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群馬県立自然史博物館研究報告(5) : 1-8, 2001 1

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OriginaIArticleZ~〆､ゴ、ノーゾLダヘゾー､ゾヘダー､ノー､ゴーL／、

PreliminarynoteontheMiocenenightlessswanfromtheHaraichiFormation,

TomiokaGroupofAnnaka,Gunma,Japan.

MATSUOKAHiroshige',NAKAJIMAHajime2,TAKAKuwAYujisandHAsEGAwAYoshikazu3

Ⅲ、幼α”〃E"jq/Geo/ogya蛇騨j梅"E池jqgMG"""EScﾉz“jQ／Scjg押蝿幻“0酌z”E芯地' fKy“0,“6-節“ノ""z

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3Gz"z糀α暇"se""zQ/Mzj"趣ノHMO7y: Z6再一Z,K""娩郡”釦α,""2"",G"""ea,37D-a345jノ”α刀

Abstract

Nearlycompleteskeletonofaflightlessswan,namedthe"AnnakaShort-wingedSwan",

wasfoundfromtheupperMiddleMioceneHaraichiFormation(11-12Ma),Tomioka

GroupinAnnakaCity,GunmaPrefecture,Japan. Thewingelementsarereduceddistal-

ly; onthecontrarythehindlegchangedlittlefromthevolantancestor, Theskeletonand

livingpostureof ､$AnnakaShort-wingedSwan"areproposedinthisreportthroughthe

preliminaryinvestigation.

KeyWords:GunmaPrefecture,Annaka,TomiokaGroup,Miocene,Flightlessbird,Cygnini

Startlingly, the fossil bird isa flightless species

belongingtoTribeCygnini,especiallyswans. Aswell

astheplotopteridswhichprosperedintheEoceneand

Oligocene (e9.OlsonandHasegawa, 1979, 1996), the

occurrenceofsuchanobviouslyflightlesscoastalbird

fromtheMiocenesignifies thetransitionofmarine

zoogeography.AIso,thefactthattheskeletonisnear-

lycompleteissignificantforstudyingavianflightless-

ness, afrequentpatternofevolution.

Adetailedosteologicaldescriptionandtaxonomical

conclusionswillbepresentedinfuturepublications,as

thespecimenneedsfartherpreparation. Herewepro-

videapreliminaryreportonthefossilflightlessswan.

INTRODUCTION

OnJanuaryl, 2000, thefirstdayofthenewmillen-

nium, juniorauthorHajimeNakajimadiscovereda

fossil vertebrate skeletonexposed on theMiddle

MioceneriverflooroftheUsuiRivernearHaraichi,

AnnakaCity,GunmaPrefecture(Fig.1).Forreinforce-

mentaflat resincoatingwasappliedfor removal.

Afterthat, theslabwaspreparedfromthebottomside

verycarefullyintoarelief-likespecimenbyHN. Sub-

sequently, itwasfoundtobeanalmostcompleteskele-

tonofa largebird, oneofthemostcompleteavian

fossilseverfoundinJapan.

Thefindingof this fossil hadverygoodtiming,

becausel49thRegularMeetingofthePalaeontological

SocietyofJapan (June24-252000) organizedbythe

GumnaMuselnnofNaturalHistorvdirectedbvY.

Hasegawawasabout ready toopen.Theauthors

decidedtopresentatalkonthisfossilatthismeeting.

Weinvestigatedinahurry, andtheperspectivewas

read. Thisisanoteonthespecimenthatwasreadin

themeeting.

SYSTEMATICS

ClassAves

OrderAnseriformes

FamilyAnatidae

SubfamilyAnserinae

TribeCygnini

aff.Mega/odytessp.

受付苫2001年1月10日，受理:2001年3月16日

MAT､suoKAHiroshige,NAKAJIMAHajime,TAKAKuwAYujiandHAsEGAwAYoshikazu２

SPecimen. ---Skeletalelementsinrougharticulation,

scatteredhorizontallyacrossaslabof70cm×maxi-

mum40cm(Fig.2, P1. 1).Clearlyrepresentingone

animal. Theelementspreservedare: cranium,man-

dible, incompletesternum, 9ribs, 16cervicalandthor-

acicvertebrae,pelvislackingonlypubisbranches,2

caudalvertebrae, leftscapula, rightandlefthumeri,

rightandleftulnae, right(?)radius, leftcarpometacar-

pus,rightandleftfemora,rightandlefttibiotarsi,right

andleftfibulae, lefttarsometatarsus, andsomeminor

bones.

Becauseit isdifficulttoassigneachvertebratothe

cervicalorthoracicinthepresentconditionofspecimen,

wehavenotreachedafinalassignment. At least,no

distalcervicalvertebraeareincluded. Possibly,more

thanseventhoracicvertebraearepreservedinthefossil.

That is, however, contrarytothefact thatCygnini

membershaveseventhoracicvertebraeallteriortothe

synsacrum. The right tibiotarsus isbroken in the

middleoftheshaft,andismissingthedistalhalf.

Local岬---NearHaraichi, AnnakaCity, Gumna

Prefecture,Japan; riverflooroftheUsuiRiver,about

600mdowntheriverfromtheNakahasiBridge.

Discoveryb ---ByH.NakajimaonJanuaryl, 2000.

HoriZonand theage. --･Massivesiltstoneof the

HaraichiFormation,TomiokaGroup. ThelateMiddle

Miocene (approximately ll-12Ma)． Benthic for-

aminifera(KanekoandNomura, 1998)andlithofacies

indicatethepeiagicdepositionalenvironmentforHarai-

chiFormation. AgedeterminationfollowedNomura

andOhira(1998).

Measurements. ---Becausehalfofbonesarecovered

bymatrix, itisimpossibletogivefinalmeasurementsof

manybones.Asafirstapproximation,werecordedthe

Figurel. LocalitymapsfortheMiocenefossilbirdfromAnnaka,Gunma,basedonthel :25,00Oscaletopographic

mapoftheGeographicalSurveyInstituteofJapan, "Tomioka"and"Matsuida".

PreliminarynoteontheMioceneflightlessswanfromtheHaraichiFormation,TomiokaGroupofAnnaka,Gunma, Japan 1

謬曾汀1um

＝

‘ andi

クⅦ″八〃咄棚〃

『

馴、~~

③Cd､V夕

10Cm

Figure2. Identificationsofeachskeletalelementofthefossil (ontherightslab),andthepositioninthebirdskeleton(inthe

leftbird,blackedbones). Abbreviationsare; d,distal ; l, left;m,middle; p,proximal ; r,right/CdV,caudalvertebra;Cm,

carpometacarpus;CV,vervicalvertebra;Fb,fibula;Fm,femur;H,humerus;R, radius;Tm,tarsometatarsus;Tt,tibitar-

sus;TV, thoracicvertebra;U,ulna;V,vertebra; cervicalorthoracicunknown.

maximumlengthofthemainelements. Themeasure-

mentsareasfollows.

Cranium,maximumlengthofthepreservedpart: 95

nlln・

Mandible,greatestlength: 105mm.

Pelvis,greatestlength(withoutpubis) : 200mm.

Pelvis, lengthalongthecenter: 170mm.

Sternum,maximumlengthofthepreservedpart : 105

1，，1．

Scapula(left),GreateSt length: 108mm.

Humerus(right),greatestlength: 220mm.

Humerus(left),greatest length: 218mm.

UIna(right),greatestlength: 125mm.

Ulna(left),greatest length: 124mm.

Radius(right?),greatestlength: 115mm.

Carpometacarpus(left),greatestlength: 66mm.

Femur(right),greatest length: 97mm.

Femur(left),greatestlength: 94mm.

Tibiotarsus(left),greatestlength: 200mm.

Tibiotarsus(left),axial length: 190mm.

Tarsometatarsus(left),greatestlength: 110mm.

humeruslength(P1.2 3)． Volantbirds, ingeneral,have

ulnaewhicharealmostequivalenttoorlongerthanthe

humeri,andshorteneddistalelementsarearemarkable

character inflightlessspecies. Theothercharacters

suchas; inhumerus,muchsmallerdistalendthanthe

proximalend, flattenedproximalend,andstraightand

slendershaft (Pl.2-2,3) ; Iowcarinaof sternum(Pl.

2-6) ; shortenedandslendercarpometacarpus(P1. 2 3) ;

narrowandsmallscapulawithreducedacromion(P1.

2 7),etc・ alsoindicatetheflightlessnessinthisfossil

bird.

Thepelvis(P1.2 8)mayalsoshowsaneotenicstateas

wellasthewell-knownexamplesinupperhalfofthe

body. Firstofall， themorphologyofthepelvisofthis

birdisatypical. Judgingfromthesizeofthefemur,

whichindicatesthetrunksizereasonablvwell,wewould

expectamuchlongerpelvisforthisbird. Theother

pointwefindpuzzlingisthenumberofproximalcer-

vical/thoracicidentificationofvertebrae. Itseemsthe

fossil includesmorethanseventhoracicvertebrae､but

theresult iscontrarvtotheseventhoracicvertebrae

foundinCygninibirdS.

Toexplainthetwoenigmasclear,wehypothesized

thefossilpelvisasa@Gmaturedbutunfused"one, i.e.,the

shortpelviswasperhapsprimitivethanthelongerpelvis

whichconsistsofmorevertebrae, thoracicvertebrae

anteriorandcaudalvertebraeposterior, but is inour

fossil lackingsomeunfusedonesonbothends,beinga

Strikingfeaturefortheecologyoffossi l bird

Themostconspicuousfeatureonthisfossilbirdisthe

evidenceofflightlessness, showingextremeadaptation

foraquaticmodeof life,withnolongdistancemigra-

tion． Forexample, lengthofulna isonly55%of

MATsuoKAHiroshige,NAKAJIMAHajime,TAKAKuwAYujiandHAsEGAwAYoshikazu4

tibiotarsus,andafemurandproximalpartsofhumerus

havebeenreferredtothisspecies. However,according

toHoward(1988),theholotypictibiotarsusisl51.9mm

Iong in axial length. The :!Annaka Short-winged

Swan'',whichhasl90mmaxiallengthoftibiotarsus, is

much larger than". wzo7Zio"", andbelongingtoa

different category. Our investigation is tooprelimi-

narytoassignthe"AnnakaShort-wingedSwan" to

particulargenus.Wehavenotexaminedthespecimens

of〃“z/0の花s”0〃o""jatanyrate,andstillneedto

examineotherflightlessanseriformes.

neoteniccondition. Thishypothesisexplainsthenot

chedcaudalmarginoffossilpelviswithshortsynsacral

caudalvertebrae・ Forfurther investigations,wemust

preparetheventral surfaceoffossilpelvis. AIsofar

therpreparationofthevertebraeisneeded.

ldentificationandSystematics

Thisfossil isthatofalargeanseriform・ Further-

more, inadditiontothecharacteristicproportionsof

widewings(eventhoughit isreduced,thelonghumerus

suggests increasedwingspan), skeletal elementshave

characteristicswhichallowustoidentifythefossilbird

asaswan. Wingelementsandpelvisshowunusual

morphologiesashavebeenmentionedabove,butsuch

modificationsareprobablvneotenicandfunctionaldif

ferencesreflectingaflightlessmodeoflife.

Herewewould liketonamethis fossil swan the

"AnnakaShort-wingedSwan''.

WeknOw"egIz/0の彫s加0画0ﾉz"jHowardl988wasa

flightlessCygnini,reportedfromtheMiddleMioceneof

California. The holotype is an almost complete

RECONSTRUCTIONOFTHE

$ $ANNAKASHORT-WINGEDSWAN' '

Osteology

Thenearlycompleteskeletoninthefossilallowsa

reconstructionofthebody(Fig. 3).

ConsultingClie"がes (Mergini), anexemplumof

flightlessanseriform, inwhichfemurchangedlittle, in

､譲舞,

ｋロ一℃‐

1夢＝琴豐讓蚤誤ジル．』

VolantCygnus

(C.(Oﾉo〃oﾉoり

FlightlessCygninispeciesfromtheMiocene,

Annaka,Gunma,Japan.

Figure3. Skeletalreconstructionof"A'makaShort-wingedSwan'' (right),comparedwiththeskeletonofvolant

swan,Q智"〃so/"(left).

PreliminarynoteontheMioceneflightlessswanfromtheHaraichiFormation,TomiokaGroupofAnnaka,Gunma, Japan 5

spiteoftheextremereductionofwingelements (Liv-

ezey, 1993),the&[AnnakaShort-wingedSwan"mayhave

evolvedfromaspecies thatwasthesizeofQ唇""S

m/郡沈6"""s. Thus,overallproportions,exceptforthe

pectoral andwingregions, resemblethoseofQg""sプ ~7D

COJ〃”Z“α邦況S・

However, thewings, especiallythedistal elements,

areremarkablvreducedinbothsizeandbulk. The

ulnais55%thelengthofthehumerus. Elbowjointof

the"AnnakaShort-wingedSwan"mightnotreachthe

coxawhenfurled; onthecontrarvvolantswanssettleit

inthebackofcoxa.

Theincompletesternumistheonlvremainsofthe△

pectoralgirdle,butitstillshowsflightlessadaptationin

thesmallsizeandlowcarina. Nocoracoidsorfurcula

arepresent.

Theshortpelvisrelativetothebodysize isalsoa

remarkablecharacterof the "AnnakaShort-winged

Swan''. However, the total lengthof thevertebral

columnincludingpelvismightnotbechangedfromits

ancestorbecausetheenigmaticpelviscanbeunderstood

asaneotenicconditionasdiscussedabove.

Thetrunkmighthavehadaslightlyhigherangled

posturethanitsancestorwhenstanding, likethegeneral

trendofflightlessbirds.

Thehindlegchangedlittlefromthevolantancestor.

Butphalangesarenotwellpreserved

Thefaceisimpossibletoknowbecausethecranium

showsonlythebasalviewandtherostrumismissing.

Themandibleisbentandhasnarrowsvmphvsialarea.

Thislooksstrangebecauseanseriformesusuallyhave

straitbillandanextensivesvmphvsisinthemandible.

Furtherpreparationisneededtofindthestateofthebill

of "AnnakaShort-wingedSwan",whether thefossil

indicatesaspecialadaptationforitsdietaryhabitator

merelydiageneticdeformation.

ACKNOWLEDGMENTS

TheauthorsthankmostsincerelvPatriciaVickers-

RichofMonashScienceCentre,MonashUniversityand

HollisW.ButtsofMuseumlmport,Tokyowhohelped

kindlytocompletemanuscript. Weare indebtedto

MakotoManabeofNationalScienceMuseum,Tokyo

forhishelpinexaminingtheosteologicalspecimensof

recentbirdshousedinNSM.

REFERENCES

Feduccia,A.andTordoff,H.B(1979) : FeathersofA7c"""-

彫γyr: asymmetricvanesindicateaerodynamicfunction.

Sc""", 203: 1021 1022.

Howard,H(1988) :NewrecordsofMiddleMioceneanserifor-

mbirdsfromKernCounty,California. 1n,K.E.Camp-

bellJr.ed.,Rzpe窓加A"jα〃Rz/""加/Ogy,230236,Natural

HistoryMuseumofLosAngelesCounty.

Kaneko,M.andNomura,M. (1998) :Fossil foraminiferaand

PaleoenvironmentofHaraichi formatiOnandlowestpart

of ltahana formation inTomiokaandAnnakaarea,

Gunmaprefecture, Japan. B""節加Q/G""脚α〃"s鋤加

Q/rMz畑mJHISZD剛, 2: 57-66.

Livezey, B.C. (1993) :Morphologyofflightlessness inCﾉzg"‐

の彫s, fossil seaducks (Anatidae:Mergini) of coastal

California. ノリ"7w(z/ qf睦吋妨緬彫Hzﾉ"""/cgy, 13 (2) :

185-199．

Nomura,M, andOhira,H(1998) :Fission trackagesof

MiocenetuffsinTomiokaGroup,Tomiokaarea,Gunma

Prefecture. B"""加QfG""”α〃"s""Q/ JV鹿加"/

賊Sm籾， 2： 35-42．

OIson,SL. (1973) :EvolutionoftherailsoftheSouthAtlantic

islands (Aves:Rallidae)． S柳"向so"""Co""""0"s /0

Zt)0/qgy, 152: 1-53.

OIson,S､L･ andHasegawa,Y. (1979) : Fossilcounterpartsof

giantpenguins fromtheNorthPacific・ Sc/"z", 206:

633635．

OIson,S.L・andHasegawa,Y(1996) :Anewgenusandtwo

newspeciesofgiganticPlotopteridaefromJapan(Aves:

Pelecaniformes). ノリ〃γ"α/ q/W減酌""Rz"0れゎjOgy, 16

(4) : 742-751.


和文要旨

群馬県安中市の富岡層群原市層から発見された

中新世無飛翔性ハクチョウについて

松岡廣繁】・中島－2 ．高栞祐司3 ．長谷川善和3

!京都大学大学院理学研究科・地質学鉱物学教室：〒606-8502京都市左京区北白川追分町2〒379-0116群馬県安中市安中1 9-15

3群馬県立自然史博物館：〒370-2345群馬県富岡市上黒岩1674 1

要』日

群馬県安中市の碓井川河床に分布する中部中新統上部の富岡層群原市層から発見された，全

身の骨格要素がほぼ完全に保存された烏類化石は，ハクチョウ族に含められるが著しい無飛翔

性の特徴を示す種であることが判明したので，ここに初期的に報告する．

化石は，尺骨の全長が上腕骨の55％にすぎないなど，翼の要素は遠位ほど退縮している．一

方下肢の要素は飛翔性のハクチョウ類と大きな違いはない．翼の退化した本化石をここでは，

"AnnakaShort-wingedSwan"アンナカコバネハクチョウと呼称することとした詳細な分類

学的検討はさらに剖出作業を進めてあらためて行うこととし，本報告では，骨格を中心に，飛

翔性ハクチョウ類とアンナカコバネハクチョウとの相違を示す．

キーワード：群馬県，安中市，富岡層群，中新世，無飛翔性鳥類，ハクチョウ族

PreliminarynoteontheMioceneflightlessswanfromtheHaraichiFormation,TomiokaGroupofAnnaka,Gunma,Japan ７

Platel.Theslabincludingskeletalelementsofonefossilbird,collectedfromtheMiddleMiocene,ofAnnaka,Gunma,Japan


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Plate2. Closeupfiguresofdistributionofbonesontheslab. 1.basalviewofcranium(leftbottom)andmandible(right) ;2.anconalviewofproximalpal-toflefthumerus; 3.wingelememts; 4. legelements; 5,posteriorviewoflefttarsometatar-

sus; 6, right lateralviewof incompletesternum; 7. dorsalviewof leftscapula; 8.dorsalviewofpelvisandtwucaudalvertebrae. Allscalebarsare5cmlong.

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