SomeFossilArvicolidRodentsfromthePinza・AbuCave,
MiyakoIsland,theRyukyuIslands,Japan
YukibumiKanekoandYoshikazuHasegawa
Abstract.Atotalof680isolatedmolarsandthreelowerJaWSWithmolarsagedasofthelatePleistocene
(25,800±900y.B.P.and26,800±1,300y.BLP・)wererecoveredfromthePinzaqAbuCave,MiyakoIsland・ theRyukyuIslands,Japan,in1982−83・Allfossilmolarswithapnsmaticenamelpatternarerootless・ Amongthem82specimensofthenrstlowermolarswereidentifiedasMicrotusjortis,fiveonesasM・ oeconomus,andsevenunidentifiednrstlowermolarswererecorded.Withoutbeingassignedtogenus,74specimensofthethirduppermolarshaveanintermediateformwithfourinternalsalientanglesandwith
opendentinespacesbetweenthenrstandsecondtriangleslbllowlngtheanteriorloop・Twospecimensof theseconduppermolarswereidentifiedasM・OeCOnOmuSbecauseoftheoccurrenceofanadditional reentrantfoldinthesecondexternalclosedtriangles・ThediscoveryofthefossilftomtheMiyakoIsland indicatesthemostsoutherndistributionofM・JbrlisandM・OeCOnOmuSinthelatePleistocene,and disagreeswithpaleobotanyandpaleogeographypreviouslyreported・ Islands・Thepurposeofthispaperistodescribeandidentify some fossils ofthe arvicolid molars,
COmparlngWiththerecentarvicolidsofJapanand
neighboringcountries,anddiscussesthemeanlngOf
the discoveries with other studies of fossils,
Paleobotany andpaleogeographyontheRyukyu
Islands.WeacknowledgetheDivisionofCulture, DepartmentofEducation,OkinawaPrefecture,and theAgencyofCulture,theMinistryofEducation,
Science and Culture,Japan forloaning fossil
materialstothepresentstudy,andtheYamashina
InstituteforOmithologyforallowlngmetOeXamine
thespecimensofMicrotusinChina・
Materials
Fossilmolars were recovered from the Pinza−Abu Cave(24044150‖N,125020rO8‖E),Whichlocatesat UenoVillage,MiyakoCounty(MiyakoIsland), OkinawaPrefecture.The altitude ofthe entrance of thecaveis53mfromthesealevel.
ThecollectionwascarriedoutduringNovember
Introduction
TheRyukyuIslandsbelongstothemostsouthem
partoftheNanseiIslands,WhichliefromKyushu, ぎ■Japan,tOTaiwanintheEastChinaSea・TherecentmammalfaunaoftheRyukyuIslandsdiffersfrom
thatofKyushuandHonshu,Japan,andtheWatase Line between the two faunae demarcates thePalaearcticfromtheOrientalRegion(Kuroda,1939; Imaizumi,1970).FromtheIslands ofMiyako and Okinawa,theRyukyuIslands,however,Onlysmal1 fossilrodentsofDtpLoth7・ixlegataand Tokudaia OSimensishavebeenreported(TakaiandHasegawa, 1971;Hasegawa et al.,1973;Kowalskiand Hasegawa,1976;Kawamura,1989)・Thus,
ZOOgeOgraphicalstudiesonsma11fossilrodentshave
beenlittleknownintheRyukyuIslands・ FromthePinza−AbuCave,theMiyakoIslandoftheRyukyuIslands,SOmekindsofArvicolidaefossil
molars andlowerJaWS Were reCOVeredinlarge
numbersin1982−83,though noneoftheliving
YukibumiKanekoandYoshikazuHasegawa
20−27,1982(thenrstDivision)andfromJuly25to August5,1982(thesecondandthirdDivisions).The environmentalcondition ofthese Divisions was
describedbyKishimoto(1985).Thedepositsinthe CaVe Were eStimated to have been formed at
25,800±900y・B・P・and26,800±1,300y.B.P.bythe14C me[hod(Hamada,1985),i.e.thela【erpart of PleistocenebytheF−COntentS(Matsuura,1985).
Thenumberofarvicolid fossils was680isolated moユars,OneloweりaWWi抽twomolars,and two
lowerJaWSWithonemolarwithapnsmaticenamel
patterns・Foridentification anddescrlptlOn Weexaminedtwospecimensoftheseconduppermolars,
740neSOfthethirduppermolars,and820neSOfthe
firstlowermolars,OneOfwhichonemolarputs
togetherwiththesecondlowermolaronalowerJaW・Othersare15lspecimensofthenrstuppermOlars,64
0neSOftheseconduppermolars,1190neSOfthe SeCOndlowermolars and4lones ofthethirdlower molars.Thefossilswerecomparedwiththefollowing
SpeCimensoftenlivlngSPeCiesofMicrotusforthe
identification:MicrotusmontebeLli=22(Kyoto, Japan),M.agrestis=8(sixfromFinlandandtwo from France),M.oeconomus=15(the Kola (=Kol’skii)PeninsulaandtheKurileIslands,Russia), Mjbrtis=15(JilinandAnhuiProvinces,China),M. mLmimowiczii=1(Heilon由iangProvince,China),M kikuchii=10(Taiwan),M mandarinus=2(Shanxi Province,China),and M.brandti=10(Inner Mongolia,Chjna).The enamelpatte川Of M.
SaChalinensiswasreferredtothefiguresofVasin
(1955)andMeyer(1978). ThemolarsweremeasuredfollowingMeyer(1978; Fig.1).Themeasurementsweretakentothenearest O・01mmunderastereomicroscope(NikkonSMZ−10)Withlevelsof40magnincationattachedanobjective
micrometerproducedbyKogaku・Enamelpatterns.姦Weredrawnuslngthemicroscopewithanaccessory
drawlngaPParatuSby14magnifier.
Enamelpatternsonthethirduppermolarswere
ClassinedintothreetypesaccordingtoMiyao(1961): Fig・1・Sixmeasurements(1−6)ofArvicolidaemolars.A,thenrstlowermolar(1=lengthand2=Width);B,the thirduppermolar(3=1engthand4=Width);C,theseconduppermolar(5=lengthand6=Width).OLIVE 香川大学学術情報リポジトリ
thecomplexformwiththreereentrantfolds onthe
lingualsideandwithposteriorconcavltyOnthe
POSteriorloop;theintermediateformwith three
reentrant folds on thelingualside andwithout
posteriorconcavltyOntheposteriorloop;thesimple
formwithtworeentrantfbldsonthelingualside.
The scientific names followed Honackie(al. (1982)andtheterminologyofthemolarmorphology followedCarleton(1985).Registrationnumbersare Shown as the collections ofthe Okinawa Prefecture
Musedm(OPM).
Results
l)Thefirstlowermolars
Allexamined molars haveno root.The銭rstlower molarhas丘,urtOfiveclosedtrianglesinfrontofthe
POSteriorloopin82specimens.Themolarwithnve
Closedtrianglesisadiagnosticcharacterforthegenus
MicrotusexceptforM oeconomus,〃.millicens,M musseri,andvariantOf〟.nivalis(Lawrence,1982).Among82specimensofthenrstlowermolars,69
isolatedmolarsandonemolarwithalowerjaw(OPM
3・4・4・18)wereidentifiedasMjbrtis,WhichhasnveClosedtrianglesandaroundanteriorloopwithasmall
anteroextemalconcavity.〟.jbrtisslightlyresembles M・kikuchiiintheshapeoftheanteriorloopamong thespeciesofMicrotuslivlnglneaSternAsia,but〟.kikuchiihastheloopwithadeeperfoldanteriorly,the
Shapeofwhichis a reverse V−OrU−1ike form (Kaneko,1987).Sixexamples ofM.jbrlis are exhibitedinFig.2(a−f).Tablelshowsmeasurements
Of63tlndamaged specimens among70fossil
SPeCimens ofM.jbrtis.The fossilmolars show
SlgnificantlylongerandwiderthanthoseoflivlngM
jbrtis(t=5・343,P<0.001andq=76inthelength;t =5・244,P<0.00land(げ=76inthewidth).NoSlgnificantdifferencebetweenthetworegression
linesofthefossilandlivingones(Fig.3;t=0.665,P >0.5and材=74).Five molars could beident摘ed asM oeconomus
(Fig.2;g−k),becausethe貞rstlowermolarhasfour
Closedtrianglesinfrontoftheposteriorloopand
threeinternalsalientangles.LivingM.oeconomushasthreeinternalsalientanglesincontrasttofour
anglesinlivingM nivalis(Hinton,1907;Kowalski, 1957),thoughthedentalspaceofM.nivalisisSOmetimesconfluentbetweenthefifthtriangleand
theanteriorloop,WhichlookslikeMoeconomus.No Slgnificantdifferencewasfoundinthelength and WidthbetweenthefossilandlivlngM.oeconomus (Tablel;t=2・025,0・05<P<0.1andq=18inthe length;t=0.553,P>0.5andU=18inthewidth). The measurements ofthe fossils areincludedin aClustercomposedofthoseofthelivlngOneSeXCept
foronespecimen(POM2.3.1.4.13indicatedasgin Fig.3).No significantdifferencebetweenthetwo regressionlinesofthefossilandlivingMicrotus(Fig. 3;J=0.662,ク>0.6and材=16).Sixfossilmolarscouldnotbeasslgnedtoanyof
theknownspecies(Fig.2;m−r).Thesemolarshave Characteristicsinwhichthetriangles meetatthemedianlongitudinalaxisandtheanteriorloophas
both externalandinternalconcavities,Which are
Observedin M・mOntebelli,arValis,agreStis, maximowiczii,andsachalinensis・Fourofthem(Fig. 2;m−P)arelargerandwiderthantwootherfossil molars(Fig・2;q−r)andspecimensoftwoliving SpeCies,MmontebelliandM.agrestis(Fig.3). Oneexamplecouldnotbeidentined(Fig.2;1).The
molarhasfo1lowlngCharacteristics:aSharpsalient
angleappearsontherightandlef[,thedentinespaceOfthenfthsalientangleisconfluenttotheanterior
loop,theshapeoftheanteriorlooplookslikea
mushroom,and the enamellamellaeis thinnerthan thefossilsexaminedhere.
2)Thethirduppermolars
ThethirduppermolarusuallylSnOtuSefu1forthe
identificationofthevolespeciesexceptforafew
CaSeS,becauseithasindividual,ageandgeographical Variations・We,therefore,Only describe some Characteristicsfoundin74specimens.Forty−One
molarsareoftherightand33areoftheleft.They
haveananteriorloopfo1lowedbythreealternatlng
YukibumiKanekoandYoshikazuHasegawa
召
\一十\
斗
’k l 1 J g ■h P qFig.2.Thenrstlowermolarsofsixspecimens(a−f)ofMicrotusjbrtis,nVeSPeCimens(g−k)of〟・OeCOnOmuS,
andnotidentifiedspecimens(1−r).a,OPM3.2.2.4・16;b,OPM2・3・1・4・10;C,OPMl・4・4;・d,OPM
2.3.1.4.22;e,OPM2.3.4.4.5;f,OPMl.4.12;g,2.3.1.4.13;h,OPM2・3・6・4・2;i,OPM2・4・4・4・5;j,OPM
2.3.6.4.3;k,OPM2.3.6.4・4;1,OPM2・4・5・4・4;m,OPMl・4・10;n,OPM2・4・4・4・4;0,OPM2・4・5・4・19;P,
OPM2・4・5・4・18;q,OPM2・4・7・4・14;ー,OPM3・5・4・1・OLIVE 香川大学学術情報リポジトリ
Tablel.Measurementsofthelengthandwidthofthenrstlowermolarsandregressionequationsinfossil(F) andliving(L)speciesofMicrotus.Mean±standarddeviationandrangeinparentheses・
Species name N M01arlength(Ⅹ)M0lar width(Y)Reg■reSSion equation ♪グ.for亡ユg 63 3.56±0.27 (F) (2.86−4.31) 〃.0eCOエコ∽uS 5 2.95±0.35 (F) (2.65−3.55) 〝.foヱ・亡ユ5 15 3.17±0.20 (L) (2.80−3.45) 〟.0eCOヱつOmuβ 15 2.71±0.20 (L) (2.47−3.07) 〝.た土加d上土 10 3.03±0.16 (L) (2.76−3.35) 〝.mon亡eわeユユi 22 2.92±0.15 (1) (2.69−3.20) 〝.a多re5日g 7 2.76±0.15 (L) (2.56−3.05) 1.42±0.11 (1.00−1.74) 1.11±0.15 (1.00−1.36) 1.26±0.07 (1.10−1.35) 1.08±0.09 (0,90−1.26) 1.25±0.06 (1.10−1.32) 1.14±0.08 (1.00−1.30) 1.07±0.07 (0.95−1.15) Y=0.30+0.31Ⅹ Y=−0.09+0.41Ⅹ Y=0.69+0.18Ⅹ Y=0.43+0.24Ⅹ Y=0.77+0.16Ⅹ Y=0.24+0.31Ⅹ Y=0.39Ⅹ
exceptlOnalformhavingslightlyshortlength,OrOne
OrtWOCOnfluentdentinespaces(Figs・4and5;f−i)・ The40specimensareslightlylongerand■Widerthan livlngSpeCiesofMicrotusexceptforthewidthin〟・ kikuchii(Table4).3)Theseconduppermolars
Two examplesofthemolarswereidentified as
thoseofM.oeconomus(Fig.3;j−k),becausetheSeCOndexternalclosedtrianglehasasmalladditional
reentrantfoldattheanterioredge.Thisadditionalfold
hasbeenreportedinbothlivingM.nivalis(Kowalski, 1957)andlivingM・OeCOnOmuS(Ruprecht,1967) amongMicro(usSpeCies.But,Weidentinedthemas themolarsof〟.oeconomusbecauselivlngMnivalisis distributed from southwestofEuropetoIran
(Corbet,1978).Theyare2.30mmlongandl・43mm Wide(POM2.2.2.2.6),and2.03mmandl.30mm (POM3.2.2.1),reSPeCtively.Thetwofossilmolars arelargerthanthoseoflivingM oeconomus(Fig.6; j−k)andotherlivingspeciesof〟fcrotus(Table5).
Discussiom
First,Wediscussthereasonwhywedonotreferthe
scientific names offossilMicrotusin the results.As Closedtriangles,i.e.oneinternalandtwoouter.Some molars,however,havethesecondandthirdtriangles, and/orthethirdandfourthtrianglesbetweenwhi.ch
theyhaveaconfluentdentine space,reSPeCtively
(Table2).NostatisticalindependencewasshowniIithedentineconfluencebetweenbothsidesbytheG−
testwithWilliams’adjustment(SokalandRohlf, 1973;G叫=4・830,0・1<P<0・25and〃、=3)・Molars with the confluence between the third and fourthtrianglesarethemostcommonamongthetotalmolars
includingthoseofbothsides.
NosimpleformoftheenamelpatternWaSfoundin
74specimens(Table3).No statisticalindependenceOfthepatternsbetweenthetwointermediateand
COmplexformswasshownbetweenthebothsidesby
the GTteSt WithWilliams’adjustment(Sokaland Rohlr,1973;G叫=0・3紬,0・5<p<0・75and‘軒=1)・
Theintermediateformisthemostcommonamongthe
totalspecimensconsistlngOfthoseofbothsides.
Among74specimensofthethirduppermolars,44
SPeCimensareabletomeasurebecauseotherscannot
measure due to damage.Five examples of44
SpeCimensareshowninFig.4(a−e)・Aregressionline
betweenthelengthandthewidth wasdrawnby40
YukibumiKanekoandYoshikazuHasegawa 0 ∩ ▲ l ▲ ′一′∵ :一′ ニニ 1▲一..′ ・∴=ノチ;一;一’▲▲ ′+ ノーニ烏 ▲ ′ ̄ ′一 + 「 m−r F∝逼ils ▲一−−一 ル′.爪0nre如〟/ トーー 〃.即便座 〓ト凸︼き a−f.0− Fossils 0
.」∵11′? 二
l−… 〃.血・始 + −−− 〃.々仇udl〟 ○匂 00虎・金/b
O0 ヱ㌻ニ。¢/。
00
I...
・づを≠一ノ
e。・
l +l f0.9
4月 mm3.5
LENGTH
2.5
Fig.3.Scatterdiagramsofthelengthandwidthofthefirstlowermolar・Theregistrationnumberforthe SPeCimens(a−r)isshowninFig.2.OLIVE 香川大学学術情報リポジトリ
epiratticepsinposition;2)theinternalconvexity
developsveryfaintlyintheanteriorloopofthenrst
lowermolar;3)theanteriortransverseloopofthe firstlowermolarlacksafoldorisfaintlydeveloped・ Tokuda(1939),however,remarkedthatthecharacters Ofl)and3)arenotsufficientfordiscriminatingthe two species.Hasegawaetal・(1977)saidthatM・ q,lratticq,uSWOuldbeasynonymofM oeconomus in splteOfthesizedifferenceinthemolarlength・ KowalskiandHasegawa(1976)andKawamuraand Kajiura(1990),however,uSed thenameofM・ eplratticeps without comments・Because some SPeCimensofM.q,iratticq,SShownbyYoung(1934) COuldbeident摘edasM.Jbrtisasmentionedabove andthefiguresdrawnbyYoung(1934)didnotaccordwithhisglVenCharacters,WeCannOtCOnnrm
his diagnostic characters.We agrqewithTokuda
(1939)whoregardedM.epirat(iceps as ajunior SynOnymOf〟.ogc(フ乃0∽瓜
ReferringtolocalitiesineasternAsia,fossils
identinedasM.oeconomushavebeenreportedboth
inJapanandChina.FossilM.oeconomushasbeen foundinManchuria(Tokuda,1939)andBeijin(Pei, 1940),China,andinHonshu,Japan(Kowalskiand Hasegawa,1976;Hasegawaetal・,1977;Kawamura andKajiura,1980)inthelatePleistocene;inBeijin, China(Young,1934;Pei,1931,1936)andinHonshu, Japan(KowalskiandHasegawa,1976)inthemiddle Pleistocene.M.cf.brandtireportedbyPei(1931)and M.complicidens by Pei(1936)also appear to COrreSpOndwithfossilM.oeconomus(=M.ratticq>S).LivingM.oeconomusoccursthroughouttheentire
tundraandtaigazonesofthenorthernPalaearctic
(Corbet,1978),andthebssilM.oeconomusontheMiyakoIslandisthesouthernmOStreCOrdbeyondthe
knownrangeofthedistributionofboththefossiland
livlng〟.oeco乃クm〟∫. AsregardsfossilM.Jbrtis,OnlyTokuda(1939)has reporteditfromHarbin,nOrtheastChina,thoughhe Calleditas〃.cf.pelliceus(=nOWM.f?rtis;Corbet, 1978).rrYle貞guredenamelpatternOftheanteriorloopOfthenrstlowermolaragreeswellwiththatoffossil
regardsfossilspeciesofMicrotusatthemiddleand
late Pleistocenein China andJapan,Microtus
q,iratticqps(Young,1934),〟.brandtioides(Young, 1934),andM compLicidens(Pei,1936)fromChina, andM.epiratticepoides(Kawamura,1988)from Japanhavebeendescribed.Young(1934)andPei (1936),however,didnotdesignatetheholotypesof 〟.甲frαJJわ甲∫,〟.あr‘フ乃dJわfdg∫,〟.co/ナ甲Jわ∫de乃∫,
respectively,andnguredsomeenamelpattemsonthe
firstlower molarsin respective species,Which
resemblethoseofliving〃.oeconomus,M・jbrtis,M mandarinus,and/orM.brandti.Becausewecannot
decidewhatcharacters canbequalified forthese
SPeCiesofMicrotus,WeCOnSiderthatthedescnptlOnS
donebyYoung(1934)andPei(1936)areproblematic
and we need to reexamine the type series and
designatethelectotypes.
Kawamura(1988)identifiedmanyfossilspeciesof
ArvicolidaefromJapanin the middle andlate
PleistoceneandrecognizedMicrotus甲i171tticq,Oides asanewspeciesreferrlng〟.q,lratticq,Sdescribed by Young(1934).In describingthe diagnostic Charactersofthenewspecies,Kawamura(1988)gave
bothcharacters ofthethirdupperandfirstlower
molars,thoughhedesignatedthethirdupperisolated
挙り、molarastheholotypeanddidnotshowafactthatthe
thirdupperand firstlowermolars are combined
togetherasonespecimen.FurthermOre,SOmeenamel
patternSOftheanteriorloopofthefirstlowermolarin
M.epiratticepoidesshownbyKawamura(1988) COincidewiththoseoffossilM.q)iratticq)S(Young, 1934).
Therefore,We SilSpend the validitシOf M. 甲IrαJggc甲∫,〟.あrαれ血0∫de∫,〟・CO〝甲Jfcよde那,and M.q,lratticepoidesuntilthereexaminationofthese
typeseriestopreventtaxonomicconfusion.
InthisstudywedealwithM.q,lratticq,SYoung, 1934asasynonymof〃.oeconomus.Young(1934) gavetheR)1lowingthreecharactersforthespecies:1)theposteriortransverseloopofthethirdlowermolar
iswiderin印Inltticq,Sthaninoeconomusandotherー ー︻.....−1−tF.−....
YukibumiKanekoandYoshikazuHasegawa
Table2・Frequencyontheoccurrenceofthedentinespaceseparatedorinconfluentinthethirdupperfossil
molars.
Dentine spaces Confluenヒ Separated Total
2nd−3rd 3rd−4th 2nd−3rd−4th 3 1 4 3 4 ︻′ ︵葛 宅 宅 3 3 3 7 6 ︻/ ︵∠ 4 3 9 0ノ ︵‖0 ⊥ 2 The lef亡 The rlgh亡 Toヒal 宅 ︶ 宅 2 宅 ︵=0 ・ 9 ・ nO ・0 1 4 ⊥ 6 つム ︵︶U 宅 宅 象U ﹁つ qノ 3 ⊥ つJ 7 5 4 4 7 ︵=0 ﹁⊃ l ⊥ 3 象じ 宅 宅 0 0ノ ⊥ 3 4 4 ⊥ 2 3 Table3.FrequencyofthreeenamelpatternSinthethirdupperfossilmolars.Threepattemsweredetermined わ110WingMiyao(1961).
Tkree enamel patterns Damaged Total =ntemediate Cornplex Total
S土Trple The lef亡 The rlg‘hヒ To亡al 24(72,7宅) 1(3.0宅) 25 8 33 38(92.7宅) 1(2.4宅) 39 2 41 62(96.9宅) 2(3.1宅) 64 10 74
、室”′い、
屯
d
e
、J㍉、
Fig.4.Thethirduppermolars(a−i)ofr10tidenti貞edninespecimensandthesecoTlduppermolars(j−k)ofM・ oeconomus.a,OPM3.2.4.3.6;b,OPM2.4.8.3.8;C,OPM2.4.8.3.7;d,OPM2.3.6.3.2;e,OPM2.4.8.3.16; f,OPM2.4.8.3.15;g,OPM3.3.3.4;h,OPM3.2.4.3.5;i,OPM2.4.8.3.1;j,OPM2.2.2.6;k,OPM3.2.2・1・OLIVE 香川大学学術情報リポジトリ
〓トロ−き 箪〉
2.0
25
3.O
LENGTH
mm
Fig・5・Scatterdiagramsofthelengthandwidthofthethirduppermolar・Theregistrationnumberforthe
SpeCimens(a−i)isshowninFig・4・ Pei,1940;KowalskiandHasegawa,1976;Kawamura andKajiura,1980),Or〃.、COmPlicidens(Pei,1936)・ ThediagnosticcharacterhentionedbyPei(1936)is notcorrect(cf.Corbet,1978)becauseheonlytook thenumberofabsolutelyclosedtrianglesonthe且rst lowermolarintoconsideration,insteadoftheenamel patternOftheanteriorloop・Twofossils(NSM9939−4andNSMlOO28)intheNationalScienceMuseumof
Japan(NSM),Which havebeendescribedasM・ 甲inltticq,SbyKowalskiandHasegawa(1976)wereidentifiedasM.jbrtisbyoneofthepresentauthors
Mjbrtisexaminedinthisstudy・Themeasurements Ofthemolar(Tablel)arelargerthanthoseofthetwo SPeCimensdescribedbyTokuda(1939)・Acharacteroftheanteriorloopofthelowerfirst
molarinM.Jbrtisagreeswiththefiguresgivenby
Young(1934),Pei(1936,1940),TeilharddeChardin andPei(1941),Chi(1974),KowalskiandHasegawa (1976),andKawamuraandKajiura(1980).These authors,however,repOrtedtheir fossils asJM・ brandtioides(Young,1934;TeiharddeChardinand Pei,1941;Chi,1974),Mq)iratticq,S(Young,1934;YukibumiKanekoandYoshikazuHasegawa
Table4.Measurementsofthelengthandwidthofthethirduppermolarsandregressionequationsinfossil(F)
andliving(L)speciesofMicrotus.Mean±standarddeviationandrangeinparentheses・
Species name N M0larlength(Ⅹ)M01ar width(Y)Regression equation
Y=0.53+0.14Ⅹ Y=0.40+0.19Ⅹ Y=0.34+0.19Ⅹ Y=0.22十0.33Ⅹ Y=0.15+0.31Ⅹ Y=0.27+0.23Ⅹ 0.90±0.06 (0.76−1.05) 0.82±0.06 (0.69−0.90) 0.72±0.07 (0.58−0.85) 0.95±0.06 (0.86−1.02) 0.73±0.08 (0.57−0.85) 0.71±0.07 (0.63−0.85) 旭cro亡u5 Spp.40 2.59±0.12 (2.37−2.88) 15 2.23±0.19 (1.90−2.50) 15 1.96±0.19 (1.50−2.22) 9 2.23±0.11 (2.06−2.44) (F) 〟.foヱ・亡is (L) 〃.0eCOnOmu5 (L) 〃.たi加cムii (L) 〟.mo刀亡ebeユユユ 22 1.84±0.18 (L) (1.60−2.10) 軋 a9reS亡is 8 1.87±0.18 (L) (1.61−2.20) ノふヾ
Table5.Measurementsofthelengthandwidthoftheseconduppermolarsandregressionequationsinfossil(F)
andliving(L)speciesofMicrotus.Mean±standarddeviationandrangeinparentheses・Species name N M:0larlength(Ⅹ) M01ar width(Y) Regression equation Y=0.50+0.37Ⅹ Y=−0.05+0.65Ⅹ Y=1二20+0.03Ⅹ Y=0.05+0.62Ⅹ Y=−0.22+0.76Ⅹ 1.20±0.08 (1.05−1.29) 1.07±0.08 (0.88−1.20) 1.26±0.05 (1.19−1.35) 1.12±0.09 (0.96−1.27) 1.05±0.10 (0.95−1.20) 〃.fbr亡上古 15 1.89±0.12 (L) (1.74−2.10) .打.0eCGnαれu5 15 1.73±0.10 (L) (1.58−1.86) 〃.太i加cカユユ 9 1.84±0.06 (L) (1.75−1.90) 〃.皿On亡ebeユユヱ 22 1.72±0.10 (L) (1.52−1.93) 軋agre5亡ユs 8 1.67±0.10 (L) (1.53−1.85) (1934),Pei(1936),TeilharddeChardin andPei (1941),andKowalskiandHasegawa(1976;NSM 9939−4)arethemiddle.Fromtheseinformation,itis
apparent that fossilM.fbrtis was distributed
throughouttheareasofMiyakoIsland,theRyukyu
Islands,Honshu,Japan,Manchuria,Beijln,and ShensiProvince,ChinainthelatePleistocene.Onthe Otherhand,thelivingM.fbrtisisfoundinthe highlandsofFukien(vonLehmann,1955;Hong, 1982),Chekiang(Zhuge,1982),andfromthelowerYangtze ValleythroughManchuriaand Korea
(Kaneko).
Aswellas fossilM.jbrtisidentifiedbyTokuda
(1939),thesefossils whichIcouldidentify asM.
f7rtismentionedinthepreviousparagraphhavebeen
agedaseitherofthelateormiddlePleistocene:
Research Group of Higher Vertebrates at the
InstitutionofPaleovertebrates(1959)estimatedthe excavationsitereportedbyTokuda(1939)asofthe latePleistocene;Pei(1940),Chi(1974),Kowalski andHasegawa(1976;NSMlOO28),andKawamura andK如iura(1980)arethelatePleistocene;Young
OLIVE 香川大学学術情報リポジトリ
Johnson,1955)than from Heilongjiang (=Manchuria),China(Ma,1986)andsouthemSiberia (Meyer,1978).Thus,thefossilM・jbrtisfromthe
MiyakoIslandmaybelongtooneofthesouthern
formsof〃.♪rtis.However,itisdifficulttoesimate theroutethroughwhichthefossil〟.jbrtismovedtoCOlonizetheMiyakoIsland:thatisfromTaiwanor
Kyushu.
ArvicolidrodentswhichincludeM.カrtisandM.northwardtotheAmurValley,WeStWardtotheLake
Baikal(Corbet,1978).mus,theoccurrenceoffossil 〟.jbrtisfromtheMiyakoIsland(about24045’N) meanstoextendthesouthern1imitofthedistribution rangeanditisveryclosetothatoftheliving〃・jbrtis inFukien,Wherethesouthemboundaryliesat270N.Thetotalmolarlengths ofrecentM.Jbrtis are
SlightlylongerfromFukien,China(vonLehman, 1955;Hong,1981)and South Korea(Jones and
mm
l.4
l…一− 〃.mα7肋〟 トーー〃.卵胞
l 〓トロ−き l…−・〃.伽′由 +−−・ 〃.欠此ud痛l.4
+ + _…_._..土l..{lて_・一 ◆  ̄● ̄−「†了コフ ー ̄ l2.O
mmLENGTH
Fig.6.Scatterdiagramsofthelengthandwidthoftheseconduppermolar・Theregistrationnumberfbrthe SpeCimensisshowninFig・4・YukibumiKanekoandYoshikazuHasegawa hairedrat(Diplothrixlegata),Originatedfromthe OrientalRegionaredistributed、Ontheislandsof Amami−00Shima,Tokunoshima,andOkinawa,the RyukyuIslands(Tokuda,1941;‥Kaneko,1994)・ Misonne(1969)explainedthatbothspecieshave COlonizedbyanoceanicdrift(=KuroShio),Which runnlngfromtheeastemcoastofLuzon,PhilipplneS,
becausethetwospecieshavenorelativesonChinese
mainlandnoronTaiwan.However,thisexplanationCOuldbedeniedbythediscoveriesofD
legataandTbkudaiaosimensisfromtheRyukyu
IslandsinthelatePleistocene(Hasegawaetal.,1973; Kawamura,1989).BecausethetwospeciesofratsliveinevergreenforestsdominatedbyCastanppsIS
sieboldii(MitsuiandIkehara,1979),theMiyakoIslandmightbecoveredbyevergreenforestsinthe
latePleistocene,ifthetwospeciesrequiredthesame適 habitatsatthetime.Thissuggestion,however,isnot consistent with the discoveries offossilMicrotusjbrtisandM.oeconomusfromtheMiyakoIslandin
thelatePleistocenewhichprefergrassyhabitats,but
agreeswellwiththefloraatthetimeestimatedby
(KameiandResearchGroupforBiogeographyfrom
WBrmGlacial,1981).Fromtheviewpointofpaleogeography,Kizakiand
Oshiro(1977)andOshima(1979)supposedthattheRyukyuIslandshavebeenisolatedfromTaiwanand
thenorthernpartofNanseiIslandsinthemiddle
PleistoceneafterconnectingwithTaiwanandthe
continentofeastemAsiaintheearlyPleistocene.On
theotherhand,Hasegawaetal.(1973)andHasegawa (1980)suggestedfromthediscoveriesofRa((us(= /叶/・り/==・しl./=・.仙‥\−=、・こ==l/・川‘t/・・川丁\、・− (Reptilia:Chelonia)fromtheMiyakoIslandthattheRyukyu Islands would be connected with the
continenteveninthelatePleistocene.Thedifference
betweenthetwooplnionsmeanswhetherthetwo
SpeCiesofMicrotuslivlnglngraSSeSandthetwo
SpeCiesofratslivlnginforestscaninhabittogetheron
theMiyakoIslandornot,eVeninasmal1area・We,therefore,takeintoconsiderationoftherecentsmall
voleslandmice■sfaunaonsmallislandsinJapan(Ota, oeconomusareHolarcticmammalsandaredistributed mainlythroughoutNorthernHemisphere魚■Omabout 23.5O N(CarletonandMusser,1984).ManyrecentPalaearctic mammalsincluding M.Jbrtis are
distributedtothenorthempartof190Cisothermsin
Fukien,China(Hong,1982).Studies on recent mammals haveindicated that the Wataseline on
NanseiIslands,Japan,andtheRiverYangtzeinChina
demarcatesthePalaearcticRegionfromOrientalone
(Kuroda,1939;HwangelaL.,1966,1978;Imaizumi, 1970).Therefore,itispossiblethatafterMjbrtisandM.oecotwmushadcolonizedontheMiyakoIsland
fromthecontinent,theIslandwasisolatedfromitand
would become a smallareain the ocean.And,
becausetheclimatehasbecomewarmingup(now
averagetemperatureinayearis23・1OcbytheJapan MeteorologicalAgency,1981)andchangingtheflora
and fauna since that time,it would cause the
extinctionof〃.jbrtisandMoeconomus・
Finallyweconsiderthediscoveriesofthe丘〉SSilM・
JbrtisandM.oeconomusontheMiyakoIslandin
relation withtheinformationofpaleobotany and
paleogeography・ThefloraoftheMiyakoIslandinthe
late Pleistocene has been estimated as evergreen
broad−leavedforests(KameiandResearchGroupfor biogeography fromWtirmGlacial,1981)・The habitatsofthetwolivlngVOles,however,aregraSSy andwetareasnearwater.Forexample,thelivlng〃・ jbr[isinhabitsbanksofrivers,mOreOrlessswampy grounds(Thomas,1902;Sowerby,1923;Hong, 1981),abandonedpaddies(JonesandJohnson,1965), and meadows(Nadachowski,1984),aS Wellas the livlngM・OeCOnOmuSpreferswet,graSSyandmarshy habitats(Corbet,1966).Ifthetwo fossilvoles
PreferredthesamehabitatsasthetwolivlngOneSdo,
thenorthernandgrassyfloramighthavebeenexisted
On the MiyakoIslandin thelate Pleistocene・
Therefore,thereis adiscrepancy between the
preferredhabitatsofthevolesandthefindingsin
paleobotany.
Twolivlngendemicspeciesofrats,i・e・theRyukyu SPinyrat(Tbkudaiaosimensis)andtheRyuktylong−
region:ataXOnOmicreview.BritishMus・(Nat・ Hist.)andCornellUniv.Press,LondonandIthaca,
314pp.
Hamada,T.1985.14CageofcharcoalfromPinza−Abu Cavedeposits,MiyakoIsland,Okinawa,Japan・ Pinza−Abu(Rep.Excav.Pinza−AbuCave):180・(in Japanese)・ Hasegawa,Y.1980.NotesonvertebratefossilsfromlatePleistoceneto HoloceneofRyukyuIslands,
Japan.TheQuaternaryRes.,18:263−267・(in JapanesewithEnglishabstract). Hasegawa,Y.,M・AimiandG・Okafuji・1977・ Pleistocene Microtinae(Rodentia)from AndoQuarry atOfukudaikarst plateau,Yamaguchi
Prefecture,Japan.TheQuaternaryRes.,16:13−17. (inJapanesewithEnglishabstract)・ Hasegawa,Y.,H.OtsukaandT.Naohra・1973・
FossilsvertebratesfromtheMiyakoIsland(Studies
OfthepaleovertebratesfaunaofRyukyuIslands,
Japan.Partl.).Mem.Natl.Sci.Mus.,(6):39T52. (inJapanesewithEnglishabstract)・ Hinton,M.A.C.1907.Ontheexistenceofthealpine VOle(Microtusnivalis,Martins)inBritainduring Pleistocenetimes.Proc.Geol.Assoc.,20:39−58. Honacki,J.H.,K.E.KinmanandJ.W.Koeppl.1982. Mammalspeciesoftheworld・AllenPress,Inc・and Assoc.Syst.Coll.,Lawrence,694pp. Hong,Chaochang.1982.Ongeographicaldistribution andfaunalreg10nSOfrodentsofFujian.ActaZool. Sinica,28:87−98.(in Chinese with English abstract). Hong,Zhengfan.1981.Anewsubspeciesofreedvole fromFujian:Microtusjbrtishianensis(Rodentia: Cricetidae).ActaZootaxon.Sinica,6:444−445.(in ChinesewithEnglishabstract). HwangWengi,WenYehhsin,HwangTseniandMoo Dawee.1966.OnthegeographicaldistributionandfaunalreglOnSOfthemammalianfaunaofKiangsu.
ActaSci.Nat.Univ.Fudan,11:77−92.(inChinese WithEnglishabstract). HwangWengi,WenYehhsin,HwangTseni,MooDa− Wee,TangZiyingandLianZuochen.1978.Onthe 1984).Two species of voles(Clethrionomysrゆcanusand C.rex)andonespeciesoffieldmice (Apodemus岬eCiosus)occurontheRishiriIsland (area=183km2),andthetwospeciesofvolesoccuron theRebunIsland(area=77km2).OnbothislandsSasa
grassesandconiferoustrees aredominant.Onthe
Otherhand,OneSpeCiesofvole(Microtusmontebelli) and two species ofmice(A.speciosus and A・ a7?enteuS)occurontheSadoIsland(area=857km2)WhereSasagrassesanddeciduoustreesaredominant,
andonespeciesofvole(Eothenomyssmithii)andthe
two species ofmice occur on the DogoIsland
(area=243km2),the OkiIslands,Wherethere are
grassesandevergreenforests.WhenMiyakoIsland
(area=159km2)isolated from the continent and becameinto a smallislandin the Pleistocene as
SuppOSedbyKizakiandOshiro(1977)andOshima (1979),tWOSPeCiesofMicrotusandtwospeciesof rats(DiplothrixlegataandTokudaiaosimensis)
WOuldnotbeabletolivetogetherduetosuchasmall
area.Therefore,aS SuggeStedby Hasegawaetal. (1973)andHasegawa(1980),Weareinclinedtoagree
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琉球列島宮古島ピンザアブ洞穴における化
石ハタネズミ科臼歯について 金子之史・長谷川善和 琉球列島の宮古島のピンザアブ洞穴で、後期更新世 (25,800±900y.B.P.と26,800±1,300y.B.P.)と判定された、 680個の遊離臼歯と臼歯のついた3個の下顎骨が1982−83 年に発掘された。化石臼歯はプリズム型のエナメル質 をもち無根歯であった。82個の下顎第一臼歯のうち、 70個は〟ねroJ〟∫♪rJ勘5個は〟.oeco〝∂∽〟∫と同定され、 ほかに7個の特徴を記載した。74個の上顎第三臼歯には、 下側に4個の凸角をもち前環うしろの第一と第二のエナ メル三角形の象牙質が連合していたが、属の同定には 至らなかった。2個の上顎第二臼歯には第二番目の閉鎖 三角形の頬側に凹角がみられたので、〟.ogco乃∂∽〟∫と 同定された。宮古島での後期更新世の〟.ノbrJ∼∫と〟. ogco乃∂∽〟∫の化石臼歯の発見は、今まで報告されていた 古地理学や古植物学の見地とはことなっていた。 (金子之史:760高松市幸町1−1香川大学教育学部生物 学教室。長谷川善和:249逗子市沼間3−16−15) inJapan.SomestraitsoftheRyukyuIslands・Geol・ News,(302):48−53.(inJapanese). Ota,K.(ed.)1984.Studiesonwildmuridrodentsin Hokkaido.HokkaidoUniversltyPress,Sapporo, 400pp.(inJapaneSe). Pei,W.C.1931.MammalianremainsfromLocality5 atChouk’outien.Paleont.Sinica,Ser.C,8:1−16. Pei,W.C.1936.Onthemammalianremainsfrom Locality3atChoukoutien.Paleont・Sinica,Ser・C, 7:1−108.Pei,W.C.1940.The upper cave fauna of Choukoutien.Paleont.Sinica,New Ser.C,10:1− 84.
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