Frugivorous and animalivorous bats (Microchiroptera): dental and cranial adaptations

The most derived fruit-eating bats have small canines, wide palates and molars with a distinctive labial rim. Paracone and metacone have moved from a dilambdodont position in the middle of the tooth to the labial side of the tooth where they form the labial cutting edge. Along with the well-developed and close fitting labial cutting edges of the premolars and canines, this cutting edge skirts nearly the entire perimeter of the palate. The labial rim of the lower teeth fit inside the labial rim of the upper teeth like two cookie cutters nesting one inside the other. Frugivores have a greater allocation of tooth area at the anterior end of the toothrow, while animalivorous species have more at the posterior end of the toothrow. The area occupied by canines of predators of struggling prey is greater than that for bats that eat non-struggling prey like fruit. In addition, frugivores have wider palates than long while many carnivores have longer palates than wide. Omnivores appear to have a more equal allocation of space to more kinds of teeth, particularly the incisors and non-molariform premolars, on the toothrow than do frugivores or animalivores. The mechanical nature of different food items is discussed and the suggestion made that describing foods in terms of their texture may be more important in tooth design than whether they are fruit or insect or vertebrate.     

A new correction procedure for calibrating dental caries frequency

The incisors and canines and the premolars and molars show differential resistance to cariogenic factors. The anterior teeth have a lower caries frequency than the posterior teeth. However, these tooth classes are lost differentially in postmortem stages due to their anatomical structures. This differential postmortem tooth loss distorts proportions between the anterior and posterior tooth classes. The disproportionality can affect the calculation of total caries prevalence. In this paper, we propose a new calibration procedure which removes this disproportionality and call it the proportional correction factor. For this procedure, the caries rates of anterior and posterior teeth are corrected by multiplying the anterior teeth by three-eighths and the posterior teeth by five-eighths. These fractions are derived from the human dental formula which contains three anterior and five posterior teeth by side. The correction factor is more effective if the proportion of anterior to the posterior teeth is extremely distorted. When this procedure is used with the caries correction factor, it provides a useful way to approach to an almost true caries prevalence. Am J Phys Anthropol 108:237–240, 1999. © 1999 Wiley-Liss, Inc.     

A functional analysis of carnassial biting

The jaw mechanism of carnivores is studied using an idealized model (Greaves, 1978). The model assumes: (i) muscle activity on both sides of the head, and (ii) that the jaw joints and the carnassial teeth are single points of contact between the skull and the lower jaw during carnassial biting. The model makes the following predictions: (i) in carnivores with carnassial teeth the resultant force of the jaw muscles will be positioned approximately 60% of the way from the jaw joint to the tooth—this arrangement delivers the maximum bite force possible together with a reasonably wide gape (remembering that bite force and gape cannot both be maximized); (ii) in an evolutionary sense, if greater bite force is required at the carnassial tooth, either the animal will get larger so as to deliver an absolutely larger bite force or the architecture of the muscles may change, becoming more pinnate, for example, but jaw geometry (i.e. the relative positions of the jaw joints, the carnassial tooth, and the muscle resultant force) will not change; (iii) if greater gape is required, the animal will get larger so as to have longer jaws and therefore an absolutely wider gape or change its muscle architecture allowing for greater stretch while the geometry remains unchanged; and (iv) in animals with a longer shearing region (e.g. the extinct hyaenodonts) the shearing region will be approximately 20% of jaw length and the muscle resultant force will be positioned approximately 60% of the way from the jaw joint to the most anterior shearing tooth.     

山西垣曲先炭兽类一新种

本文主要报道1983年9月,在山西省垣曲县寨里发现的一件较完整的先炭兽类老年个体上颌骨.带有颇为完整的左、右齿列. I~1-P~2 各齿前、后均有较长的齿隙. P~1、P~2、P~3 前的齿隙颌骨上,保留有乳前臼齿的齿槽.这块标本在大小及形态特征上,与目前所知先炭兽属 Anthracokeryx 中任何种都有相当大的差异.它代表了该属中的一个新种.     

内蒙古乌兰塔塔尔地区中渐新世几种肉食动物

这篇短文记述了乌兰塔塔尔地区中渐新世的两种肉齿类和四种食肉类化石,其中有两种在我国为首次报道。     

A NEW GENUS OF TAPIRIDAE FROM SHANWANG, SHANDONG

<正> While helping to curate the jumbled specimens accumulated at the Shanwang Paleontological Museum in 1985, the senior authors of the present paper were happy enough to find a tapirid specimen. Through careful preparation it turned out to be a part of articulated skeleton consisting of skull, lower jaw, cervical and some anterior dorsal vertebrae and a scapula. As most of the other fossils from Shanwang, it is laterally compressed, therefore, no width could actually be measured. The nasal bones of the skull have become vertically oriented through compression. Otherwise the skull is little deformed. In order to study the tooth morphology closely, we had to extract most of the teeth from the left side of the tightly occlused tooth battery. All this notwithstanding, the skull represents one of the few well preserved specimens among the tapirid fossils ever found.     

Location of the vector of jaw muscle force in mammals

Previous work has suggested that the third molar lies just in front of the point where the resultant vector of jaw muscle force, estimated from dissections, intersects the tooth row. This point meets the jaw such that the vector is 30% of jaw length from the jaw joint. Thus, the vector divides the jaw in the ratio of 3:7 when measurements are taken perpendicular to the vector. In practice, however, distances along mammalian jaws are typically measured on an easily determined line such as a line from one end of the tooth row to the other. The position of the jaw joint is then projected onto this line. As a rule, such a line is not perpendicular to the vector and so the distance from the projection of the joint, out to the rear of the third molar (and the vector's intersection), is different in different mammals. Rarely is this distance 30% of total jaw length. However, when the location of the vector's intersection is measured along the tooth row, this position varies directly with the inclination of the vector; a vector inclined posteriorly intersects the tooth row far from the projection of the joint and an anterior vector's intersection is relatively close. Only a vector perpendicular to the line from one end of the tooth row to the other intersects at 30%. This obvious point suggests a way to test the above hypotheses when the inclination of the vector is not known exactly. The predicted relationship between the distance to the molar, as a percentage of the total jaw length, and the approximate inclination of the vector derived from muscle weights (posterior or anterior depending on whether the temporalis or the masseter/pterygoid, respectively, is dominant) was observed in a sample of 46 different mammals.     

内蒙古阿左旗乌兰塔塔尔早渐新世鬣齿兽化石

记述了在内蒙古阿左旗乌兰塔塔尔早渐新世乌兰塔塔尔组中发现的鬣齿兽一新种——内蒙古鬣齿兽(Hyaenodon neimongoliensis sp．nov．)。新种在大小和特征上与Hyaenodonpervagus相近或相似,但它的pl为单齿根,前面的下前臼齿之间有齿隙,下颊齿无舌侧齿带。     

Eating with a saw for a jaw: Functional morphology of the jaws and tooth‐whorl in Helicoprion davisii

The recent reexamination of a tooth‐whorl fossil of Helicoprion containing intact jaws shows that the symphyseal tooth‐whorl occupies the entire length of Meckel's cartilage. Here, we use the morphology of the jaws and tooth‐whorl to reconstruct the jaw musculature and develop a biomechanical model of the feeding mechanism in these early Permian predators. The jaw muscles may have generated large bite‐forces; however, the mechanics of the jaws and whorl suggest that Helicoprion was better equipped for feeding on soft‐bodied prey. Hard shelled prey would tend to slip anteriorly from the closing jaws due to the curvature of the tooth‐whorl, lack of cuspate teeth on the palatoquadrate (PQ), and resistance of the prey. When feeding on soft‐bodied prey, deformation of the prey traps prey tissue between the two halves of the PQ and the whorl. The curvature of the tooth‐whorl and position of the exposed teeth relative to the jaw joint results in multiple tooth functions from anterior to posterior tooth that aid in feeding on soft‐bodied prey. Posterior teeth cut and push prey deeper into the oral cavity, while middle teeth pierce and cut, and anterior teeth hook and drag more of the prey into the mouth. Furthermore, the anterior‐posterior edges of the teeth facilitate prey cutting with jaw closure and jaw depression. The paths traveled by each tooth during jaw depression are reminiscent of curved pathways used with slashing weaponry such as swords and knifes. Thus, the jaws and tooth‐whorl may have formed a multifunctional tool for capturing, processing, and transporting prey by cyclic opening and closing of the lower jaw in a sawing fashion. J. Morphol. 276:47–64, 2015. © 2014 Wiley Periodicals, Inc.     

The jaw lever system in ungulates: a new model

In ungulates the distance from the jaw joint to the last molar is approximately the same as that of the grinding tooth row length. An hypothesis is presented that attempts to explain why ungulate grinding teeth are positioned where they are along the jaw. If the jaw joint on the balancing side serves as the fulcrum in anisognathus animals, a region along the jaw is defined, corresponding to where teeth are actually found, where rather simple muscle action can apply equal forces at any point. The ability to produce the same force at any point in this region, as such, may not be the critical feature since anterior or posterior to this region, tooth placement produces either a relatively inefficient or an unstable condition.     

On the definition of variables in studies of primate dental allometry

Cranial and dental measurements are taken on 253 adult female primates from 32 species. Regression equations are calculated to determine allometric relationships between anterior tooth size, posterior tooth size, and body size. When cranial length or skull length is used as the measure of general size, the results of the equations differ from when body weight is the reference dimension. Similarly, using different definitions of posterior tooth size (such as mandibular second molar length and maxillary postcanine area) alters results substantially. The same occurs with different definitions of anterior tooth size. It has been common in studies of primate dental allometry to generalize from the specific variables measured to broad functional interpretations. However, highly correlated variables cannot be substituted one for another in allometric analyses without important changes in the results of the equation. Interpretation of allometric data is more highly restricted to the precise variables measured in a particular study than has been generally recognized.     

Postschizotherium下颌的新发现

<正> Postschizotherium是我国新生代后期哺乳动物化石中引起过长期争论的一个属。关于这些争论,童永生和黄万波在“山西上新蹄兔一新种”一文中已有概括的介绍。这里想强调指出的一点是,虽然现在一般都倾向于把这个属归入蹄兔目,但化石的正面证据仍嫌不足。事实上,现有的化石并没有超过1939年德日进把这个属归入爪兽科时所掌握的材料。这些材料中头骨保存得太差,在目一级的分类上起不了多大的作用。P~4—M~3倒是保存得较好,发现得也较多。但也正是在这几个上颊齿上,蹄兔和爪兽这两类动物是很相似     

新疆吐谷鲁群天山贫齿鳄的再研究

本文对杨钟健1973年记述的—原鳄类成员——天山贫齿鳄 (Edentosuchus tienshanensis) 进行了修订和补充描述,并依据头骨及脊椎的特征将原订的贫齿鳄科 Edentosuchidae 归人中鳄亚目.文中对这一鳄类的年龄及齿列的功能形态进行了初步的探讨.     

Mammals with a long diastema typically also have dominant masseter and pterygoid muscles

A few orders of mammals contain many individuals with dominant masseter and pterygoid muscles that pull up and forward as they close the jaw. A dominant temporalis muscle that pulls the jaw up and to the rear is the more common condition in mammals. A long toothless region (diastema) is present in almost all mammals with a large masseter/pterygoid complex. The presence of a diastema, when few teeth have been lost and their size has not changed significantly over evolutionary time, implies that the jaws have lengthened, as in horses and selenodont artiodactyls. (A long jaw with a shorter diastema will also form if very long incisors develop as in rodents.) The sum of the forces of all the jaw muscles (represented by an arrow) typically divides the jaw into a posterior, toothless region and an anterior region where the teeth are located. In most mammals, the sum of all the bite forces at the teeth is maximized when the lengths of the projections of these two regions, onto a line perpendicular to the arrow, are in the ratio of 3 : 7. If the tooth-bearing region of the jaws becomes longer over evolutionary time this ratio will obviously be disturbed. A change in the location of some basic bony features of the jaw mechanism could maintain this ratio, but this requires major disruption of the skull and jaws. Alternatively, simply changing the masses of the muscles that close the jaw (smaller temporalis, larger masseter and/or pterygoid, or some combination), so that the lower jaw is pulled up and forward, rather than backward, also maintains the ratio. According to this view, if the jaw lengthens over evolutionary time, the relative sizes of the jaw muscles will change so that the masseter/pterygoid complex will become dominant.  © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society , 2008, 153 , 625–629.     

Static intraspecific allometry of the dentition in Otoletnur crassicaudatus

Adult static intraspecific allometry of tooth size was evaluated in a sample of 66 Otolemur crassicaudatus (34 male, 32 female). Tooth areas were calculated from mesiodistal and buccolingual measurements of canines and postcanine teeth of both arcades and were scaled to four viscerocranial measurements: bimaxillary width; maxillo-alveolar length; mandibular length and bigonial width. Individual tooth crown areas were also scaled to total skull length, body length and body weight. From the log-transformed analyses it is concluded that postcanine tooth size was unrelated to body length or weight, and poorly correlated to skull length or jaw size. Although viscerocranial size appears to be independent of body size, these measures are well correlated to skull length. It is shown that the longer the skull, the shorter and narrower the maxilla, and the longer and broader the mandible. Canines are shown to scale negatively allometric to skull length, hence, large animals will have relatively small canines.     

Tooth growth and replacement in Ctenolucius hujeta, a neotropical characoid fish

The predaceous neotropical characoid fish Ctenolucius has an essentially homodont dentition, the number of teeth increasing linearly with age. The basic manner of tooth replacement suggests that Ctenolucius is a primitive characoid. Tooth replacement continues throughout life and is similar to that of tetrapods, involving replacement waves which pass from the back to the front of the jaws. The waves containing the greatest number of teeth are found just anterior to the middle of the jaws. In the upper jaw the increase in the number of teeth is restricted to the anterior portion (premaxillary) whereas the number on the posterior part (maxillary) remains constant. In specimens measuring from 68–230 mm in standard length the posterior portion of the upper jaw doubles in length whereas the anterior portion triples. It is suggested that the area immediately anterior to the middle of the jaw, where replacement waves are longest, is where most of the increase in tooth numbers occurs. During growth of the teeth the absolute height is always greater than the absolute width as the shape changes. The final shape of the recurved conical teeth is determined only in the last stages of tooth formation when the main axis of growth abruptly changes.     

Comparative functional analysis of skull morphology of tree-gouging primates

Many primates habitually feed on tree exudates such as gums and saps. Among these exudate feeders, Cebuella pygmaea, Callithrix spp., Phaner furcifer, and most likely Euoticus elegantulus elicit exudate flow by biting into trees with their anterior dentition. We define this behavior as gouging. Beyond the recent publication by Dumont ([1997] Am J Phys Anthropol 102:187-202), there have been few attempts to address whether any aspect of skull form in gouging primates relates to this specialized feeding behavior. However, many researchers have proposed that tree gouging results in larger bite force, larger internal skull loads, and larger jaw gapes in comparison to other chewing and biting behaviors. If true, then we might expect primate gougers to exhibit skull modifications that provide increased abilities to produce bite forces at the incisors, withstand loads in the skull, and/or generate large gapes for gouging.We develop 13 morphological predictions based on the expectation that gouging involves relatively large jaw forces and/or jaw gapes. We compare skull shapes for P. furcifer to five cheirogaleid taxa, E. elegantulus to six galagid species, and C. jacchus to two tamarin species, so as to assess whether gouging primates exhibit these predicted morphological shapes. Our results show little morphological evidence for increased force-production or load-resistance abilities in the skulls of these gouging primates. Conversely, these gougers tend to have skull shapes that are advantageous for creating large gapes. For example, all three gouging species have significantly lower condylar heights relative to the toothrow at a given mandibular length in comparison with closely related, nongouging taxa. Lowering the height of the condyle relative to the mandibular toothrow should reduce the stretching of the masseters and medial pterygoids during jaw opening, as well as position the mandibular incisors more anteriorly at wide jaw gapes. In other words, the lower incisors will follow a more vertical trajectory during both jaw opening and closing.We predict, based on these findings, that tree-gouging primates do not generate unusually large forces, but that they do use relatively large gapes during gouging. Of course, in vivo data on jaw forces and jaw gapes are required to reliably assess skull functions during gouging.     

贵州的短尾鼩(Anourosorex)化石

贵州发现的属于食虫类 Anourosorex 属的182件标本按齿式可分为两种类型,齿式为的是 A kui; 齿式为的是两新种, A. edwardsi sp. nov. 和 A. qianensis sp. nov.. 含有 A. kui 的岩灰洞、天门洞及穿洞动物群的地质时代可与四川盐井沟及歌乐山中更新世中晚期动物群相对比. A. kui 与较原始的 A. edwardsi 共生的岩灰洞和穿洞动物群的时代可能较之天门洞稍早.较进步的绝灭种 A. qianensis 单独存在于挖竹湾洞、天桥裂隙、白脚岩洞并和云南呈贡三家村晚更新世地点的材料可以对比. 根据齿式及形态特征 A. kui 应是现生种 A. squamipes 的直接祖先.     

The orientation of the force of the jaw muscles and the length of the mandible in mammals

Ungulates generally have large masseter and pterygoid muscles and a necessarily large angular process provides attachment surface on the mandible. The temporalis muscle tends to be small. It has been suggested that this is an adaptation for enhanced control of the lower jaw and reduction of forces at the jaw joint. I suggest an additional reason: because of the geometry of the jaw, the length of that segment of the lower jaw that spans the distance from the jaw joint to the most posterior tooth is significantly reduced when the masseler and pterygoid are the dominant muscles; this region is necessarily much longer when the temporalis is large.