The trade-off between tooth strength and tooth penetration: predicting optimal shape of canine teeth

We investigate the shape of canine teeth under the assumption that the tooth's morphology is optimized by the evolutionary trade-off to minimize breakage and maximize ease of the penetration of prey. A series of experiments using artificial teeth to puncture the hides of a deer Odocoileus virginianus and pig Sus scrofa domesticus were conducted to establish the relationships between the tooth shape and the force needed to puncture the hide. The shapes of these teeth were also used in a beam theory analysis to calculate the strength of the teeth. Because the relative costs of puncturing and breakage were not known, a complete prediction of tooth shape was not possible. Instead, we used two independent measures of tooth shape: aspect ratio (total tooth length/tooth width at base) and rate of taper along the shank of the tooth. We quantified rate of taper in several species of felids, and by assuming this was the optimal design, we determined the relative costs of breakage and puncturing that would produce such a taper. Then, we used the relative costs to predict the aspect ratio of the optimum tooth. The average predicted value is about 2.5, very close to the average value in extant species of cats.     

广西南宁渐新世基于咽齿的鲤亚科一新属

记述了产自广西南宁盆地渐新世早—中期的鲤科鲤亚科一新属种——伍氏南宁鲤(+Nanningocyprinus wui gen.et sp.nov).化石材料包括一些咽喉骨和咽齿.这些咽喉骨和咽齿的以下特征组合明显不同于其他鲤科鱼类:齿式-3·2·1,主行第一枚咽齿大小是第二枚的3～4倍,第二枚咽齿及第二行第一枚咽齿咀嚼面上各仅有一条沟纹,咽骨前角很发育.该属种的发现进一步证明鲤亚科是鲤科中较早的分支,中国南方很有可能是鲤亚科的起源和分化中心.     

Dentition of the apron ray Discopyge tschudii (Elasmobranchii: Narcinidae)

The present study provides quantitative and qualitative analyses of the dentition of Discopyge tschudii. Overall, 193 individuals (99 males and 94 females) of D. tschudii were collected on scientific trawl surveys conducted by the National Institute for Fisheries Research and Development (INIDEP) and commercial vessels in Argentina. Discopyge tschudii has rhombic‐shaped teeth, arranged in a semipavement‐like dentition; each tooth has an erect cusp slightly inclined posteriorly and holaulachorized root. Mature males have greater tooth lengths than females and immature specimens. Discopyge tschudii exhibits dignathic homodonty and gradient monognathic heterodonty where teeth of the commissural row are shorter than those of the symphyseal and internal rows.     

禄丰古猿前部牙齿的釉面横纹与牙冠形成时间

釉面横纹的数目可用于推断个体牙齿的牙冠形成时间,在生长发育研究中具有重要的意义。本研究运用数码体视显微镜和扫描电镜观察了云南石灰坝禄丰禄丰古猿(简称禄丰古猿)30枚齿冠完整的前部牙齿,包括上下颌中门齿6枚、侧门齿10枚和犬齿14枚。根据唇侧面釉面横纹计数的观察结果,分别以7天和9天芮氏线生长周期,估算各齿型的牙冠形成时间,结果显示:以生长周期7天计算,中门齿牙冠形成时间约为3.6-4.1年,侧门齿牙冠形成时间约为2.7-3.7年,犬齿牙冠形成时间约为4.2-7.0;以生长周期9天计算,中门齿牙冠形成时间约为4.4-5.2年,侧门齿牙冠形成时间约为3.4-4.7年,犬齿牙冠形成时间约为5.2-8.8年。为更深入地了解禄丰古猿牙冠形成时间在不同齿型及性别间足否存在明显差异,本文用SPSS软件对其进行显著性差异检验。采用小样本平均值的t值假设检验(置信区间为95%),结果如下:禄丰古猿前部牙齿的牙冠形成时间在各类牙齿的上下颌中不存在显著性差异;犬齿牙冠形成时间存在非常显著的性别差异,雄性牙冠形成时间明显长于雌性,侧门齿也存在显著的性别差异,而中门齿性别间则无显著性差异。此外对禄丰古猿中门齿,侧门齿和犬齿的牙冠形成时间进行单因素方差分析并两两对比,结果显示中门齿与侧门齿的牙冠形成时间不存在显著性差异,而犬齿与中门齿和侧门齿均存在显著性差异,犬齿牙冠形成时间明显长于门齿。同时也对禄丰古猿前部牙齿的牙冠形成时间与齿冠高进行相关性分析,其结果表明两者有显著的正相关性。将禄丰古猿与其他古猿和现生大猿、南方古猿以及人属成员进行对比,结果显示其前部牙齿牙冠形成时间长于原修康尔猿、南方古猿、傍人、人属成员,接近于蝴蝶禄丰古猿和大猩猩,而明显小于黑猩猩、华南化石猩猩及现生猩猩。     

Sex differences in anthropoid mandibular canine lateral enamel formation

Previous research has demonstrated that great ape and macaque males achieve large canine crown sizes primarily through extended canine growth periods. Recent work has suggested, however, that platyrrhine males may achieve larger canine sizes by accelerating rather than prolonging growth. This study tested the hypothesis that the ontogenetic pathway leading to canine sexual dimorphism in catarrhines differs from that of platyrrhines. To test this hypothesis, males and females of several catarrhine genera (Hylobates, Papio, Macaca, Cercopithecus, and Cercocebus) and three platyrrhine genera (Cebus, Ateles, and Callicebus) were compared in the number and spacing of perikymata (enamel growth increments) on their canine crowns. In addition, perikymata periodicities (the number of days of growth perikymata represent) were determined for five genera (Hylobates, Papio, Macaca, Cebus, and Ateles) using previously published as well as original data gathered for this study. The central findings are as follows: 1) males have more perikymata than females for seven of eight genera (in five of the seven, the differences are statistically significant); 2) in general, the greater the degree of sexual dimorphism, the greater the sex difference in male and female perikymata numbers; 3) there is no evidence of a systematic sex difference in primate periodicities; and 4) there is some evidence that sex differences in enamel formation rates may make a minor contribution to canine sexual dimorphism in Papio and Cercopithecus. These findings strongly suggest that in both catarrhines and platyrrhines prolongation of male canine growth is the primary mechanism by which canine crown sexual dimorphism is achieved. Am J Phys Anthropol, 2009. © 2009 Wiley‐Liss, Inc.     

中国全新世人群颞下颌关节尺寸的时代变化

本文通过对中国北方地区新石器时代(54例)、青铜铁器时代(189例) 和近代(92例) 成年男性颞下颌关节的多项测量项目的对比、分析, 对中国全新世人群颞下颌关节测量性状的变异问题进行了研究。结果显示近7000年来颞下颌关节的不同部位在全新世不同阶段有不同的变化特点。髁突、冠突在全新世厚度变薄, 髁突的变薄主要在新石器-青铜铁器时代, 冠突的变薄主要在青铜铁器-近代。髁突面积在全新世也在缩小, 在新石器-青铜铁器时代缩小的幅度更大。髁突顶缘弧度的变平、下颌窝的变浅主要发生在新石器-青铜铁器时代。髁突面积/下颌窝面积, 其变化主要发生在青铜铁器时代。这些变化可能与生活环境、食物结构改变、下颌骨与头骨不同的演化速率等有关。     

Comparison of dental measurement systems for taxonomic assignment of Neanderthal and modern human lower second deciduous molars

Traditional morphometric approaches for taxonomic assignment of Neanderthal and modern human dental remains are mainly characterized by caliper measurements of tooth crowns. Several studies have recently described differences in dental tissue proportions and enamel thickness between Neanderthal and modern human teeth. At least for the lower second deciduous molar (dm₂), a three-dimensional lateral relative enamel thickness index has been proposed for separating the two taxa. This index has the advantage over other measurements of being applicable to worn teeth because it ignores the occlusal aspect of the crown. Nevertheless, a comparative evaluation of traditional crown dimensions and lateral dental tissue proportion measurements for taxonomic assignment of Neanderthal and modern human dm₂s has not yet been performed.In this study, we compare various parameters gathered from the lateral aspects of the crown. These parameters include crown diameters, height of the lateral wall of the crown (lateral crown height = LCH), lateral enamel thickness, and dentine volume of the lateral wall, including the volume of the coronal pulp chamber (lateral dentine plus pulp volume = LDPV), in a 3D digital sample of Neanderthal and modern human dm₂s to evaluate their utility in separating the two taxa.The LDPV and the LCH allow us to discriminate between Neanderthals and modern humans with 88.5% and 92.3% accuracy, respectively. Though our results confirm that Neanderthal dm₂s have lower relative enamel thickness (RET) index compared with modern humans (p = 0.005), only 70% of the specimens were correctly classified on the basis of the RET index. We also emphasize that results of the lateral enamel thickness method depend on the magnitude of the interproximal wear. Accordingly, we suggest using the LCH or the LDPV to discriminate between Neanderthal and modern human dm₂s. These parameters are more independent of interproximal wear and loss of lateral enamel.     

Monophyly and affinities of albanerpetontid amphibians (Temnospondyli; Lissamphibia)

The Albanerpetontidae are Middle Jurassic-Miocene amphibians that have variously been regarded as caudates (salamanders), a clade distinct from caudates, or incertae sedis lissamphibians. Here I test for monophyly of the Albanerpetontidae and examine the affinities of the group, within the framework of a more inclusive Temnospondyli, by performing a cladistic analysis using 59 informative characters scored for four non-lissamphibian temnospondyl genera, stem- and crown-clade caudates, salientians (frogs), gymnophionans (caecilians), and the two recognized albanerpetontid genera Albanerpeton and Celtedens . Monophyly of the Albanerpetontidae is corroborated. I interpret synapomorphies of the marginal teeth (non-pedicellate; crowns chisel like, labiolingually compressed, with three mesiodistally aligned cuspules) in albanerpetontids as being associated with a shearing bite. Other synapomorphies evidently strengthened and increased the mobility of the skull, mandible, and cervical region for burrowing, feeding, or both. Nested sets of synapomorphies place the Albanerpetontidae within the Lissamphibia, as the sistertaxon of Caudata plus Salientia. None of the 17 characters previously advanced as albanerpetontid-caudate synapomorphies convincingly places the Albanerpetontidae within the Caudata or allies the two groups as sistertaxa. Albanerpetontids are better interpreted not as aberrant caudates, but as a distinct clade of lissamphibians in which numerous apomorphies are superimposed upon an otherwise primitive lissamphibian body plan.