Skull and Dental Characters, and Skull Measurements of Microtus kikuchii Kuroda, 1920 from Taiwan-香川大学学術情報リポジトリ

J．Mamm．Soc．Japan12（1・2）：31−39 September 1987

Skulland DentalCharacters，and SkullMeasurements of

Microtus kikuchiiKuroda，1920ftom Taiwan

YukibumiKANEKO

βわJ曙タcαJエα∂0和わり，ダαC祝妙げE血cαfわゎ， ん柳川・〃【J′血・′■巾・．T‘血川〝′ざJJ符（）．ノ‘ゆけ〃

（Accepted March28，1987）

Abstract．Skullcharacter and dentalpattern were described and16skullmeasure− ments weregivenin14specimens ofMicrotus kikuchii．The skullwas ratherlarge butless ridgy and angular．The number of re−entrant folds varied greatly at both Sidesin M3：threeinner and outer folds are most frequent among the specimens

examined．The number of closed dentalspaces ofM3varied from four to six，and

fiveonesweremostcommon・TheanteroTeXternalconcavityoftheanteriorloo20f

MIvaried fromindistinct to distinct type．A prominant first outer fold of M3is

Observedin allspecimens studied，andit suggests that the foldis a characteristic of the vole．The re−entrant fold ofthe secondloop ofM3didnot appear consistently． Significant regression coefficients of seven skullmeasurements on zygomatic width （ZW）were shownexceptforinterorbitalwidth．Byaregressionlineofcondylobasal length（CBL）onZW，the95％confidenceintervalforCBLoftheholotype specimen， Whose basalpart ofbraincaseis damaged，WaS eStimated as30．97−31．99mm，Which islongest among the specimens examined and reported．

Kqy u，Ords：Microtus kikuchii；Skull；Dentalpattern；Variation；Taiwan．

Introduction

The kikuchi’sfield vole Mimtus kikuchii，an endemic Taiwan species，WaS

first described by Kuroda（1920）on the basis ofone adult female collected from

Mt・Morrison・Afterwards，Veryfewdetailsoftheliteraturehavebeenreported based on a few specimens：On Skullcharacter（Tokuda，1941；Aoki＆Tanaka， 1941），On dentalpattern（Kuroda，1920；Tokuda＆Kano，1938；Tokuda，1941； Aoki＆Tanaka，1941），On SOme eXternalmeasurements（Kuroda，1920，1935； Horikawa，1932；Tokuda＆Kano，1938；Tokuda，1941；Aoki＆Tanaka，1941）， and on some skullmeasurements（Kuroda，1920，1935；Tokuda，1941；Aoki＆ Tanaka，1941）．

This paperpresents skullcharacter，dentalpattern，and skullmeasurements of 14specimens of theKikuchi’s鎖eld vole and discusses on the variation of the

vole．

Iwish to thankthelate Dr・M・Tokuda，KyotoUniversity，forprovidingme llspecimens・Institute ofYamashina Ornithology，Abiko，Chiba Prefecture，Very

kindlyallowed me to examine three specimens．Ishouldlike to thank Prof．E． W・JameSOn，Jr・，University ofCalifornia，forhis readingand commenting on the

32

early draft．

】’．〟（J〃（−ノわ

Materials and Methods

Nine crania withlower jaws，One Cranium，and onelowerJaW Were pre−

Sented by thelate Dr・M・Tokuda（K4943to K4953）（Table2）・Amon写the

SpeCimens dentalpattern of three specimens was丘gured by Tokuda ＆Kano

（1938）and externaland skullmeasurements of four specimens weregiven by

Tokuda（1941）．Thelocality，the date of collection，SeX and externalmeasure− ments of K4946and K4952wereidentihed by the Tokuda’s field note：the two SpeCimens were collected from Mt．Arisan（now Mt．Alishan）（23031′N，

12lO47′E，alt．2270m）．Other specimens studied have not beenidentified by

the author．Some skulls or molars are damaged orlost．

Three specimens collected from Mt．Taiheisan（now Mt．Taipingshan） （24032′N，121O33′E，alt．1922m）and keptintheInstitute ofYamashina Ornithoト Ogy（Ⅰ．Y．0．）were examined and measured（609to611）（Table2）・Kuroda （1935）reported thelocality，the date ofcollection，and the range ofexternaland

a few cranialmeasurements of the specimens．Certain skullmeasurements and

dentalpattern ofthe two specimens cannot be taken，because muscles have not

been removed from skulls．

The fo1lowing16sknllmeasurements were taken to the nearest O・1rnmwith

a dialcaliper by the author；paired structures were prlnClpally measured on the

left side except for some parts ofskulldamaged ormisslng：COndylobasallength

（CBL）・・・distance between occipitalcondyle and anterior point ofpremaxillae；ba−

sallength（BL）…distance frommidpoint oflowermargin offoramen magnum to

the anterior point of premaxillae；COndylo−ZygOmaticlength（C−Z）…distance be−

tween occipitalcondyle and antero−Superioredge ofpremaxillae；COndylo−mOlarl length（C−Ml）…distancebetweenoccipitalcondyleandanterioredgeofM主；inci−

sive−mOlar31ength（Ⅰ−M3）…distancefrom the most anterior point ofincisor■to

the most posterior edge of M蔓；length of diastema（Dias）…distance from the

posterior edge of incisive alveolus to anterior edge of alveolar space of molar

row；palatilarlength（PL）‥・distance from the posterior edge ofincisivealveolus totheforemostpointonthe hindmarginofthepalate；uppermOlarlength（些L）

…distance from the most anterior edge of Mlto the most posterior edge of

M蔓；lowermolarlength（ML）…distancefromthemostanterioredgeofMito the most posterior edge of M3；1ength ofincisive foramen（IFL）・・・maXimum

length of palatine slit；length of nasal（NL）…maXimumlength of nasalbone； zygomatic width（ZW）…maXimum spread ofzygomatic arches；interorbitalwidth （IOW）…least diameter of frontalbones between orbits；mOlar width（MIW）… maximum distance betweenlateralborders of M主；breadth of M主（BM主）・・・ greatest breadth of M主；rOStrum Width（RW）…maXimum distance between

acrosslateralfaces of rostrum at roots ofincisors．

Skulland dentalpattern were drawn by the Stereoscopic Microscope（SMZ−

10）produced by Nippon K6gaku with an accessory drawing apparatus by35

SkullandMolaYSqfMicrotuskikuchii

33 inI．Y．0．

The scientinc names usedin Honackietal．（1982）were followed here．The current name，1atitude，andlongitude of the mountain where specimens were co11ected were obtained from Sanseido（1984）except for Mt．Taiheisan，Whose

current name was based on Chinese pronunciation and whoselocation was esti−

mated from a map（Anonymous，1930）． Results and Discussion

Sゐ〝JJcゐα用Cfgγ作、な．ヱノ

Fig・1・Dorsal（a），Ventral（b），andlateral（c，dande）views。fskull。fMmtus

1’．〟（J〃t，たり

34

The craniumis ratherlarge butless angularin M．kikuchii．Thelateral probleis rather round and thereis muchless pronounced declivity at the ros−

trum・Squamosalandinterorbitalridges are not welldeveloped．The weakly developed ridges on the frontalbones do notfuse，and to form two separate

interorbitalcrests．Incisive foramenis mediuminlength without posterior con− Striction except for one specimen（K4950）．The posterior palatalshelf termi−

natesinamedianproJeCtion，Whichis borderedbyslightly shallowlateralpits on

either side・Externalauditory meatus、islarger．Auditory bullae arelarger also

Withweekly developed spongytissue．Paroccipitalprocess attaches to the bullae

andis not welldeveloped evenin thelargest specimen（K4947）．Pterygoid fos− Sae are deep．Infraorbitalforamenislarge and wide．Zygomata are not well

Spread out from the sides ofthe skull・Lambdoidalcrestis not welldeveloped・ Mandibular foramenis situatedlabially at the base of articular process oflower

a蜜愈笥

、∴∴∵ノ、二十†

_{j宴V ′っ．}

・・彦V宏毒

血寄書 止

g分寄居誓篭

、＼、■∴÷∴

Fig・2．Upper molar patterns oflO specimens of M． kikuchii．a，K4943；b，K4944；C，K4945；d，K4946； e，K4947；f，K4948；g，K4949；h，K4950；i， K4951；j，K4953．

SkullandMolaYS〆Microtuskikuchii ₃₅

b亀

_{C垂巷専i壷仇箸塞}

d︵喜j憂患

e

寅hへ聾尭

ぺ

藍七

Fig．3．Lower molar pattern oflO specimens of M kikuchii．a，K4943；b，K4944；C，K4944；d，K4945； e，K4946；f，K4947；g，4948；h，K4949；i， K4950；j，K4951；k，K4952．

JaW，Where the posterior end ofincisive pulp capsule terminates．The position

Of the foramenis on the anterior border of the capsule．

Kuroda（1920）has not described the skullcharacters of the holotype speci− men collected from Mt．Morrison（now Mt．Yushanch’ienfeng）（23028′N， 120054′E，alt．3050m）．Tokuda（1941）wrote that the ridges and angles of the Skullshowed rather feebly，Whereas Aoki＆Tanaka（1941）stated that the sku11 was rather angular and ridged．Tokuda’s（1940）descriptionis wellagreed with

the present specimensinvestigated，COmpared with the skullof other four spe−

cies of Microtus：namelyjbrtis（Kirin Prov．and AnhweiProv．，China），OeCOnO− mus（Kol’sky Peninsula and the Kuriles，USSR），maXimou）iczii（Heilungkiang Prov．，China），and montebelli（Kyoto，Japan）．

JJ川山／／）′J／／（川・F王ぐ．ご・仙／・一丁J

Frontalsurfaces ofupperincisors are orangein colour．Mlhas an anterior

36 r助乃g烏0

three alternating closed triangles without postero−internalheel．

M3has an anteriorloop with three closed・triangles and a posteriorloop， Which shows some variations．Tablelgives the variation of the number of re−

entrant folds at each side of the molar：threeinner and outer re−entrant folds With or without the forth smallconcavity were observedin seven specimens

among ten．

Kuroda（1920）has described the number of re−entrant folds of M蔓in the

holotype specimenas three at theinner side andfouratthe outer side．Tokuda

＆Kano（1938）figured two molars of M蔓With fourinner and outer re−entrant

folds，and with fourinner and three outer folds．Aoki＆Tanaka（1941）reported

five specimens with fourinner and three outer folds，Six specimens with five inner andthree outer folds，and four specimens with fiveinner and four outer

Tablel．Thenumberofre−entrantfolds oneitherside ofM3inMicrotuskikuchii．

Side Inner fold−Outer fold

Left 3−3 3＋s＊−3 3−3＋s＊ 3−4 3−3＋s＊ 3＋s＊−3＋s＊ Right 3−3 3＋s＊−3 3＋s＊−3＋s＊ 3＋s＊−4 3−3＋s＊ 3＋s＊−3＋s＊ Registered K4943 K4945 K4946 K4944 K4953 K4947 number K4948 K4949 610 K4951 ＊3＋s，Theforthsmallconcavewasfoundasfiguredinc，e，gandiofFig■2

folds．Tablelshows that the number ofinner and outer folds varies greatlyln

M30fM．kikuchii，and threeinner and outerfolds are most common，and there

are some specimens with fourinner and three outer，and with threeinner and

four outer folds，Which have not been described by Kuroda（1920）and Aoki＆

Tanaka（1941）．

InM3five closed dentalspaces were observedinbothsides ofsevenspeci−

mens（K4944，K4947，K4948，K4949，K4951，K4953，and610），inthe right side ofK4946，andin theleft side of K4943．Furthermore，because the second and

third dentalspaces of the molar are confluent at the right side of K4943and

both sides of K4945，these three molars have four closed dentalspaces． Kuroda（1920）has reported that the holotype specimen has five closed dentalspacesin M蔓．Tokuda＆Kano（1938），however，nOted that there were five to six closed spacesin this vole．Aoki＆Tanaka（1941）丘gured one speci−

menwithfive spaces・Thus，thenumberofthe spaces varies fromfourto six，

and 銭ve ones are most common．

Mlhas a posteriorloop with five closed triangles and an anteriorloop・

The firstinnerre−entrantangle ofthe anteriorloopforms adeeperfoldanterior− 1y：the dentalspace of theloop shows a revprse V−1etter or U−1etter・Two

specimens（K4946and K4949）hav？a distinct antero−eXternalconcavityin the

loop，Whereas other two specimens（K4943and610）1ack the concavityin the

loop．

SkullandMolaYSqfMicrotuskikuchH ₃₇

loop of Mlin the holotype specimen．The present study，however，indicates that this vole vari占s fromindistinct to distinct concavity．

M2has a posteriorloop with four alternating closed triangles without varia−

tion．M3has three transverselQOpS．A prominent antero−eXternalre−entrant fo1d of the丘rst transverseloop was observedin both sides of the molarinal1

SpeCimens examined．Furthermore，the fold sometimes forms a smallanterior Closed dentalspaceintheloop（K4947inbothsides and K4952inthe right side）

（Fig．3−f）．The same condition was figured by Aoki＆Tanaka（1941）．There− fore，aS Tokuda（1941）hasalready pointed out，it appears that the prominent 銭rst fold of M3is a characteristic of this vole．

The re−entrant fold of the secondloopin M3was not developedin theleft

side of K4943，K4945，and K4946，andin the right side of K4953，Whereas the fold was found clearlyln Other specimens．Therefore，the fold does not appear consistently，thoughTokuda＆Kano（1938）noted the second outer fold was Characteristical1y deep．

〃ぐ〟5〃れ一肌川雨

Skullmeasurements of14specimens are glVenin Table2．Fig．4shows

SCatter diagrams and regressionlines of eight skullmeasurements against ZW， based onTable2．Because specimens withthe dimension ofZWare greatestin

number，ZW was used as a standard dimension．Regression coefficients were

Table2．Skullmeasurements（mm）ofMicrotuskikuchii． Registered number Sex K4943 K4944 K4945 K4946＊ K4947 K4948 K4949 K4950 K4951K4952＊ K4953 609† 610† 611† ＿ ＿ − ♀ − − − − − ♀ − ♂ ♂ ♂ CBLB㌶Ⅷ諾ML監NLZW馴MW叫RW B L 一 8 7 2 8 7 8 4 6 6 4 8 5 4 5 1 4 9 1 5 2 5 7 1 5 5 7 3 4 1 5 3 7 1 2 2 2 1 1 1 134448752129 ＝ ： m8． 1 1 2 3 3 4 0 8 3 8 4 1 9 9 1 5 3 1 9 7 2 8 8 8 4 6 6 5 8 5 4 5 1 5 2 2 2 1 1 1 1 8 2 5 2 7 7 4 6 5 1 0 6 0 5 4 9 8 7 2 8 7 8 4 6 6 5 8 5 4 5 1 4 2 2 2 1 1 1 1 9 8 3 9 8 9 5 7 7 4 8 6 4 2 2 2 1 1 1 1 0270005725449 ■一■ ■ 1 1 379192122189220 弧 2 1 8 0 4 0 4 1 4 0 0 8 9 4 2 5 4 8 29．3 30．8 − l 一一一一一一一一7．一一一一一一一 1 3．︼ ■ ■一 2 8073 3． 21 6 2．︻一■ ■ 2 052357677129 一m8． 1 1 549 998126 ︻ 1 1 5418 一 1 6 0 1 3 9 2 0 4 3 6 7 5 9 6 4 6 1 5 1 925 ■ 8． 1 8 2 1 3 1 3 0 4 8 6 4 5 1 5 1 082 9． 1 ＊，ThetwospecimenswerecollectedfromMt．AlishanOn17February1939．Theexternalmeas11rementS recorded（mm）areasfollowsintheorderofheadandbodylength（HBL），tai11ength（TL），hindfootlength （HFL）andearlength（EL）＝99，73，22，and13■7inK4946；122，89，23，and13．7inK4952．†，Thethree specimenswerecollectedfromMt，Taipingshanon17November（609），6December（610），and20December （611），1932，The externalmeasurements recorded（g ormm）are as followsin theorderofbodyweight，

HBL，TL，HFL，andEL：41．3，114，66，24，and18in609；45．1，120，77，23，and16in610；45．1，122，73， 24，and16in611．

l′．〟〟J押如 38 mm 8 7 6

／

Di誠＝僅桝・−5 ●●／ ●／ ML＝G23ZW◆2．96 （t＝2β9★）

ィノ

● Dias ML 10 9 8 7 5 ・・

・・ニノ

mm 31 30 29 28 CBL三1．37王W◆750 （t＝13．58キり ● NL NL＝0．69王W−2鼻9 （t＝4．65♯り ● cBL _ム ■l レ・ナ・し・一盲／ ＿一＿ ● IOW三0］3王W●2．09 IOW （t＝1．91NS）

／4

；：［：； 14 13 12

／。L

3 5 4 2 l ● PL三181ZW−1．57 （t＝552…） MIW＝GO8王W◆OJO （t＝ユ05♯） ＿．＿＿＿＿．一・占・√●￣●〆￣ MIW 14 15 16 17 18mm14 15 16 17 18mm ZW ZW

Fig・4・Scatter diagrams and regressionlines of skullmeasurements against ZygOmatic width（ZW）in M kikuchii，Ho1low trianglesindicate the

ValuesofmeasurementsoftheholotypespecimendescribedbyKuroda

（1920）∴0．001＜ク＜0．05；＝，ク＜0．001．

statistically slgnificant except for a relationship between ZW andIOW・

The skullmeasurements of the holotype specimen（Kuroda，1920）arein− Cludedin the 95％ confidenceintervalfor PL（15．23−16．99mm），for NL （9．04−10．14mm），and for Dias（9．25−10．15mm）but deviate from theintervalfor ML（6．61−7．33mm），for MIW（1．39−1．61mm），and forIFL（4．89−5．79mm）．

Theseintervals are estimated by the regressionlines mentioned above because

ZW of the holotypeis17．5mm（Kuroda，1920）．Pne ofthe reasons why these

three measurements of the holotype deviate from theintervals may be alower

Significant figure（Kuroda，1920）than thosein the present study．Because the

basalpart ofbraincase ofthe holotype specimen was damaged and not measured

（Kuroda，1920），the95％confidenceintervalfor CBL of the specimen can be predicted as30．97−31．99mm．Because Aoki＆Tanaka（1941）measured ZW of

SkullandMolaYSqfMicrotuskikuchii 39

One SpeCimen（no．3368）as16．3mm，the con丘denceintervalfor CBL can be estimated as29．55−30．11mm．Theseintervals suggest that the overallskullsize Of the type specimen described by Kuroda（1920）islongest among the speci−

mens examined and reported．

References

Anonymous．1930．Map of Taiwan．Chigaku Zasshi，42：pl．6．（inJapanese）

Aoki，B．＆R．Tanaka．1941．The rats and mice of Formosa，illustrated．Mem．Fac．Sci．Agri． TaihokuImp．Univ．，23：121−191．

Honacki，J．H．，K．E．Kinman＆J．W．Koepple．1982．MammalSpecies ofthe World．Allen Press， Inc．＆Assoc．Syst．Coll．，Lawrence．

Horikawa，Y．1932．［A Monograph of the Mammals of Formosa．】Zool．Soc．Formosa．（inJapanese） Kuroda，N．1920．On two species of Muridae obtainedin the centralmountains of FormOSa．Zool．

Mag．，32：36−43．（inJapanese and English）．

Kuroda，N．1935．Formosan mammals preservedin the collection of Marquis Yamashina．）．Mamm． 16：277−291．

Sanseido（ed．）．1984．［Concise GeographicalDictionary of Foreign Mountains．］Sanseido，Tokyo．（in Japanese）．

Tokuda，M．1941．A revised monograph of theJapanese and Manchou−Korean Muridae．Trans． Biogeogra．Soc．Japan，4：1−155．

Tokuda，M．＆T．Kan0．1938．［Thealpine Muridae of Formosa with a biogeographicalreference of Muridae fauna ofIsland（I）．］Bot．＆Zool．，5：1115−1122．（inJapanese）．