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Journal of Human Evolution 59 (2010) 123e132

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Journal of Human Evolution

journal homepage: www.elsevier .com/locate/ jhevol

New evidence for a 67,000-year-old human presence at Callao Cave,Luzon, Philippines

Armand Salvador Mijares a,*, Florent Détroit b, Philip Piper a, Rainer Grün c, Peter Bellwood d,Maxime Aubert c, Guillaume Champion b, Nida Cuevas e, Alexandra De Leon e, Eusebio Dizon e

aArchaeological Studies Program, Palma Hall, University of the Philippines, Diliman, Quezon City 1101, PhilippinesbUMR 7194, CNRS, Département de Préhistoire du Muséum national d’histoire naturelle, 57, rue Cuvier, 75005 Paris, FrancecResearch School of Earth Sciences, Bldg 61 Mills Road The Australian National University, Canberra ACT 0200, Australiad School of Archaeology and Anthropology, AD Hope Building, The Australian National University, Canberra ACT 0200, AustraliaeArchaeology Division, National Museum of the Philippines, P Burgos Ave., Manila, Philippines

a r t i c l e i n f o

Article history:Received 24 August 2009Accepted 22 April 2010

Keywords:Cave faunasHominin dispersalSoutheast AsiaU-series dating

* Corresponding author.E-mail address: armand.mijares@up.edu.ph (A.S. M

0047-2484/$ e see front matter � 2010 Elsevier Ltd.doi:10.1016/j.jhevol.2010.04.008

a b s t r a c t

Documentation of early human migrations through Island Southeast Asia and Wallacea en route toAustralia has always been problematic due to a lack of well-dated human skeletal remains. The bestknown modern humans are from Niah Cave in Borneo (40e42 ka), and from Tabon Cave on the island ofPalawan, southwest Philippines (47� 11 ka). The discovery of Homo floresiensis on the island of Flores ineastern Indonesia has also highlighted the possibilities of identifying new hominin species on islands inthe region. Here, we report the discovery of a human third metatarsal from Callao Cave in northernLuzon. Direct dating of the specimen using U-series ablation has provided a minimum age estimate of66.7� 1 ka, making it the oldest known human fossil in the Philippines. Its morphological features, aswell as size and shape characteristics, indicate that the Callao metatarsal definitely belongs to the genusHomo. Morphometric analysis of the Callao metatarsal indicates that it has a gracile structure, close tothat observed in other small-bodied Homo sapiens. Interestingly, the Callao metatarsal also falls withinthe morphological and size ranges of Homo habilis and H. floresiensis. Identifying whether the metatarsalrepresents the earliest record of H. sapiens so far recorded anywhere east of Wallace’s Line requiresfurther archaeological research, but its presence on the isolated island of Luzon over 65,000 years agofurther demonstrates the abilities of humans to make open ocean crossings in the Late Pleistocene.

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Introduction

Hominin movement into Island Southeast Asia has always beenproblematic due to the lack of well-dated human remains. Thehumid tropical environment of Island Southeast Asia contributes tothe problems of bone preservation. Early modern human remainshave, however, been recovered in Niah Cave in Sarawak, MalaysianBorneo (Harrisson, 1975; Barker et al., 2002), dating to 42 ka(Barker et al., 2007), and from Tabon Cave in Palawan (Fox, 1970;Dizon et al., 2002), dating to 47�10/11 ka (Détroit et al., 2004).Borneo is located on the Sunda shelf and was possibly joined by dryland to Sumatra, Java and Peninsular Malaysia during periods oflowered sea level in the Pleistocene. The island of Palawan mayhave been intermittently attached to northeastern Borneo when

ijares).

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sea levels reached their minima during the most extreme climaticphases. Thus, migrating human populations could have reachedboth islands without necessarily requiring a sea crossing. To reachthe rest of the Philippine archipelago and other islands in theWallacean group (e.g., Sulawesi, Flores, Timor) that were neverattached to either mainland Asia or Australasia (Sahul), open seacrossings were required. The Lake Mungo remains from Australiadating to 40� 2 ka (Bowler et al., 2003) are evidence that modernhumans were capable of making very early sea crossings. Homofloresiensis, discovered on the islands of Flores, Indonesia, is anotherhominin that managed to cross the Wallace line. While its remainsare only dated to 18e38 ka (Morwood et al., 2004), Flores also hasstone artifact assemblages suggesting that a hominin of unknownaffinity reached the island more than 800 ka years ago (Brummet al., 2006). Our recent excavations (2007) in Callao Cave (Fig. 1)have produced what is probably one of the earliest hominin fossilseast of Wallace’s Line, from the island of Luzon, northernPhilippines.

Figure 1. The Location of Callao Cave and the 2003 excavation.

Figure 2. Stratigraphic profile of Square 2, Callao Cave. Layer 14 is the breccia thatcontained the human metatarsal (Callao MT3).

A.S. Mijares et al. / Journal of Human Evolution 59 (2010) 123e132124

Materials and methods

The excavation of Callao Cave

In 2003, archaeological excavations under the direction ofA. Mijares at Callao Cave in Peñablanca, Cagayan Valley, northernLuzon (Fig. 1), were designed to investigate the regional transitionfrom Paleolithic hunting and gathering to the introduction offarming during the MideLate Holocene. At the commencement,there was no intention of exploring the earlier history of the cave,but the excavations exposed an Upper Pleistocene layer 130 cmbelow present ground level that contained chert flake tools, burntanimal bones and a hearth feature. A radiocarbon determination of25 968� 374 (uncalibrated) BP (Mijares, 2005, 2007) made this theoldest known human occupation in the main Philippine archi-pelago (excluding Palawan) and demonstrated that there wasPaleolithic occupation in the cave entrance. To investigate thisfurther, a joint partnership between the University of thePhilippines Archaeological Studies Program, the National Museumof the Philippines, and the Australian National University wasestablished to continue excavation in Callao Cave in 2007.

The 2007 excavations started at 130 cm below surface, the levelat which the 2003 excavation had ended (Fig. 2). Proceduresfollowed the 2003 system of excavating in 5 cm spits and recordingeach archaeological find three dimensionally by spit and strati-graphic layer. The excavation was reduced in size from the 2003excavations, and only Square 1 in the north (2� 2 m) and thenorthern portion of Square 2 (2�1 m) were excavated below130 cm. Since water for wet sieving was not available in the cave,most sediment was dry sieved through a 4 mm mesh. In addition,samples were also collected for flotation.

At a depth of 160 cm below the surface (BS), the excavation areawas further reduced and only the southern end of Square 1 and thenorthern end of Square 2 were excavated. Between 160 cm and250 cm, BS archaeological remains were scarce, with just a flaketool, chert core and deer bones recovered from Layer 11, and severalpoorly preserved deer bones, including a scapula, the proximal endof a humerus and several fragments of antler identified in Layer 12.There was no evidence of human occupation similar to thatobserved in the Upper Pleistocene Layer 8.

In Layer 13 (255e265 cm BS), the bones and teeth of deerbecamemore abundant, and in Layer 14 (270e295 cm BS), the teamencountered cemented sediment (carbonized breccia) containinga relatively dense concentration of animal bone. In this layer, ata depth of 275 cm below the cave surface, we found the humanthird metatarsal (MT3) bone, which is the subject of this paper.Beyond 300 cm depth, the excavation unit became too confinedbetween the cave wall and a large stalagmite for excavation tocontinue.

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Dating

Three osseous samples from the breccia were selected fordating. Two cervid teeth (Callao 1 and Callao 2) recovered from 275to 295 cm below present ground surface were dated by ElectronSpin Resonance (ESR) and Uranium Series (U-series) analysis. Laserablation U and U-series analysis was carried out at by R. Grün at theAustralian National University (see Eggins et al., 2003, 2005 for theexperimental set-up and Grün et al., 2005, 2006, 2008 for previousapplications). The ESR dating of the teeth followed proceduresroutinely applied in the ANU ESR dating laboratory (Grün et al.,2001). For ESR dose analysis, the enamel was powdered andaliquots were successively irradiated in ten steps to 372 Gy.Radiation doses were monitored with alanine dosimeters andevaluated against a calibrated dosimeter set provided by A. Wieser,Messtechnik, München. Dose values were determined by partialspectrum fitting (Grün, 2002). The external dose rate was deter-mined from a single representative sample from the breccia. TheU-concentration in the dentine of the two cervid teeth had onlysmall variations along the laser track, 71.6� 8.2 ppm U for Callao 1and 100� 5 ppm U for Callao 2, as usually observed in dentine.

In order to obtain an age estimate for the hominin metatarsal,the Callao MT3was also directly analyzed. A diamondwire sawwasused to cut the bone 2 mm away from the break described below.Four laser ablation scans were then recorded on the cross-section(Fig. 3).

Preservation, conservation and cleaning of the Callao MT3

The Callao specimen with National Museum of the Philippinesaccession number II-77-J3-7691 is a right thirdmetatarsal (Fig. 4). Itis broken in two parts around the mid-shaft, but with the exceptionof the distal head, which is broken, the bone is almost complete.The missing head has not been identified among the other bonesrecovered from the same layer. The overall state of preservation ofthe bone is rather good, most being preserved under a thinyellowish coat of calcium carbonate concretions. Several smallpatches of hard and compact sediment are also attached to thebone. Smaller scratches (which occurred presumably during exca-vation) are visible on the medial and lateral surfaces of the shaftwhere the white cortex of the bone is exposed.

Both surfaces (proximal and distal) of the transverse breakaround mid-shaft are covered by a very thin layer of carbonateconcretions, which indicates that the fracture is ancient. However,it is neither oblique nor spiral, and has no helicoidal morphology.No scars or peeling around the fracture are visible. This indicatesthat breakage did not occur on fresh bone. This transverse break,

Figure 3. Cross-section of the Callao meta

almost perpendicular to the long axis of the shaft, resulted from thepost depositional fracture of already dry bone (Lyman, 1994). Thetwo parts of themetatarsal join almost perfectly at the fracture, andonly the presence of a thin layer of concretion inhibits a perfectrefitting.

Before cleaning the bone, a complete set of photographs, a 3Dsurface scan and a mCT-scan were made for archival records andfuture analysis. The object of cleaning the bone was to remove thethickest patches of sediment in order to observe its shape andmorphological features. Whenever possible, the thin carbonatedcoating was kept intact to avoid damaging the underlying surface,which was cleaned using dental tools under a stereo-microscope.Only purified water and a 50e50 mix of purified water and alcoholwere used to soften the compact sediment.

Except where noted, all descriptions and comparisons weremade after cleaning. Observations and measurements were madedirectly on the original specimen and on the 3D surface scan, aftervirtual refitting of the proximal and distal portions of the bone atthe mid-shaft fracture.

Results

Faunal remains

From the 2007 field season, the Callao Cave excavationsproduced a late Pleistocene vertebrate assemblage of 807 frag-ments of bone. In Layer 11, just a few isolated and potentiallyre-worked fragments of animal bone, including several skeletalelements of deer, were recovered. There was no evidence ofanything that could be considered an in situ human-derived boneaccumulation and no evidence of butchery or lithics. Humans,however, appear to have been present during this period of depo-sition, given the discovery of a terminal foot phalanx in Spit 36(180 cm BS), with an interpolated date of 30 ka.

Bone concentrations increased below Spit 47 (Layer 12). Downto Spit 53 (265 cm BS), all of the bone fragments were recoveredfrom clayey silt sediments and were very poorly preserved. Spit 54contained numerous mid-dark brown skeletal elements, similar inappearance to those recovered throughout the clayey silt depositsabove, as well as a few weathered and eroded fragments witha creamy appearance, similar to those from the underlying breccia(Layer 14). It is likely that, after the Layer 14 breccia had formed,erosional processes caused some bones to be redistributed into theaccumulating clayey silt sediments above. Alternatively, it ispossible that the boundary between clayey silt and breccia hasmigrated downwards as the breccia has decalcified, and that Spit 54(270 cm BS) forms a transitional zone between breccia and clay.

tarsal showing the scanned transects.

Figure 4. The Callao right metatarsal III (II-77-J3-7691).

Figure 5. Cut marks on the surface of a cervid bone.

A.S. Mijares et al. / Journal of Human Evolution 59 (2010) 123e132126

The breccia contains by far the greatest number of bone frag-ments (66%, or 533 fragments), indicating that bone survival wasgood within the calcium carbonate precipitate. As a result, bonesfrom the breccia are in much better physical condition than thepieces of bone recovered from the overlying clayey silts.

Surface modifications consistent with subsurface weathering,erosion and water-transport suggest that the bones were derivedfrom elsewhere in the cave system and were redeposited againstthe wall, where they were incorporated into a carbonate-cementedsandy silt loam breccia. The complete absence of any evidencefor bone-accumulating large carnivores and porcupines in thePhilippines (excluding Palawan), in addition to the presence ofthree parallel cut-marks caused by a sharp implement on themedial surface of a deer tibia shaft fragment (Fig. 5), indicates thatthe bone assemblage was almost certainly derived from humanactivity (Piper and Mijares, 2007). The lack of any lithics from the1980 (Cuevas, 1980) and present excavations at the depth of thebreccias in Callao Cave could imply the use of organic tools. Alter-natively, the differential transport of bones has caused spatialseparation of archaeological materials in the cave entrance.

Three large species of mammal were recorded in the Callao Cavebreccia: the native brown deer (Cervus mariannus), the Philippinewarty pig (Sus philippensis), and an extinct bovid evidenced by twosmall tooth fragments (Piper and Mijares, 2007). Brown deerconstitute more than 90% of the identifiable bone fragments. Thearticular ends of long bones and metapodials are relativelycommon in the assemblage. Loose maxillary and mandibular teethindicate that crania were originally present, and scapula, pelvic andvertebral fragments indicate the deposition of axial elements aswell. This suggests that whole, or different skeletal elements ofvarious deer carcasses were possibly once brought into the cave onoccasion.

Age determination

The cervid two teeth yielded U-series ages of 52�1.4 ka(Callao 1) and 54.3�1.9 ka (Callao 2). Sub-sampling of small peaksand troughs in the U-concentration had yielded U-series age esti-mates that were in the same statistical population as the meanvalues. We could not identify any regions that may indicate delayedU-uptake or leaching, compared with the average values. Thus, theU-uptake must have taken place over a relatively short period oftime (Pike et al., 2002). However, as U-accumulation in bones maybe delayed after burial, any U-series age estimates have to beconsideredminimum age estimates. ESR dating yielded a combinedESR/U-series result (Grün et al., 1988) for Callao 1 of 66þ11/�9 ka,

while Callao 2 did not yield a result (the closed system ESR ageestimate was younger than the U-series result). The discrepantcombined ESR/U-series results point to some reworking, asconfirmed by taphonomic examination of the bones from thebreccia.

It can be seen that the U-concentration varies greatly along theprofiles (Fig. 6). We carried out U-series age estimates for allconcentration features to check whether delayed uptake or leach-ing has taken place, such as peaks and troughs (Fig. 6). We foundonly a small number of results (seven of 69) where the 1� sweighted means did not overlap. This is somewhat less thanexpected from a normal statistical distribution and points to thefact that our error bars are probably somewhat too large.

On the whole, there is no relationship between U-concentrationand age estimate (Fig. 7). This points to a rapid uptake and excludesleaching along pores. Instead, as an indication for U-leaching, thedrops in U-concentration are probably caused by heterogeneities inthe bone structure, which had little influence on the mode ofU-mobilization.

Single age estimates may be affected by a number of processesrendering them inaccurate, and for this reason the U-series resultsmust be considered minimum estimates. This alone precludes anyclaim for accuracy. In this regard, the interpretation of APNIAH1 inBarker et al. (2007) has been used to cast doubt on the results ofU-Series dating at Niah. Barker et al. (2007, p. 253) write “.a

Figure 6. Comparative diagrams of the four laser ablation scans on the Callao metatarsal.

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uniform date profile [of APNIAH1] may also be reached after furtheruptake or leaching of uranium, which would give an erroneous result,so on its own the date should only be taken as provisional.”. In thecontext of MT3, we do not have to consider further U-uptake,because this would only lower the calculated apparent U-series

estimates. The question is whether our results could seriouslyoverestimate the correct age of the sample. Under normalcircumstances, leaching would start at the surface and be accom-panied by lower U-concentrations. While some of the profiles showsignificantly lower U-concentrations at or close to the surface, these

0

20

40

60

80

100

0 20 40 60 80 100

U-s

erie

s ag

e es

timat

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U concentration (ppm)

Figure 7. Apparent U-series age versus U-concentration (error bars omitted forclarity).

A.S. Mijares et al. / Journal of Human Evolution 59 (2010) 123e132128

sections do not show any significantly older apparent U-series ageestimates. The only region where leaching could perhaps be iden-tified is in the centre of the fourth track between cycles 2190 and2310 (lower diagram, Fig. 6). The U-concentrations drop by 50%,while the average apparent U-series results are around 15% olderthan the surrounding data without being statistically significantlydifferent.

If the bone was younger than 40 ka, the minimum averageamount of uranium leached from it must have been at least 35%,and the leaching must have happened relatively recently. On top ofthis, it must have affected the whole bone in the same manner, i.e.,parts with high U-concentrations lost 35% of their total uranium,and the same would have to be lost from parts with lowU-concentrations. Any such process must be regarded as purelyhypothetical, and the above discussion reinforces the need fordeveloping combined mass spectrometric Pa/UeTh/U analysis ofbones to address questions of U-mobilization (Grün et al., in press).

To summarize, it cannot be excluded that some leaching mayhave taken place in the past, causing an increase in the averageapparent U-series results by some unknown amount. However, wedo not find any clear evidence for leaching, nor could it have beenon a scale sufficient to reduce the minimum age of MT3 to 40 ka oryounger. On balance, we regard the U-age estimate of 66.7�1 ka,derived from the weighted mean of all data points, as a minimumage estimate for the MT3. This agrees with the ESR age estimate ofCallao 1, although this may be purely coincidental due to the natureof the deposit.

Taxonomic identification of the Callao MT3

The general morphology, shape and size of the Callao right MT3indicate the bone belongs to a primate. For taxonomic identifica-tion, morphological comparisons were first undertaken withprimates of medium to large body size presently living in IslandSoutheast Asia (Fig. 8). Even thoughMacaca and Homo are the onlytwo extant genera of catarrhines in the Philippines (Fooden, 1991;Brandon-Jones et al., 2004; Harrison et al., 2006), representativesof the genera Pongo and Hylobates are added to this comparison.Indeed, their present geographic extension reaches the neighboringisland of Borneo, and the morphology of their metatarsals ispotentially close to the morphology of the Callao specimen. Forcomparison from a palaeontological perspective, the left MT3 ofHomo habilis, OH8, is included in the comparative sample. Thisspecimen (whose 3D model is mirrored in Fig. 8 for easiest directcomparison) is part of one of the oldest groups of foot bonesattributed to the genusHomo, and related to a partly or fully bipedallocomotion (Day and Napier, 1964; Archibald et al., 1972; Kidd et al.,1996; Berillon, 2000; Susman, 2008; seeWood,1974; and Gebo andSchwartz, 2006 for a different taxonomic attribution of OH8).

Several diagnostic features of the Callao metatarsal can beunderlined from this comparison (Fig. 8). In the comparativesample, the global size of the Callao metatarsal is medium: it issmaller than Pongo, larger than Hylobates and Macaca, and fitswithin the genus Homo. In medial view, the dorsal face of the shaftof the Callao specimen is straight, as seen in the two representa-tives of the genusHomo, and not convex as in Pongo,Hylobates, or toa lesser extentMacaca. In dorsal view, the proportions of the CallaoMT3 shaft, the shape of the base, and the oblique orientation of theproximal articular facet for the lateral cuneiform are close in shapeto those observed in other Homo specimens. In this view, themedial and lateral borders of the shaft of the CallaoMT3 are slightlyand regularly convergent from the proximal portion to the distalend of the shaft, which is a condition also encountered in OH8 andHomo sapiens in general. A different morphology is observed in theother genera: the medial and lateral borders of the shaft appearsub-parallel in Pongo, and they are slightly divergent anteriorly inHylobates and Macaca. The proximal view shows an outline of thebase of the Callao MT3, which is definitely closer to Homo than toany other primates included in the comparison. Its elongatedtriangular outline is completely different from the outline found inPongo, Hylobates and Macaca. In those genera, the medial andlateral borders of the base have very different sizes and shapes,with articular facets for MT2 and MT4, which are organized andorientated differently. In this comparison, the base of the CallaoMT3, which is proportionally shorter in the dorso-plantar direction,tends to be closer in shape to OH8 than to the Philippine Negritospecimen used for comparison. However, variability in this featureis rather common in H. sapiens.

Altogether, these features indicate that the Callao MT3 belongsto the genusHomo. It is especially close to small-bodied Homo, suchas African H. habilis and present-day Philippine Negritos, the latterbeing much closer chronologically and geographically. However,some differences, such as the reduced proportions of the base, wereobserved. They will be discussed further in the morphological andmetrical descriptions that follow.

Age at death

During individual growth, the head is the last anatomical part tofuse onmetatarsals, between the ages of 12 and 16 years on averagein anatomically modern H. sapiens (Scheuer and Black, 2000). Theabsence of the head could thus indicate a non-adult individual (i.e.,with the distal head being unfused at the time of death) or, alter-natively, a broken, fully developed and fused adult metatarsal. Thedistal extremity of the Callao metatarsal has a fracture, whichoccurred at the level of the dorsal tubercles and is obliquelyorientedwith respect to the long axis of the shaft. The broken distalextremity is slightly eroded and partly covered by sediment, whichmakes it difficult to ascertain the presence or absence of a meta-physeal surface. Such a surface can also not be detected from anal-ysis of CT-scan data through close-up observation of the CT slices atthe distal extremity (Fig. 9). On the other hand, themorphology andsize of the preserved portion of the medial tubercle seem to berather large and fully developed. Thiswould better correspond to anadvanced stage of growth, with a distal head that was about to fuse,or was already fused at the time of death. These observations pointmore to an adult or young adult metatarsal, which was brokendistally after burial. However, it is impossible to discard entirely thepossibility that the specimen is from a juvenile or adolescent.

Morphological and metrical features: comparisons with H. sapiens

As seen in the anatomical comparisons, the general morphologyof the Callao metatarsal matches those observed in the genus Homo

Figure 8. Comparison of (A) the Callao MT3 in proximal, dorsal and medial views with right third metatarsals of (B) Homo sapiens, male Negrito; (C) Homo habilis, OH 8 e mirrored3D model of a cast of the left MT3; (D) Macaca, (E) Hylobates; and (F) Pongo. 3D models obtained by surface scanning with a NextEngine Desktop 3D Scanner.

A.S. Mijares et al. / Journal of Human Evolution 59 (2010) 123e132 129

and appear close to H. sapiens. Some morphological particularitiesalso diverge to some extent from the general morphologyencountered in anatomically modern H. sapiens (see Fig. 4 for themorphological features discussed, and Fig. 8 for comparison withthe MT3 of a male Philippine Negrito).

In proximal view, the shape of the base is typically human. Itshows a triangular contour with slightly depressed medial andlateral sides, the latter being more depressed just under the artic-ular facet for the fourth metatarsal. However, the medial facet forthe second metatarsal appears to be more plantarly oriented thangenerally encountered in H. sapiens. In lateral view, the proportionsand especially the dorso-plantar development of the proximal partare reduced compared with the size and development of the shaft.The proximal articular facet for the lateral cuneiform showsa marked dorso-plantar convexity where it is usually flat or slightlyconcave in anatomically modern H. sapiens. More precisely, theconvexity of the facet in lateral view is mainly due to the orienta-tion of the plantar portion of the base that is clearly oblique to themain axis of the bone and thus marks an angle with the dorsalportion of the base. On the lateral side of the base, the articular

facet for the fourth metatarsal is clearly visible; it is well developedand slightly elongated. A bulging tubercle is also present, distal tothe lateral articular facet. On the medial side, only one articularfacet for the second metatarsal is visible and located on the dorsalcorner of the base. After cleaning the attached sediment, theplantar portion of the medial side of the base appears to be ratherflat, but no delimited facet is visible. It remains possible thatinsufficient cleaning prevents us from observing the plantar facet,but it is not uncommon in the H. sapiens MT3 for the second facetfor MT2 to be reduced in size or even totally absent. In a study of100 MT3, Singh (1960) found 41 specimens without this plantarfacet.

The shape of the shaft is also unusual, especially when seen inlateral view. The dorsal face of the shaft is very slightly convex,almost straight and horizontal, and with a longitudinal ridgerunning along the dorsal surface. In H. sapiens, the plantar surfaceof the shaft generally tapers gradually from the base to the head.Accordingly, the plantar surface around the mid-shaft has a slightlongitudinal concavity, with more marked and abrupt concavitieslocated just anterior to the base and posterior to the distal head.

Figure 9. CT-scan views of the Callao MT3. A: midsagittal CT slice; B: 3D model with transparency (lateral view); C: close-up view of a sagittal CT slice of the distal extremity(the slice is parallel to A but more medially located). Images A and C show the distal extremity of the MT3, which is broken and partially filled-up by sediment. No transversemetaphyseal surface is visible.

A.S. Mijares et al. / Journal of Human Evolution 59 (2010) 123e132130

The Callaometatarsal shows amarked concavity just anterior to thebase and then a more regular and pronounced concavity of theplantar surface of the shaft from the first third of its length tothe most distally preserved portion. No clear and marked change inthe angle towards the head is visible. Consequently, the cross-section at the mid-shaft is almost circular, flattenedmedio-laterallyand enlarged in the dorso-plantar direction for the distal-mostthird of the shaft.

While not formally developed in this paper, general metricalcomparisons with H. sapiens samples were undertaken with datafrom the literature (for instance Volkov, 1903e1904; Gabunia et al.,2000a); and also with data gathered by one of us (Détroit) from lateUpper Pleistocene and Holocene H. sapiens from Indonesia and thePhilippines (see Détroit et al., 2004; Détroit, 2006). This firstapproach confirmed that one of the most striking features of theCallao specimen is its overall small size. As a result, it was decidedto focus, for comparative morphological purposes (and not taxo-nomic identifications), on a series of third metatarsals of recentNegritos from the collections of Musée de l’Homme (Muséumnational d’Histoire Naturelle) in Paris (Table 1). Indeed, Negritos aresmall-sized and slightly built Philippine H. sapiens, inhabitingregions of Luzon Island close to where Callao Cave is located. Thecollections from Musée de l’Homme also have the advantage ofbeing well documented and repeatedly studied from variousanthropological perspectives (see, for instance, Genet-Varcin, 1951,who includes sex determinations of the skeletons; and Volkov,1903e1904 for the first published study of the foot bones).

The partial length of the Callao bone, taken parallel to the mainaxis of the shaft from the proximal tip of the base to the level of themedial tubercle, overlaps with the range of variation measured for

male and female Negritos. However, the dimensions of the base ofthe bone and the section of the shaft are smaller, indicating peculiarproportions for the Callao metatarsal. At the mid-shaft, the shaftappears to be considerably smaller in the dorso-plantar directionthan in the Negrito comparative sample. As shown by the reduceddimensions obtained for the dorso-plantar height and medio-lateral breadth of the proximal facet for the lateral cuneiform, thebase is very small. It is the smallest of our sample, confirming theparticular shape and proportions of the bone as seen from lateraland superior views.

Discussion

For more detailed future comparisons, it is important to takeinto account the paucity of Southeast Asian Homo erectus andUpper Pleistocene H. sapiens postcranial remains. The fossil recordis particularly deficient in foot bones, with none recorded so far forSoutheast Asian H. erectus (Widianto, 1993; Antón, 2003). ForH. sapiens, several rather complete late Upper Pleistocene andHolocene human skeletons have been recovered from Indonesia(Jacob, 1967; Détroit, 2002, 2006; Simanjuntak, 2002; Sémah et al.,2004), and a few fragmentary postcranial remains come from thePhilippines, including foot bones (Détroit et al., 2004). For thosespecimens we are able to observe and measure, the dimensionslargely exceed the dimensions of the Callao metatarsal, and theproportions of the base are never reduced to the extent seen in theCallao metatarsal.

From broader taxonomic, chronological and geographicperspectives, metatarsal bones appear to have been relativelystable in terms of overall morphology and size since the first African

Table 1Comparative measurements of the Callao metatarsal with Negrito samples

Total length Partial length(from the base tothe medial tubercle)

Shaft Proximal facet for lateralcuneiform

Facet 1 (dorsal)for metatarsal 2

Facet formetatarsal 4

Dorso-plantardiameter

Medio-lateraldiameter

Dorso-plantarheight

Medio-lateralbreadth

Length Height Length Height

Callao 60.99a 52.58 6.58 5.99 11.28 8.69 5.76 3.82 6.46 4.92

Negritos males (n¼ 11)Mean 64.69 55.66 8.51 7.32 18.79 11.72 6.46 4.74 8.02 7.73Std error 0.862 1.033 0.107 0.268 0.427 0.245 0.418 0.269 0.277 0.323Min. 59.5 49.4 8 6.5 16 10.2 4.5 3.2 7 6Max. 68.3 60.5 9.1 9.6 21.1 13.3 8.9 6.3 10.2 9Median 65.2 56.8 8.5 7.1 18.8 11.7 6.3 4.7 8 7.7

Negritos females (n¼ 12)Mean 59.21 51.33 7.33 6.42 16.87 10.88 6.54 4.95 8.06 7.98Std error 0.554 0.357 0.091 0.179 0.209 0.211 0.198 0.131 0.353 0.329Min. 56.5 49.2 6.9 5.1 15.5 9.5 5 4.3 6.2 5.7Max. 62.7 53.5 7.8 7.3 17.9 12.3 7.4 5.9 10.5 9.9Median 58.55 51.15 7.35 6.45 16.95 10.8 6.8 4.8 7.9 8

a Estimated from the regression of total length against partial length for the pooled-sex sample of 23 adult Negrito metatarsals III (r¼ 0.93, p< 0.01;Ltot¼ 1.022Lpartþ 7.2519).

A.S. Mijares et al. / Journal of Human Evolution 59 (2010) 123e132 131

representatives of the genus Homo (i.e., H. habilis and Homorudolfensis). Differences in function have been widely discussed forthe morphology and anatomical position of MT1, as well as theimplication of metatarsals in the development of longitudinal andtransverse plantar arches (see for instance Aiello and Dean, 1990;Berillon, 2000; Zipfel et al., 2009). As far as the third metatarsal isconcerned, the particular form (or relative proportions) of the baseand shaft of the Callao bone has apparently not been described sofar from other early fossil specimens of the genus Homo fromEastern Africa, Southern Europe, or the Caucasus. This observationis confirmed by direct comparison with the H. habilis left MT3 ofOH8 (Fig. 8, and see Day and Napier,1964; Kidd et al., 1996; Berillon,2000), and from comparisons with published data from AtapuercaGran Dolina (Lorenzo et al., 1999) and Dmanisi (Gabunia et al.,2000a,b; Lordkipanidze et al., 2007).

Interestingly, the remains discovered at Liang Bua in Flores,representing several individuals attributed to the species H. flor-esiensis, include foot bones, and especially the complete series ofright and left metatarsals of the individual LB1 (Brown et al., 2004;Morwood et al., 2005; Jungers et al., 2009a). The length of the leftMT3 (LB1/23), at 60.4 mm (Jungers et al., 2009b), is near the esti-mated length for the Callao specimen (60.99 mm; see Table 1).Although few details are available regarding the exact morphologyand shape of this particular bone, it certainly calls for interestingfuture comparisons. It is very difficult to determine accuratelya taxonomic attribution from a single bone and, with the exceptionof the Liang Bua remains, the MT3 recovered from Callao Cave onLuzon Island is the only Upper Pleistocene foot bone attributed tothe genus Homo discovered beyond Wallace’s Line in IslandSoutheast Asia. Additionally, the preliminary description of theCallao MT3 clearly indicates a reduced general size only known inthis region in H. floresiensis and in small-bodied H. sapiens, such aspresent-day Philippine Negritos.

Conclusions

The Callao Cave metatarsal indicates that a species of hominincrossed water gaps between Sundaland and Wallacea to reachnorthern Luzon by 67,000 years ago. The specimen leaves us witha conundrum e in size, it compares with modern Negritopopulations, but a few morphological features are unusual.A comprehensive analysis of size and shape characteristics,including comparisons with larger samples of H. sapiens and fossilspecies of the genus Homo, is now needed.

Provisionally attributed to a rather small-bodied H. sapiens, theCallao MT3 documents the presence of a hominin species on theisland of Luzon as early as 67 ka, and is testimony to a capability tocolonize new territories across open sea gaps. The Philippinespecimen also indicates that Flores was not the only island inWallacea to be occupied by hominins more than 50,000 years ago.

The discoveries at Callao Cave also raise some other importantquestions about the cultural behavior of these early colonizers ofthe Philippine archipelago. For example, even though there isevidence of butchery in the animal bone assemblage, not a singlestone implement was recovered, suggesting perhaps the use of analternative technology. To answer such questions, more archaeo-logical research in the caves of karstic limestone formations of thePhilippines is required.

Acknowledgement

We are grateful for the support of the National Museum of thePhilippines, the Cagayan Provincial Government, and the ProtectedArea Management Board-Peñablanca. Roberto Macchiarelli andArnaudMazurier are acknowledged for the CT-scan of the bone.Weare also grateful to Eduardo Bersamira and Myra Lara for theillustrations, and Archie Tiauzon as a member of the excavationteam. Funding for this research came from an Australian ResearchCouncil Discovery Grant to Peter Bellwood and a University of thePhilippines Research Grant to Armand Mijares. Florent Détroitreceived support from Asia-Link HOPsea and Erasmus MundusAction 3 exchange programs. We are grateful for the support ofPhilippeMennecier and Aurélie Fort for the access to the collectionsat the Musée de l’Homme. The Office of the Vice Chancellor forResearch and Development, University of the Philippines fundedPhilip Piper. The dating aspects of this study were supported byAustralian Research Council Grant DP0664144 (Grün et al.) Micro-analysis of human fossils: new insights into age, diet and migration.

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