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甘肃东乡首次发现熊化石——龙担哺乳动物群补充报道之二

2009年第47卷 第4期: 245-264

发表日期:2009-11-04来源:放大 缩小

                                                                编辑:邱占祥  王伴月

摘要:2006年编辑在和政县发现了两件产自东乡龙担动物群的熊类化石:一完整下颌(HMV 1422)和一个咬合在一起的头骨及下颌(HMV 1454)。熊类系龙担哺乳动物群中未曾描述过的新成员。这两件标本虽然有少许不同,但都和李亦征 (1993) 所记述的沂南熊Ursus (Protarctos) yinanensis 十分接近,而被归入该种。该种修订后的鉴别特征是:头骨长头型,头长接近中等大小的现生黑熊,头骨最大宽约为最大长的一半;矢状嵴长,约为顶长的1/3;眶下孔与眼眶前缘相距近,两者均在M1上方;颧骨前端仅组成眼眶下缘,其后端止于关节窝前缘水平;硬腭短,齿列之后的腭长小于P4长的1.5倍或M2长的3/4。前臼齿数目全;P4原尖小,位于裂凹正内方;M1短长方形,宽/~80%M2跟座中长,M2/56%~58%M2/M1133%~153%m1无前下后尖及前下内尖,分隔下三角座和跟座的横沟窄(前后),横沟中没有明显的嵴和沟;m2短于m1,其前、后接近等宽。与U. boeckhi相比,P4相对更小;臼齿相对更窄长;M1不呈五边形;M2跟座更大;m1横沟短,V形。

现生熊亚科的6个种在分子和生化特性上非常接近,且其分异的时间非常短。这使以生化和分子生物学为研究手段的遗传学家越来越倾向于把它们归入同一个属,即Ursus。但是以形态特征为研究对象的古生物学家却大多依据形态上的明显差异而把它们分成多个属。不过古生物学家也常把欧亚大陆上新世?第四纪早期的熊类化石简单地归入Ursus一个属。在对比研究东乡熊化石时,大家对欧亚大陆同期的熊化石作了较仔细的观察,发现m1的形态变化在熊亚科的演化中分异显著,在分类中应具重要意义。结合头骨及牙齿的其他特征,这一时期熊类化石主要可以分为三组:1) m1形态简单者,无前下后尖和前下内尖,横沟表面基本光滑。2) m1具嵴形图案者,具前下后尖,但无前下内尖,在三角座后壁和横沟中形成V, YX形嵴。这一组熊类的m1和现生黑熊者最为接近。3) m1具前下后尖、前下内尖,次级附尖很发育,主尖及附尖多为圆锥形。这一组熊类的m1和现生棕熊者最为接近。属于第一组的有Baróth-K?peczU. boeckhi, 沂南熊及Serrat d’en Vacquer的一件左下颌(1890年描述)。第二组包括产自Perrier, W??e, Layna, W?lfersheim等地点的熊类及Serrat d’en Vacquer的一件头骨及下颌(1892年描述)。第三组包括发现于欧洲众多地点(Val d’Arno, St. Vallier)U. etruscus。上述三组熊类在m1形态上的差异和组内变异的程度,使大家倾向于把它们分为不同的属,其属名分别应为:Protarctos, EuarctosUrsusProtarctos包括P. boeckhi (MN 14), P. ruscinensis (MN 15)P. yinanensis (相当于MN 16?17)Euarctos包括E. pyrenaicus (MN 15), E. minimus (MN 16?17)和现生美洲及亚洲的黑熊。而Ursus则包括U. etruscus (MN 17)及许多后期类型,如U. spelaeus等,以及现生的U. arctos (可能还有U. maritimus)

关键词:甘肃东乡,上新世,早第四纪,龙担哺乳动物群,熊亚科,分类

卷期:47 04

 

First bear material from Dongxiang, Gansu

--- Addition to the Longdan Mammalian Fauna (2)

QIU Zhan-Xiang, DENG Tao, WANG Ban-Yue

 

 

Abstract  Two bear specimens obtained from Dongxiang area were noticed from the purchased “dragon bones” of the Hezheng County in 2006: a complete mandible (HMV 1422) and a skull in association with its mandible (HMV 1454). They represent the first bear material of the Longdan mammalian fauna. Although slightly different in morphology, they are found to be very close to Ursus (Protarctos) yinanensis described by Li Yizheng in 1993, and thus referred to this species. A revised diagnosis of this species is given in the text.

Based on high degree of genetic homogeneity and short divergence time of the 6 extant ursine species, molecular and biochemical biologists are being increasingly confident that all the extant ursines should be assigned to a single genus, Ursus. On the other hand, most of the paleontologists, governed by their factual knowledge of morphologic distinctions between these ursine species, are inclined to separate them into different genera. Nevertheless, the Eurasian Pliocene?Early Quaternary bear fossils have often been indiscriminately referred to Ursus. A closer observation of the bear materials during our comparative study of the Dongxiang bear specimens revealed great variety in bear m1 morphology, implying its particular importance in classification of the Ursinae. Based mainly on m1 morphology, coupled with other skull and dental features, the majority of the Eurasian Pliocene?Early Quaternary bears can possibly be divided into three groups: 1) The bears having simple m1’s, lacking pre-metaconids and pre-entoconids, with the transverse groove surfaces being basically smooth. 2) Those having m1’s with pre-metaconids and V-, Y-, or X-shaped ridges on the transverse grooves, but no pre-entoconids. The m1 morphology of this group is close to that of the extant black bears. 3) Those having m1’s with bunodont pre-metaconids, pre-entoconids and well developed accessory cusplets. The m1 morphology of this group is basically that of the extant brown bears. The 1st group includes the specimens from Baróth-K?pecz, Yinan (and Dongxiang), and the left hemimandible of Serrat d’en Vacquer described in 1890. The 2nd group includes those from Perrier, W??e, Layna, W?lfershein, etc., and the skull and mandible from Serrat d’en Vacquer described in 1892. The 3rd group includes U. etruscus of many European localities, among which Val d’Arno and St. Vallier are the principal ones. Morphologic distinctions between, and the degree of variability within, these three groups strongly inclined us to separate them into different genera. If the above viewpoint is tenable, three generic names would be suitable for them: Protarctos, Euarctos and Ursus. In this case, Protarctos would include P. boeckhi (MN 14), P. ruscinensis (MN 15) and P. yinanensis (equivalent to MN 16?17). Euarctos would include E. pyrenaicus (MN 15), E. minimus (MN 16?17) and the extant American and Asian black bears. Ursus would contain U. etruscus (MN 17), U. spelaeus etc., and the extant brown bear (and possibly U. maritimus).

Key words  Dongxiang of Gansu, Pliocene, Early Quaternary, Longdan mammlian fauna, Ursinae, classification

 

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