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Quaternary Science Reviews 28 (2009) 2897–2912

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Quaternary Science Reviews

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Homo floresiensis and the late Pleistocene environments of eastern Indonesia:defining the nature of the relationship

K.E. Westaway a,b,*, M.J. Morwood b, T. Sutikna c, M.W. Moore d, A.D. Rokus c, G.D. van den Bergh b,R.G. Roberts b, E.W. Saptomo c

a Department of Environment and Geography, Faculty of Sciences, Macquarie University, NSW 2109, Australiab GeoQuEST Research Centre, School of Earth and Environmental Sciences, University of Wollongong, Wollongong, NSW 2522, Australiac Indonesian Centre for Archaeology, Jl. Raya Condet Pejaten No. 4, Jakarta 12001, Indonesiad School of Human and Environmental Studies, University of New England, Armidale, NSW 2351, Australia

a r t i c l e i n f o

Article history:Received 5 February 2009Received in revised form29 July 2009Accepted 31 July 2009

* Corresponding author. Tel.: þ61 2 9850 8429; faxE-mail address: kira@els.mq.edu.au (K.E. Westawa

0277-3791/$ – see front matter � 2009 Elsevier Ltd.doi:10.1016/j.quascirev.2009.07.020

a b s t r a c t

Evidence from Liang Bua, a limestone cave on the island of Flores in East Indonesia, provides a uniqueopportunity to explore the long term relationship between hominins and their environment. Occupationdeposits at the site span w95 ka and contain abundant stone artefacts, well preserved faunal remainsand evidence for an endemic species of hominin: Homo floresiensis. Work at the site included detailedgeomorphological and environmental analysis, which has enabled comparisons to be drawn betweenchanges in the occupational intensity in the cave, using stone tool and faunal counts, and changes in theenvironmental conditions, using the characteristics of the sedimentary layers in the cave and speleothemrecords. These comparisons demonstrate that H. floresiensis endured rapidly fluctuating environmentalconditions over the last w100 ka, which influenced the geomorphological processes in the cave and theiroccupational conditions. The intensity of occupation in the cave changed significantly between 95 and17 ka, with peaks in occupation occurring at 100–95, 74–61 and 18–17 ka. These correlate with episodesof channel formation and erosion in the cave, which in turn correspond with high rainfall, thick soils andhigh bio-productivity outside. In contrast, periods of low occupational intensity correlate with reducedchannel activity and pooling associated with drier periods from 94 to 75 and 36 to 19 ka. This apparentlink between intensity of hominin use of the cave and the general conditions outside relates to theexpansion and contraction of the rainforest and the ability of H. floresiensis to adapt to habitat changes.This interpretation implies that these diminutive hominins were able to survive abrupt and prolongedenvironmental changes by changing their favoured occupation sites. These data provide the basis fora model of human–environment interactions on the island of Flores. With the addition of extra data fromother sites on Flores, this model will provide a greater understanding of H. floresiensis as a unique humanspecies.

� 2009 Elsevier Ltd. All rights reserved.

1. Introduction

Asia is a key region in hominin dispersals out of Africa (Dennelland Roebroeks, 2005), and the wealth of new discoveries on thiscontinent in the last decade confirms its significance, e.g., Dmanisi,Georgia (Gabunia et al., 2000), Longuppo, China (Huang et al., 1995)and Riwat, Pakistan (Dennell et al., 1998). Indeed, rather than justbeing a recipient of new species, Asia may well have encouragedspeciation events and directed dispersal back into Africa (Dennelland Roebroeks, 2005).

: þ61 2 9850 8420.y).

All rights reserved.

The Asian continent contains dynamic and often violent land-scapes and environments. For example, the Indonesian archipelago(Fig. 1) evolved on an actively converging plate margin, where theEurasian Plate subducted the Indian Plate creating extensivevolcanism (Simandjuntak and Barber, 1996; Westaway et al., inpress-a) and a region of tectonically uplifting landscapes(Simandjuntak and Barber, 1996; Kopp et al., 2006). In addition, thepresence of the Indo Pacific Warm Pool (IPWP) (Fig. 1) and themovement of the Intertropical Convergence Zone (ITCZ) (Tapper,2002) created a dynamic climatic zone, which was significantlyaltered during glacial periods causing a reduction in rainfall,expansion in grasslands, contraction in rainforests and the expo-sure of the Sunda Shelf (Nanson et al., 1992; Johnson et al., 1999;van der Kaars et al., 2000; Wyputta and McAvaney, 2001; De

mailto:kira@els.mq.edu.auwww.sciencedirect.com/science/journal/02773791http://www.elsevier.com/locate/quascirev

Asia

Solo River

Pacitan

Ngandong

Punung

East Java West Flores

0 100 km

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Ruteng

Liang Bua

0 40 km

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GunungSewu

Sangiran

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Domed front

chamber

Limestonecave walls

Wide entrance and dripline

Sinkhole

Sinkhole

Passage Small cave

Rounded

rear

chamber

d

Fig. 1. The Indonesian archipelago (a) showing the location of western Flores and eastern Java (dashed boxes). The dark shading represents the limits of the Indo Pacific Warm Pool.(b) Eastern Java showing the location of Punung (triangle) within the Gunung Sewu karst mountains (dashed line), (c) Western Flores showing the location of Ruteng and Liang Bua(triangle). The main focus of this research is Liang Bua, but a sample for palaeoclimate analysis has been collected from a cave site near Punung in East Java. (d) A plan view of LiangBua showing the location of the conglomerate deposits at the rear of the cave (dark shading), the flowstone and stalagmite accumulations (medium shading), and the surroundinglimestone cave walls (light shading). The dashed line denotes the boundary between the front and rear chambers (Westaway et al., in press-a,-b) and the dotted line marks thedripline at the present cave entrance. The Sectors excavated from 2001 to 2004 are shown as boxes containing Roman numerals. The four arrows refer to the four main connectionsto other caves in the system. (Fig. modified from Morwood et al. (2004, 2005)).

K.E. Westaway et al. / Quaternary Science Reviews 28 (2009) 2897–29122898

Deckker et al., 2002). This presented a number of environmentalchallenges to humans attempting to occupy or disperse throughthis region, such as violent volcanic eruptions, changing habits,

long sea crossings and rising and falling sea levels. The extent ofthese environmental and tectonic changes during the last 3.5 Mahas been largely ignored, and little attention has been paid to the

Table 1A chronology and average rate of sedimentation for each of the main sedimentaryunits in Liang Bua based on the chronological results and supporting evidencepresented in Roberts et al. (in press). The slowest sedimentation occurs during thedeposition of pool deposits by the east wall. Note that there is no sedimentation ratefor the conglomerate unit as it was deposited in one depositional event and thensubsequently reworked.

Unit Description Age (ka) Sedimentationrates (mm/ka)

8 The younger occupation level andmodern slopewash

w11–3 326

7 Volcanic sediments w16–12 4286 The occupation level containing

the skeletonw18–17a 750

5 The eroded and reworked conglomerate w50–40 3004 Channel sediments by east wall w55–50 2003 Occupation level capped by flowstone w74–61 1422 Collapse material w100–95 1901 Basal cave sediments w130–100 70

a Recent excavations at Liang Bua indicate that the disappearance of Homo flor-esiensis and Stegodon from the sequence coincided with a volcanic eruption atw17 ka, not w12 ka as previously interpreted.

K.E. Westaway et al. / Quaternary Science Reviews 28 (2009) 2897–2912 2899

environmental factors that aided or impeded dispersal or occupa-tion (Dennell, 2004). Few archaeological studies in Asia haveexamined changes in hominin use of sites within the context of theprevailing environmental conditions, and essential Quaternaryresearch in this region has been limited (Flenley, 1997; Dam et al.,2001). Reconstructions of the climates and environments ofwestern Flores, Indonesia (Fig. 1c) (Westaway et al., in press-a,-b)have revealed their complexity, and the potential role that theymay have played in influencing the timing of human arrival andpatterns of dispersal through Indonesia.

Liang Bua is a large limestone dissolution chamber in westernFlores (Fig. 1d) that contains cultural deposits spanning the lastw95 ka, with abundant stone artefacts and faunal remainspreserved within a complex stratigraphic record (Morwood et al.,2004, 2005; Westaway et al., in press-b). This record includesevidence of occupation between 95 and 17 ka (Morwood et al.,2004, 2005, in press; van den Bergh et al., in press) by a small-bodied, endemic species of human, Homo floresiensis (Morwoodet al., 2004, 2005). This discovery was made east of Wallace’s Lineon an isolated island, which has never been connected to the Asianor Australasian mainlands. This isolated location suggests that non-modern hominins were more capable of adapting to Indonesia’senvironmental challenges than was previously thought possible.However, the extent to which this diminutive species was influ-enced by its environmental conditions will remain unclear until theenvironmental data from this region (e.g., Westaway et al., in press-a,-b) is directly compared to the archaeological evidence.A comparison of this manner will greatly contribute to our under-standing of this new species of human and the nature of the rela-tionship between hominins and their environments in SoutheastAsia.

In this paper, we aim to define the nature of the relationshipbetween H. floresiensis and its Pleistocene environment bycomparing: 1) the sedimentary record (Morwood et al., 2004, 2005,in press; Westaway et al., in press-b); 2) the intensity of humanoccupation inferred from stone tool (Moore et al., in press) andfaunal counts (bone and teeth) (van den Bergh et al., in press); and3) environmental reconstructions from both inside (Westawayet al., in press-b) and outside the cave (Westaway et al., 2007a, inpress-a). These data sets have already been presented elsewhere,but in this paper we aim to synthesise this evidence to provide thefirst preliminary comparison of environmental and cultural datawithin this region and establish a solid foundation for furtherdetailed assessments of Late Pleistocene human–environmentinteractions.

2. Materials and methods

Archaeological excavations in Liang Bua (Fig. 1d) revealedsections that were cleaned, drawn, described and sampledaccording to the methods described in Morwood et al. (2004, 2005,in press) and Westaway et al. (2007a, in press-a,-b). Archaeologicalmaterials, such as stone tools and bone, found within 10 cmsections (spits) from each excavation were cleaned and recordedaccording to techniques described in Moore et al. (in press) and vanden Bergh et al. (in press). In the laboratory, we analysed thecharacteristics of the sediments using a Malvern Mastersizer 2600and a Phillips X-ray diffraction unit (Westaway et al., in press-b). Toreconstruct the climatic changes occurring within the IPWP regionduring a w40 ka period, we analysed two contemporaneous spe-leothem samples collected from western Flores and eastern Java(SP22 and SPJ3) for the d18O and d13C values from calcite layersaccording to the methods described in Westaway et al. (2007a, inpress-a). A chronology for the O and C records was constructedusing precise thermal ionisation mass spectrometry (TIMS)

U-series ages as described by Zhao et al. (2001). The calcite layerswere also scanned to determine the tonal intensity and the amountof organic material present according to the techniques of West-away et al. (in press-b) and the principles of Xia et al. (2001). Inaddition, the palaeoenvironmental signal contained within thestalagmite core from Java (SPJ3) was analysed using a fibre-opticprobe coupled to a Varian Cary Eclipse fluorescence spectropho-tometer (Drysdale et al., 2006; Westaway et al., in press-a), whichstimulates a fluorescence response from humic and fulvic acidslocked in the calcite (Baker and Genty, 1999). A chronology and agerange for the sedimentary units and the associated archaeologicalevidence (Table 1) was established by a combination of lumines-cence (red TL and single-grain OSL) dating, U-series, 14C andcombined ESR/U-series (Westaway, 2006; Westaway and Roberts,2006; Westaway et al., 2007b, in press-a,-b; Roberts et al., in press).

To enable a comparison of these data sets with the archaeo-logical evidence, the climatic and environmental data are plotted(according to the U-series chronology) against the stone and faunalcounts using the established chronology (using the above tech-niques) for each sedimentary unit. According to this chronologicalframework, continuous sedimentary sequences do not occur in thesections as a whole (revealed by sector excavations) due to theinterbedded nature of the deposits (Westaway et al., in press-b). Inaddition, the rate of sedimentation is known to differ between eachof the main sedimentary units (Westaway et al., in press-a, Table 1),however, within each unit the pattern of sedimentation is close tolinear. Thus, the artefact and faunal counts are plotted within thecorrect age range for each unit, using the specific sedimentationrate (Table 1).

3. Evidence for comparisons

3.1. The sedimentary record

The sediments in the cave are divided into two areas: the rearcave, comprised mainly of in situ and modified conglomerate andslopewash deposits, and the front chamber, consisting of deeplystratified sediments (Fig. 1d). Excavations in Sectors I, III, IV nearthe centre of the cave, and Sectors VII and XI close to the easterncave wall have revealed the structure of the deposits in the frontchamber, which have been described in detail by Morwood et al.(2004, 2005, in press). By correlating between deposits in the frontand rear chambers, a composite stratigraphy of eight main

K.E. Westaway et al. / Quaternary Science Reviews 28 (2009) 2897–29122900

sedimentary units was identified by Westaway et al. (in press-b).In order of age they consist of: 1) basal cave sediments, 2) collapsematerial, 3) occupation level capped by flowstone, 4) channeldeposits by the east wall of the cave, 5) reworked and erodedconglomerate, 6) occupation level containing the skeleton, 7)volcanic sediments, and 8) younger occupational level and modernslopewash (Fig. 2). According to the established chronology, theage of the sedimentary units extends from 110 ka up to present-day (Table 1) (Roberts et al., in press). Not all of these units are

NORTH EAST SOUTH WEST

0 2 4 6 m

0

2

4

6

8

0

2

4

6

8

NORTH EAST SOUTH WEST

0 2 4

0

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N

1 Basal sediments130-100 ka

2 Collapse material100-95 ka

3 Main occupation74-61 ka

4 Channelsediments

55-50 ka

1

2

3

8

1

2

37

8

mm

m

a b

c d

Fig. 2. The eight main sedimentary units in Liang Bua cave based on the sedimentary charashaded for clarity, the numbers correspond to the key (top left) and a chronology for each

found in each Sector, but, when chronologically combined, theyprovide evidence for a sequence of geomorphological and sedi-mentological events that influenced the cave environment and itshistory of occupation. Archaeological evidence found in theseunits suggest H. floresiensis occupied the cave from 95 to 17 ka(Morwood et al., 2004, 2005, in press), but to enable an assess-ment of the archaeological evidence within the context of thebroader environmental changes, the age range for this analysis hasbeen extended to 110–5 ka to incorporate a wider range of the

0

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NORTH EAST SOUTH WEST

1 2 3 m

ORTH EAST SOUTH WEST

5 Reworkedconglomerate

50-40 ka

6 Skeleton level18-17 ka

7 Volcanic sediments

16-12 ka

8 Younger occupation

and modern

slopewash

11-3 ka

8

1

3

7

6

4

6

7

8

m

54

5

cteristics of Sector I (a), Sector III (b), Sector IV (c), and Sector VII/XI (d). The units areunit has been included, based on the results presented in Roberts et al. (in press).

K.E. Westaway et al. / Quaternary Science Reviews 28 (2009) 2897–2912 2901

sedimentary (110–12 ka) and palaeoclimate evidence (47–5 ka). Afluvial conglomerate deposit, found at the rear of the cave,contains stone tools and has been discussed in detail by Westawayet al. (2007b). Although it provides evidence of occupation outsidethe cave due to its allogenic origin, this occupation occurred priorto cave exposure (at w190 ka) and is not within the age range ofthis study.

3.2. Intensity of human occupation

3.2.1. Faunal countsThe Liang Bua stratigraphic record contains a diverse fossil

faunal record that either represents animals that were living in thecave or that were brought into the cave by humans or other faunasuch as owls (van den Bergh et al., in press). In this respect, faunalremains can be consistently found throughout the sedimentcolumn, but these numbers generally increase when humans aredominant in the cave environment. For example, the horizontaland vertical distribution of large animal bones, butchery marks onsome of the bones and their association with artefacts and hom-inin skeletal evidence indicate that humans were responsible forthe accumulation of most of the bone (Morwood et al., 2004,2005; van den Bergh, in press). Therefore, the number of bonesfound in each sedimentary unit has been used as a crude estimateof the intensity of occupation in the cave. The use of these data inthis manner will be discussed further in a later section. The rawfaunal counts have been plotted as number of identifiable speci-mens (NISP) according to stratigraphic depth and presented inFig. 3, while the total faunal counts for each Sector have also beenplotted in Fig. 4 using the established chronology. The latter plotincludes Stegodon and Homo, but not rats, bats and flying foxes(Fig. 4, columns 1–5). Generally, owls, rather than humans, areresponsible for bringing small and intermediate sized rats into thecave as prey, in contrast to the larger rats, which generallyrepresent human refuse (van den Bergh et al., in press). In addi-tion, the occupation of the cave by bats may have been deterred bythe presence of humans (van den Bergh et al., in press). Thus, ratand bat faunal counts may be inversely related to human occu-pation intensity (e.g., Fig. 4 towards the top of Unit 3, and Units 4,5 and 7 all have rat/bat counts greater than Homo) and mayinstead reflect the prevailing environmental conditions. However,the plots in Fig. 4 also demonstrate that there is some correlationbetween rat and bat counts and human use of the cave (e.g., Unit6) suggesting that the subsistence practices of H. floresiensis mayhave provided many scavenging opportunities for rat communities(van den Bergh et al., in press). To enable these relationships to beinvestigated further, the rat and bat counts are plotted in a sepa-rate column.

The total Stegodon counts reflect human influences, becausethe presence of cutmarks on some of the bones (Morwood et al.,2005; van den Bergh et al., in press) and the overwhelmingdominance of juvenile individuals (van den Bergh et al., in press)suggests that Stegodon carcasses were brought into the cave to bebutchered (column 7). The total Homo counts provide an addi-tional measure of human occupation intensity within the cave(column 8), but in comparison to Stegodon they are relativelyinfrequent in the sediment column. It is important to note thatthe use of these data sets assumes that bone preservation is thesame in units with different sedimentary structures, and thatpreservation does not decrease with increasing time over theinterval 110–12 ka. The identification of diagnostic skeletalelements and teeth from the earliest to the most recent deposits(van den Bergh et al., in press) indicates that this assumption isnot unwarranted.

3.2.2. Stone tool countsThe presence of a few stone tools in the sediment layers suggests

that humans were present within the vicinity of the cave; however,a large concentration of tools within sedimentary units may indi-cate that humans were intensively using or occupying the cave.Therefore, the total number of stone tools found in each sedi-mentary unit (Table 2) has also been used as a crude estimate ofhuman occupation intensity (Moore and Brumm, 2007; Mooreet al., in press). The stone tool counts may have been influenced byfrequent slopewash, channel erosion and pooling in some areas ofthe cave (Westaway et al., in press-b) and by the inflation of artefactnumbers due to fire-induced fragmentation from the increased useof fire up-section (Moore et al., in press). These limitations and theuse of these data as a proxy for occupation intensity will be alsodiscussed further in a later section. The stone tool counts have beenplotted using the established chronology and are presented as totalcounts (Fig. 5) for each Sector (columns 1–5) and total for all Sectors(column 6) and are plotted next to Stegodon and Homo counts forcomparison. Peaks in the stone tool and faunal counts are compa-rable during the w80 ka human occupation period, and suggestthat these crude proxies for human occupation are in broadagreement.

4. Environmental reconstructions

4.1. Outside the cave

Evidence for the palaeoclimate changes that occurred in theIPWP region during a w40 ka period (47–5 ka) are derived from thed18O, d13C and fluorescence values of stalagmites from East Java(SPJ3) and western Flores (SP22). For locations see Fig. 1, for detailson the caves, sampling sites and speleothems see Westaway (2006)and Westaway et al. (2007b, in press-b). Analysis of the calcitelayers has revealed fluctuating isotopic signals that reflect changesin the isotopic composition of the soil water above the cave and thecomposition of rainfall in eastern Indonesia. The isotopic variationsrepresent a 3.0–4.0& shift from 50 to 35 ka and a 2.5& shiftbetween the LGM and the Holocene. These d18O isotopic shifts canbe attributed to changes in palaeoprecipitation and changes to themoisture sources and transport patterns (Westaway et al., 2007a, inpress-a), thereby making these records useful proxies for estab-lishing the climatic and environmental changes that occurredoutside the cave. However, as the isotopic variability in calcite isinfluenced by a number of complex processes occurring in therainwater, vegetation, soil water, soil and cave atmospheres, thefollowing interpretations are based on estimated relationshipsbetween isotopic values and climate conditions (outlined inWestaway et al., in press-a) and are limited by a degree of uncer-tainty. To overcome these uncertainties, correlations are drawnbetween six separate proxies representing different climatesignals: d18O, d13C, growth rate (Fig. 6a) tonal intensities, fluores-cence wavelength and intensity (Fig. 6b).

As fast growth rates in these records correlate with periods ofdepleted 18O (Westaway et al., 2007a, in press-a) they are used toidentify periods of high rainfall (Xia et al., 2001), while slowergrowth rates correlating with phases of enriched 18O are used toidentify significant dry phases. d13C variability can be used to inferchanges in the production of carbon dioxide in the soil by eithera Calvin C3 (trees and some grasses) or Hatch–Slack C4 (mostlygrasses) photosynthetic pathways, allowing these variations to belinked to changes in the palaeovegetation of an area (Baker et al.,1997). But carbon isotope variations can also be localised in nature,reflecting inorganic processes that act on the CO2 in the soil abovethe cave, such as the partial pressure of soil CO2 levels and therate of water seepage flow over the surface of the speleothem

Unconformity: Erosion and formation of flowstone

BTS

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37.7 ka‡

54-91 ka†

95 ± 13 ka@

Macaca sp

H. floresiensis

radius

H. floresiensis

premolar

Stegodon

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37 ± 21 ka@

Sector VII

0 20 40 60

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55 ± 8 ka@

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Varanidae

AvesSuidae

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8

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77

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WTS

Total identifiablebone fragmentsTotal Mollusca

Fish remainsFrog remains

Total number ofidentifiable specimens

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Total number of identifiable specimens

6

a

b

K.E. Westaway et al. / Quaternary Science Reviews 28 (2009) 2897–29122902

80

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e (k

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Sedimentaryunit

20

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1250 5000 3750 55 110 165 50 150 400 800 1200 1600 2000100TOTALStegodonRat / bat Homo floresiensis

2.5

5.5

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18-17 ka

Depth (m)

1

Fig. 4. The intensity of occupation for the eight main sedimentary units, derived from the faunal counts for each Sector and the total for all five Sectors combined. The total countsinclude Stegodon and Homo bones, but does not include the bones of rat, bat and flying foxes. Instead, these species are presented separately for individual comparison. The faunalcounts for Stegodon and Homo are also presented separately, as the presence of these species indicates occupational activities were occurring within the cave. The vertical lines inthe Sector III and Stegodon columns indicate the presence of bones, but they are in too small in number to show at the scale of this graph. Note that the columns for the total numberof bones from each Sector have the same scale, but the rat/bat, Stegodon, and total columns have different scales. The horizontal light grey line at the top of the figure represents thedeposition of the white silts containing tephra (WTS on Fig. 3), while the horizontal dark grey line below represents the deposition of the black volcanic sand unit (BTS on Fig. 3).Both of these stratigraphic markers are included as they represent a period of archaeological and faunal transition within the cave. Note: Unit 1 does not contain any faunal remains.The inset box contains an enlarged version of the rat/bat, Stegodon, Homo and total data sets for comparison. In this box, the faunal counts are plotted according to depth usinga linear depth/age time scale and the estimated age range of each unit is placed alongside the left axis.

K.E. Westaway et al. / Quaternary Science Reviews 28 (2009) 2897–2912 2903

(Dulinski and Rozanski, 1990; Baker et al., 1997). These influencesmake d13C variability difficult to interpret without the use ofadditional supporting proxies, such as fluorescence data.

Variations in the peak emission wavelength of fluorescencewithin stalagmite layers suggest changes in the breakdown oforganic acids (Baker and Genty, 1999) and can be used as a proxy forthe degree of humification and amount of effective rainfall abovethe cave (Baker and Genty, 1999; McGarry and Baker, 2000). Periodsof shorter fluorescence wavelength imply that there is a morecomplete breakdown of organic molecules into simpler short-chainmolecules that fluoresce at shorter wavelengths reflecting anincrease in humification and a longer residence time in the soil,representing lower effective precipitation. Periods of longer emis-sion wavelengths represent high effective precipitation, whichwashes organic matter out of the soil into the karst fissure networkabove the cave, effectively reducing its residence time in the soil,which restricts the breakdown of complex long-chain organicmolecules increasing the levels of humic-like compounds anddecreasing the degree of humification (Baker and Genty, 1999).When these data are combined with the d13C record it providesa useful indication of changes in effective precipitation (Westawayet al., in press-a). Thus, the d18O, d13C and fluorescence wavelengthsdata sets for samples SPJ3 and SP22 are combined to providea palaeoclimate record from 47–5 ka (Fig. 6a).

Changes in the fluorescence emission intensity are interpretedas reflecting the degree of organic matter in the soil above the cave

Fig. 3. Total number of identifiable fossil specimens, unidentifiable bone fragments and ndepths), arranged per stratigraphic unit for Sectors IV (a), XI and VII (b). Note that for the Hothese were not consistently recorded during the excavations before 2001. WTS indicates alayer, which both represent stratigraphic marker beds and correspond to volcanic eruptionspress-a). Dates to the left and right are from various sources (Morwood et al., 2004, 2005; Roon charcoal 650� and 850� temperature fractions, z ¼Uranium-series dating of flowstone, yquartz grains. The circled numbers correspond to the eight main sedimentary units from F

in response to an increase in humification (Baker and Genty, 1999;McGarry and Baker, 2000). Similarly, changes in the tonal intensi-ties of the growth layers from the scanning records are used toidentify the amount of organic material in the calcite layers. Asa lighter colouration in the calcite can indicate organic-rich growthlayers, and a darker colouration can indicate organic-poor growthlayers (Xia et al., 2001; Westaway et al., in press-a), these tonalchanges can be used to reconstruct the environmental conditionsoccurring above the cave during speleothem formation. Therefore,fluorescence emission wavelength, fluorescence emission intensityand tonal intensities for sample SPJ3 are combined to providea palaeoenvironmental record from 47–5 ka (Fig. 6b). For localisedproxies such as fluorescence and d13C, these data sets from Java canonly be used as a rough indication of the conditions above the caveon Flores, but their correlation with d18O data and growth ratesfrom Flores (Fig. 6a, Westaway, 2006; Westaway et al., 2007a, inpress-a) suggest that their use is not unwarranted.

Volcanic influences outside the cave are determined by evidenceof volcanic products within the sedimentary record in the cave. Themost obvious volcanic events occurred at w17 ka (Morwood et al.,in press; Roberts et al., in press; Westaway et al., in press-a,-b) andw12 ka (Morwood et al., 2004, 2005; Westaway et al., 2007a, inpress-b) as they are represented by a 75 cm thick black volcanicsand unit (BTS in Fig. 3), and a 1 m thick tephra deposit (WTS inFig. 3), respectively (Fig. 6b; two dark grey vertical lines). Both unitsrepresent primary airfall deposits but the former was deposited as

umber of individual fossil specimens (NISP) of various taxa per excavated spit (10 cmlocene sequence no amounts of unidentifiable bone fragments could be given because

white volcanic tuffaceous silt layer and BTS indicates a black volcanic tuffaceous sandoccurring at w12 and w17 ka, respectively (Roberts et al., in press; Westaway et al., inberts et al., in press): #¼ 14C on bulk charcoal samples, $¼median calibrated 14C ages¼ coupled ESR/Uranium series dating of juvenile Stegodon molar, @¼ red TL dating of

ig. 2.

Table 2Raw stone tool counts for the nine main sedimentary units in Liang Bua, after Moore et al. (in press).

Age range (ka) and stratigraphic unit

11–3 18–17 74–61 100–95 130–100

Artefact type 8 6 3 2 1 Total

Contact removal flake 20 47 8 1 76Early reduction flake 1980 141 5088 648 67 7924Redirecting flake 158 26 538 58 10 790Uniface retouching flake 31 1 124 23 2 181Truncation flake 46 9 274 30 3 362

Redirecting/contact removal flake 2 1 1 4Eraillure flakea 12 22 2 36Reflex flakea 4 2 6Unidentified flake 378 21 446 36 4 885Assayed cobble 9 9 18

Flake blank core 40 7 178 13 9 247Radial core 24 2 100 13 2 141Multiplatform core 27 2 59 3 91Single platform core 12 4 1 17Unidentified core 3 5 1 9

Bipolar artefact 7 74 4 85Retouched contact removal flake 1 1Retouched early reduction flake 64 6 166 14 2 252Retouched redirecting flake 2 6 8Retouched truncation flake 2 2

Retouched slab 1 1Truncated early reduction flake 9 1 60 8 78Truncated redirecting flake 2 1 3Early reduction flake with edge polish 18 18Flake blank core with edge polish 2 2

Radial core with edge polish 1 1Redirecting flake with edge polish 4 4Retouched early reduction flake with edge polish 3 3Retouched redirecting flake with edge polish 1 1

Potlid 58 2 60Heat fracture fragment 317 13 330Anvil 3 2 5Anvil/hammerstone 2 2Hammerstone 11 4 1 16

Hammerstone spall 4 4Multiplatform core/hammerstone 1 1 1 3Radial core/hammerstone 1 1

Total 3255 217 7230 864 101 11667

a These are ‘spin-off’ flakesduncontrolled byproducts of stone flaking of little technological significance.

K.E. Westaway et al. / Quaternary Science Reviews 28 (2009) 2897–29122904

windblown material and the latter was deposited in a poolstretching from the east wall to the centre of the cave. The occur-rence of additional volcanic events at w110 and 70 ka is suggestedaccording to the presence of volcanic glass shards found in the cavedeposits by XRD analysis (Westaway et al., in press-b) (outside theage range of Fig. 6).

4.2. Inside the cave

Using evidence from the eight main sedimentary units, fourgeomorphological processes are identified that have shaped thedevelopment of the cave environment: channel development,erosion by slopewash, pooling, and flowstone precipitation(Westaway et al., 2007b, in press-b). These processes all rely onwater flowing through the cave, which plays a dominant role indetermining the sedimentology of the cave in specific areas andwhich has influenced human occupational activities. According tostratigraphic evidence (Westaway et al., in press-b) and geochro-nological results (Roberts et al., in press), the timing and location ofspecific geomorphological events, such as channel erosion andpooling, are plotted on Fig. 7, and are accompanied by the climatic

and environmental data from Fig. 6 for comparison. The palae-oclimate data only extends from 47–5 ka (compared to the 110–5 karange of sedimentary evidence), but as the inferred wet phases(Fig. 7, blue shading) correlate with the main erosion events from47 ka onwards, the timing of erosion events prior to 47 ka (i.e.,110–47 ka) have been used to estimate the remaining wet phases(identified by questions marks). This evidence allows the recon-struction of the cave environment during different periods of caveevolution (Westaway et al., in press-b).

In addition, the arrangement of pools and channels within thecave environment created remnant areas of higher ground thatenabled zones of occupation to develop (Westaway et al., in press-b). Evidence from the location of sloping relief, the concentrationand distribution of archaeological material, and the in situ locationof the H. floresiensis skeleton (Morwood et al., 2004, 2005) wereused to identify the location of at least three of these zones ofoccupation. Two zones were established w74–61 ka, located by thewest wall and in the centre of the cave, and a later zone, establishedw18 ka, was located by the east wall (Westaway et al., in press-b).The identification of these zones (marked by vertical boxes in Fig. 5)may inform on where the hominins were living in the cave at

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Sedimentaryunit

20

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200 400 600200 400 600200 400 600200 400 600200 400 600 200

CharcoalBurnt stonesStone tools insmall numbersZones of occupation

1

Fig. 5. The intensity of occupation for the eight main sedimentary units, derived from the stone tool counts for each Sector and the total for all five Sectors combined. The verticalline in some of the columns indicates the presence of stone tools in numbers too small to show at the scale of the graphs, while the smaller horizontal lines indicate the presence ofcharcoal. The long horizontal light grey line at the top of the figure represents the deposition of the white silts containing tephra (WTS w 12 ka) while the horizontal dark grey linebelow represents the deposition of the black volcanic sand unit (BTS w 17 ka), and is included as they represent a period of significant transition within the cave. The total counts forStegodon and Homo (from Fig. 4) are included in this figure, as these data sets also represent useful proxies for the intensity of occupation within the cave, and can be correlated tothe stone tool counts. The timing of the main zones of occupation are plotted as vertical rectangles in Sectors I, IV and VII. Note that the columns for the total number of artefactsfrom each Sector have the same scale, whereas Stegodon, Homo and total columns have different scales.

K.E. Westaway et al. / Quaternary Science Reviews 28 (2009) 2897–2912 2905

certain times. This information can be compared to the location andtiming of geomorphological events in the cave environment(Westaway et al., in press-b, and described in Fig. 7) to determinethe extent that these processes influenced their choice of location.

5. Results

The evidence presented in Figs. 4 and 5 provides a crude proxyfor changes in human occupation intensity within the cave.According to the stone tool and faunal data, the most intensivephases of occupation occurred during the deposition of Units 3, 6,and 7, representing the periods 100–95, 74–61 and 18–17 ka, andthe least intensive during Units 1, 4 and 5 representing the periods110–101 and 55–40 ka. In addition, there are three periods from94–75, 60–54 and 36–19 ka that are not represented by the sedi-mentary units or associated archaeological material. From thefaunal evidence (Fig. 4), the intensity of Stegodon bones correlateswith Homo counts until w17 ka, after which a volcanic eruptionoccurred (marked by a thin horizontal grey line in Figs. 4 and 5) andboth Stegodon and H. floresiensis bones disappear from the sedi-ment column. This absence may represent the extinction of bothspecies at this site, and possibly in Flores (Morwood et al., 2004,2005). Changes in rat, bat and flying fox counts are similar to thechanges in Homo counts in Units 2 and 6, but increase duringperiods of lower occupational intensity (e.g., Units 4 and 5). Inparticular, some rat bones are found in Unit 7 after the first volcaniceruption, and the peak in Unit 5 represents a concentration ofbones generated by a nest of flying foxes by the east wall at a timewhen other fauna, including Homo are found only in small numbers(van den Bergh et al., in press).

The stone tool evidence from each Sector (Fig. 5) providesinsights into when and where most of the stones were being struck.This evidence suggests that tools were predominantly made andused in the centre and by the east wall of the cave in Sectors IV andXI, respectively, which has assisted in determining the location ofthe three zones of occupation (Figs. 5 and 7: pink vertical andhorizontal boxes, respectively). The total stone tool countsdemonstrate the intensive use of tools in the cave by H. floresiensis,and the strong correlation between stone tool use and the numberof Stegodon bones (columns 7 and 8) agrees with the evidence usingthe Homo bones counts.

During the w80 ka period in which H. floresiensis occupied LiangBua, wide variations in the intensity of occupation are observed.These variations are influenced by: internal cave processes, such aspooling and channel formation; processes external to the cave, suchas climate, environmental change, and volcanic eruptions; orhuman-based influences, such as competition for food. An under-standing of the environmental relationships established by thereconstructions outside and inside the cave assists in unravelingthe main influences on changes in the intensity of occupation.These relationships will be outlined in the next few paragraphs.

The climate and environmental changes inferred from the d18O,d13C, fluorescence emission wavelength, fluorescence emissionintensity and tonal intensity data sets are presented in Table 3 (seeWestaway et al., in press-a for an explanation of the interpreta-tions). This environmental backdrop for the last w50 ka in easternIndonesia demonstrates the rapidly fluctuating nature of theclimate at this time, ranging from high rainfall with dense rainforestvegetation (mainly C3 species) to periods of reduced rainfall withorganic-poor open grassland environments (mainly C4 species).These changes may have influenced human occupation in the cave.

According to the reconstructions outside the cave there were atleast two wet phases and one drier phase during a w42 ka period(from 47 to 5 ka) (Fig. 6a, dark grey and light grey vertical boxes,respectively). Periods of lower fluorescence intensity, shorter fluo-rescence wavelength and lower tonal intensity, e.g., 45–40 and 33–31 ka are interpreted as representing lower effective precipitation,while high emission intensities and longer emission wavelengthsare interpreted as high effective precipitation (e.g., at w46 ka). Afterw15 ka, however, the rapid shift towards shorter fluorescencewavelengths indicates a gradual increase in soil temperatures anda shift to C3 vegetation, which affects the rate of organic matterdecay and thus increase the production of shorter-wavelength ful-vic-like compounds. From these relationships, at least two mainorganic-rich periods and one main organic-poor period (punctu-ated with brief organic-rich phases) are identified over the lastw45 ka (Fig. 6b). When the climatic and environmental recon-structions are combined, at least two high-rainfall, organic-richphases are inferred that were of sufficient magnitude to haveinfluenced the food and water supply in the area around the cave. Incontrast, one reduced-rainfall, organic-poor phase can be identifiedthat may have represented a reduction in food and water resources.

-8.5

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(‰ V

PDB)

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(‰ V

PDB)

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SP22 18O

Age (ka)

Inte

nsity

of t

one

(a.u

.)

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460

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on w

avel

engt

h(n

m)

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60 Fluorescence wavelengthFluorescence intensityScanning data

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Climate

Environment

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tanc

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mtip

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)

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60SPJ3 18OSPJ3 13C

SP22 13C

Java

Flores

SPJ3 fluorescenceSPJ3 growth rateSP22 growth rate

WetDryloca

lised

wet

ting

WetWet loca

lised

dryi

ng

Organic-rich

Organic-rich

Organic-poor with brief organic-rich phases

Fig. 6. A reconstruction of the environmental conditions outside the cave from 47 to 5 ka. (a) Palaeoclimate information derived from the d18O and d13C isotope records of twospeleothem from Flores and Java. SP22 (grey diamonds with and without black fill represent d13C and d18O, respectively) is from Liang Neki cave in western Flores; and SPJ3 (filledblack diamonds and open black diamonds represent d13C and d18O, respectively) is from Gua Gebang in eastern Java. Further details on the cave sites, and samples can be found inWestaway et al. (2007b, in press-b). In addition, changes in the wavelength of the fluorescence signal for sample SPJ3 (blue triangles) and growth rates for samples SPJ3 and SP22 areincluded in this figure (black and grey circles, respectively), as Westaway et al. (2007b, in press-b) demonstrated that these data sets (combined with the d13C record) providea useful indication of changes in effective precipitation. From the evidence provided by these three data sets, at least two wet phases (vertical blue boxes) and one drier phase(vertical light brown boxes) are inferred, with two smaller transitionary phases that may represent localised conditions. (b) Palaeoenvironmental data derived from changes in thefluorescence emission wavelengths (blue triangles), fluorescence emission intensity (orange diamonds) and tonal intensities (black line) of sample SPJ3 from Gua Gebang in easternJava between 47 and 5 ka. Periods of shorter fluorescence wavelength, higher fluorescence intensity and lower tonal intensity (e.g., 45–40, 33–31 ka) are interpreted as representinglower effective precipitation that has enabled a greater degree of humification in the soil. During periods of high effective precipitation, for example at w46 ka, the organics arerapidly washed out of the soil, preventing humification, and this is reflected in the longer fluorescence wavelengths and lower intensities. From these relationships, at least eightorganic-rich phases (vertical green boxes) and at least 3 organic-poor phases (vertical brown boxes) are identified, and have been grouped into two organic-rich and one prolongedorganic-poor period. According to the sedimentary evidence, the timing of volcanic events (at w17 ka BTS, and w12 ka WTS) are included in the form of two dark grey vertical lines(for interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).

K.E. Westaway et al. / Quaternary Science Reviews 28 (2009) 2897–29122906

The reconstructions inside the cave (Fig. 7) suggest that the maingeomorphological events occurred in cycles. Three main phases ofpooling occurred throughout the w80 ka occupation period, with fivephases of flowstone precipitation and at least six phases of channelerosion and significant erosion events. These cycles did not occursimultaneously but were inversely linked, e.g., pooling occurredwhen channel formation and erosion events had reduced, andflowstone precipitation occurred directly after channel erosion hadreduced but prior to pool formation. According to the comparison

with the reconstruction outside the cave, the periods with thegreatest channel formation and erosion within the cave correlatewith the highest rainfall, while reduced channel activity and poolingcorrelate with the drier periods. In contrast, flowstone precipitationoccurs in the transition between these two phases. The timing of thezones of occupation (Fig. 7, vertical pink boxes) correlates with theerosion cycles (occurring in other areas of the cave) and the periods ofclimate change that represent the highest rainfall. Deposition of mostof the sedimentary units occurred mainly during the wet phases.

Table 3A summary of the d18O, d13C, fluorescence emission wavelength, fluorescence emission intensity and tonal intensity data sets from the analysis of stalagmites SP22 from Floresand SPJ3 from Java, with the inferred climate and environmental conditions and estimated influences on occupation (from Westaway et al., in press-b).

Time (ka) Sedimentary unit Proxy evidence Inferred climaticconditions

Possible interpretation ofenvironmental conditions

Estimated influences onoccupation

1 49–39 5 reworkedconglomerate

Fast growth rate, d18Ofluctuating but mainlydepleted, d13C graduallyincreases to enriched, longfluorescence wavelengths andlow intensity, high tonalintensities

Wet and organic-rich Closed woodland conditions,unstable with rapid fluctuationsin rainfall

Vegetation plentiful, largesupplies of water, huntingdifficult?

2 38–37 Fast growth rate, shortwavelengths and low intensity,d18O and d13C increasing, layersdarken

Transitionary –decreasing rainfall

Gradual reduction in rainfalland shift to C4 vegetation andopen landscapes

Reduction in water supply,vegetation changing

3 36–19 Slow growth rate, d18O and d13Cenriched, with a decrease at25 ka, short fluorescencewavelengths low intensity, lowtonal intensities

Dry and organic-poorbut stable

Open landscapes – less treecover, decrease in soil organicmatter, increase in C4vegetation, decreasinghumidity, reduction inrainforest cover, shift towardsmore grassland environments

Low water supplies, changevegetation causing a change infauna? Less rainforest covereasier for hunting activities

4 18–15 6, 7 skeleton leveland volcanicsediments

Slow growth rate, d13Csignificant excursion todepleted values, d18O staysenriched, rapid shift to longerfluorescence wavelengths, tworapid shifts to lower intensity

Recovery I – increase inrainfall

Rapid shift to wetter climates,increase in montane andlowland forest taxa, increase insoil temperatures, volcanicactivity

Increase in water availability,vegetation changing andaffected by volcanic ash?

5 14–11 7 volcanicsediments

Growth rate increases, d18Oexcursion to depleted values,smaller d13C excursion todepleted values, shortfluorescence wavelengthsintensity increasing, tonalintensity increases

Recovery II – the returnof the monsoon

Closed-canopy conditions –increase in soil thickness andshift to monsoonal seasons,volcanic activity

Vegetation plentiful, largesupplies of water butinfiltrated by ash?

6 10–5 8 youngerslopewash

Fast growth rates, d18O and d13Cdepleted, long fluorescencewavelengths and high intensity,high tonal intensity

Stabilises into earlyHolocene, wet andorganic-rich

Wet conditions – increase inhumid forests, increased soiltemperatures and humidity

Vegetation plentiful, largesupplies of water, huntingdifficult?

K.E. Westaway et al. / Quaternary Science Reviews 28 (2009) 2897–2912 2907

To compare these environmental relationships with thepatterns of human occupation within the cave, their relativetimings are plotted against the eight main sedimentary units. Thus,climatic and environmental events occurring outside the cave(Fig. 6) and geomorphological events occurring inside the cave(Fig. 7) are compared with the total bone and stone tool data (Figs. 4and 5, respectively). This comparison (Fig. 8) enables the relation-ship between hominins and their environment (both inside andoutside the cave) to be explored. The highest intensities of occu-pation, according to the greatest stone tool and faunal counts(Fig. 8, columns 1 and 2, red shading), correlate with periods ofchannel formation and erosion (column 3, blue shading), highrainfall (column 4, blue shading), thick soils and high bio-produc-tivity (column 5, green shading) during 3 main periods: (1) 100–95 ka, (2) 74–61 ka, and (3) 18–17 ka (column 6, numbered 1–3 andmarked with dashed lines). The phases of reduced channel activity,pooling and flowstone formation, and change in bio-productivitycorrelate with drier periods and a lower intensity of occupation(highlighted in yellow) from 94–75 ka and 36–19 ka.

6. Discussion

The total number of stone tools and bones found in each sedi-mentary unit has been used as a crude estimate of human occu-pation intensity (Moore and Brumm, 2007; Moore et al., in press).This assumption does not hold true for many cases in the archae-ological record. For example, in Australian prehistory the amount of

stone tool debris depends on the stone tool technology (or reduc-tion sequence) utilized (Hiscock, 1981). However, at Liang Bua,Moore et al. (in press) have demonstrated that the stone toolsrepresent the same reduction sequence top-to-bottom. In thiscontext, changes in flake counts can be seen as a proxy of theamount of knapping occurring in a particular primary context. Inaddition, the increase in stone tool count correlates quite closelywith an increase in H. floresiensis bones, Stegodon bones, charcoaland burnt stones suggesting that the amount of knapping is closelyaligned to increases in occupation. This evidence suggests thatusing the discard rate of stone tools is justified as a crude proxy foroccupation intensity.

The distribution of hominin material within the cave could beattributed to a number of causes, such as taphonomic processes ofchanneling and erosion of the cave floor, the result of rubbishaccumulations or ‘toss zones’, or genuine zones of occupation.Westaway et al. (in press-b) determined that slopewash, chan-neling and pooling processes occurred only in specific areas of thecave leaving a few locations relatively unaffected. This notion issupported by the mostly fresh, pristine and ‘as struck’ nature of thestone tools in these unaffected locations, with no signs ofsubstantial or sustained artefact movement within the cave. Anexception to this observation is some of the artefacts recoveredfrom the cobble layer in Unit 5 (Fig. 2), which is derived from theallogenic fluvial conglomerate at the rear of the cave and havetherefore been transported within the bedload of the river. Addi-tional evidence for the pristine state of the lithics is the presence of

5 25 45 65 85 105

SI, SIIISVII / SXI, SIVSVIISIV

SXISIII, SIV,

SVII SIV SI, SIII SIV, SIII CON

SI SISIV E-CON CON CON

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Erosion eventChannelerosion

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CON

12345678Sedimentary unit

Conditionsinside the

cave

Timescale

Fig. 7. A reconstruction of the environmental conditions inside the cave from 110 to 5 ka according to the timing of geomorphological events. The timing of erosion, pooling andchanneling events in Liang Bua (red arrow, blue rectangle and blue semi-circle, respectively), inferred from the stratigraphy (Fig. 2) are plotted according to the results of a numberof dating techniques (Roberts et al., in press). The Sectors containing evidence for each event are included next to the corresponding symbol. Periods of flowstone precipitation (greyrectangles) and zones of occupation (pink rectangles) have also been plotted, with the corresponding Sectors in which they were found. CON refers to the alluvial conglomeratedeposit found at the rear of the cave (Westaway et al., 2007b), while E-CON refers to an eroded section of this conglomerate (Westaway et al., in press-a). All of these data sets arepresented next to the climate record inferred from reconstructions based on data obtained from outside the cave (Fig. 6); inferred periods of high and low rainfall are marked in blueand yellow shading, respectively, to facilitate correlations. The timing of the wet and dry phases from 110–47 ka has been estimated (indicated by question marks) according to therelationship between erosion events and wet phases established from 47–5 ka. From these comparisons, a temporal pattern of geomorphological and sedimentological events isdiscernible. Erosion events correlate with periods of high rainfall, pooling events with periods of lower rainfall, and flowstone precipitation occurs at the beginning or the end of wetphases (for interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).

K.E. Westaway et al. / Quaternary Science Reviews 28 (2009) 2897–29122908

sequential conjoins and broken-flake conjoins that were observedin Sector IV. These conjoins confirm that the material has notmoved more than 1–2 m (Moore et al., in press). Furthermore, thedistribution of size grades is what would be expected for primarymaterial. This evidence for artefact distribution does not supportthe notion of transport by sedimentary processes or accumulationin a rubbish pile, and the concept of ‘toss zones’ are inferred fromthe use of space by modern human behaviour and therefore need tobe demonstrated given the context with H. floresiensis in this cave.In addition, the composition of the sediments, revealed by theluminescence sample preparation procedure is not dominated byheavy minerals as would be expected from a lag deposit.

The evidence of bone preservation also supports the notion ofminor post-depositional transport and re-organisation of thesediments and associated material. For example, small vertebrateremains in excellent condition were recovered from all depthswithin the stratigraphic sequences, as were Komodo dragonvertebrae, which are known to be brittle and prone to breakage(van den Bergh et al., in press). In addition, some hominin boneswere still articulated (Brown et al., 2004) suggesting minimalmovement in the sediment column and a few bone fragments(especially Stegodon skull fragments) could be re-fitted in a similarmanner to the stone tool evidence (van den Bergh et al., in press).Considering this evidence, the most parsimonious explanation forthe distribution of hominin material is one of a zone of occupationrather than accumulations of material derived from sedimentary ortaphonomic processes.

The highly variable amounts of cultural data between sectorssuggest that there may be other large densities of material else-where in the cave that has not yet been revealed by excavation. Thepresent excavations cover w60 m2 of a cave floor measuringw1800 m2. However, the excavations have been conducted in key

locations so that the main sedimentary units have been well-defined and the geomorphological sequence of events in the cavehas been either determined or estimated, along with reconstruc-tions of the main channel activity (Westaway et al., in press-b). Inaddition, excavations by previous researchers have increased thearea of exploration up to w100 m2 (Morwood et al., in press) so thatcomprehensive understanding of the sedimentary, geomorphic andoccupational history in the cave has been obtained. However, thereis always the possibility that there are other densities of materialelsewhere in the cave and undiscovered zones of occupation, so allinterpretations are limited by potential future discoveries.

According to the palaeoenvironmental and lithic evidence(Fig. 8), during wet and organic-rich periods H. floresiensis knapperswere making many stone tools and their subsistence practices werecreating high numbers of bones in the sediment column. Thisrelationship could represent an increased use of the cave foroccupation during these wetter phases. In the same manner, duringdrier, organic-poor periods the stone tool and faunal countsdeclined suggesting hominins were not using the cave so inten-sively for occupation purposes. These correlations provide a modelof human–environment interactions for Flores over a w80 kaperiod, with occupation intensive wet phases occurring duringthree main periods: (1) 100–95 ka, (2) 74–61 ka, and (3) 18–17 ka.During period 1, a specific zone of occupation in the cave could notbe identified in the sedimentary and archaeological evidence. Incontrast, periods 2 and 3 are associated with zones of occupationlocated in the centre and by the east wall of the cave. Periods 1 and2 lie outside the range of environmental data outside the cave, butwet conditions have been inferred from previous relationshipsbetween events in the cave and environmental conditions between55–40 and 18–12 ka. This leaves 3 as the only period that is linkedto a specific zone of occupation in the cave and corresponds to

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Zone of occupation established

Channel formation

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Presence of stone tools and fauna (in small numbers)

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InterpretationPeriods of greatest occupation intensity

Periods of lowest occupation intensity

Events requiring largeamounts of water

Events requiring lessamounts of water

Increased rainfall

Decreased rainfall

Increased bio-productivity, organic-richDecreased bio-productivity, organic-poor

Known volcanic event

Estimatedvolcanic event? Estimated fromstratigraphic

evidence

1

2

3

1 2 4 63 5

Fig. 8. The intensity of occupation for the eight main sedimentary units, derived from the stone tool and faunal counts for each Sector, compared with the timing of the maingeomorphological and sedimentological events in the cave, the environment and climate outside the cave, and the timing of volcanic events. The total stone tool (column 1) andfaunal counts (column 2) are taken from Table 2 and Figs. 3–5, while the geomorphological events inside the cave (column 3) are taken from Fig. 7. The climate data (column 4) aretaken from Fig. 6a, while the environmental data (column 5) are taken from Fig. 6b. The known (Fig. 6b) and estimated volcanic events are also plotted (column 6), depicted bybrown arrows with solid and dashed lines, respectively. Each column contains an interpretation of the data that is colour coded for clarity with the individual keys found ina separate ‘interpretation’ panel at the base of the figure. The greatest intensity of occupation occurred during three main periods: 100–95, 74–61, and 18–17 ka, (marked with redshading). These correlate with the periods of greatest channel formation and erosion inside the cave, and with the highest rainfall, thickest soils and highest bio-productivity outsidethe cave during 3 main periods. These relationships are highlighted using large dashed rectangles and numbered 1–3 in column 6. The key to the right depicts the symbols used incolumns 1–3 (for interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).

K.E. Westaway et al. / Quaternary Science Reviews 28 (2009) 2897–2912 2909

events in the cave and environmental data that infer wet condi-tions. Thus, this period represents the strongest case for the linkbetween wet conditions and increased cave use in Flores, despite itsabrupt termination w17 ka.

Initial observations of these correlations seem to suggest thatperiods of increased rainfall (e.g., 18–5 ka) nourished a flourishingflora and provided an ample food supply for a growing faunalpopulation, which, in turn, could have positively influenced thepopulation of H. floresiensis. Consequently, these organic-richperiods (green shading in Fig. 8) coincide with the three mostintensive phases of occupation (Units 2, 3 and 6).

Conversely, the decrease in bio-productivity during prolongedperiods of reduced rainfall (e.g., 36–19 ka, and possibly during anearlier period 94–75 ka) would have changed the type of vegetationavailable and impacted most heavily on smaller mammals. Thisfaunal group is less resilient to dry and variable climates as theirenergy and water requirements are high relative to their dailyforaging range (Brook et al., 2007). Thus, they do not have a greatcapacity for migration, and this has implications for their survival. Incontrast, Stegodon and H. floresiensis as larger bodied mammals mayhave been more resilient to changes in vegetation due to theircapacity to disperse over longer distances, so rather than becomingextinct they simply migrated to a more favourable location. Fluctu-ations in climatic conditions occurred relatively rapidly, at least inthe terminal Pleistocene, so changes in vegetation type may haveencouraged Stegodon and human migration to other parts of theisland containing the preferred food sources. Indeed, these

prolonged periods of reduced rainfall are not represented by themain sedimentary units as the deposition occurred mainly duringthe wet phases. This absence may be due to the erosion of theselayers during the drier periods, but this is unlikely due to the lowrainfall. Alternative explanations are either these layers wereremoved by the succeeding wet phase and replaced by Unit 3 or 6sediments, or less sediment entered the cave due to reduced erosionand slopewash. The presence of thin soils during the 36–19 kaperiod, as inferred from the fluorescence emission intensity data(Fig. 6b), supports the latter proposition. This evidence suggests thatthe environment was experiencing a reduction in geomorphologicaland biological activities. During the later dry period, the dominanttype of vegetation also changed from trees to grasses, as indicated bylocal pollen records (van der Kaars and Dam, 1995). Although Den-nell and Roebroeks (2005) argue that hominins in Southeast Asiawere adapted to grassland environments, this change may havealtered hunting and gathering techniques. Thus, we speculate thatthe drier and organic-poor periods may have caused a change invegetation resources and created pressure to relocate on the largermammals, such H. floresiensis. This pressure was exacerbated bytheir island location, which prevented the option of inter-islandmigration that was available to other hominins in mainland South-east Asia.

An alternative explanation for the link between wet phases andthe greatest intensity of occupation relates to the expansion andcontraction of the rainforest and the ability of H. floresiensis toadapt to habitat changes. It has been suggested that some

K.E. Westaway et al. / Quaternary Science Reviews 28 (2009) 2897–29122910

hominins found it particularly difficult to adapt to rainforestenvironments (e.g., Storm, 2001a,b) and instead favoured forestedge environments, such as savannah (Bettis et al., 2004) orgrasslands (Dennell and Roebroeks, 2005). The drier, organic-poorperiods (e.g., 94–75 and 36–19 ka) would have caused thecontraction of the rainforests and the expansion of grasslandenvironments, as supported by the incidence of diurnal raptorfossils within Liang Bua: such raptors favour open environments(Meijer, 2006; van den Bergh et al., in press). This opening ofenvironmental conditions may have enabled H. floresiensis tooccupy open-air locations that were conducive to hunting. Hencethe evidence for occupation during this period would be locatedoutside the cave. In contrast, the wet, organic-rich phases (e.g.,100–95, 74–61 and 18–17 ka) would have resulted in the expan-sion of rainforest environments and the contraction of thesavannah, as supported by the first appearance of parrots in thefossil faunal record before 16 ka; parrots favour closed-canopyenvironments (van den Bergh et al., in press). This habitat changemay have forced H. floresiensis to favour cave dwellings, and issubsequently reflected in the stratigraphic and archaeologicalrecords of Liang Bua as an increase in the occupational intensity.This suggests that H. floresiensis was able to adapt to abrupt andprolonged environmental change by altering their favouredoccupation sites. Archaeological evidence of hominin occupationin Liang Bua from 95–17 ka (Morwood et al., 2004, 2005) andwithin the vicinity of the cave prior to w190 ka (Westaway et al.,2007b) suggests that this tactic was successful for at leastw175 ka.

To test the robustness of this model, evidence from additionalsites on Flores is required. At this point in time, H. floresiensismaterial and associated evidence is currently restricted to only onecave site in western Flores. This makes the discovery of new sites incentral and eastern Flores a priority. In addition, this new siteevidence should be combined with further palaeoenvironmentaldata from Flores spanning the entire w80 ka occupation period.This new evidence will strengthen the existing model and identifythe potential migration pathways of fauna (including H. floresiensis)during adverse environmental conditions, such as the volcaniceruption at w17 ka.

The uniqueness of H. floresiensis as a species deems this modelapplicable to only Flores Island and not the wider Southeast Asianregion. There are a number of other reasons. According to thecurrent palaeoenvironmental data for Flores, the inferred increasein rainfall at w18 ka occurs slightly earlier than other palae-oenvironmental data for this region. For example, rainfall in Javaincreased between 17 and 14 ka according to the Bandung andBanda Sea records (van der Kaars and Dam, 1995; van der Kaarset al., 2000), while rainfall increased in Australia and China around13.2 ka (Wang et al., 2001; Wyputta and McAvaney, 2001; Dykoskiet al., 2005). The inferred increased at w18 ka on Flores may in factbe a localised change in environmental conditions that might notbe region-specific. Furthermore, the archaeological evidence foundin this region during the last w100 ka, such as in Niah Cave (Sar-awak), Leang Burung II (Sulawesi), Jerimalai (East Timor), Tabon(the Philippines), and Lang Rongrien (Thailand) (Glover, 1981;Anderson, 1987; Detroit et al., 2004; Barker et al., 2007; O’Connor,2007) represents modern human occupation, which differs fromH. floresiensis evidence due to different occupation habits andtypically different reduction technologies. Therefore, the assump-tions used to devise this model, such as stone and bone counts asa proxy for occupation intensity, are not valid so alternate proxiesmust be developed. Added to this, the scarcity of environmentaldata in this region (Flenley, 1997; Dam et al., 2001) preventsdetailed correlations between human and environmental evidence.These factors currently restrict the application of this human–

environment model to other Indonesian islands or the widerSoutheast Asian region. Despite these limitations, the Flores modelprovides valuable new insights into H. floresiensis as a species andidentifies the environmental challenges that influenced their fav-oured occupation sites on Flores.

In the face of adverse environmental and habitat pressures, theH. floresiensis population was able to survive throughout extendeddry periods (94–75 and 36–19 ka) by occupying open-air locationsor by migrating to another area in Flores. From w18 ka onwards, theincrease in zones of occupation and Homo remains in the cave(Fig. 5, Unit 6) suggests that H. floresiensis was once again flour-ishing in this area and was increasingly using the cave for occu-pation. However, this increase was cut short by a volcanic eruptionat w17 ka (Morwood et al., 2004, 2005; Westaway et al., 2007a, inpress-a,-b). The absence of evidence for H. floresiensis in the sedi-mentary record after w17 ka implies that despite surviving reducedrainfall and widespread habitat changes for over w175 ka, thisvolcanic event may have signified the end of occupation of LiangBua by this hominin. This event may not necessarily have causedthe total extinction of the species on Flores, but rather forceda migration away from Liang Bua to more favourable environments,possibly to the east, which were not affected by ash accumulationon vegetation or ash contamination of water supplies (Westawayet al., in press-a,-b). In this respect, the volcanic event at w17 kawas the greatest environmental impact on H. floresiensis asa species during their occupation of Liang Bua.

7. Conclusions

The application of an interdisciplinary approach to Liang Buaand its surrounding area has generated a wealth of archaeologicallyrelevant data. By analysing and constraining the pattern of sedi-mentation, the cave environment has been reconstructed for thelast 95 ka, offering small glimpses of the occupational conditions. Inaddition, an environmental backdrop to the arrival and dispersal ofhumans throughout Indonesia reveals that the movements ofH. floresiensis were governed in large part by the contemporaneousenvironmental conditions. Furthermore, the expansion of rain-forest environments could be interpreted as a governing influenceover their choice of cave or open-air occupation, thus demon-strating the strong influence that the environment exerted uponthe local hominin populations. This influence is further demon-strated by the volcanic eruptions in the terminal Pleistocene, whichmay have been the primary cause for the absence of H. floresiensis inLiang Bua after w17 ka.

This analysis represents an initial comparison of environmentalreconstructions with low-resolution archaeological evidence toform a foundation for further detailed correlations using evidencefrom new potential H. floresiensis sites. The use of these techniqueshas helped to identify the tempo and mode of human–environmentinteractions in the vicinity of Liang Bua, has provided insights intooccupation practices by early hominins in Indonesia, and hasdemonstrated the value of Quaternary analysis in the karst regionsof Southeast Asia. Furthermore, this study has established thenature of the relationship between H. floresiensis and the environ-ments that they encountered in western Flores. Analysis of higherresolution archaeological evidence, and further archeological datafrom new sites, correlated to this environmental backdrop, isrequired to identify additional archaeological turning points thatmay have been associated with changing environmental condi-tions. Similar studies in other cave sites in island Southeast Asia willfacilitate comprehensive assessment of Late Pleistocene human–environment interactions and will further contribute to ourunderstanding of its hominin populations.

K.E. Westaway et al. / Quaternary Science Reviews 28 (2009) 2897–2912 2911

Acknowledgements

This study was funded by a Discovery Project grant to K.E.W. andM.J.M. from the Australian Research Council (ARC), with additionalfunding to R.G.R. from the University of Wollongong. We also thankthe ARC for a Senior Research Fellowship to R.G.R.; colleagues at theCentre for Archaeology (Jakarta) for logistical support in Flores andJava; M. Gagan and H. Scott-Gagan for stable isotope measurementsconducted at the Australian National University, and for usefuldiscussion; D. Wheeler for stable isotope measurements conductedat the University of Wollongong, and A. Chivas for useful discus-sion; Y.-x. Feng for U-series measurements; and P. Westaway andthe University of Wollongong (University Postgraduate Award andTuition Fee-Waiver Scholarship) for financial support of K.E.W.

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