Delayed increase in stone tool cutting-edge productivity at the Middle-Upper Paleolithic transition in southern Jordan

Domain: earth_science
Published: 2024-02-07
Editorial outcome: minor_revision

Abstract
Althoughthelithiccutting-edgeproductivityhaslongbeenrecognizedasa
quantifiableaspectofprehistorichumantechnologicalevolution,there
remainsuncertaintyhowtheproductivitychangedduringtheMiddle-to-
UpperPaleolithictransition.Herewepresentthecutting-edgeproductivityof
eightlithicassemblagesintheeasternMediterraneanregionthatrepresenta
chrono-culturalsequenceincludingtheLateMiddlePaleolithic,InitialUpper
Paleolithic,theEarlyUpperPaleolithic,andtheEpipaleolithic.Theresultsshow
thatamajorincreaseinthecutting-edgeproductivitydoesnotcoincidewith
theconventionalMiddle-UpperPaleolithicboundarycharacterizedbythe
increaseinbladesintheInitialUpperPaleolithic,butitoccurslaterinasso-
ciationwiththedevelopmentofbladelettechnologyintheEarlyUpper
Paleolithic.GivenincreasingdiscussionsonthecomplexityofMiddle-Upper
Paleolithicculturalchanges,itmaybefruitfultohavealong-termperspective
andemployconsistentcriteriafordiachroniccomparisonstomakeobjective
assessmentofhowculturalchangesproceededacrossconventionalchrono-
culturalboundaries.

Introduction
The Middle to UpperPaleolithic transition (the MP-UP transition) geographically diverse cultural patterns that involve both con-
has long been known as a key prehistoric cultural process or tinuous and discontinuous aspects as well as various timings of
chronologicalrangetoinvestigatehumanbioculturalevolutiondue changedependingonculturalelements6–9.
to its temporal proximity to the wide geographic expansion of TheculturalframeworkoftheMP-UPtransitionhasbeeneffec-
Homo sapiens ca. 50–40 thousand years ago and concomitant tively delineated by techno-morphological attributes ofstone tools,
demiseofarchaichumansincludingNeanderthals1–3.Mainlybased which constitute the most abundant cultural remains at Paleolithic
on European records, the MP-UP cultural transition was con- sites10–12,anddetailedexaminationsoflithictechno-morphologyled
ventionally regarded as a discontinuous process or “revolution” researchers to reassess the conventional view and propose more
marked by the introduction of new cultural/behavioral packages complicatedculturalprocessesattheMP-UPtransition2,13–15.However,
associated with a wave of dispersing Homo sapiens population4,5. in order to compare variations of lithic assemblages over different
However, more recent increase in the recovery of archeological periodsorregions,itremainsamethodologicalchallengeforarche-
records, particularly in Africa and Asia, has suggested ologiststoestablishconsistentandquantitativecriteria(ratherthan
descriptions)thatallowobjectiveillustrationandassessmentoftem-
poral/spatialculturaldynamics.

Here,wepresentaquantitativeexaminationofdiachronicchan-
gesinstonetoolassemblagesattheMP-UPtransitionbyfocusingon
theproductionrateofstonetoolcuttingedges.MostPaleolithicstone
artifactshavesharpedgesastheirfunctionalparts(e.g.,forcuttingand
scraping),and sharp edges arecreated byknapping offflakesfrom
siliciousrocks,suchasobsidianandflint16.Thus,thelengthofcutting
edgepermassofstonehasbeenusedinnumerousstudiestoquantify
theefficiencyinstonetoolproduction,inotherwords,theefficiencyin
theconsumptionofrawrockmaterial17–22.Althoughthecutting-edge
production rate has been widely recognized as a consistent and
quantifiable aspect of prehistoric human technological evolution,
thereremainsuncertaintyabouthowtherateactuallychangedduring
theMP-UPtransition.Conventionally,ashiftfromdominantLevallois
technologyintheMPtothebladetechnologyintheUPwasconsidered
to have increased the cutting-edge production rates23,24. However,
uncritical recourse to such a progressive view is currently being
reconsidered under recent recognition of Paleolithic technological
variabilityandinsightsfromlithicexperimentalstudies(SeeSupple-
mentaryNote1fordetails).

Inaddition,itiswellknownthatlithicproductionactivitiescanvary
dependingontheavailabilityofrawmaterials,andparticularlyinthe
caseofPaleolithicmobileforagers,toolproductionanduseactivitiesare
oftensegmentedbyresidentialmovesandperformedinmultiplestages
overdifferentplaces25–27.Thismaycausesynchronicvariabilityinlithic
assemblages depending on the nature of sites, such as raw material
quarry/workshop, short-term transitory site, and base camp. Because
ourmainconcerninthisstudyisdiachronicchangesratherthansyn-
chronic variations, it is critical to use research materials/lithic
assemblagesthatsharethesamerawmaterialconditionandoccupa-
tionalnature.Tothisend,weselectivelyusedeightassemblagesfrom
fivesitesintheLevant(eastMediterraneanregion),focusingonsouth-
ernJordan,wherethesitessharethesameenvironmentalsettings,par-
ticularlyintermsoftheavailabilityoflithicrawmaterial(Fig.1;Methods;
Supplementary Figs. 1–5). All the five sites are situated under rock
sheltersandrepresentsmallhabitationsiteswithhearthremains,where
palimpsestoflithicproductionanduseactivitiesaccumulated28–31.

Importantly, the selected lithic assemblages cover the MP-UP
transition(SupplementaryFig.6),includingtwoassemblagesofthe
LateMiddlePaleolithic(LMP)fromTorSabihaandTorFaraj,twoInitial
UpperPaleolithic(IUP)assemblagesfromWadiAgharandTorFawaz,
twoEarlyUpperPaleolithic(EUP)assemblagesfromTorHamarLayers
HandLayersF–G,andtwoEpipaleolithic(Epipal)assemblagesfrom
TorHamarLayerE2andLayersB–E1(SupplementaryTable1).Thetwo
assemblages in eachof the EUP and the Epipalare stratigraphically
sequencedatTorHamar,butwedonotassumeachronologicalrela-
tionshipbetweenthetwoassemblageswithineachoftheLMPandIUP.
Thus,chrono-culturalunits assumed inthis study arethe LMP(Tor
Sabiha and Tor Faraj), IUP (Wadi Aghar and Tor Fawaz), EUP1 (Tor
Hamar Layers H), EUP 2 (Tor Hamar Layers F–G), Early Epipal (Tor
HamarLayerE2),andMiddleEpipal(TorHamarLayersB–E1).

RegardingtheMP-UPtransitionintheLevant,aslightincreasein
theratewaspreviouslydetectedbytwostudiesthatactuallymeasured
the cutting-edge length of archeological specimens, but the early
studies were based on small sample size, lacked a detailed chrono-
cultural sequence from the IUP to EUP, and employed unprecise
methodsforedge-lengthmeasurement19,21,29.Thispaperupdatesthe
previous studies by adding IUP and EUP (more specifically, the
Ahmarian) assemblages that establish more detailed cultural
sequences at the MP-UP transition. The addition of the IUP assem-
blagesisparticularlyimportantbecausethischrono-culturalconcept
is used not only in the Levant but also in other regions, such as
Central–SoutheasternEuropeandCentral–NorthAsia,tocharacterize
uniqueculturalchangesatthebeginningoftheUP(Supplementary
Note2)2,14,32,33.TheIUPandtheAhmarianlithictechnologyhavealso
beenincreasinglyrecognizedaskeyculturalrecordsthatcanbecor-
relatedtopaleoanthropologicalandgeneticevidencetoexaminethe
dispersalprocessesofHomosapiensinEurasia2,34,35.

Tomakeanaccurateassessmentofcutting-edgeproductivity,we
measured the cutting-edge length of all debitage types except for
retouchedpieces,cores,anddebris(suchaschipsandchunks),fol-
lowingmethodsproposedbyrecentlithicexperimentalstudies18,20.To
achieveaccurateandprecisemeasurementofirregularedgeforms,a
rigorousprotocolofdigitalmeasurementwasappliedtothecutting-
edge length of more than 5000stone tools18,20 (Methods; Supple-
mentaryFig.7).

Thefollowingresultsshowthatamajorincreaseincutting-edge
productivitydoesnotcoincidewiththeconventionalMP-UPboundary
characterizedbytheincreaseinbladesintheIUP,butitoccurslaterin
associationwiththedevelopmentofbladelettechnologyintheEUP.
Thelowcutting-edgeproductivityintheIUPderivesfromthelarge
massandvolumeofblankswithwidestrikingplatforms.Thedegreeof
theproductivityincreaseintheEUP,realizedbytheminiaturizationof
multipleblanktypes,isgreaterthanthesubsequentoneintheEpipal.

Results
Temporaltrendsinthecutting-edgelengthpermassfromLMP
toEpipal
FromtheLMPtotheIUP,therelativefrequenciesofblades/bladelets
clearlyincreasedwithoutsignificantchangesintheirsize(Fig.2).In
contrast, from the IUP to EUP, blades/bladelets increased only
slightly,buttheirsizeclearlydecreased,reflectingthedevelopment
ofbladelettechnology.FromtheEUPtotheEarlyEpipal,therelative
frequencyofblades/bladeletsdidnotchangesignificantly,andtheir
sizereductionwasmarginalincomparisonwiththatoftheIUP-EUP
transition. From the Early to Middle Epipal, the relative frequency
andsizeofblades/bladeletsincreased.

Regardingthetotalcutting-edgelength/massratio,thetwoIUP
assemblages(WadiAgharandTorFawaz)showedthelowestvalues
amongthelithicassemblagesanalyzedinthisstudy.Diachronically,
thetotallength/massratiodecreasedfromtheLMP(particularlyfrom
TorFaraj)totheIUPandthendistinctivelyincreasedintheEUP,fol-
lowedbyasubtleincreaseintheEpipal.

Asimilartemporaltrendwasobservedintheindividuallength/
massratios(Fig.3a),whichrepresentthecutting-edgelengthpermass
foreachoftheunmodifiedblanks(Methods).Pairwisecomparisonsby
theDunn–Bonferronitestdetectedsignificantdifferencesbetween21
pairsoutofallpossiblepairs(=28)amongtheeightassemblages.Allof
the21significantdifferencesareconsistentwithaproposeddiachronic
changethroughwhichtheedgelength/massratiodecreasedfromthe
LMPtoIUP,increasedfromtheIUPtoEUP,andagainincreasedfrom
theEUPtoEpipal.ThedataoftheLMP(TorSabiha)isnotstatistically
differentfromthoseofthetwoIUPassemblages,whicharetheonly
differencesthatareexpectedbytheproposeddiachronicchangebut
notstatisticallysignificant.

Variationsinthecutting-edgelength/massratioby
debitagetypes
Clearly,bladeletsshowthegreatestratiosamongthedebitagetypesin
allperiodsfromtheLMPtoEpipal(Fig.3b).Inmoredetail,however,
thelength/massratiosofbladeletsfromthetwoIUPsitesarelower
thanthoseoftheLMP,EUP,andEpipal assemblages (p<0.03 by
Dunn–BonferronitestforthedifferencesbetweenIUPandEUP/Epi-
pal).Similarly,flakesandbladesofthetwoIUPsitestendtoshowlower
length/massratiosthantheLMP,EUP,andEpipal(seeSupplementary
Tables2–4forstatisticalsignificance).

Relationsofthecutting-edgelength/massratiostodimensional
attributesofblanks
Clearnegativecorrelationswereobservedbetweenthelength/mass
ratio and the mass of each lithic artifact (Supplementary Fig. 8),
although this result is self-evident because the mass is used in the
calculation of the length/mass ratio. More importantly, other attri-
butesthatshowedclearnegativecorrelationswiththeedgelength/
massratioarewidth,thickness,andtheplatformarea,asindicatedby
high absolute values of Spearman’s Rs (Figs. 4–5; Supplementary
Figs. 9 and 10). This means that narrower and thinner blanks with
smallerstrikingplatformstendtohavegreaterratiosofedgelength
per mass. As typically shown in the case of width (Fig. 4), such a
negative correlation is observable similarly in each of the debitage
types. Weaker correlations were observed for length, the ratio of
lengthtowidth(i.e.,elongatedness),andtheratioofwidthtothickness
(i.e.,flatness)(SupplementaryFigs.11–13).Thesepatternswerecon-
sistentlyobservedinalltheassemblagesfromtheLMPtoEpipal,and
nodiachronictrendwasobservable(Fig.5).

Methods
PaleolithicassemblagesinsouthernJordananalyzedin
thisstudy
Forthestudyofcutting-edgeproductionrates,weusedeightPaleo-
lithicassemblagesfromfivesitesinthewesternHismaBasin,southern
Jordan.OurarcheologicalfieldworkinJordanwasconductedaccord-
ingtothe“RegulationsforArcheologicalProjectsinJordanbasedon
theprovisionsoftheJordanianAntiquitiesLawNumber21fortheyear
1988anditsamendments”.Thepermissionstoconductthefieldwork
and the export of archeological materials to Japan, where analyses
wereconducted,wereobtainedfromtheDepartmentofAntiquitiesof
Jordan.

Thefollowingisthelistofpermissionsforourfieldworkandthe
exportofmaterialstoJapan.ExcavationPermits:No.2016/51(issued
on24July2016),No.2017/44(issuedon16August2017),No.2018/18
(issuedon29May2018),No.2019/49(issuedon15August2019),and
No.2022/43(issuedon21August2022).ExportPermits:No.12/5/2899
(issued on 15 August 2016), No. 12/5/3414 (issued on 18 September
2017),No.12/5/2290(issuedon21June2018),No.12/5/382(issuedon
16September2019),No.12/5/35/7(issuedon13September,2022).

ThewesternHismaBasininthesouthernJordanareawasorigin-
allyinvestigatedbyD.O.Henrybetween1976and199928,29,59,82,83,and
therenewedfieldworkhasbeenongoingsince201684.Theeightlithic
assemblagesanalyzedinthisstudyarethecollectionsoftherenewed
investigations. They consist of two Late Middle Paleolithic (LMP)
assemblages from Tor Sabiha29 and Tor Faraj59, two Initial Upper
Paleolithic(IUP)assemblagesfromWadiAghar45andTorFawaz42,two
EarlyUpperPaleolithic(EUP)assemblagesfromTorHamarLayers
H
andLayersF–G62,84,andtwoEpipaleolithic(Epipal)assemblagesfrom
TorHamarLayerE2andLayersB–E184–86.

Theuseofthesematerialsisparticularlysuitableforthepurpose
ofthisstudybecausethesitesarelocatedclosetoeachother(within
2km)exceptforTorSabiha,whichisstillonly14kmawayandsituated
in very similar environmental settings particularly in terms of the
availabilityoflithicrawmaterial,chertinthiscase.Thefivesitesshare
thesamegeologicalsettingscharacterizedbyextensiveexposureof
Umm‘IshrinSandstone87.Afewsmallspotsofchertsourcesareloca-
ted 2–8km away from the Jebel Qalkha area30, and more extensive
chertoutcropsaredistributedintheMa’anPlateautothenorth,which
is15kmawayfromJebelQalkhaand6kmfromTorSabiha.

TorFaraj.TorFaraj(29°56'19.9“N,35°19'33.6“E)isarocksheltersitein
theJebelQalkhaarea(SupplementaryFig.1).Ithasatleast1.5m-thick
deposits, from which LMP remains have been recovered. The first
investigationin1983openedatesttrench,andmoreextensiveexca-
vations in 1993 and 1994 revealed an area of 7m×12 m29,59. These
originalexcavationsdetectedsixstratigraphiclayers,includingLayers
A,B,C,D1,D2,andE,inastratigraphicorderfromthetop.LayersAand
Baresandydepositsof20–30cminthicknessthatwereaccumulated
bymodernlocalinhabitantswholeveledtheshelter’sfloor.Theyare
underlain by Layer C, which measures 30–75cm in thickness and
consists of homogeneous reddish-yellow silty sand. Layer D1 repre-
sents rockfall (10–35cm in thickness) and consists of weathered
sandstone rubble that is partially cemented. Layer D1 is distributed
only in the southwestern corner ofthe excavation area. Underlying
LayersD1andC,LayerD2consistsoflightredtoredsandandmea-
sures30–75cminthickness.ThelowestlayerdetectedsofarisLayerE,
whichconsistsofreddish-yellowsiltysand.Thestratigraphicbound-
ariesbetweenLayersC,D2,andEarediffuseandgradual.

TheaboveinvestigationsbyD.O.Henrydetectedthreeoccupa-
tionallevels(reported asFloors 1 and 2)in LayersC and D2 upper
throughintrasitespatialanalyses59.Severalradiometricdates(TL,AAR,
andU-series)wereobtainedfromLayerC,rangingbetween43.8and
69.0kya59.

Therenewedinvestigationin2017re-openedUnitsA4,B2,B3,and
B484.UnitA4retaineddepositsofLayersD2andEwhileonlyLayerE
remainedintheotherunits.AsreportedbyKadowakiandHenry84,the
densityoflithicartifactsinLayerEiscomparabletothoseofFloors1
and2inLayersCandD2upper.Inaddition,thedepositsinLayerE
contained ash patches and many charcoal fragments that probably
represent another occupational level. All the units yielded LMP
artifacts62,whichareusedinthisstudy.

TorSabiha.TorSabiha(29°57'46.36"N,35°28'10.30“E)isarockshelter
site located in the Judayid Basin, southern Jordan (Supplementary
Fig.2).TheinitialexcavationbyD.O.Henrytookplacein1979–198029.
Anareaimmediatelyoutsidetherockshelterwasmainlyexcavatedina
3m×4mtrench,andadepositof1.3minthicknesswasdetected.The
toptwolayers(LayersAandB)consistofloose,reddish-brownsand
andcontainbothChalcolithicandLMPartifacts.AnunderlyingLayerC
consistsoffriable,pinkish-graysandandcontainsLMPartifacts.The
lowermostLayerDiswhitesand,lyingontopofbedrock.Inadditionto
lithicartifacts,somefaunalremainswererecovered,includinggazelle,
bos, equid, and ostrich eggshell fragments. A single AAR date
(69,000±6000BP)wasobtainedfromanostricheggshellfragment
fromLayerC29.

In the 2019 and 2022 seasons, a renewed excavation by the
authorsopenedeightnewexcavationareas(Units100–107,eachof
whichis1m×1m)(SupplementaryFig.2).Fiveofthemwereplacedin
the terrace next to the previous excavation areas while three units
(Units 105–107) were opened inside the rock shelter.In the terrace
(Units100–102and104),theexcavationrevealedabout1m-thicksand
deposits,inwhichLMPartifactsweremainlycollectedfromLayersC
andD.Insidetherockshelter(Units105–107),theexcavationuncov-
eredabout4m-thickdepositsontopofthebedrock.Whilemostofthe
depositsaresiltyanddatetotheHolocenewithalmostnoartifacts,
LMPlithicartifactsandsomefaunalremainssuddenlyappearinthe
lowest layer (Layer 11). This layer is about 60cm in thickness and
composedoffriable,pinkish-graysand,likelycorrespondingtoLayer
Contheterrace.ThisstudyusesLMPlithicartifactscollectedfrom
LayersC,D,and11intherenewedinvestigation.

WadiAghar.WadiAgharisashallowrocksheltersite(29°56'11.99“N,
35°19'53.53“E)intheJebelQalkhaarea(SupplementaryFig.3).Thesite
wasinitiallyinvestigatedinthe1983–1984season88,inwhichseveral
1×1msquareswereopenedwithinasurfacescatteroflithicartifacts
betweenthebedrockwallandthelargeboulder.Therenewedinves-
tigationinthe2016and2018seasonsexcavatedafewsquaremeters
besidesthepreviousexcavationareas45.

Thedepositsarelessthan1minthickness,withinwhichLayersA,
B, C, D1, and D2 weredetected. The previous work by D. O. Henry
excavatedLayersA–C,whiletherenewedworkexcavatedLayersB–D2.
LayerAconsistsofpowdery,grayish-tansand,andLayerBcontains
light,reddish-brownsandysilt.LayerCconsistsofcementedsand,and
itisunderlainbyorange,sandydepositsofLayerD.Theupperpartof
LayerD(LayerD1)islesscompactandcontainsmanylithicartifacts,
whileit becomes increasingly compactinthe lower part(Layer D2)
withonlyafewlithics.

The lithic assemblages from the two investigations are techno-
typologically similar to each other, and both can be affiliated with
IUP45,62,88.ThisstudyusestheIUPassemblagefromLayersC–D1that
weredatedto45–40kabyOpticallyStimulatedLuminescence(OSL)
andradiocarbondating45.

Tor Fawaz. Tor Fawaz is another rock shelter site (29°56'49.44“N,
35°20'9.03”E)locatedintheJebelQalkhaarea(SupplementaryFig.4).
TheinitialexcavationbyD.O.Henryin1983/84openedfive1m×1m
units29,andthefollowinginvestigationin1994excavatedalargerarea
(3m×4m) within the rock shelter where about 1m-thick deposits
weredividedintoLayersA,B1,B2,C,andDfromthetop53.LayerAisa
recent deposit near the surface, consisting of loose, dark gray silt.
LayerBconsistsofsiltydeposits.ThelowerpartofLayerBdepositsis
compactedandunderlainbyLayerC,whichconsistsofverycompact
yellowsilt.TheyellowsiltofLayerCispartlyunderlainbyredsand
(LayerD)restingonbedrock.

Therenewedexcavationin2017setupfive1m×1munits(Units
6–10).Units6and10wereexcavatedtothedepthof30–45cmbelow
thesurface,whileonlysurfacefindswerecollectedinUnits7–942.The
excavationofUnits6and10detectedLayersBandC,fromwhichmore
than5000lithicartifactswererecovered.Wesuggestedthatmostof
the lithic artifacts were re-reposited on the basis of multiple exam-
inations,includingOSLdating,radiocarbondating,micromorphology,
andtheanalysisofphytolithanddungspherulite.However,thelithic
assemblagesconsistentlyshowIUPtechno-morphologicalcharacter-
isticsdespiteafewpossibleinclusionsofAhmarianartifactsin1994
trench42,62. Considering the complicated depositional processes, we
estimated the dates of IUP occupations around ca. 45–36ka42. This
studyusedthelithiccollectionsfromUnits6a,6b,and10a,whereno
inclusionoflaterlithicartifactswasdetected.

TorHamar.TorHamar(29°56'17.34“N,35°19'8.90“E)isarockshelter
site in the Jebel Qalkha area (Supplementary Fig. 5). The initial
soundingin1983/84openedtwo1m×1mtestpits(Units1and2),and
amoresubstantialexcavationin1988openedtwo2m×2msquares
(Units 3–10)88. The renewed investigations since 2016 continued
excavationinUnits7–10andnewlyopenedUnit11.

Theexcavationsrevealedmorethan2m-thickdepositsthatwere
dividedinto11layers:LayersA,B,C,D,E1,E2,F,Gupper,Glower,H,
andIinastratigraphicorderfromthetop.Oftheselayers,LayersA–E2
constitute Epipaleolithic (Epipal) cultural deposits, and they can be
subdividedintotheMiddleEpipal(Mushabian)componentinLayers
A–E1andtheEarlyEpipal(QalkhanorNebekian)componentinLayer
E2.Thelowerlayers(LayersF–H)yieldedEUPbladeletassemblages.
LayerAisatopsoilconsistingofsoftyellow-redfinesand.Itis
likelyasurfaceexposureofunderlyingLayersB–Dthatalsoconsistof
yellow-red fine sand but are more compact and include ash con-
centrations. This deposit is thicker in Units 3–6, where it was sub-
divided into Layers B, C, and D. In Layer C, a hearth was found in
associationwithaprobablewindbreakfeatureandagrindingstone29.
LayersB–Dbecomethinnertowardsdownslopeandcannotbesepa-
ratedfromeachotherinUnits7–10.ThelowerpartofLayerDcontains
a large amount of sandstone rubble that is underlain by dark gray
depositswithashandcharcoal(LayerE1).LayerE1isunderlainbylight
brownsandysiltdeposits(LayerE2)inUnits9,10,andpartly11.Layer
E2containsmuchlessashandcharcoalthanLayerE1.Thenorthern
stratigraphicsectionofUnit11showsthatLayerE2isobliquelycutby
LayerE1andnotdetectableinUnits3–6.

Lithic artifacts from Layers A–E2 include many microliths, and
theirproductionusesthemicroburintechnique.MicrolithsfromLay-
ersA–E1arecharacterizedbytheabundanceofarch-backedbladelets,
straight-backed points, and La Mouillah points. Blades/bladelets of
LayersA–E1areslightlybroaderthanthoseofLayerE2.Thesetechno-
morphologicalcharacteristicsareconsistentbetweenthepreviousand
newcollections,andtheyareaffiliatedwiththeMushabianindustry
thatbelongstotheMiddleEpipal84,89,90Inaddition,faunalremainsin
Layers A–E1 are relatively well preserved85,86,91, and they also char-
acteristically include abundant marine shells, many of which are
perforated92.Aseriesofradiocarbondatesindicate15.5–15.2kacal.BP
fortheMushabianoccupations85.

MicrolithsfromLayerE2arecharacterizedbytheabundanceof
narrowarch-backedandpointedbladeletsor“attenuatedlunates”90.
Blades/bladeletsofLayerE2arenarrowerthanthoseofLayerA–E1.
AlthoughthepreviouscollectionsincludedQalkhanpointsasadiag-
nostictypeoftheQalkhanindustry29,thistypewasnotrecognizedin
the new collection. Instead, we identified several scalene bladelets,
whichmightbecalledQalkhanpoints,butanyhow,theirfrequencyis
low.Thus,thelithicassemblagefromtherenewedexcavationisvir-
tuallyindistinguishablefromtheNebekianindustry.Regardlessofthis
culturaltaxonomicissue,theLayerE2assemblageisstratigraphically
lower than the Mushabian and associated with radiocarbon dates
around24–18kacal.BP85,whichisconsistentwiththedesignationof
theEarlyEpipal.

IncontrasttotheEpipaldeposits(LayersA–E2),theunderlying
EUP layers (F–I) are distributed more continuously across all the
excavationareas.LayersFandGconsistoflightbrownsandysiltlike
LayerE2,andtheboundarybetweenLayerE2andLayerFisunclear.
The upper part of Layer G is ashy while it becomes progressively
compacttowardsthelowerpart.ThebottomofLayerGisadistinct
stratumofverycompactdepositsofangularsandstonerubble.This
gravellayer(LayerGlower)isunderlainbyLayerH,whichconsistso
compactredsand.LayerHisfurtherunderlainbyaverycompact,light
brownsiltwithrubble(LayerI).

Lithic technologyfrom Layers F–His characterized bythe pro-
duction of bladelets with small butts and fine overhang removals.
Thesetechno-morphologicalfeaturesseparatetheEUPfromtheIUP,
andtheyappearintheAhmarianindustry62.Severalel-Wadpointswere
recoveredfromLayersFandG,andthus,theassemblagesfromthese
layersweregroupedtogetherastheAhmarianassemblage.Inaddition
to these techno-typological characteristics, the dominance of
unidirectional flaking is consistent with the previous collections88,
indicating the southern Ahmarian affiliation93. A single radiocarbon
datefromLayerFis38–37kacal.BP85.

Lithic artifacts from Layer H are also characterized by bladelet
productionbutseparatedfromLayerGbecauseofclearstratigraphic
differencesmarkedbyredsandinLayerH.IntheJebelQalkhaarea,
Ahmarianassemblagesareoftendepositedinyellowsilt,asattestedat
Tor Hamar Layers F–G, Tor Aeid, and Jebel Humeima94. Thus, the
occurrenceofbladeletassemblageinredsandisuniquetoLayerHof
TorHamar.Althoughthismightindicatechronological/environmental
differences,suchpossibilitiesarecurrentlyunderstudy.

Measurementofcutting-edgelength
Tomakeaccurateandprecisemeasurementsofirregularedgeforms,
we measured the length of the outlines of lithic blanks from their
digitalphotographsbyfollowingthemethodsproposedbyErenetal.18
andfollowedbyotherresearchers20,95(SupplementaryFig.7a).Lithic
blankswereplacedwiththeirventralfacedownonasheetofgraph
paper,andtheirdigitalphotographsweretaken.Thedigitalphotos
werethenprocessedinAdobePhotoshopversions17–23toadjustthe
scaleandtoclarifytheedges,whichwerethenautomaticallytracedby
AdobeIllustratorversions20–27toextractoutlines.Thelengthofthe
outlineswasmeasuredinAdobeIllustrator.Followingtheinstructions
inErenetal.18andMullerandClarkson20,wemadecloseobservations
ofeachstonetooltoexcludedulledges,suchasthestrikingplatform,
brokenedges,andobtuseangles,fromthemeasurement.

Retouchedtoolswereexcludedfromtheanalysisbecauseofdif-
ficultyinestimatingtheoriginallengthoftheircuttingedge22.Wealso
did not measure the length of the cutting edge ofchips,which are
flakes whose maximum length issmaller than25mm18. Microburins
werealsoexcludedfromtheedge-lengthmeasurementastheyaretiny
byproducts in the manufacturing process of microliths. Cores and
chunkswerealsoexcludedastheydonothavesharpcuttingedges.
Chunks are fragmented pieces that do not clearly show ventral or
dorsalsurfaces.

Thus,wemeasuredthecutting-edgelengthofunmodifiedblanks,
whichconsistofseveraltechno-morphologicaltypes,suchasflakes,
blades,bladelets,andcoretrimmingelements(CTE).Abladeisdefined
as a flake whose length is equal to or greater than twice its width.
Usually,abladealsohasparallellateralsidesandridges.Wefollowa
definitionofbladeletproposedbyTixier96.Abladeletisabladewitha
lengthof<50mmandawidthof<12mm.CTEsareflakesorbladeswith
distinctive morphologies, such as core tablets and crested pieces,
whichresultfromtheirdetachmentfromspecificpartsofcoresforthe
maintenance of core-surface morphology. Crested blades and core
tabletsfollowthedefinitionsbyInizanetal.16.

Theuseofunmodifiedblanks,asdescribedabove,isastandard
methodforcalculatingtheproductionrateofcutting-edge.However,
whenweinterprettheresultsintermsoftechnologicalbehaviors,itis
importanttobeawarethatnotalltheunmodifiedblankswereactually
usedorintendedforuse.Althoughitwouldbeidealforextracting“end
products”desiredbyknappers,suchclassificationisdifficulttorealize
objectivelyasitiswidelyknownthatapparent“by-products”,suchas
CTEs,areoftenretouchedintotoolslikescrapers.

Calculationofcutting-edgeproductionrates
Theproductionrateoflithiccutting-edgeisbasicallyquantifiedbya
ratioofthecutting-edgelengthtothemassofstonetools.Inthisstudy,
weemployedtwotypesofratios(SupplementaryFig.7b).

Thefirsttype,called“thetotallength/massratio”,usesthesumof
thecutting-edgelengthofallunmodifiedblanksinthelithicassem-
blageandthendividesitbythetotalmassofallunmodifiedblanks,
cores,chunks,chips,andmicroburins.Thisratiorepresentsthetotal
production rate of cutting-edge from the entire mass of lithic raw
material,anditistheoreticallyclosetotheratioofcutting-edgetocore
mass(CE:CM)inErenetal.18andthecuttingedgepergramofcore
(mm/g)inMullerand Clarkson20.Asingle value ofthetotallength/
massratioisobtainedforeachofthelithicassemblages.

Thesecondtype,called“theindividuallength/massratio”,uses
the cutting-edge length of each of the unmodified blanks and then
divideitbythemassofeachblank.Thus,thisratioisobtainedforeach
of the unmodified blanks that constitute a lithic assemblage, and a
group of the ratios characterizes the cutting-edge production effi-
ciencyofthelithicassemblage.Incontrasttothetotallength/mass
ratio,theindividuallength/massratiodoesnotincludethemassof
cores,chunks,chips,andmicroburinsinitscalculation.

Statisticaltest
We used Microsoft Excel 2019 to organize the data of cutting-edge
length,mass,andseveralmorphometricmeasurementsofthelithic
artifactsanalyzedinthisstudy.Becausemostofthemeasurementdata
inthisstudydeviatefromthenormaldistribution,weusedthenon-
parametricKruskal–WallistestandtheposthocDunn’stestformul-
tiple comparisons with Bonferroni correction to examine whether
differencesamongthelithicassemblagesweresignificantintermsof
the cutting-edge production rates and lithic morpho-metric mea-
surements,suchaslength,width,thickness,andtheplatformsize.All
tests were two-tailed where applicable. All box plots indicate the
median (middle line) and interquartile range (box). The upper and
lower ends of the whiskers represent the maximum and minimum,
excludingoutliers(singlepoints)definedbytheTukeymethod.The
Spearman correlation coefficient was obtained to examine the sig-
nificance of correlations between the cutting-edge production rate
and lithic morpho-metric measurements. These statistical examina-
tionswereperformedwithIBMSPSSversion27.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "I think that the authors have done an excellent job at addressing the concerns and comments of the\nreviewers. Reviewers will always complain about the number of sites and the sample sizes (particularly\nthose who did not actually do real comparative studies it seems!). I think the authors have a good and\nrepresentative sample here, and make good arguments along these lines. In my opinion, the paper is\nready to be published. I just have a few very minor points:\nI think the abstract needs a sentence or so at the end summarising the wider implications of the\nfindings.\nLine 24, “more recent increase” is slightly odd grammar, better to say something like “Recently there\nhas been an expansion of the archaeological record” or “improved knowledge of the archaeological\nrecords in Africa and Asia” etc\nLine 35, “Most of” should be just “Most”\nLine 234, should be “the behavioral significance” not just “behavioral significance”\nLine 381….this is a true enough point, but given that another possibility is that IUP represents a new\ngroup coming from Africa…then the point is the background here is also things like platform faceting,\nhard hammer percussion etc….these are not distinctive local features which imply continuity. So I\nwould emphasise more continuity of broad patterns of behaviour rather than specific continuity of\ntechnological methods and or actual social groups.\nLine 382 – should be “the long-term” not “a long-term”\nLine 394, should be “permission to conduct fieldwork” not “permission of fieldwork”\nGiven that an important outcome of the study is an emphasis on the importance of miniaturization…I\nsuggest the addition of a reference at some suitable point, Shipton et al. (2018) in Nature\nCommunications on the site of Panga ya Saidi. This is a long MSA-LSA cultural sequence. The key\npoint here is that within the MIS 4-2 deposits every single different way that the LSA has been defined\ncomes and goes…the one thing that stays consistent is that there is a switch to miniaturization around\n71 ka. This then is key technological change in this sequence. I just think this a useful analogous point\nwhich is worth mentioning in the discussion perhap.", "reviewer_2": "In this study, the authors examined a series of Paleolithic assemblages from Jordan to evaluate\nchanges in lithic cutting edge production rate over time. Using the ratio of cutting edge to mass in\nindividual flakes and whole assemblages as a proxy for the efficiency of cutting edge production, the\nstudy showed that increases in the rate of cutting edge production did not correspond with the\nMiddle/Upper Paleolithic transition, and instead appear to relate to the development of bladelet\ntechnology in the Early Upper Paleolithic. Interestingly, the IUP assemblages produced the lowest\ncutting-edge productivity rates, which the authors attributed to the manufacture of large blades that\nwould have been suitable for prolonged use.\nThere are several noteworthy aspects of this study that have significant implications on Paleolithic\narchaeology. First, this is among the first systematic analysis using objective quantitative measures to\nexamine diachronic patterns in Paleolithic technology in the study region. The methodology is sound\nand clearly described. The large sample size of the artifacts analysed adds valuable new data to\nPaleolithic research. I strongly encourage the authors to make their data openly available at some\npoint to allow future studies to conduct more larger scale, big data inter-assemblage analyses.\nSecond, the results provide important empirical evidence highlighting variability and complexity of\nPaleolithic assemblages that are incompatible with conventional linear models of Paleolithic cultural\nevolution.\nI think the authors have done a good job addressing the concerns raised in the previous round of\nreviews. In particular, shifting the paper's focus away from broad evolutionary processes to specific\ntechnological developments has made the revised paper stronger and more substantiated. However, I\nfind the current justification for the study in the Introduction a bit weak, and I think the authors can\nmake a stronger and more compelling case for the significance of this study. Specifically, in lines 91-\n94, the authors noted that previous studies have examined cutting edge production patterns across\nthe MP and the UP in the Levant, and these studies detected a slight increase. The authors argued that\nthese results need further clarification for three reasons - 1) small sample size, 2) the lack of IUP in\nthe sample, and 3) imprecise methods. The first and third reasons are self-explanatory, but the\nsecond reason regarding the IUP should be elaborated upon. What is the IUP and why is it important?\nIf I were the author, I would emphasize that IUP is an extremely important phenomenon, particularly\nin this region. Its absence in previous studies represents a significant knowledge gap.\nMy other comments are relatively minor, some of which echo comments from Reviewer #2 in the\nprevious round of review regarding the assumption of temporal sequence among the assemblages. I\nsee that the authors have specified the grouping of the assemblages and clarified in figure captions\nregarding their assumed temporal relationships (or lack thereof). However, the way these figures are\npresented can still be confusing to readers. Take Figure 2 as an example, while the authors have\nclarified in the caption that no chronological sequence is assumed between LMP1 and LMP2 and\nbetween IUP1 and IUP2, the lines still imply a sequence. This is confusing because a temporal\nsequence is indeed represented for the later assemblages. Thus, despite the clarification in the\ncaption, it is still very easy for readers to misinterpret the figure. The same comment can be\nextendsed to Figure 3a and 6. I recommend the authors to combine LMP1 and LMP2 into a single\nassemblage unit called 'LMP', and IUP1 and IUP2 into a single 'IUP' unit. Looking at the data\npresented, combining these assemblages is unlikely to change the general results of this study (hence\nnot impact the conclusion), but these combined assemblages would be not only clear and easier to\nunderstand, but also consistent with the assemblage groupings defined in lines 88-90.\nOther minor comments:\n- I do not understand the purpose of Figure 4. The relationship between edge length per mass and\nflake width is barely mentioned in the paper. I can see the point that cutting edge length ratio\ndecreases with flake size - if this is the point, it needs to be better fleshed out in the results section.\n- Line 24-25: \"However, more recent increase in archaeological records...\" The wording here is odd.\nThe archaeological record is typically defined as the body of physical evidence left behind by past\nhuman activities. I assume the authors meant something more along the line of \"more recent increase\nin the recovery of archaeological records...\"?\n- Line 67: Consider citing the study by Hoggard and Stade (2019) on the comparison of cutting edge\nproduction between Levallois and UP blade technologies. Hoggard, C. S., & Stade, C. M. (2019). The\nefficiency of Middle Palaeolithic technological blade strategies: An experimental investigation. Lithics–\nThe Journal of the Lithic Studies Society, (39), 52."}, "author_response": "Responses to the reviewer’s comments\nWe appreciate the reviewers’ careful reading and comments to our revised manuscript. The\nfollowing shows our responses to the comments.\nReviewer #1 (Remarks to the Author):\nI think that the authors have done an excellent job at addressing the concerns and comments of the\nreviewers. Reviewers will always complain about the number of sites and the sample sizes\n(particularly those who did not actually do real comparative studies it seems!). I think the authors have\na good and representative sample here, and make good arguments along these lines. In my opinion,\nthe paper is ready to be published. I just have a few very minor points:\nReply\nWe deeply appreciate the reviewer’s positive comments to the revision of our paper.\nI think the abstract needs a sentence or so at the end summarising the wider implications of the findings.\nReply\nThank you for the suggestion. We added a sentence at the end of the abstract to highlight\nthe wider implications of our study. In addition, we added a sentence to provide the\nbackground of the study according to the formatting instructions of Nature\nCommunications.\nLine 24, “more recent increase” is slightly odd grammar, better to say something like “Recently there\nhas been an expansion of the archaeological record” or “improved knowledge of the archaeological\nrecords in Africa and Asia” etc\nReply\nThank you for the comments and suggestion of re-phrasing. This correction was also pointed\nout by Reviewer #2. We corrected a sentence accordingly. See Line 23 in the revised text.\nLine 35, “Most of” should be just “Most”\nReply\nCorrected. See Line 35 in the revised text.\nLine 234, should be “the behavioral significance” not just “behavioral significance”\nReply\nCorrected. See Line 174 in the revised text.\nLine 381….this is a true enough point, but given that another possibility is that IUP represents a new\ngroup coming from Africa…then the point is the background here is also things like platform faceting,\nhard hammer percussion etc….these are not distinctive local features which imply continuity. So I\nwould emphasise more continuity of broad patterns of behaviour rather than specific continuity of\ntechnological methods and or actual social groups.\nReply\nThank you for the thoughtful comments about the recognition of “cultural continuity”. We\nagree that some lithic production techniques that were prevalent in the MP, such as platform\nfaceting, could occur as technological convergence and may not be strong evidence for the\ncontinuity of specific cultures or social groups. To clarify our argument, we deleted a word\n“continuity” from the sentences. See Lines 275 and 281 in the revised text.\nLine 382 – should be “the long-term” not “a long-term”\nReply\nCorrected. See Line 278 in the revised text.\nLine 394, should be “permission to conduct fieldwork” not “permission of fieldwork”\nReply\nCorrected.\nGiven that an important outcome of the study is an emphasis on the importance of miniaturization…I\nsuggest the addition of a reference at some suitable point, Shipton et al. (2018) in Nature\nCommunications on the site of Panga ya Saidi. This is a long MSA-LSA cultural sequence. The key\npoint here is that within the MIS 4-2 deposits every single different way that the LSA has been defined\ncomes and goes…the one thing that stays consistent is that there is a switch to miniaturization around\n71 ka. This then is key technological change in this sequence. I just think this a useful analogous point\nwhich is worth mentioning in the discussion perhap.\nReply\nThank you for suggesting a broad implication of our study. We agree that our study of the\nlink between the increased edge productivity in the EUP and the lithic miniaturization is\nrelevant to the discussion on the lithic miniaturization and its behavioral implications at the\nMSA-LSA transition in Africa. Thus, we added the citation of Shipton et al. (2018) in Nature\nCommunications, and we also added their subsequent, more recent study (Shipton et al.\n2021 in Journal of Human Evolution) that focuses on the lithic technology.\nSee Line 261-264 in the revised text.\nReviewer #2 (Remarks to the Author):\nIn this study, the authors examined a series of Paleolithic assemblages from Jordan to evaluate\nchanges in lithic cutting edge production rate over time. Using the ratio of cutting edge to mass in\nindividual flakes and whole assemblages as a proxy for the efficiency of cutting edge production, the\nstudy showed that increases in the rate of cutting edge production did not correspond with the\nMiddle/Upper Paleolithic transition, and instead appear to relate to the development of bladelet\ntechnology in the Early Upper Paleolithic. Interestingly, the IUP assemblages produced the lowest\ncutting-edge productivity rates, which the authors attributed to the manufacture of large blades that\nwould have been suitable for prolonged use.\nThere are several noteworthy aspects of this study that have significant implications on Paleolithic\narchaeology. First, this is among the first systematic analysis using objective quantitative measures to\nexamine diachronic patterns in Paleolithic technology in the study region. The methodology is sound\nand clearly described. The large sample size of the artifacts analysed adds valuable new data to\nPaleolithic research. I strongly encourage the authors to make their data openly available at some point\nto allow future studies to conduct more larger scale, big data inter-assemblage analyses. Second, the\nresults provide important empirical evidence highlighting variability and complexity of Paleolithic\nassemblages that are incompatible with conventional linear models of Paleolithic cultural evolution.\nI think the authors have done a good job addressing the concerns raised in the previous round of\nreviews. In particular, shifting the paper's focus away from broad evolutionary processes to specific\ntechnological developments has made the revised paper stronger and more substantiated.\nReply\nWe appreciate the reviewer’s careful following of the revision process. Regarding the data of\nthis study, we will make them openly available. Below is our statement in Data Availability.\nThe data of cutting-edge length, mass, and several morphometric measurements of\nPaleolithic stone tools analyzed in this study are available to the public in the figshare.\nhttps://doi.org/10.6084/m9.figshare.23577093\nHowever, I find the current justification for the study in the Introduction a bit weak, and I think the\nauthors can make a stronger and more compelling case for the significance of this study. Specifically,\nin lines 91-94, the authors noted that previous studies have examined cutting edge production patterns\nacross the MP and the UP in the Levant, and these studies detected a slight increase. The authors\nargued that these results need further clarification for three reasons - 1) small sample size, 2) the lack\nof IUP in the sample, and 3) imprecise methods. The first and third reasons are self-explanatory, but\nthe second reason regarding the IUP should be elaborated upon. What is the IUP and why is it\nimportant? If I were the author, I would emphasize that IUP is an extremely important phenomenon,\nparticularly in this region. Its absence in previous studies represents a significant knowledge gap.\nReply\nWe appreciate the reviewer’s suggestion to emphasize the significance of the IUP samples\nincluded in this study. Following the comments, we added a few sentences to explain the\nsignificance of the IUP chrono-cultural concept by referring to its wide geographic implications\nand its association with the dispersals of Homo sapiens.\nSee Lines 87-91 in the revised text.\nMy other comments are relatively minor, some of which echo comments from Reviewer #2 in the\nprevious round of review regarding the assumption of temporal sequence among the assemblages. I\nsee that the authors have specified the grouping of the assemblages and clarified in figure captions\nregarding their assumed temporal relationships (or lack thereof). However, the way these figures are\npresented can still be confusing to readers. Take Figure 2 as an example, while the authors have\nclarified in the caption that no chronological sequence is assumed between LMP1 and LMP2 and\nbetween IUP1 and IUP2, the lines still imply a sequence. This is confusing because a temporal\nsequence is indeed represented for the later assemblages. Thus, despite the clarification in the caption,\nit is still very easy for readers to misinterpret the figure. The same comment can be extendsed to Figure\n3a and 6. I recommend the authors to combine LMP1 and LMP2 into a single assemblage unit called\n'LMP', and IUP1 and IUP2 into a single 'IUP' unit. Looking at the data presented, combining these\nassemblages is unlikely to change the general results of this study (hence not impact the conclusion),\nbut these combined assemblages would be not only clear and easier to understand, but also consistent\nwith the assemblage groupings defined in lines 88-90.\nReply\nThank you for the suggestion to make further clarification of the chrono-cultural units for\ncomparison in this study. As the reviewer points out, we do not assume the chronological order\nbetween LMP1 and LMP2, but these data are taken from different sites. Thus, we consider them\nas samples from different distributions and would like to keep our current statistical results. The\nsame argument applies for IUP1 and IUP2.\nHowever, we understand that the numerical order of the two assemblages in the LMP and\nIUP (i.e., LMP1, LMP2, IUP1, and IUP2) and the layout of the graphs can be still misleading.\nSo, we removed the use of “LMP1, LMP2, IUP1, and IUP2” and added dotted lines in the graphs\nto clarify the chrono-cultural units used in this study. This led to the revision of most of the\nfigures and the table.\nOther minor comments:\n- I do not understand the purpose of Figure 4. The relationship between edge length per mass and\nflake width is barely mentioned in the paper. I can see the point that cutting edge length ratio decreases with\nflake size - if this is the point, it needs to be better fleshed out in the results section.\nReply\nThe suggested point is exactly our purpose of Figure 4. Thus, we added the following\nexplanation. See Line 130-132 in the revised text.\n“This means that narrower and thinner blanks with smaller striking platforms tend to have\nthe greater ratios of the edge length per mass. As typically shown in the case of width (Fig. 4),\nsuch a negative correlation is similarly observable in each of the debitage types.”\n- Line 24-25: \"However, more recent increase in archaeological records...\" The wording here is odd.\nThe archaeological record is typically defined as the body of physical evidence left behind by past\nhuman activities. I assume the authors meant something more along the line of \"more recent increase\nin the recovery of archaeological records...\"?\nReply\nThank you for the comments and suggestion of re-phrasing. This correction was also pointed out\nby Reviewer #1. We corrected a sentence accordingly. See Line 23 in the revised text.\n- Line 67: Consider citing the study by Hoggard and Stade (2019) on the comparison of cutting edge\nproduction between Levallois and UP blade technologies. Hoggard, C. S., & Stade, C. M. (2019). The\nefficiency of Middle Palaeolithic technological blade strategies: An experimental investigation.\nLithics–The Journal of the Lithic Studies Society, (39), 52.\nReply\nWe were not aware of this study and highly appreciate the suggestion to add it in the citations.\nWe cited it in the Methods. See Line 295 in the revised text."}]

Decision letter