貴州浙江成就性纖用幻龍一新種半翅目幻龍科

貴州浙江成就性纖用幻龍一新種半翅目幻龍科

胡貴州龍是第一個(gè)三疊紀(jì)海生動物?；a(chǎn)自法郎組竹桿坡段。1965年楊鐘健先生記述了發(fā)現(xiàn)于同一層位、同一地點(diǎn)的幻龍亞目扁鼻龍科的意外興義龍(Nothosauria,Simosauridae,Shingyisaurusunexpectus)。Rieppel(1998)對意外興義龍化石材料進(jìn)行了重新研究,依據(jù)錐狀的牙齒,明顯收縮的頂骨平臺,后置的松果孔,水平暴露的三角形的上枕骨和膨脹于頜關(guān)節(jié)之下的上隅骨將其修訂為幻龍的未定種(Nothosaurussp.)。Rieppel(2000)又進(jìn)一步認(rèn)為這一化石材料在可歸入Nothosaurus的同時(shí),存在歸入另一密切相關(guān)屬的可能性?；谬垖僦饕植加谖魈靥崴箙^(qū)(包括歐洲、西亞和北非等地)的下安尼階至上拉丁階,個(gè)別種(如N.edingeraeSchultze,1970)可達(dá)下卡尼階。Rieppel(2000)在編寫鰭龍類的百科全書時(shí)確認(rèn)了該屬8個(gè)有效種,它們是N.mirabilisMünster,1834,N.cymatosauroidesSanz,1983,N.edingeraeSchultze,1970,N.giganteusMünster,1834,N.haasiRieppeletal.,1997,N.juvenilisEdinger,1921,N.marchicusKoken,1893和N.tchernoviHaas,1980。2001年他又記述了發(fā)現(xiàn)于德國殼灰?guī)r(Muschelkalk)上部的幻龍一新種N.jagisteus。前述發(fā)現(xiàn)于貴州頂效的Nothosaurussp.化石,僅包括一扭曲的不完整頭骨和5節(jié)前部頸椎(中國地質(zhì)博物館NGMCVm1308)。材料雖不完整但它卻是中國發(fā)現(xiàn)的第一個(gè)幻龍屬的代表。自20世紀(jì)90年代以來,在貴州興義及相鄰地區(qū)的法郎組竹桿坡段陸續(xù)有一些幻龍類的骨架被發(fā)現(xiàn)。本文記述了2001年野外工作期間獲得的幻龍一新材料?；谬垖貼othosaurusMünster,1834楊氏幻龍(新種)Nothosaurusyoungisp.nov.(圖1～3)釋名種名獻(xiàn)給中國古脊椎動物研究的奠基人及中國三疊紀(jì)海生爬行動物研究的開創(chuàng)者已故楊鐘健院士(1897～1979)。正模一近于完整的頭骨、下頜及不完整的頭后骨架(古脊椎動物與古人類研究所,IVPPV13590)。產(chǎn)地及層位貴州興義,中三疊統(tǒng)法郎組竹桿坡段。特征幻龍屬一小型的種(頭骨中線長度160mm);吻部適度發(fā)育,吻端鈍圓,后部有明顯的收縮;具5個(gè)呈匍匐狀的前頜骨獠齒和4個(gè)彎曲向上的下頜縫合部獠齒;細(xì)條狀的軛骨前端未伸達(dá)眼眶邊緣,上頜骨和眶后骨在軛骨之后相接;眶后弓窄;外翼骨形成明顯的腹向凸緣;下頜具清晰的冠狀突,夾板骨前端進(jìn)入下頜縫合部;腕骨4塊。描述見英文部分。對比與討論在眾多的Nothosaurus種中,N.giganteus大型,僅具4個(gè)前頜骨獠齒(fangs);N.mirabilis的頭長460mm,吻部細(xì)長,上頜齒列可伸達(dá)上顳孔中點(diǎn);N.tchernovi的頭骨中等大小,細(xì)長吻部的兩側(cè)近于平行,軛骨缺失;依據(jù)這些特征它們都明顯地區(qū)別于V13590。在Nothosaurus小型的種中,它們以下列的特征有別于V13590:N.edingerae的松果孔之后具矢狀脊,前頜骨后突伸達(dá)外鼻孔后緣之后;N.juvanilis翼骨強(qiáng)烈前伸,非?？拷鼉?nèi)鼻孔,下頜關(guān)節(jié)的位置比枕髁更靠后;N.haasi吻部細(xì)長,前頜骨與額骨相接,前額骨和軛骨缺失,上顳孔小;N.jagisteus的吻部細(xì)長,兩側(cè)邊近于平行,上頜齒列后端可延至上顳孔的1/3～2/3。在頭骨大小和形狀上與V13590最為相似的是發(fā)現(xiàn)于德國柏林附近Rudersdorf中三疊統(tǒng)Karlstadt組的N.marchicus。N.youngi與N.marchicus一樣屬小型幻龍類,二者在頭骨形態(tài)及各部比例上極為相似。N.youngi也有相對短而寬的吻部,吻端-眼眶前緣與吻端-外鼻孔前緣之比為1.9,吻端-上顳孔前緣與吻端-外鼻孔前緣之比為3.0,外鼻孔長與寬之比為1.5,它們分別落在N.marchicus中與之對應(yīng)的數(shù)據(jù)——1.8～2.0,2.9～3.4和1.0～1.4(1.6)——范圍之內(nèi)(RieppelandWild,1996)。二者之間的區(qū)別體現(xiàn)在一些具體的結(jié)構(gòu)特征上,如N.marchicus的鑒定特征中包括,在一對上頜骨獠齒之前有5個(gè)小的上頜骨齒,但在N.youngi中僅有4個(gè)小齒;N.marchicus的外翼骨前伸至腭部的1/2處,N.youngi的外翼骨短小,沒有特殊的前伸的跡象。二者都有較短的上頜齒列,但比較起來N.youngi的更短一些,它未達(dá)上顳孔的1/4處。上顳孔長與上顳孔前端-上頜骨后端長度之比為6.1,大大超過N.marchicus中相應(yīng)的值3.4～3.6(RieppelandWild,1996)。N.youngi與N.marchicus的鼻骨形態(tài)相似,都為寬的葉片狀,表面具放射狀紋飾。N.youngi中鼻骨后側(cè)方與后額骨相連,阻隔了額骨與上頜骨。而N.marchicus中的鼻骨受額骨與上頜骨的阻隔,不與前額骨相連。N.youngi的夾板骨前端進(jìn)入了上頜縫合部,這在幻龍類中是獨(dú)特的。N.youngi的另一個(gè)獨(dú)有的特征是它的下頜上有小的喙?fàn)钔弧＿@兩個(gè)特殊的結(jié)構(gòu)不僅未發(fā)現(xiàn)于其他的幻龍中,亦未見于Simosaurus(Rieppel,1994)。除楊氏幻龍外,發(fā)現(xiàn)于貴州興義法郎組竹桿坡段的幻龍科成員還有幻龍未定種和興義鷗龍(Lariosaurusxingyiensis)(李錦玲等,2002;Rieppeletal.,2003)。如前所述Nothosaurussp.(NGMCVm1308)系意外興義龍(ShingyisaurusunexpectusYoung,1965)的修訂名稱,化石材料包括一不完整的頭骨和5個(gè)前部頸椎。因NGMCVm1308保存的不完整性及頭骨的強(qiáng)烈扭曲,二者間很難進(jìn)行全面的比較?？梢员孀R的區(qū)別包括Vm1308的額骨-頂骨骨縫位于上顳孔前端之后的2/5處,比N.youngi中的骨縫要更靠后;從保存較好的頭骨左側(cè)來看眼眶與上顳孔之間的距離相對較寬,它大于外鼻孔與眼眶之間的距離的1/2。目前尚未發(fā)現(xiàn)充足的理由將它們歸入Nothosaurus的同一種。興義鷗龍的頭骨與歐洲產(chǎn)Lariosaurus的頭骨在頂骨平臺(parietalskulltable)的形狀上有較大差別,而與Nothosaurus的頭骨更為相似。它與N.youngi同屬小型幻龍類,頭骨的形狀也很相似。特別是興義鷗龍也有非常窄的眼眶-上顳孔間距離。二者的區(qū)別在于:Lariosaurusxingyiensis的頂孔位于頂骨的后1/3處,頂孔之后形成一窄的頂脊,而N.youngi的頂孔位于一深凹中,在頂孔之后未見矢狀脊;L.xingyiensis中額骨-頂骨骨縫比N.youngi的要更靠后;L.xing-yiensis?的鼻骨被前頜骨的背突排除出外鼻孔的內(nèi)緣,而N.youngi的鼻骨有一前突沿外鼻孔的內(nèi)側(cè)緣向前延伸。二者之間在頭后骨骼的結(jié)構(gòu)上區(qū)別是明顯的。Rieppel等(1999)選取了25個(gè)性狀,對Pachypleurosauroidea、Simosaurus和幻龍屬的8個(gè)種(包括一個(gè)未描述的Winterswijk的材料)進(jìn)行了分支系統(tǒng)分析,獲得了一個(gè)最簡約的樹(TL=62,CI=0.677,RI=0.661)?；谬垖賰?nèi)的親緣關(guān)系在這一分析中得到了解決。2001年Rieppel對25個(gè)形狀中的2個(gè)稍作調(diào)整,加入了新訂立的種Nothosaurusjagisteus進(jìn)行分析,得到一個(gè)與1999年結(jié)果十分相似的最簡約的樹(TL=65,CI=0.662,RI=0.651)。在這兩次分析中雖然幻龍屬的單系性質(zhì)得到證實(shí),但幻龍屬各種在支序圖上排列的順序與它們在地層中出現(xiàn)的先后并不完全相符。此次將V13590的性狀加入Rieppel(2001)的矩陣(見表3),應(yīng)用PAUPVersion4.0b10進(jìn)行分析。計(jì)算時(shí)所有性狀均為“無序”和“等權(quán)”處理,以Pachypleurosauroidea、Simosaurus和Germanosaurus為外類群,用Branch-and-Bound方式搜索,得到12個(gè)最簡約的分支樹及它們的嚴(yán)格合意樹(圖5)。其中第7個(gè)最簡約的分支樹(圖4)與Rieppel(2001)最簡約的樹極為相似。在所有12個(gè)最簡約樹中新種都作為除N.juvenilis之外的所有Nothosaurus種的姐妹群。Nothosaurus屬征(節(jié)點(diǎn)23～22)的性狀與Rieppel(2001)分析結(jié)果相同,同樣是4(1),5(1),19(1),21(1),22(2),23(2)和24(1)。新種與除N.juvenilis之外的其他幻龍種的共近裔性狀是:10(1)后額骨未進(jìn)入上顳孔的邊緣;12(1)眶后骨占據(jù)全部的上顳孔前緣;以及18(1)上顳孔的前部因頂骨的側(cè)向突出而收縮。雖然此次分析又一次確認(rèn)了Nothosaurus的單系性,但在得到的嚴(yán)格合意樹中N.gigantius,N.mirabilis,N.jagisteus(N.haasi,N.tchernovi)之間的關(guān)系,及它們與N.edingerae,N.marchicus,Winterswijk之間的關(guān)系是無解的。分析證實(shí)了貴州興義的楊氏幻龍的原始性僅次于N.juvenilis。前已述及,幻龍屬主要分布于西特提斯區(qū)的中三疊統(tǒng),只有N.edingerae的一些材料發(fā)現(xiàn)于上三疊統(tǒng)的卡尼階。與N.youngi關(guān)系密切的N.marchicus分布于歐洲的安尼階至拉丁階?；谬埿路NN.youngi具有Nothosaurus中的一些原始特征,短的下頜縫合部,短的上頜齒列和窄的眶后弓,新種在法郎組竹桿坡段的發(fā)現(xiàn)支持含化石地層為拉丁期的結(jié)論(楊鐘健,1958;陳宗富,1985;李錦玲等,2002)。civilussp.3.3.4與法定證據(jù)相關(guān)的文獻(xiàn)記載完成本文的過程中得到金帆博士、王原博士、徐星博士的大力幫助。標(biāo)本由丁今朝精心修理,楊明婉繪制插圖,高偉制作照片,筆者在此致以誠摯的謝意。ThefirstrepresentativeofthegenusNothosaurusintheEasternTethyianfaunalprovinceisNothosaurussp.(Rieppel,1998),representedbyaseriouslydamagedskulland5cervicalvertebrae(NationalGeologicalMuseumofChinaVm1308),andpreviouslyrecognizedasasimosaurShingyisaurusunexpectusbyYoungCCin1965.Sincethe1990s,manynothosaurspecimenshavebeendiscoveredfromtheZhuganpoMemberoftheFalangFormationinXingyi,Guizhouandinadjacentareas.Thematerialdescribedinthepresentpaperwascollectedduringthefieldseasonof2001.ndoperion反應(yīng)Nothosaurusyoungisp.nov.(Figs.1～3)EtymologyNamedinhonorofthefounderofChinesevertebratepaleontologyandthepioneerofChineseTriassicmarinereptilestudy,lateAcademicianChung-chienYoung.HolotypeAnearlycompleteskull,lowerjawsandincompletepostcranialskeleton(IVPPV13590).LocalityandhorizonXingyi,Guizhou;ZhuganpoMember,FalangFormation,MiddleTriassic.DiagnosisAsmallsizedspeciesofNothosauruswithskullcondylobasallength160mm;5largeprocumbentfangspresentonpremaxillaand4curvedfangsonmandibularsymphysis;jugalnarrowandsplintlikewithitsanteriorendexcludedfromorbit,andpostorbitalandmaxillaincontactbehindjugal;distinctandwelldevelopedventrallyprojectingectopterygoidflangespresent;lowerjawbearinganobviouscoronoidprocess;splenialenteringthemandibularsymphysis;4carpalossifications.DescriptionThespecimenIVPPV13590isexposedonitsventralside.Itisanincompleteskeleton,withthepalatalsurfaceofskull,manus,pesandgastraliabroken,theleftanteriorlimblost,andthedorsalvertebraeandribsembeddedinmatrix.Theskullwasflattenedduringfossilization,butitsdorsalsurfaceisperfectlypreserved.TheskullissimilartothatofNothosaurusmarchicusincontourandsize.Thesnoutisshortandblunt,withaweaklydevelopedrostralconstriction.Boththeexternalnarisandorbitareshortandwide.Theelongateuppertemporalfenestraisconstrictedattheanteriorcorner.Itslongitudinaldimensionisuwotimesasthatoftheorbit.Theratioofskulllengthtowidth(dividethedistanceofanteriorendofsnout-occipitalcondylebyskullwidthatpostorbital)is2.75,smallerthanthecorrespondingratioinN.mirabilis(3.97～4.08)andinN.giganteus(3.32)(measurementsfromRieppelandWild,1996,Fig.58andFig.10).Thepremaxillaformingtherostrumcontactsthemaxillaattheanterolateralcorneroftheexternalnaris.Theposteriorprocessofthepremaxillaextendsbackwardbetweentheexternalnarestomeetthenasalattheleveloftheposteriorendoftheexternalnaris.Itssurfaceissculpturedwithsmallandscatteredpits.Fivepremaxillaryfangsarevariouslypreservedonleftandrightside.The1strightpremaxillarytoothislost,representedbyalargealveolus.The3rdisthestoutestfangandthe4thand5tharereducedsuccessivelyinsizeontherightside.The1st,3rdand5thfangsarecomparativelysmall,butthe2ndislargeandthe4thisthestrongestontheleftside.Thenasalisalargeandleaf-shapedelement.Itmeetsitscounterpartalongthemidline,separatingthepremaxillafromthefrontal.AshortandslenderanteriorprocessofthenasalextendsforwardtothemiddlepointofthemedialmarginoftheexternalnarisasisalsothecaseinN.haasi,incontrasttotheprocessesreachingtotheanteriorendoftheexternalnarisinN.juvenilis,N.giganteusandN.mirabilis.Thenasalcontactsthemaxilla,prefrontalandfrontallaterally.Thesurfaceoftheboneisdecoratedwithadistinctradiatingpatternofgroovesandridges.Thefrontalisfused.ItsanterolateralcornerisseparatedfromthemaxillabyacontactofthenasalandprefrontalasinN.juvenilis,whereas,inN.marchicusandN.jagisteusthefrontalcontactsthemaxilla.Thelateralmarginofthefrontaliscomparativelystraight,ashortdistanceofwhichentersthemedialborderoftheorbit.Thefrontalextendsposteriorlytomeettheparietalinaninterdigitatingsuturewellbehindtheanteriorendoftheuppertemporalfossa.Therearemanydeeplongitudinalgroovesandridgesonthefrontal.Theprefrontalisasmallbonelocatedbetweenthemaxilla,nasalandfrontal.Itoccupiestheanteromedialborderoftheorbit.Thesculpturingofthesurfaceoftheboneisdeepandstout.Thepostfrontaldefinestheposteromedialborderoftheorbit,withadistinctpostorbitalconstriction,anditsposteriorlypointingapexisembracedbetweenthepostorbitalandtheparietal.Theposteriorendofthepostfrontalreachestoapointbehindtheanteriorendoftheuppertemporalfossa,butdoesnotenterthemarginofthefossa.Theparietaliselongateandunpaired.Anelongatedpinealforamenislocatedinatroughneartheposteriorendoftheparietal.Beforethepinealforamentheparietalnarrowstoaslenderskulltable,whereasasagittalcrestisbehindthepinealforameninN.edingerae.Posteriorly,theparietalisbroadened,withaconcaveposteriormargin.Awelldefinedoccipitalcrestseparatestheparietalskulltablefromtheoccipitalexposureoftheparietal.Themaxillaformsasignificantpartofthelateralmarginsoftheexternalnariesandtheorbit,extendingposteriorlyfromtheantero-lateralcorneroftheexternalnaristoalevelbehindtheanteriorend,butinfrontof1/4lengthoftheuppertemporalfossa.AsinN.marchicus,N.juvenilis,N.giganteusandN.mirabilisthereisasmalldepressiononthemaxillalateraltotheexternalnaris,andasmallforamenispresentonthefloorofthedepression.Therightmaxillarydentitionisalmostcompletelypreserved.Onebasalpartofacrownwithalargecrosssection,representsthefirstmaxillaryfangthatisretainedonthelaterallybuldgingpartofthemaxillabetweentheexternalnarisandtheorbit.Followingthatalargealveolusindicatesthepresenceofthesecondmaxillaryfang.Thereare4positionsforsmallerteeth(onlythe3rdispreserved)infrontofthefangs,but16(11teethpreserved)behindthefangs.Thelargepostorbitalformspartoftheposteriormarginoftheorbit,andtheanteriormarginoftheuppertemporalfossa,withaposteromedialbranchthatisshorterthantheposterolateralone,thelatterreachingalmosttothemiddlepointoftheuppertemporalfossa.ThepostorbitalarchformedbythepostorbitalisrelativelynarrowerthanthatofotherspeciesofNothosaurus.Thedistanceorbit-externalnaris(15mm)dividedbythedistanceorbit-uppertemporalfossa(7mm)is2.14,butaround1inN.marchicus.Thejugalisasmallandstrap-shapedbone,locatedbetweenthemaxillaandpostorbital.Itsanteriorenddoesnotenterthemarginoftheorbit,anditsposteriorendseemstobeembracedbythepostorbitalandthemaxillaasinN.jagisteus,whichshowsonlyonthelateralviewoftheskull.Thesquamosalisatriradiateelement,withitsanteriorramuscontactingthepostorbitalatthemid-pointofthetemporalarchandthemaxillaatalevelanteriorto1/4lengthoftheuppertemporalfossa.Posterolateraltotheuppertemporalfossa,thesquamosalisdrawnoutintoadistinctandlonglateralramus,whichcoverstheupperendofthequadrate.Ontheoccipitalsurfacethesquamosalmeetsthesupraoccipitalandtheopisthotic.Therightquadrateisslightlybroken,whiletheleftoneiscompletelypreserved.Thebonehasawideconnectionwiththequadrateramusofthepterygoidontheventralview.Thelateralcondyleofthequadrateislargerthanthemedialone.Theyaresituatedindifferenthorizontalandverticallevels—thelateralcondyleishigherandanteriorerthanthemedialone.Theocciputisclosedandplatelike,butnoposttemporalforamenandopeningofcranioquadratepassagecanbedetected(perhapsduetodorsoventralcompressionoftheskull).Becausesomeanteriorcervicalvertebraeoverlapthelowerpartoftheocciput,theoccipitalcondyleisonlyexposedontheventralsurface.Itislocatedatthesamelevelasthemandibularcondylesofthequadrate.Thesupraoccipitalisaleave-shapedelementthatcarriesadistinctsagittalcrest,whichdoesnotreachtheanteriormarginofthebone.Theforamenmagnumisobscuredbythedislocatedexoccipitals.Theopisthoticislarge,anditslateralmarginseemsnotcontactthequadrate.Themajorfeaturesofthepalatecanbeestablished,althoughsomebonesarecrushedanditsanteriorportioniscoveredbythesymphysisofarticulatedlowerjaws.Theexactshapeofthevomerisdifficulttodetermine,becauseitwasdeformedbysomelongitudinalgrooves.Butitdoesshowevidenceofformingthemedialmarginofthechoanaandcontactthepalatinelaterallyandthepterygoidposteriorly.Thepalatineisaquitelarge,thinbonethatformstheposteriormarginofthechoana,whichislocatedfurtherposteriorlyrelativetotheposteriormarginoftheexternalnaristhanisthecaseinN.haasiandN.marchicus.Alongnarrowportionofthemaxillaisexposedonthepalatelateraltothepalatine.Thedistinctectopterygoidflangesarepreservedonbothsides,formingtriangularprojectionwithitsmedialapexpointingposteromediallyandsharplyturneddownward.Theposteriorportionofthepterygoidsincludingleftandrightquadraterami,arewellpreserved.Twoelementsofthehyobranchialskeletonarepreserved,therightoneislocatedontheventralsurfaceofthepterygoid,andtheleftoneneartheleftectopterygoidflange.Thelowerjawiselongateandslender.Correlatedwiththeshortpremaxillaryrostrum,themandibularsymphysisisshortandbroad,withitsratiooflengthtowidth0.96,muchsmallerthan1.46inN.jagisteus.Themandibularsymphysisbears4enlargedfangs,whicharecurvedupwards,insteadofbeingprocumbent.The1st,2ndand4thleftdentaryfangsareofapproximatelyequalsize,butthe4thfanghasaslightlymoresturdytoothbase.Asmalltoothisjusteruptingfromthe3rdalveolus.Ontherightsidethe1stfangislost,the3rdisthemostslender,andthe4ththestrongest.Thedentaryisnarrowandlong,extendingalong69%ofthelengthofthelowerjaw.Becauseofthetightcontactofthelowerjawwithskull,thedentarydentitionremainsobscure.Butitispossibletoascertainthatthedentarytoothrowextendsalittlefurtherposteriorlythanthemaxillarytoothrow.Thecoronoidisarathersmallbonelocatedonthemedialsideofthejaw.ItdiffersfromallotherspeciesofNothosaurusinformingadistinctcoronoidprocess.Theanteriorendofthesplenialappearstoenterthemandibularsymphysis.Thejawarticulationisformedbythesuprangularinitslateralpart,andbythearticularinitsmedialpart.Theretroarticularprocessiselongate.MeasurementsSeeTable1.Thepostcranialskeletonisincompletelypreserved.Withinthevertebralcolumn,thecervicalandcaudalvertebraearepreservedinarticulation,twoanteriordorsalvertebtaeareexposedinlateralview,theotherdorsalandthesacralvertebraeareobscuredbyoverlappingelementsandmatrix.Twosmalltriangularelementswhichmeeteachotheralongthemidlinerepresenttheneuralarchoftheatlas,whicharedirectlyoverlappingtheanteriorpartofthe3rdcervicalvertebra(Fig.1).Theneuralarchoftheaxisispreservedinisolationlateraltothevertebralcolumn,butthecentrumoftheaxiscannotbeidentified.The3rd～20thcervicalvertebraeexposetheirventralsurfaces,whichareflattened,longerthanwide,withoutlateralconstriction,andwithoutadistinctventralridge.Thecentraareplatycoelouswithatransverselywidenedellipticcontourasindicatedbythe4thand5thcervicalcentra.Thereisashortribpresentonthe18thcervicalvertebra,showingastoutproximalendandtaperinggraduallydistally.Twoarticularfacetsarepresentseparatelyontheneuralarchandthecentrumofthe19thcervical,indicatingthattheribsoftheposteriorcervicalvertebraearedouble-headed.ThesacralvertebraecannotbeseeninthespecimenIVPPV13590,whereastwoleftsacralribsareexposedasfairlyprominentelements.Theyarerelativelylongelements(35mm),withanarrowproximalendandwideneddistalend(15mm×8mm).37caudalvertebraearepreserved,exposedmostlyinrightlateralview.Thecaudalcentrahavenoventralsagittalridgenoraretheylaterallyconstricted.Theribsontheanteriorportionofthetailarerelativelylong,expandedintheirmiddleregionandtaperingtowardstheirdistalends.ManyV-shapedandslender,rod-likegastraliaarepreserved,scatteredintheregionbetweenthepectoralandpelvicgirdles.ThepectoralgirdleinV13590isingeneralsimilartothatofNothosaurus(Romer,1956fig.148A),butdiffersfromthelatterinsomedetails.Forexample,thetriangularinterclavicleisrelativelylarge,withitsposteriorborder(36mm)longerthen1/2oftheanterioredgeoftheclavicle(70mm).Theposteriorstemoftheinterclavicleisabsent,butitisdifficulttoascertainwhetheritislostorabsentoriginally.Onlytheflattenedventralsurfacesofthelowerpartofbothscapulaeareexposed.TheleftcoracoidissimilartothatofotherNothosaurusspecies(Romer,1956fig.148A)ingeneralshape,butitcannotbedescribedbecauseitisoverlappedbysomegastralia.Amongthepelvicgirdletwoiliaandtherightpubisarepreserved.Theiliumissmallandlow,butthepubisisalargeplate-likeelement,withaconcaveanteriormargin,arelativestraightposteriormargin,andadistinctobturatorforamen.Theleftanteriorlimbispreservedincompletely—thedistalportionofthehumerusiscoveredbygastraliaandsomephalangealsarelost.Thehumerushasastoutproximalendandarelativenarrowdiaphysis.ThecompleteulnaandradiuspositionedoriginallyresemblethatofotherNothosaurus.ThespecimenV13590isdifferentfromotherNothosaurusspeciesinhaving4,ratherthan3elementsincarpalregion,whichareintermedium,ulnareandtwodistalcarpals.ComparisonanddiscussionThespecimenV13590fromtheZhuganpoMemberoftheFalangFormationofXingyi,GuizhouismoresimilartothatofNothosaurusmarchicusthantootherspeciesofNothosaurusinsize,shapeandproportionsofskull.Bothofthemaresmallsizedanimal,withskullcondylobasallength160mminV13590andlessthan200mminN.marchicus.Theirskullsshowrelativelyshortandbroadrostrumwithroundedcontoursandadistinctrostralconstriction.TheskullratiosofV13590fitintotherangesofN.marchicuscompletely,asshowninTable2.Inaddition,V13590sharesanumberofimportantcharacterswithN.marchicus,suchasnasalsbroadandleafshaped,withradiatingornamentation,postfrontalwithadistinctpostorbitalconstriction,squamsalcloselyapproachingtheposteriorendofthejugal,andsoon.Theydistinguisheachotherinsomerespects.InV13590thereare4smallmaxillaryteethinfrontofthemaxillaryfangs,ratherthan5asinN.marchicus.TheectopterygoidinV13590isgeneralnothosaurshaped,butittaperstoablunttipanteriorlyandreachestoaboutthelevelofthemidpointofthepalatineinN.marchicus.ThespecimenofV13590isdifferentfromallotherspeciesofNothosau-rusinhavingadistinctcoronoidprocessandasplenialenteringthemandibularsymphysisregion.Twoothernothosaurtaxa-Nothosaurussp.(Young,1965;Rieppel,1998)andLariosaurusxingyiensis(Lietal.,2002)werealsoreportedfromZhuganpoMemberoftheFalangFormation,Xingyi,Guizhou.ThepoorlypreservedspecimenofNothosaurussp.(NGMCVm1308)isdifferentfromV13590inhavingawiderpostorbitalarchandamoreposteriorlypositionedfrontal-parietalsuture.AlthoughLariosaurusxingyiensishasatypicallariosaurpostcranialskeleton,butmorenothosaur-likeskull,itisdistinguishedfromV13590inhavinganasalexcludedfromthemedialmarginoftheexternalnaris,andasaggitalcrestbehindthepinealforamen.Adatamatrixincluding25charactersof11taxa(Pachypleurosaurs,Simosaurus,Ger