have a weighted mean of 44.0 ± 0.8 ka. U-series dates on several non-human bone fragments distributed across this sequence fall in the Holocene and were rejected on methodological grounds. Hence, the estimated bracketing ages of 38-44 ka for the human fossils.

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Liujiang (41,42). An anatomically modern human cranium and post-cranial remains were recovered in 1958 by miners working in Tongtianyan Cave. Taxonomic identification of the cranium as H. sapiens is not disputed but its original stratigraphic position is uncertain. Discussion in Shen et al. (41) favors recovery from a “refilling breccia” bracketed by flowstones dated by U-series at 68 ka and 153 ka, respectively. Analysis of calcites deposited within the breccia is said to suggest a date of 111-139 ka. Assignment of the fossil to an underlying sandy clay layer would indicate a date >153 ka. An age estimate of >68 ka may be appropriate but concerns about fossil provenience remain critical.

Longtanshan (43,44). Two hominin teeth. Curnoe et al. (44) report that comparative morphological and metric analyses indicate ”strongest affinities to anatomically modern humans.” U-series ages on a single non-human bone found in the same stratigraphic component are 64 ka and 83 ka, respectively. Analyses of bone from underlying components yielded five estimates in the range 60-81 ka, 60 ka stratigraphically the lowest. Curnoe et al. place the ages of the hominin teeth at 60-83 ka. Chronology is clearly problematic.

Luna (45). The sample includes two teeth, one “confidently” identified as H. sapiens, the other “likely,” both based on specimen robusticity. Martinón-Torres et al. (46) are skeptical of these assignments. Both teeth were recovered from sandy clay sediments (Level 3), probably underlain by a flowstone layer U-series dated at 126.9 ± 1.5 ka, and at about the same depth or slightly above a second flowstone dated at 70.2 ± 1.4 ka. Bae et al. (45) place the fossils at 70- 127 ka but their stratigraphic diagram suggests an age close to 70 ka. Discussion of the dating also suggests unresolved problems in analysis marked by inconsistencies between age estimates and stratigraphic position. Their report also refers to a dozen stone artifacts recovered in the overlying stratum (Level 2), which appears to be of Holocene age.

Zhiren (47,48). Human remains from this location consist of a mandible fragment and two isolated teeth representing two, possibly three individuals. The mandible fragment represents a relatively small individual with both modern and archaic human features. It has a chin but is relatively robust by modern human standards. Teeth are comparable to West Eurasian Late Pleistocene H. sapiens but the connection with modern humans in south China is not clear. Kaifu and Fujita (49) and Dennell (1) are skeptical of an H. sapiens assignment, preferring a Late H. erectus designation, but Martinón–Torres et al. (46) support it.

U-series analyses of flowstones overlying the sediments from which fossils were recovered yielded age estimates in the range 28-106 ka, the former date taken to represent a minimum age for the fossils. Associated faunal remains were seen to suggest an early MIS 5 or late MIS 6 date; hence the original estimate of 100-113 ka for the fossils. Subsequent paleomagnetic analyses (48) suggest an adjusted estimate of 106-116 ka.

SI.1.2.2 Laos

Nam Lot (50-52). This is a single incisor assigned to H. sapiens, recovered from a fossiliferous breccia in a depositionally complex cave deposit. Bacon et al. (52) suggest that the tooth might be better identified as Pongo. Bacon et al. (51) estimate the age of the tooth via luminescence and U-series analyses of the deposit contents at 46-72 ka. Barnes’ (50) OSL analysis of the deposit suggests a range of 46-50 ka.

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Tam Pà Ling (53-56). The sample includes remains of five individuals recovered from the base of a 65m slopewash deposit inside a cave. All are in secondary context, having originated at or near the cave entrance. All are relatively well preserved.

Two specimens (TPL 4-ribshaft, TPL 5-hallucal phalanx) are Homo sp. indet.; others are described as H. sapiens. TPL 1 is a partial cranium; TPL 2 and 3 are complete and partial mandibles, respectively. All represent relatively small individuals. TPL 1 is fully modern in form; TPL 2 and 3 display a mix of modern and archaic human characteristics. Archaic markers include bone thickness, robusticity, and overall shape. Demeter et al. (55) see this as a range of variability “typical of early modern humans in Southeast Asia at a relatively early time period.”

Dating is based on a combination of 14C, luminescence and U-series techniques. Direct U-series dates on TPL 1 and 2 are said to be minima: >63 ka and >36-44 ka, respectively. “Neither [sample] provided the opportunity for U-series profiling to establish the integrity of the result” (55). The TPL 1 date was originally reported as 63.6 ± 6 ka and identified at the time as a maximum age for the specimen (53).

Luminescence dates on sediments bracketing TPL 1 are 33 ± 3 ka (above) and 43 ± 7 ka and 46 ± 4 ka (below); a 14C date of 51.4 ka is reported above the skull, leading to Demeter and associates’ (53) original age estimate of 46-51 ka. This 14C date is now reported as >40 cal ka (55). For TPL 2, the luminescence dates are 43 ± 7 ka and 46 ± 4 ka (above), 46 ± 5 ka and 46 ± 6 ka (below); for TPL 3, 48 ± 5 and 70 ± 8 ka (both above [55,56]). Authors conclude that TPL 1-3 were deposited toward the early end of the range 46-70 ka (55). Apart from the unconstrained 63 ka U-series estimate for TPL 1, the ”early end” qualification seems unwarranted. TPL 1, the critical fossil from this site, might well date 40-50 ka, the same age as the sediments from which it was recovered. The U-series date on the fossil itself is highly questionable, given the lack of information on its original depositional context and the observation that bone is not a closed system for purposes of U-series analysis (57).

SI.1.2.3 Borneo

Niah (58,59). A partial cranium (Niah Deep Skull) and some post-cranial elements were recovered in 1958 and identified as H. sapiens. That assignment remains unchallenged. Subsequent excavations beginning in 2000 were aimed at establishing the original stratigraphic position of the fossils and producing a reliable age estimate. Dating analysis is based on mainly on 14C; details are presented by Barker et al. (58) and Higham et al. (59). Results suggest an age range of 39-45 ka for the cranium, although Hunt and Barker (60) prefer a slightly younger estimate. Archaeological remains from the site may be as old as 50 ka.

SI.1.2.4 Java

Punung (61-63). This is a human premolar recovered from a fossiliferous breccia in south central Java. Storm et al. (61) assigned the tooth to H. sapiens based on its small size relative to a sample of H. erectus. Originally given an estimated age of 81-126 ka, the associated fauna was subsequently dated by luminescence and U-series analysis at 118-143 ka, indicating a Last Interglacial (MIS 5e) arrival of H. sapiens on Java (62). Assignment of the tooth to H. sapiens has been challenged by Polanski et al. (63), who demonstrate a long-term diachronic size reduction in the posterior teeth of Javan H. erectus, ending in overlap with H. sapiens. The Punung

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premolar falls in the zone of overlap and is non-diagnostic with respect to the sapiens/erectus distinction. Kaifu et al. (64), Barker et al. (58), and Bacon et al. (65) are skeptical of both the assignment to H. sapiens and the MIS 5 date.

SI.1.2.5 Sumatra

Lida Ayer (also called Lida Ajer) (66). Two teeth from this location are both labeled H. sapiens on the basis of size and morphology. Analyses of enamel thickness and the enamel/dentine junction morphology may be the strongest evidence in support of this assignment (24).

The teeth were recovered by Dubois (67) from a fossiliferous breccia discontinuously distributed in a small cave. However, they were not recognized as human until Hooijer (68) revisited Dubois’ fossil collection in the late 1940s. The breccia is a secondary deposit; contents were washed in from elsewhere. Analyses of various components of the breccia by luminescence, U-series and combined U-series/ESR produced a composite age estimate of 63-73 ka. The relationship between recently dated sediments and fossils recovered more than century ago was established by reference to Dubois’s detailed field notes and is thought by the team involved to be reliable. They may be right but there is room for skepticism on this point, if only because of the length of time that passed between initial recovery and identification of the fossils as human and the still later assessment of the recovery point(s). The lack of discoloration relative to other teeth thought to have been retrieved from the same sediments (66, Fig. 3) underlines this concern.

SI.1.2.6

Callao (Luzon) (18,69). Specimen is a human metatarsal; small in size, gracile in structure; similar in form and size to modern small-bodied H. sapiens, H. habilis, and H. floresiensis. Assignment to H. sapiens may be the simplest reading but Morwood and van Oosterzee (70) prefer H. floresiensis.

The fossil was recovered from a breccia containing remains of other fauna. Two cervid teeth from this deposit were dated by U-series at 52 ± 1.4 ka and 54.3 ± 1.9 ka, respectively; one of these was also dated via combined ESR/U-series at 66 + 11/-9 ka. The human metatarsal itself was dated by combined ESR/U-series at 66.7 ± 1.1. All dates are regarded by Détroit et al. (69) as minima. Caution about U-series dates on bone is advised, but the 66.7 ka minimum is widely accepted (71). Grün et al. (72) report U-series analysis of a “human” tooth (species not stipulated), possibly from the same breccia (no detail provided), as follows: "The age calculations indicate an age of around 50 ka, somewhat younger than the U-series results obtained on a small human foot bone, but essentially the same as the U-series data from faunal teeth from the site [noted above, citing ref 18].” Reconsideration of the dating of all human remains from this site appears to be in order.

Tabon (Palawan) (69,73-76). The latest report on this site (76) refers to several hundred human remains from a “highly disturbed and reworked” context. Attention is drawn to the 14 specimens described so far, all attributed to H. sapiens. “Preliminary results of the anthropological analysis of the whole collection tend to confirm the presence of two morphotypes, one small and gracile and one large and robust, which seems to be difficult to explain by sexual dimorphism in a single population only” (75). One undated mandible fragment

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is characterized as being larger and more robust than any Southeast Asian H. sapiens but similar to regional H. erectus.

Three specimens assigned to H. sapiens have been dated via U-series analysis: a complete frontal at 16.5 ± 2.0 ka, a mandible fragment at 31.0 + 8.0/–7.0 ka, and a tibia fragment at 47.0 + 11.0/–10.0 ka. As above, caution about U-series dates on bone is in order.

SI.1.2.7 Sahul

Willandra (77-83). Two specimens from this location are of particular interest: WLH 1 is a small- bodied young adult, partially cremated; WLH 3 is a near-complete, anatomically modern human, formally interred and covered in red ochre. Both are unambiguously assigned to H. sapiens. Comprehensive analysis of the sedimentary context indicates burial ages of c. 40-42 ka for both individuals. Alternative age assessments of 60-100 ka for WLH 3 (79,82) have been rejected (cf. 57). Archaeological remains are abundant in surrounding sediments.

SI.1.3 - Summary

Fossil identification as H. sapiens. Assignment to H. sapiens is most confidently made by reference to cranial material. On that basis, WLH 1&3, Niah, Tam Pà Ling 1, Liujiang, and Laibin are all anatomically modern. Other assignments to H. sapiens, based on teeth – an important part of the sample – are problematic in that they refer primarily to specimen size (H. sapiens smaller, archaic forms larger/more robust). Not much is known about late Middle and Late Pleistocene changes in East and Southeast Asian hominin teeth confidently assigned on cranial form to erectus or archaic sapiens, including possible Denisovans. Late examples of these taxa could have dentitions that fall in the modern human size range, regardless of any connection with H. sapiens populations. Questions raised about the Punung tooth as H. sapiens illustrate the problem. Identification of at least one tooth each from Zhiren, Longtanshan, and Luna can also be challenged in this ground. Assignments made by reference to post-cranial remains (Callao, Tabon) are similarly problematic. However, the identification of two Lida Ayer teeth as H. sapiens is based on more comprehensive, probably more reliable criteria, and so is not as readily disputed as the Chinese samples.

Dates. Age estimates >50 ka are derived mainly via U-series analysis. Particularly important is the direct 63 ka date on Tam Pà Ling 1. This fossil is definitely anatomically modern and might be of about the same age as 40-50 ka context from which it was recovered. It could also be older. The question is whether the 63 ka date is reliable. We are skeptical. U-Th ratios in bone may be affected by exchange of U with the environment, complicating their relationship with age in the absence of analytic control.

Relationships between dated flowstones and the human remains they are said to bracket. The lack of attention to taphonomy at most of these sites is striking, since it has been at the heart of many important archaeological controversies over the last 40 years (84). It may well be that depositional processes were more complex in the sites at issue here than authors of the basic reports recognize or acknowledge, and that the link between fossils and sediments is less certain than they claim. This is the basis for published skepticism about the purported ages of very modern looking teeth from Fuyan and Huanglong. Parallel issues are apparent where there is

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uncertainty about fossil recovery points relative to dated sediments. Liujiang, Longtanshan, and Laibin have all been questioned on this ground; Lida Ayer might be as well.

SI.2

SI.2.1 Brief history

Madjedbebe, originally in the literature as Malakunanja II, is a rock shelter in the Arnhem Land region of north Australia. It was first excavated in 1973, as was another rock shelter in the region called Nauwalabila (85) c. 65 km south of Madjedbebe. In 1981 Nauwalabila was re- excavated (86) but the deepest deposits yielded insufficient material to provide radiocarbon dates at that time, although 14C dates were subsequently produced by Bird et al. (87) – see below. Both sites, Nauwalabila and Madjedbebe, were re-excavated in 1989 to obtain luminescence dating samples. Three thermoluminescence (TL) dates for Madjedbebe, KTL-164, 45 ± (6, 9) ka, 230-236 cm below surface; KTL-158, 52 ± (7, 11) ka, 241-254 cm, and KTL-162, 61 ± (9, 13) ka, 254-259 cm were interpreted as demonstrating occupation of this site between 50 ka and 60 ka (88). These dates were later refined using optically stimulated luminescence (OSL) but did not change significantly (89). The claim, which extended human occupation in Australia by 10-20 kyr, provoked initial critical debate (e.g. 90-94) concerned with dating techniques, dating precision, and site formation processes. Subsequently Nauwalabila was dated using the OSL, with initial occupation bracketed between OxODK168, 53.4 ± (4.4, 5.4) ka and OxODK169, 60.3 ± (5.8, 6.7) ka (95).

Despite the general age agreement between these sites, an Australia-wide re-investigation of previously excavated old sites using OSL, together with the use of OSL to date new sites, failed to reproduce ages approaching those claimed for these two Arnhem Land sites. Of relevance, where paired dates were available, luminescence and 14C ages were mostly very similar. The corpus of pre-Last Glacial Maximum (>20 ka) Arnhem Land sites now includes two shelters with large protective overhangs. Malangangerr (96), c. 10 km from Madjedbebe, was re-dated by TL (KTL-126) to 32 ± (7, 9) ka, 192-201 cm below surface (88). Nawarla Gabarnmang (97-99), about 100 km southeast of Madjedbebe on the Arnhem Land escarpment, has a covered surface area of c. 360 m2 and has yielded an earliest AMS 14C date of 47.2 – 51.7 ka.

Suggestions to explain the continuing age mismatch settled on post-depositional termite bioturbation as a likely cause (100). This argument was advanced for Nauwalabila only, since at that time the 1989 excavation of Madjedbebe remained unpublished.

We review the bioturbation argument in SI.2.2.

Subsequently, soil particle size analysis for Nauwalabila was undertaken to question the termite bioturbation theory (87). While the results were inconclusive, the same analysis yielded small pieces of charcoal continuing to the bottom of the site. When subjected to AMS 14C dating, using intensive pre-treatment methods, the results were chronologically incoherent, with the bulk of the samples below 180 cm depth yielding ages around 10 ka. Bird et al. (87) argued that these fragments had been pervasively altered and contaminated by fluctuating groundwater levels. However, detracting from this argument, these authors also acknowledged that some charcoal samples were unaltered, still exhibiting their woody structures, and that these provided similar

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ages to the altered pieces. They concluded (87, p 1070-1071) that these pieces had travelled down termite galleries.

Importantly, these tests included three new 14C AMS samples from Madjedbebe, two from 149 cm depth and one from 254 cm depth. All three returned ages similar to the deep Nauwalabila samples, ranging between c. 11.9 ka and 16.7 ka. These were also considered aberrant, perhaps reflecting an unspecified “regional phenomenon” (87, p 1074).

While the recent excavations at Madjedbebe occurred in 2012 and 2015, the first detailed account of the stratigraphy and artifacts from the 1989 excavation only appeared in 2015, authored by the new excavation team (101). In supporting the original age claims for this site, these authors argued that artifact depths originally pegged at 252 cm below surface could now be extended to 280 cm below surface (see Fig. S3 below) and that at this depth could be bracketed by the TL dates KTL-162, 61 ± (9, 13) ka and KTL-141, 65 ± (10, 14) ka, 215-295 cm below surface (101, p 53). The authors also offered an OSL age estimate of 55.5 ± 8.2 ka for KTL- 162, following Roberts et al. (89).

The integrity of the stratigraphy was argued on various grounds, including the appearance and disappearance of raw materials at different depths and associated technology. The logic of the argument that mixing would have blurred raw material pulses and technological transitions is opaque, particularly in a site where local quartzite and quartz are present throughout the sequence and together account for c. 87% of the total assemblage. Silcrete (4% of the assemblage) occurs in the lower half of the sequence, where it was “only selected for use from the earliest occupation until just after the LGM” (101, p 53) – a period on the authors’ 2015 chronology of c. 30 kyr.

Reliance was also placed on a “pit” containing artifacts at 235 cm below surface. Also referred to in 2015 as a “lens,” it is considered by the original excavators and Clarkson et al. (101, p 57) to be anthropogenic in origin and evidence for the intactness of the lower deposits. We consider it reflects dripline erosion and argue this in SI.2.3.3.

In considering both these 1989 excavation results and the 2012 and 2015 excavations reported in Clarkson et al. (102), our focus here is on the earliest occupation data and claims stemming from them.

SI.2.2 Site location: taphonomic and bioturbation factors

Madjedbebe is situated about 12o south of the equator and c. 60 km inland from the current northern Australian coast. The dominant vegetation is tropical savanna, with the current annual rainfall c. 1250 mm. The main landscape elements comprise a large sandstone plateau flanked on the west by plains and floodplains with seasonal freshwater swamps. The junction between these landforms is the Arnhem Land escarpment, marked by outlier buttes and rock formations that were once part of the plateau. Madjedbebe is at the base of a large outlier called the Djawumbu Massif. The site faces northwest and currently provides little shelter from the elements. Clarkson et al. (101) indicate a depth of 5 m inside the dripline and excavation suggests only 1-2 m additional depth at the time of initial occupation, assuming that the 2015 estimation did not include this.

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Depending on the time of initial occupation, lower Late Pleistocene sea levels resulted in the absence or severe reduction of local estuarine/floodplain resources, with the coastline much further away than now. This raises questions about the possible functions of a site at this locality through time. Clarkson et al. (102) contend that dense artifact bands reflect different periods of intense site use centered on 59 - 65 ka, 13 - 27 ka and the Holocene estuarine phase of 7 ka to the present. During the earliest of these periods the coast was c. 300 km distant and the local climate dryer than at present; during the LGM the coast was further away and the region colder, much drier and windier than today (103).

SI.2.2.1 Impact of termites and erosion on soils and sand sheets in the seasonally wet tropics

Colluvial-alluvial sand sheets are common in the seasonally wet tropics of Africa, Australia and South America and overlie older rock formations that have undergone multiple cycles of Cenozoic deep weathering and erosion (104). The sand sheets can be many meters thick and are often interstratified with stone layers. The climate in these regions is highly seasonal, with one dry season and one wet season. The wet season decreases from about nine months’ duration near the equator to a few months in higher tropical latitudes. Annual precipitation varies from >1,500 mm to <500 mm and supports a savanna vegetation of trees, shrubs, and both perennial and seasonal grasses. Sub-surface stone layers are common in tropical Africa, Asia, and South America as well as in the sub-tropical Piedmont region of the . They have been variously attributed to soil creep; burial of stony colluvium, alluvium or erosional lag gravels; to slope retreat; to the swelling of clay soils; and to termite activity (104,105). Mound-building termites are ubiquitous in these landscapes and play a major role in soil turnover, topsoil replenishment, and the formation of subsurface stone layers (104-108).

Cahen and Moeyersons (109) and Moeyersons (110) demonstrated how initially sporadic Paleolithic stone artifacts within the Cenozoic Kalahari Sands of tropical Central Africa can become consolidated into a buried stone layer. They used laboratory experiments and direct observation to show that creep and termite activity acting together can destroy the original stratification of stone artifacts within a creeping mantle of unconsolidated sand. More recently, McBrearty (111) has reviewed evidence of post-depositional disturbance of other archaeological sites in Africa caused by termite activity. The question then arises whether a similar set of processes could also be operating in the seasonally wet tropics of northern Australia.

SI.2.2.2 Erosion and termite activity west of Arnhem Land, tropical northern Australia

Among the various agents of erosion active in this region (103, 112), four in particular will interfere with the stratigraphic integrity of any archaeological site in the area. These are rain splash erosion (113), subsurface lateral eluviation (114), creep (115), and termite activity (105,106).

Falling raindrops may embody up to a thousand times more kinetic energy than the equivalent volume of runoff (116). Rain splash erosion is particularly effective at the onset of the wet season, before a protective cover of annual grasses has been established, with up to 40 times more soil loss (for the same unit momentum of rain) on slopes of 1-2 % in November-December than in February (113,117). The net effect is detachment and removal of the finer soil particles, leading to compaction. Subsurface lateral eluviation is a neglected but highly effective process in loose sandy soils, where soil water moving downslope causes removal of finer soil particles

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below the surface, resulting in further compaction (114,118). Creep is downslope movement of soil and sediment under the influence of gravity and is active throughout this region even on very gentle slopes. Creep rates monitored during 23 years between 1965 and 1988 on 12 sandstone slopes and 13 granite slopes showed that creep was volumetrically only slightly less effective as an agent of downslope soil movement than the combined effects of rain splash and runoff and was significantly more rapid on soils prone to disturbance by termites (115, 119). Surface lowering by raindrop impact and runoff (overland flow) amounted to 54 ± 40 mm/kyr on low-angle weathered granite slopes and to 56 ± 30 mm/kyr on weathered sandstone slopes. Corresponding rates for creep were 18 ± 12 mm/kyr on granite and 11 ± 9 mm/kyr on sandstone. Slope angles ranged from 1% to 12%. Downslope movement (DM) of 480 surface stone on 24 sandstone slopes ranged from 2 to 20 mm/yr and was proportional to the sine of the slope angle α (DM = 10.263 sin α – 0.109) (120).

Northern Australia has over 150 species of termites and they play a major role in savanna ecosystem dynamics (121). They are ubiquitous in this region and are particularly active during the wet season, when they build and repair their mounds. Collapse of termite galleries promotes creep, as does any form of physical or biological disturbance, including wetting and drying, and plant root growth and decay. The mining activities of termites result in widespread stone layers. Termites avoid poorly drained and waterlogged sites, and stone layers are not found in such localities (Fig. S1a-b). Monitored rates of termite activity in this region are far from negligible (105, 106). In the case of Tumulitermes hastilis, for example, at one site on the Brocks Creek granite intrusion there were 500 mounds/ha, of which 42% were defunct. Defunct mounds were eroded within three years. Mean mound solid volume (excluding voids) amounted to 4000 cc. This species removed 0.48 m3/ha/yr from the subsoil. Eroded mounds add 0.3 m3/ha/yr or 30 mm/kyr to the soil surface. Another species, Nasutitermes triodiae, had mean mound solid volumes of ca. 3 m3. When eroded, these mounds add 0.2 m3/ha/yr to the topsoil or 20 mm/kyr.

Stone layers can form in several ways. Removal of sand particles finer than 2-3 mm will lead to downward movement of any surface stones or stones within the soil profile. In deeply weathered rocks with veins of quartz or pegmatite, removal of particles <3mm in size will ultimately lead to the creation of a buried stone layer. On the granite soils studied by Williams (105,106), the stone layers were up to 0.5 m thick and lay beneath a surface layer of coarse sand 0.15-0.3 m thick, formed as a result of mound erosion. At current rates of surface erosion and mound growth and decay, a stone layer 0.3 m thick will take 11,500 to <17,000 years to develop. Stone layers formed through termite activity in Australia and Africa are often associated with three-layered soils consisting of a surface horizon of sand, a stone layer, and a weathered parent rock (104,105). The buried stone layers extend across the landscape irrespective of surface topography (Fig. S1c).

In archaeological sites (Fig. S2a), consolidation resulting from creep and termite activity will eventually lead to lateral and vertically downward displacement of stone artifacts to form a concentrated stone layer (Fig. S2b). Single grain optically stimulated luminescence (OSL) ages of sand grains within such a layer may show a broader dispersion range and will not necessarily provide reliable ages for the stone artifacts.

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Fig. S1 (a) The Brocks Creek granite intrusion, Northern Territory, Australia. Area A is poorly drained, has no termite mounds and no buried stone layer (105, Fig. 5.1; 117, Fig. 7.7). Area B is well drained, has abundant termite mounds, and a buried stone layer. (b) Soils developed on poorly drained and seasonally-waterlogged slopes underlain by deeply-weathered granite. Note the absence of termite mounds and of any stone layers. The soils are developed on the same deeply weathered granite intrusion as in (a), and so have the same parent material and local climate. The only difference is topography and associated poor drainage. Should stream channel incision occur, leading to better soil drainage, then termites would colonize this area and a buried stone layer would develop within a few thousand years (105, Fig. 5.4b; 117, Fig. 7.15). (c) Soils developed on well-drained slopes underlain by deeply-weathered granite. Note the presence of termite mounds and stone layers. The termites mine the deeply- weathered granite and bring to the surface quartz particles up to 3 mm in size together with silt and clay to build their mounds. Once abandoned, the mounds are soon eroded, the finer particles are washed downslope, a sand mantle up to 30 cm thick develops at the surface, and the vein quartz particles within the weathered granite become concentrated at the top of the granite weathering profile into a buried stone layer up to 50 cm thick (105, Fig. 5.4a; 117, Fig. 7.12).

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(a)

(b)

Fig. S2. (a) Sporadic prehistoric stone artifacts within a sandy matrix at the foot of a sandstone rock shelter. The sand mantle is derived from the sandstone bedrock as a result of physical and chemical weathering which is relatively rapid in this seasonally wet tropical environment. If there was no disturbance from plant roots, soil creep, mechanical eluviation and termite activity, this pattern of sporadic artifacts distributed within a sand mantle would persist. (b) Prehistoric stone artifacts concentrated in a basal stone layer as a result of soil creep, subsurface lateral eluviation, and termite activity. Downslope movement of sand-sized particles under the influence of soil creep, eluviation and disturbance by burrowing termites leads to sediment compaction and subsidence of the coarser particles and formation of a stone layer near the base of the sand mantle.

SI.2.2.3 Physical evidence of disturbance at the Madjedbebe site, tropical northern Australia

At the Madjedbebe site, the surface slope can be estimated from the contours shown on Clarkson et al. (102, Fig. 1c), and amounts to ca. 2%, which is enough to promote both creep and subsurface lateral eluviation during the wet season. The buried “indistinct stratigraphic boundaries” shown in Extended Data (ED) Fig. 1a are often somewhat steeper, so that prior phases of creep cannot be excluded. ED Fig. 2a shows a concentration of artifacts downslope. Fig. ED 8f indicates that the lower four OSL samples occur in a band of consolidated sand. The most likely agents of such compaction are creep and termite activity.

In their treatment of the Madjedbebe geoarchaeology, Clarkson et al. (102, SI section 10) describe (but discount) widespread evidence of disturbance within the sand mantle at the site. Clay coatings around quartz sand grains, charcoal fragments impregnated with clay stained red by hydrated iron oxides, reworked particles of soil, and plant roots are all common throughout the sand mantle. The presence of the clay raises the question of where it might have come from. A likely source is clay and silt derived from the disintegration of defunct termite mounds. Termites do not build their nests and mounds exclusively from sand or they would lack coherence. Sampled mounds contained 9-16% silt-sized particles and 20-35% clay-sized

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particles. Sand content ranged from 48% to 67%. Clay content on very gentle granite slopes in this area increases in the subsoil downslope as a result of subsurface movement of clay-sized particles (105, p 137). In thin section the illuvial (re-deposited) clay layering is very evident. Subsurface lateral eluviation (removal) of fine soil particles is an important process in this region. Some of these fine particles are washed away in runoff. Some are washed down through the sand by eluviation until they either are washed out downslope or accumulate as illuvial clay coatings on sand grains and within porous charcoal fragments.

The published stratigraphic sections at Madjedbebe (102, ED Figs. 1, 2 and 8) are entirely consistent with disturbance from creep, termites, lateral eluviation and rain splash erosion. In loose sandy soils, such disturbance will lead to consolidation of the sand column and concentration of the stone artifacts. However, once former termite galleries become closed as a result of creep, there will be few visible traces of this type of disturbance after the lapse of even a few years. Even so, current termite activity is visible in the immediate vicinity of Madjedbebe and noted within the site.

SI.2.3 Artifacts

During the 2012 and 2015 seasons Madjedbebe was excavated to a maximum depth of 3.4 m without encountering bedrock (102). The lowest sands (Phase 1) are identified as sterile, with human occupation said to begin in Phase 2, defined both by a thick artifact layer and also using an age phase model for the OSL dates. The latter provided a depth zone 215-260 mm below surface at the front of the site and 190-230 mm nearer the shelter wall*. Phase 2 is dated between the modelled mean start and end ages of 65.0 ± (3.7, 5.7) and 52.7 ± (2.4, 4.3) ka. While this possible range is large, the authors argue for “around 65 ka” or “conservatively 59.3 ka” for human arrival; 65 ka has been taken up as the promoted age within and beyond the scientific community (e.g. 122-124).

As far as can be determined from the published data, the two measures used for the beginning of human occupation, the age-phase zone and the lowest thick artifact unit, are not the same thing. Indeed, the latter appears on available evidence to be contained within the former (Fig. S3). While we recognize that conflating three-dimensional data on two-dimensional diagrams can lead to ambiguities, currently the available data impede any clear understanding of site formation processes.

Beyond this, five other aspects of artifact distribution in the site promote concern.

*Information supplied by Clarkson et al., contained in email, H.Gee to A. Cooper, March 10, 2018.

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Fig. S3. The stratigraphic relationship of Madjedbebe Phases 1 and 2 constructed by us from data in Clarkson et al. (101; 102, especially ED Fig. 1a, ED Fig. 2a; 125, Appendix N; attachment in email H. Gee to A. Cooper, March 10, 2018). “Lowest artifact 2015” refers to 2015 analysis of 1989 excavation data. Hearth and pit features on this figure are discussed in text.

SI.2.3.1 Artifact disposition

Clarkson et al. (102) argue that human occupation begins in Phase 2 of the Madjedbebe sequence, noting on multiple occasions that Phase 1 is sterile or contains just a few artifacts.

Published data exist for only two of the 20 excavated squares, where Squares B6 and C4 together contain 143 artifacts in Phase 1 (102, SI Tables 13 and 14). This suggests that there are likely to be at least many hundreds of artifacts in Phase 1. Clarkson et al. (126) variously suggest that Phase 1 artifacts may reflect anthropogenic pits dug from the lowest occupation layer, post-depositional displacement, or even in situ earlier occupation of Madjedebe.

Anthropogenic pits appear to be improbable since Phase 1 artifacts are located across most of the excavated area (102, ED Fig. 2a). If the excavators believe that these artifacts are possibly in situ and that first occupation could date to between 72.9 - 87.4 ka and 65.4 -76.6 ka, why is this not explored in text? Lastly, if these artifacts are the product of post-depositional displacement

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up to 70 cm below the base of Phase 2, what displacement vectors might be responsible, and why did they cease to operate in Phase 2 and above?

SI.2.3.2 Artifactual stone lines

Clarkson et al. (102) describe the artifacts occurring in three distinct bands at depths of 2.15 - 2.60 m, 0.95 - 1.55 m and 0.35 - 0.70 m. The lowest, in Phase 2, is said to contain >10,000 stone artifacts (102, p 309). While the authors contend that these bands reflect different periods of intense site use centered on 59 - 65 ka, 13 - 27 ka and 0 - 7 ka, they are equally consistent with post-depositional physical and biological movement, as described in SI.2.2.3, above. Multiple stone lines were encountered but not recognized as such in Nauwalabila (86, p 174) where stone layers, distributed across the extent of the excavation, were only a few centimeters deep. While the clusters of Madjedbebe artifacts as defined have a deeper spread across the majority of the excavated squares, those in Phase 2 in particular reflect a much tighter vertical distribution. Artifacts were plotted in three dimensions in the 2012 Madjedbebe excavation but non-artifactual rocks were not, so evidence which might have further tested the stone line hypothesis is lost.

SI.2.3.3 Dripline influence

Clarkson et al. provide two stratigraphic drawings (102, ED Figs. 1a and 2a) where artifacts from the B and C (roughly east-west) rows of squares are projected onto the south-western wall. These show an unusual distribution. The rows extending out from the wall of the shelter indicate artifact concentrations near the shelter wall (Rows 1 and 2) and in Row 6 and the northern half of Row 5, which together show many artifacts and concentrated rock fall. Rows 3 and 4, in between, have many fewer artifacts. The base of this conglomeration of artifacts and rocks in rows 5 and 6 is shown as a short, steep slope in ED Fig. 1a and as a 20 cm step in Fig. ED 2a. This gutter and the accumulation of rocks and artifacts above it mark the wet season dripline, identified in Square B6 by Clarkson et al. (101, p 47; 102, p 307).

Clarkson et al. explain the dearth of artifacts from B4 and the southern half of B5 as the result of the 1989 finds not being plotted on this diagram. However, this does not account for fewer artifacts in Row 3, nor the apparently small number of artifacts in C4 and C5, adjacent squares to B4 and B5, that were piece-plotted and projected onto the diagram, nor the contrast between a “low” artifact density in C5 and the much higher density in C6, both shown in Fig. S4.

Given the intensity of wet season rain (113, Fig. 2) and rock deposition from the cliff above, the positional integrity for artifacts and OSL dating samples from this part of the site must be considered low. Even so, many more artifacts in this zone than in the shelter further question whether this reflects site maintenance with secondary deposition into the dripline gutter and possibly beyond. Data from this region of the site should be treated cautiously.

SI.2.3.4 1989 pit

As noted, the 1989 excavation covered the area of squares B4 and the south-eastern half of B5, just missing the dense deposits at the front of the site (102, ED Fig. 1a). In the western corner of this 1989 square the excavators described a pit disappearing into both the north-western and south-western walls (101, Figs. 3 and 4) and shown on Fig. S3. As noted, reliance was placed on

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the anthropogenic origin of this pit as evidence for site integrity; but given its location at 235 cm depth below surface, the c. 20 cm depth of this feature and its comparability to the dripline “step,” and that its contents comprise a “dense concentration of artifacts and rocks,” this feature appears to be an edge of the larger dripline feature exposed by the 2015 excavation.

Fig. S4. Madjedbebe artifact densities (artifacts per liter of deposit) for six excavated squares (126). Note that scales differ for each square.

SI.2.3.5 Artifact density distributions

Clarkson et al. (126) provide artifact densities for six of the excavated squares (Fig. S4). In five of them artifact densities in Phase 2 (shown by red lines) far exceed subsequent phases. Only the dripline affected square B6 is different.

Given that Madjedbebe is represented as continually (if not continuously) occupied through the Late Pleistocene and Holocene and allowing that stone artifact densities are frequently taken as a proxy for population densities, the notion that human population densities (or even merely stone artifact densities) were highest at the time of initial settlement appears improbable and unlike the pattern regularly seen at other early Australian sites where earlier levels normally contain many fewer artifacts than later ones (e.g. Devil’s Lair [127]). Such an unusual pattern does not even occur at the disturbed Nauwalabila site (86, Table 9.4). Indeed, for this whole region Jones (128, pp 291-293) emphasized that Holocene population increase and transformation took place as rising sea-levels eventually created local freshwater swamp

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environments. Before this, he argued, population density was low and perhaps sporadic and seasonal.

We conclude that the disposition of the stone artefacts in Madjedbebe reflects their post- depositional downward movement.

SI.2.4 The ages of distinctive artifact types at Madjedbebe

The chronology, evolution and function of unifacial and bifacial stone points, mostly from north Australia, has been a long-term focus of extensive research in Australia (129). There is debate as to whether unifacial and bifacial points are one type or two and whether they might have performed functions other than being hafted projectile points, their widely implied or argued function (130). However, it is almost universally accepted that points are a mid- to late- Holocene age artifact type (e.g. 131,132) with only Cochrane and Doelman (133) suggesting that two bifacially flaked pieces from late Pleistocene contexts (<20 ka) in Kenniff Cave, Queensland, might be points.

Clarkson et al. (101, p 55-56; 102, p 307) identify points and thinning flakes, sometimes argued to be the debitage of point production, in Madjedbabe Phase 2, c. 60 kyr before the accepted appearance of points in Australian sequences. This seems improbable (132).

Clarkson et al. (101, p 53; 102, p 307, Fig. 2a, ED Fig. 4)) identify “edge ground hatchets” (a.k.a. “ground-edge axes”) from Madjedbebe Phase 2. Geneste et al. (98) provide a global summary of information on this implement type, noting examples from various sites in northern Australia, including Arnhem Land, dated >20 ka. The oldest, dated c. 35 ka, is from the Arnhem Land site of Nawarla Gabarnmang, where initial occupation dates to c. 50 ka (99). Hiscock et al. (134) identified a ground axe fragment from the Carpenter’s Gap 1 site in Western Australia, dated to 44-49 ka. Similar ground-edge axes are reported from at c. 38 ka (135), while all other examples from Eurasia date <30 ka. This makes the claimed examples from Madjedbebe Phase 2 >15 kyr older than any known from elsewhere in what was then Pleistocene Sahul, >25 kyr older than the Japanese examples, and >40 kyr older than all but a handful reported from anywhere else in the world.

Clarkson et al. (102, p 307) report three stone grinding tools from Phase 2, two of which (GS 39; GS 73) have wear patterns or residues consistent with plant processing. Seed processing is mentioned specifically. This finding is unexpected, since seed processing is a labor-intensive exercise. Experimental and ethnographic data indicate returns on the order of 500-600 kcal/hr, an order of magnitude lower than those available from plant foods that require less intensive handling. The implication is that seeds in particular should enter the human diet only when other, more profitable resources are unavailable, either as a function of habitat characteristics or because of competition from other consumers (136). The Sahul archaeological record is consistent with this expectation. Evidence for high cost plant exploitation in the form of specialized grinding tools is a Late Holocene (<5 ka) phenomenon that tracks indicators of sharp population growth all across the continent (137,138). Exceptions to this generalization are very limited (139, cf.140).

Clarkson et al. (101, p 55-56) observe that the Phase 2 assemblage is unique, never having been

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reported in Sahul at such great antiquity. This is true but equally anomalous. Such an industry at this age has been reported from nowhere else in the world, and we argue that these data more likely result from post-depositional movement in the site.

SI.2.5 Further proposals for site integrity

In addition to data already addressed above, Clarkson et al. (102) offer several other propositions to defend the integrity of the site. These include claims for an in situ hearth in Phase 2, lithic raw material distributions, conjoin analysis, and the distribution of burnt artifacts. We briefly address each of these.

SI.2.5.1 Phase 2 hearth C1/43A

A hearth in Phase 2 would offer support for stratigraphic integrity in this early part of the deposit, but to date no descriptive evidence has been provided to evaluate this claim. Although a doctoral thesis has been written on the anthracology of the Madjedbebe hearths (125) it contains little stratigraphic information or descriptions of the hearths.

As far as can be inferred, older hearths were not distinguished on form but rather as localized clusters of charcoal fragments (102, SI.10, p 75). Hearth C1/43A is said to measure only 10 cm by 10 cm, suggesting that it can only be such a cluster and not a hearth per se (102, SI.6, Table 19). Nineteen pieces of charcoal were recovered of which 13 pieces were identified to six taxa, mostly Acacia sp. (102, SI.6; 125,126).

Two questions emerge on the available data. The first concerns the location of this hearth at c. 260 cm below surface (see Fig. S3), data taken from Carah (125, p 418, Appendix N). This feature, claimed to be in Phase 2 (102) actually occurs in Phase 1 and in this part of the site it is >40 cm below the dense layer of artifacts that defines first occupation archaeologically. This denies the anthropogenic of this feature.

The second matter concerns the fact that the charcoal in this feature has not been dated by radiocarbon. Clarkson et al. (126) indicate that a sample from this feature did not survive pre- treatment, although how many pieces of charcoal comprised this sample is unclear. We find it puzzling that two-thirds of the 19 charcoal pieces remained sufficiently structurally intact to allow taxonomic identification but cannot be dated.

SI.2.5.2 Lithic raw material distributions

In SI.2.1 (above) we questioned the logic that argues that change in raw material percentages through time must reflect site integrity. Raw material sources can change in many ways over thousands of years of intermittent site occupation and such sequence changes do not deny post-depositional movement. Clarkson et al. (102, SI.4, p 47) propose the opposite, suggesting that post-depositional movement might be expected to result in even distribution of raw materials down the sequence. Why?

Clarkson et al. (102, p 307) claim that the Phase 2 assemblage is “mostly from quartzite, silcrete, mudstone and dolerite;” that in the Phase 4 assemblage “quartzite is rare and quartz is abundant;” and that in Phase 6 raw materials are “dominated by quartz and chert.” Statistical

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tests indicating non-random distributions of raw materials (102, SI.4, p 48) are based on incorrect data, now withdrawn (126) although these authors argue that the correct data yield the same statistical results.

Table S1 shows the percentage distributions for raw materials in the three squares for which data are available. Commenting on the Clarkson et al. distributional claims we can note that for Phase 2, as for the site as a whole, quartz (not “quartzite, silcrete, mudstone or dolerite”) is everywhere dominant except for the 1989 Square B4-5. Quartzite, silcrete and mudstone are certainly more prevalent in Phase 2 than in the younger phases, but also differ proportionately between squares, suggesting localized variability in the array as much as changed cultural behavior through time. For Phase 4, quartzite is not “rare,” there being 379 pieces in square B6 and 71 in C4, while for Phase 6 quartz dominates, but not chert, which is present only in small percentages throughout the site and with the lowest percentages in Phase 6.

Quartzite Quartz Chert Silcrete Mudstone Volcanic Phase 6 B4-5 3.3 95.3 1.4 0 0 0 B6 0.8 98.5 0.3 0.1 0.0 0.3 C4 1.3 98.2 0.4 0.0 0.1 0.0

Phase 4 B4-5 10.4 83.7 3.1 1.2 0.3 1.3 B6 7.9 88.9 1.3 1.8 0.1 0.0 C4 2.4 90.6 3.2 0.6 0.1 3.1

Phase 2 B4-5 46.2 37.8 1.5 12.1 1.8 0.6 B6 24.7 69.5 2.2 2.8 0.2 0.6 C4 20.9 55.8 4.4 11.7 3.9 3.3

Table S1. This table combines three types of quartzite and two of quartz to align with the Clarkson et al. (102) text and shows the percentage distributions of raw materials for three Madjedbebe squares using Clarkson’s et al. (101, Table 2; 102, SI 4) data and categories. Note that dolerite is not listed in the Clarkson et al. (102) data, explaining why it is absent here.

These data cannot be read as support for the stratigraphic integrity of Madjedbebe (nor the opposite).

SI.2.5.3 Conjoin analysis

Clarkson et al. (102, p 307) report three conjoins from Phase 4 and 14 from Phase 2. Only silcrete was used for this analysis. Without sample numbers it is difficult to assess these data, but since the three squares reported in Table S1 yielded 704 silcrete artifacts this would suggest that conjoins were infrequent. The observation to make about conjoins is that while vertically 20

separated conjoin pieces suggest post-depositional disturbance, the opposite is not true because conjoining pieces may move post-depositionally in unison. In this instance eight of the 17 conjoins are vertically within 10 cm of each other and nine are not; four are within 20 cm of each other, three are between 25 cm and 30 cm and two are in excess of 40 cm apart (102, ED Figure 6b). This is in a site where OSL samples SW4C and SW5C, 8 cm apart, overlap at 2sd but differ in their central tendencies by 10,000 years.

The conjoin data set is small and offers no support for the integrity of the site.

SI.2.5.4 Burnt artifacts

Lastly, Clarkson et al. (102, p 307) point to the higher abundance of burnt artifacts in Phases 2 and 4 to suggest that this patterning implies site integrity. Without the available data this claim cannot be assessed but it seems likely that proportionally burnt artifact numbers are merely tracking overall increased artifact abundance in these phases.

SI.3 References

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