内蒙古脑木根地区渐新世啮齿类及相关地层问题1)(2)

前面的讨论已表明,巴润索平台的巴润索组的时代为晚始新世,显然要比要脑木根敖包顶部岩层(所谓的巴润索组)的时代(早渐新世)早得多。同样,额尔登敖包顶部被称为巴润索组的浅色砂砾岩层产有Paraceratheriumtransouralicum(早渐新世)、Entelodongobiensis(晚始新世-早渐新世)、Schizotheriumavitum(晚始新世-早渐新世)和Schizotheriumsp.(晚始新世-晚渐新世),时代也应以早渐新世为宜,也比巴润索平台的巴润索组的时代晚。这样脑木根敖包和额尔登敖包地点顶部岩层的时代相同,同为早渐新世,而不同于巴润索平台的巴润索组的时代。前面的叙述已表明,脑木根敖包顶部岩层的岩性与巴润索平台的巴润索组的岩性是不同的。显然,脑木根敖包(或者包括额尔登敖包)顶部岩层不是巴润索组,而代表另一岩组。这一套岩层实际上并未被中亚考察团命名过。额尔登敖包顶部的岩层后来被江浩贤(1983)命名为上脑岗代组。它的典型地点是额尔登敖包附近的脑岗代,其时代原定为晚渐新世。这一命名已被RussellandZhai(1987)采纳。但齐陶(1990)称上述地层为呼尔井组,认为其时代为中渐新世,而称其下伏的红色岩层(即中亚考察团的“上部红

)为巴润索组。笔者认为,齐陶的这种划分有两点值得质疑:1)呼尔井组本身的问题比层”

较复杂,有些化石的时代是始新世的(王伴月,1997),将额尔登敖包顶部的岩层命名为呼尔井组显然不合适;2)前面已提到过,在层型地点(巴润索平台)的巴润

1)SpockJrLE,1928(MS).FieldNotesofCentralAsiaticExpeditionsofAmericanMuseumofNaturalHistory,BookIII.NewYork.1～119

2)GrangerW,1928(MS).RecordsoffossilscollectedinMongoliain1928.TheAmericanMuseumofNaturalHistory,NewYork.1～77

内蒙古脑木根地区渐新世啮齿类及相关地层问题1)

216古　脊　椎　动　物　学　报　　　　　　　　　　　　　41卷索组的岩性为浅色砂砾岩层,将额尔登敖包的“上部红层”称为巴润索组显然不符合关于岩石地层单位———组———的概念。笔者赞同江浩贤(1983)的意见,称其为上脑岗代组,但时代应为早渐新世。该组在层型地点(额尔登敖包)的岩性为灰白色、黄色粗砂岩,猪肝色泥岩以及松散的黄色砂砾岩(江浩贤,1983)。这样,脑木根敖包和额尔登敖包顶部的岩层不但在地质时代上相同,而且彼此的岩性也很相似,很可能二者同属一岩组———上脑岗代组。但因脑木根敖包和额尔登敖包两地相距较远(约80km),它们顶部的岩层是否确属同一岩层,还有待进一步考察才能确定。因此,笔者暂称脑木根敖包顶部岩层为上脑岗代组。

致谢　纽约美国自然历史博物馆D.R.Tedford博士邀请笔者赴该馆访问,Tedford和孟津博士允许笔者借阅该馆有关标本、档案资料和提供参考文献,并毫无保留地同意笔者对这批标本进行研究和在我国的刊物上发表;笔者赴美国自然历史博物馆的访问由该馆卡特基金资助;笔者在纽约停留期间,得到美国洛杉矶自然历史博物馆王晓鸣博士多方面的帮助;照片由邱占祥教授摄制,诚致谢意!

OLIGOCENERODENTSFROMTHENOMOGEN(=NOMKHONG)AREAOFNEIMONGOL,CHINA,ANDCOMMENTSONRELATEDSTRATIGRAPHY

WANGBan2Yue

(InstituteofVertebratePaleontologyandPaleoanthropology,ChineseAcademyofSciencesBeijing100044)

Keywords　ErlianBasinofNeiMongol,Oligocene,Eocene,BaronSogFormation,Upper

NaogangdaiFormation,Rodentia

Summary

TheBaronSogFormation,oneoftheclassicPaleogeneformationsinAsia,wasestablishedbytheCentralAsiaticExpeditionoftheAmericanMuseumofNaturalHistory(AMNH)in1925basedonbedsatthetopoftheBaronSogMesa.TheBaronSogFormationwasalsoappliedtosometopebedsofothermesas,suchasEastMesa,ErdenObo(=UrtynObo)andNomKhongObo(=NomKhongShirehorHolyMesa)oftheNomogen(=NomKhongorNaomugen)areaintheErlianBasin,NeiMongol,China(Osborn,1929;Berkeyetal.,1929).However,thewideapplicationofthisformationtosovastanareahasneverbeenseriouslytested.WhilevisitingtheAMNHinMayandJune,2001,invitedbyDr.D.R.TedfordofAMNH,theauthorwasabletoobservethespecimenscollectedbytheCentralAsiaticExpeditionandreadtherelatedpartsoftheAMNHarchives.Havingstudiedandcheckedthespecimensagainsttheoriginalarchives,theauthorproposesthattheageandnameofthetopbedattheNomKhongOboaretobecorrected.Inthispaper,somerodentspecimensfromthetopbedontheNomKhongOboaredescribedandtheageoftheBaronSogFormationisdiscussed.

AllthespecimensdescribedherewerecollectedbytheCentralAsiaticExpeditionin1928.TheterminologyofthecheekteethandthedirectionofthemeasurementsfollowWang(2001).

内蒙古脑木根地区渐新世啮齿类及相关地层问题1)

3期　　　　　　　　王伴月:内蒙古脑木根地区渐新世啮齿类及相关地层问题2171　Systematics

TsaganomyidaeMatthewetGranger,1923

　TsaganomysMatthewetGranger,1923

　　TsaganomysaltaicusMatthewetGranger,1923

(Fig.1)

　　Specimen　Asegmentofrightlowerjawwithm1～3(AMNH26185,Fieldno.777).

Localityandhorizon　NomKhongObo,ErlianBasin,NeiMongol;lateearlyOligocene,UpperNaogangdaiFormation(?).

Remarks　Thelowerjawishystricognathous.Thecylindricallowercheekteethareconcaveanterolinguallyandgrowbuccallytolowerincisor.Thercheekteetharestronglyunilaterallyhypsodont,andhaveopenrootsandconicpulpcavitieswithpointedapex,andhaveenamelontheposterobuccalwall.Theocclusalsurfacesoftheworncheekteetharesmooth,slightlyconcaveandhavenocore.AllofthefeaturesareidenticalwiththoseofTsaganomysaltaicus.Inaddition,thesizeofthecheekteethofAMNH26185iswithintherangeofthevariationofthespecies.(DimensionsseeinChinesetext).

CyclomylusMatthewetGranger,1923

　CyclomylusintermediusWang,2001

(Fig.2)

　　Specimens　Asegmentofleftlowerjawwithi2andp4～m3andasegmentofrightlowerjawwithi2andp4～m2belongingtoonesameindividual(AMNH26186,Fieldno.778),andasegmentofleftlowerjawwithm1～3(AMNH26187,Fieldno.779)

Localityandhorizon　NomKhongObo,ErlianBasin,NeiMongol;lateearlyOligocene,UpperNaogangdaiFormation(?).

Remarks　Thelowerjawishystricognathous,withthementalforamenlocatedanteriorlytothep4.Lowerdentitionformula:/1013.Thep4growsabovethelowerincisor,andthelowermolarsextendfromthebuccalsideofthelowerincisor.Thecheekteethareunilateralhypsodont,with2closedroots.Oftheyoungindividualthelowermolarshave4lophids,distinctmetalophidI,hypertrophichypoconidandposterolinguallyobliqueexternalvalley.AllofthefeaturesareidenticalwithCyclomylus.

Cyclomylusisknowntoinclude3species:C.lohensis,C.intermediusandC.biforatus.ThecheekteethfromNomKhongOboaremoderatelyunilaterallyhypsodont,higherthanthoseofC.lohensis,lowerthanthoseofC.biforatus,butsimilartothoseofC.intermediusinthecrown.Theintervaloftheeruptionofthecheekteethissimilartothat …… 此处隐藏：5852字，全部文档内容请下载后查看。喜欢就下载吧 ……