记中国首次发现的"真古兽类" (eupantotherian)化石

记述了在中国首次发现的采自辽宁黑山县八道壕矿区早白垩世晚期沙海组的一件“eu- pantotherian”(“真古兽类”)下颌骨化石。标本保存了最后两个前臼齿和4个臼齿,它以抬高的下颌角突,半臼齿化的最后一枚前臼齿,臼齿上面积增大但未发育成完整盆形的跟座,尚未形成的facet-5,及加长的最后臼齿等特点有别于所有已知的“eupantotherian”和具有雏形磨楔式臼齿的Kielantherium,被命名为一新属新种,Mozomus shikamai gen.et sp.nov.(鹿间明镇古兽),并由它而创建了一新科,Mozomuridae fam.nov. “Eupantotherian”是早期哺乳动物演化中的一个重要环节,是从无跟座的对齿兽(sym- metrodont)到具有磨楔式(tribosphenic)臼齿兽类的中间类型。早期兽类进化的成功模式是发育成具有磨楔式的臼齿,即在上臼齿上发育出原尖,而下臼齿的跟座形成由3个齿尖围成的盆状。这种结构扩大了牙齿的面积,使咀嚼切割能力更趋完善,今天的有袋类和真兽类均是如此。但在哺乳动物系统发育史上,“eupantotherian”类的化石发现不多,这给探讨具有磨楔式臼齿构造的两大门类(后兽类和真兽类)的起源带来不少困难和疑惑。而传统上的真古兽类形态分异又很大,并不是一个单系类群。其中有跟座发育较好者,如peramurans有可能更接近具有磨楔式臼齿兽类的基部位置,本文记述的Mozomus shikamai也应属于这一类型。具有雏形的被认为处于基干上的磨楔式臼齿类化石,迄今只有两种,即发现在英国早白垩世地层中的滨齿兽(Aegialodon)和蒙古早白垩世晚期Hoobor层的Kielantherium,前者仅有一颗下臼齿,后者由一枚下臼齿和一具有4颗臼齿的下牙床为代表。两种化石在分类上被归入单一的滨齿兽目(Order Aegialodontia Butler,1978),视为Boreosphenidans的基干(stem)。本文记述的Mozomus,其时代与Kielantherium的大体相当,在大小、齿式及臼齿形态上与后者也多有相近之处,但前者以其臼齿的facet-5尚未出现和跟盆发育不全等特点表明它较Kielantherium更为原始,不具备磨楔式臼齿的模式,因之不能归人Aegialodontia,而只能纳入”eupantotheri- ans”。但在后一类的组合中,Mozomus以它半臼齿化的最后前臼齿和面积增大但未发育成盆形的跟座等特点,又是组合中相当进步的类型。无论如何Mozomus的发现是在为数极少的向磨楔式臼齿模式进化的中间环节上增添了一件重要的化石标本,也增加了不少新的信息。它必会引起学者对这一进化过程的更加深入的反思和新的启示。     

关于原始真兽类臼齿构造命名和统一汉语译名的建议

一、问题的提出现行的哺乳动物臼齿构造的命名法,是奥斯朋(H.F.Osborn)于1907年首次比较系统地提出来的。它构成了后来柯普-奥斯朋的“三尖、尖·切齿理论”(Cope-Osborn'stritubercular,tubercular—sectorial theory)的一个组成部分。半个多世纪以来,虽然这个理论本身有了若干修订,甚至连名称都被改为“磨楔式理论”(tribosphenic theory)(Simpson,1936),但这套命名法却几乎没有多大改变地被古哺乳动物学家所采用,而且在动物学、     

中国尖齿兽牙齿替换方式及其对哺乳动物进化的意义

中国云南下禄丰组的早侏罗世中国尖齿兽的新材料显示出从前未曾认识到的早期哺乳动物牙齿特征．中国尖齿兽的门齿和犬齿,像非哺乳类犬齿兽一样,是多次替换的。新的中国尖齿兽幼体标本保存有前臼齿,前臼齿替换一次之后,在较大（更老）的标本上就永久消失。犬后齿分化为前臼齿与臼齿,以及前臼齿仅替换一次是现代哺乳动物的衍生特征。中国尖齿兽前边的臼齿可能无后继齿替换而消失;后边的臼齿替换一次．中国尖齿鲁当其成体的牙齿还在经受替换期间,头骨仍在继续生长。中国尖齿首是所有其他哺乳动物的姊妹类群。中国尖齿兽的牙齿替换方式可解释为从爬行类原始多出齿系向哺乳动物进步的二出齿系进化的中间过渡类型。由中国尖齿兽的多出齿系和其头骨无期限式生长推知,该类动物尚不具备现代哺乳动物所具有的有期限生长方式和哺乳特征。     

贵州毕节发现古人类化石与哺乳动物群

2008年12月在贵州毕节团结乡首次发现麻窝口洞化石点,经2009年、2012年和2013年3次发掘,在麻窝口洞上部砂质黏土地层中共发现了四千余件哺乳动物牙齿化石。2013年7月发现的3枚古人类牙齿,分别为左上犬齿、左上第一臼齿和右上第二臼齿。人类牙齿尺寸偏小,臼齿咬合面沟纹简单,没有复杂的咬合面皱纹和附尖齿带结构,牙根短而不显粗壮,上述特点有别于我国已经发现的直立人和早期智人,可归入解剖学上的现代人。与人类相伴的哺乳动物化石,经初步鉴定共计8目20科43属53种,动物群组合反映出亚热带森林生态环境。根据动物群的时代特点,地貌地层及堆积物的光释光年代测定,指示毕节麻窝口洞古人类的时代可能为中更新世晚期,或者晚更新世早期,毕节古人类牙齿的发现为东亚地区现代人的起源及演化增添了新的证据。     

植食性哺乳动物牙齿磨痕分析方法简介及其在古食性恢复中的应用前景

通过研究古哺乳动物的食性来探讨哺乳动物演化与古生态环境变化之间的关系是目前古生物学研究领域的一个热点,而牙齿磨痕分析是恢复古食性和重建古生态环境的重要手段。牙齿磨痕(dental wear)分析包括微痕(microwear)分析和中痕(mesowear)分析,两种方法均强调食性与牙齿磨痕模式的严格对应,即不同食性的动物具有不同的牙齿磨痕特征模式。近年来,牙齿磨痕分析方法以其简单、快捷和高效等优点已被广泛应用于奇蹄类、偶蹄类、啮齿类、长鼻类和食肉类等哺乳动物的食性研究。但哺乳动物的食性和摄食习性比较复杂,很可能会影响微痕和中痕分析对食性的分辨率。所以,为了获得更加详细的古食性信息和更高的食性分辨率,一方面要对微痕和中痕分析方法进行改进,增添稳定并具有食性识别意义的观测变量,另一方面,需要同时结合微痕和中痕分析,从而获得更加全面的食性信息。虽然牙齿磨痕分析目前主要应用于植食性哺乳动物的食性研究,但其原理对哺乳动物的其它类群也是适用的,随着磨痕分析方法的不断改进和其它类群磨痕数据库的建立,未来的牙齿磨痕分析将可以恢复更多类群的古食性,从而可以更加全面和准确地揭示古食性与古环境信息。     

几何形态测量学方法在小哺乳动物化石分类鉴定中的应用——4种(鼠平)类化石大样本的个案研究

小哺乳动物化石在晚新生代生物地层学和生物年代学研究中具有重要作用,尤其是筛洗法在古生物调查中得到广泛应用后,通常可以采集到数量可观的标本,使得其地位较大型哺乳动物化石更加彰显.因此,小哺乳动物化石标本的分类鉴定也成了一项十分关键的工作.然而,传统形态学方法在对大量标本进行分类鉴定时,往往容易受主观因素影响而将不稳定的细微性状变异作为依据建立新种,或者忽视一些肉眼难于察觉的形态学差异而将两个甚至多个类群合并到一起,导致基于形态学的化石分类鉴定随意性增加,失去客观性.此外,对于不具鉴定意义的非关键性单个牙齿,很难凭借肉眼或显微镜观察进行区分.针对这些问题,本文选取了安徽繁昌人字洞早更新世早期三种(鼠平)类甘肃模鼠Mimomys gansunicus,郑氏异模鼠Heteromimomys zhengi和繁昌维蓝尼鼠Hllanyia fanchangensis的1284件臼齿并以早上新世内蒙古比例克的比例克模鼠Mimomys bilikeensis的163件臼齿作为参考,采用几何形态测量学方法在各个臼齿咬合面上分别选取了7～14个同源landmark对咬合面的形态特征进行了线性判别分析,建立了针对这4个种的臼齿咬合面形态差异判别函数.分析结果表明,根据这些landmark所提供的形态差异信息,人字洞的1284件臼齿标本中的确存在3个可以明显区分且形态学性状稳定的类群,先前的分类鉴定得到了验证.与之不同地点不同时代的比例克模鼠也可以很好区分.因此,建立在大样本基础上的这4种(鼠平)类臼齿咬合面同源形态特征的判别函数可以用来描述这些种类较为稳定的形态特征差异,并用来作为今后对样本较少的标本进行分类鉴定时的判别依据.因为几何形态测量学的方法不仅可以对二维的离散landmark数据以及重要形态学特征的轮廓线进行分析,甚至还可以扩展至三维空间,所以上述方法对于较为容易获得大样本标本的小哺乳物化石分类鉴定具有普遍意义.     

华南新发现的巨猿牙齿化石*

1935年荷兰古生物学家孔尼华(G.H.R.von K(?)nigswald)在香港中药铺所购得的大量哺乳动物的牙齿化石中,发现了一个巨大的下右第三臼齿,认为是属于高等灵长类的一个新种新属,定名为步氏巨猿(Gigantopithecus blacki)。魏敦瑞最初(1937年)以为它是一种巨大的猩猩,但以后又根据孔尼华所购得的另外两个巨猿牙齿,进行研     

河南淅川始新世核桃园组树鼩化石

本文记述了河南李官桥盆地始新世沉积物中找到的几颗单个牙齿,认为可归入攀鼩目 (scandentia).根据新材料,推断树鼩类动物上臼齿次尖缺失并不是次生退化,而是原始性状.     

东胡林4号人牙齿形态特征观察

北京门头沟区斋堂镇东胡林遗址是重要的新石器时代早期遗址。本文描述了东胡林4号人(14C年龄约为8540aBP., 树轮校正年龄约为7500aBC.) 的上颌牙、下颌牙21枚。多数牙齿重度磨耗, 意味着当时人类处于狩猎—采集经济时代, 食物结构可能主要以坚硬食物(如朴树果核) 或高纤维食物为主。上第三臼齿退化缩小, X光透视检查为东胡林人下第三臼齿阻生提供了确凿无疑的证据。在4枚牙齿上发现龋洞, 其中左上第一臼齿、第二臼齿的龋蚀已破坏牙本质全层。严重的龋齿病揭示了东胡林4号人的口腔状态, 在一定程度上可能与经常性地摄取富含碳水化合物的食物有关。     

分辨巨猿第一与第二臼齿的多元分析方法

根据齿冠长度或宽度单一性状很难区分巨猿第一臼齿与第二臼齿。本文采用主成分分析方法,综合第一和第二上臼齿的齿冠长度、齿冠宽度和原尖长指数(新定义)等三个性状,显示存在有两个类型。合理的解释是它们分别代表第一上臼齿和第二上臼齿。下臼齿的分辨基于齿冠长度和齿冠宽度两个性状。在此二性状构成的坐标系中,第一与第二下臼齿各自的一系列椭圆代表一定比例的样本分布的范围。在此基础上得到区分此两种牙齿的判别直线。     

广东南雄古新世一种类似裂齿目的哺乳类

本文记述了一种近似裂齿目的小型哺乳类,订名小迷兽。这是一种性质很特殊的原始哺乳类。从现在仅有的一个上颌和一个下颌推断,可能是一种近似裂齿目的哺乳类。     

Contours of maxillary molars studied in Australian aboriginals

Distances from the central pit to the perimeter of the crown of permanent upper molars were measured on standardized occlusal photographs of dental casts representing 210 male and 181 female Aboriginals from Yuendumu in the Northern Territory of Australia. In both males and females the first molar was the largest tooth but it showed least variability. Variabilities of the distances tended to be greater for radii constructed in the buccolingual direction than for the transverse mesiodistal radii. The most marked size reduction in the molar series from first to third related to the distolingual part of the crown, which was also the most variable region. Size differences between molars in the mesial contour radii were not marked. Sexual dimorphism was evident in most crown radii, being most marked for the second molar.     

Brief communication: intertooth and intrafacet dental microwear variation in an archaeological sample of modern humans from the Jordan Valley

Dental microwear was recorded in a Bronze-Iron Age (3570-3000 BP) sample of modern humans recovered from Tell es-Sa'idiyeh in the Jordan Valley. Microwear patterns were compared between mandibular molars, and between the upper and lower part of facet 9. The comparison revealed a greater frequency of pits and shorter scratches on the second and third molars, compared to the first. Pit frequency also increased on the lower part of the facet on the first molar, compared to the upper part. These results support previous calls for standardization when selecting a molar type for a diet-microwear study. Otherwise the microwear variations along the tooth row could mask any diet-microwear correlations. The results also suggest that there may be a need to choose a consistent location on a facet in order to enhance comparability among studies.     

MOLAR OCCLUSION IN LATE TRIASSIC MAMMALS

1. A new genus and species of late Triassic mammal, Megazostrodon rudnerae, from Lesotho in southern Africa is described. The molars are similar to those of the British Eozostrodon parvus except that they are slightly larger and the upper molars have a large external cingulum supporting well-developed cusps. 2. Molar occlusion is discussed in two groups of late Triassic mammals: Eoxostrodon and the closely related Megazostrodon on one the hand and the unnamed primitive symmetrodonts on the other. It is shown that in Eoxostrodon the upper and lower molars did not have matching occlusal surfaces upon eruption but that wear produced matching occlusal surfaces. These surfaces are confined to the internal surface of the upper molars and the external surface of the lower molars and form a series of wide-angled triangles. The main cusp of an upper molar occluded between the main and posterior subsidiary cusp of the lower molar and the main cusp of the lower molar occluded between the main and anterior subsidiary cusp of the upper molar, 3. It is shown that the molars of Docodon and HaIdanodon were possibly derived from those of a primitive mammal such as Eozostrodon. The transition involved the development on the upper molars of an internal extension which, as it increased in size, established contact with the dorsal surfaces of two adjacent lower molars. The process involved is fundamentally different from that leading to tribosphenic molars. 4. In Megaxostrodon the main cusp of the upper molars occluded between the posterior and anterior subsidiary cusps of two adjacent lower molars, i.e. more posteriorly than in Eozostrodon. Primitive Rhaetic symmetrodonts were derived from mammals which had this type of occlusion and which were also closely related to Eoxostrodon and Megaxostrodon. The transition involved a rotation of the subsidiary cusps of the upper molars externally and those of the lower molars internally. This rotation increased the shearing surfaces between occluding upper and lower molars. Cusp rotation was carried further in the acute-angled symmetrodonts (Peralestes and Spalacotherium) and pantotheres. It appears that marked cusp rotation was coupled with the acquisition of transverse movements of the lower jaw during mastication. Transverse movement was apparently not possible in cynodonts, in Eoxostrodon (and related forms) and in Docodon. 5. The evolution of therian molars involves cusp rotation as originally proposed by the Cope—Osborn theory. Criticisms of the Cope—Osborn theory are re-evaluated in light of the new late Triassic material. 6. In Rhaetic symmetrodonts, molar wear produces matching occlusal facets, but the amount of attrition necessary to produce these facets was considerably less than in Eoxostrodon. In acute-angled symmetrodonts and in pantotheres, the molars erupt with more precise occlusal surfaces and attrition was not necessary to produce matching surfaces. 7. On the basis of the structure of the molar teeth it was concluded that Eozostrodon, Megazostrodon and Erythrotherium were closely related to the Rhaetic symmetrodonts. Slightly different occlusal relationships between upper and lower molars indicated that in these early mammals constant occlusal relations were being established. 8. Primitive cynodonts, such as Thrinaxodon, are characterized by alternate tooth replacement; there is a total lack of a constant occlusal relationship between upper and lower postcanine teeth. In Thrinaxodon individual postcanines were replaced several times. The crown structures of successive generations of postcanines were different so that a freshly erupted postcanine tooth had a crown structure quite distinct from the tooth which it replaced. It has been shown that the crown structure of one of the generations of postcanine teeth of Thrinaxodon is almost identical to that of Eozostrodon except that Thrinaxodon postcanines have a single root, On the basis of this similarity and the over-all structure of the primitive cynodont skull, it was concluded that Rhaetic mammals (excluding ictidosaurs and haramyids) could be derived from primitive cynodonts. 9. All the orders of Jurassic mammals (with the possible exception of multituber-culates) were probably derived from late Triassic mammals. The apparent close relationship of late Triassic mammals is evidence of a monophyletic origin of this class.     

Position and growth of upper and lower tooth primordia in prenatal mouse--3D study

The secondary palate formation in mouse has been associated with the period of fast growth of the mandible from embryonic days (ED) 13.0 to 16.0. During that time, the incisors and first molars develop from the bud to the bell stage. We investigated the position and growth of the tooth during prenatal elongation of the lower and upper jaws, and searched for the developmental stage when alignment of opposing teeth was achieved. Computer-aided 3D representations allowed us to represent the position of incisors and molars in the embryonic head from ED 13.5 to 18.0 on the basis of data obtained from histological sections. The atlas-hypophysis connection exhibited minimum change in length and orientation during the prenatal period, and thus was used as a reference line. The length of the teeth was calculated from 3D data. The upper first and second molars were longer than the lower ones. When viewed from the upper side, the upper and lower molar primordia were parallel from ED 13.5 to 15.0. During this period, the upper molars had a more lateral position than the lower ones. This situation was maintained in the anterior extremity of the first molars at later stages, while the posterior part of the upper and lower molar epithelia reached opposition in the medio-lateral direction from ED 16.0. The lower incisors exhibited an apparently backward position when compared to the upper incisors at earlier stages. However, the distance between the prospective anterior tips of the opposing incisors gradually decreased. The part of Meckel's cartilage associated with the lower dental quadrant elongated more than 3-fold from ED 13.5 to 18.0, and the lower jaw grew faster than the upper one. This difference resulted from the fast growth of the lower diastema from ED 14.0 to 18.0. The different growth speeds of the upper and lower jaws did not change the relative antero-posterior adjustment of the upper and lower molars, but contributed to achieving the opposition of the gnawing ends of the incisors.     

Factors Predisposing to Maxillary Anchorage Loss: A Retrospective Study of 1403 Cases

Anchorage loss is very disturbing for orthodontists and patients during orthodontic treatment, which usually results in bad treatment effects. Despite the same treatment strategy, different patients show different tendencies toward anchorage loss, which influences the treatment results and should preferably be predicted before the treatment is begun. However, relatively little research has been conducted on which patients are more likely to lose anchorage. The mesial tipping of the first molar marks the onset of anchorage loss, and changes in the angulation of the first molar are closely related to anchorage loss. This cross-sectional study aimed to determine how the mesiodistal angulation of the upper first molars changes during general orthodontic treatment and to identify the individual physiologic factors leading to these changes in a large sample of 1403 patients with malocclusion. The data indicate that the upper first molars tend to be tipped mesially during orthodontic treatment, and this constitutes a type of anchorage loss that orthodontists should consider carefully. Compared to treatment-related factors, patients'' physiologic characteristics have a greater influence on changes in the angulation of the upper first molars during orthodontic treatment. The more distally tipped the upper first molars are before treatment, the more they will tip mesially during treatment. Mesial tipping of the upper first molars, and therefore, anchorage loss, is more likely to occur in adolescents, males, patients with class II malocclusion and patients who have undergone maxillary premolar extraction. This finding is of clinical significance to orthodontists who wish to prevent iatrogenic anchorage loss by tipping originally distally tipped upper molars forward, and provides a new perspective on anchorage during orthodontic treatment planning.     

Structural Morphology of Molars in Large Mammalian Herbivores: Enamel Content Varies between Tooth Positions

The distribution of dental tissues in mammalian herbivores can be very different from taxon to taxon. While grazers tend to have more elaborated and complexly folded enamel ridges, browsers have less complex enamel ridges which can even be so far reduced that they are completely lost. The gradient in relative enamel content and complexity of structures has so far not been addressed within a single species. However, several studies have noted tooth position specific wear rates in small mammals (rabbits, guinea pigs) which may be related to individual tooth morphology. We investigate whether differentiated enamel content by tooth position is also to be found in large herbivores. We use CT-scanning techniques to quantify relative enamel content in upper and lower molar teeth of 21 large herbivorous mammal species. By using a broad approach and including both perissodactyls and artiodactyls, we address phylogenetic intraspecific differences in relative enamel content. We find that enamel is highly unevenly distributed among molars (upper M1, M2, M3 and lower m1, m2, m3) in most taxa and that relative enamel content is independent of phylogeny. Overall, relative enamel content increases along the molar tooth row and is significantly higher in lower molars compared to upper molars. We relate this differential enamel content to prolonged mineralisation in the posterior tooth positions and suggest a compensatory function of m3 and M3 for functional losses of anterior teeth.     

Effects of easily chewable diet and unilateral extraction of upper molars on the masseter muscle in developing mice

The effects of easily chewable diets and unilateral extraction of upper molars on the masseter muscle were studied in developing mice. A liquid diet requiring no mastication suppressed the development of the masseter muscles more than a fine-grained diet, and extraction of unilateral upper molars also caused inhibition of muscle development. Moreover, both unilateral extraction of upper molars and a liquid diet had an additive effect on the suppression of the postnatal development of the masseter muscle, and bilateral suppression of the development of the masseter muscle was induced following unilateral extraction of upper molars. These findings suggest that the sensory input from the sensory endings in the periodontal ligament may also play an important role in the postnatal development of the masseter muscle and that there may be some crossing pathways to convey the sensory input coming from the side of the extracted upper molars to the contralateral motor neurons via the interneuronal circuits.     

On the phylogenetic position of monotremes (Mammalia,Monotremata)

Henosferida from the Middle-Upper Jurassic of Western Gondwana is the most probable sister group for monotremes. They share the derived pretribosphenic structure of lower molars combined with the presumably absent protocone on the upper molars and the plesiomorphic retention of postdentary bones and pseudangular process of the lower jaw. In addition, the two groups share the dental formula with three molars and the position of the Meckel’s groove, which passes ventral to the mandibular foramen. In the course of subsequent evolution, monotremes acquired the mammalian middle ear with three auditory ossicles independently of therian mammals and multituberculates. Jurassic Laurasian Shuotheriidae are probably a sister group of the Gondwanian clade Henosferida + Monotremata. The Jurassic shuotheriid Pseudotribos shows a great plesiomorphic similarity to monotremes in the structure of the pectoral girdle, with a large interclavicle immovably connected to the clavicle. In the lineages leading to therian mammals and multituberculates, the pectoral girdle changed probably independently and in parallel in connection with the establishment of the parasagittal posture of the forelimbs (reduction of the interclavicle, mobile articulation of the interclavicle with clavicle, reduction of the procoracoid, and development of a supraspinous fossa of the scapula) and formation of the mammalian middle ear with three auditory ossicles.     

记江苏泗洪首次发现森林古猿类化石

本文记述了在江苏泗洪松林庄发现的一种古猿类化石,它以个体小、颊齿宽、有发达的齿带等特征有别于我国云南的腊玛古猿、西瓦古猿;它也有别于在同一地点、同一层位发现的双沟醉猿。其形态与非洲的Proconsul属接近,根据这些形态特点和它的地史分布,我们订立了一新属一新种:Platodontopithecus jianghuaiensis,地质时代为中新世。