Influence of development rate on pharyngeal teeth formula in <Emphasis Type="Italic">Abramis brama</Emphasis> (L.) bream: Experimental cata

An experiment on acceleration and retardation of ontogeny with thyroid manipulation has revealed direct changes in definitive dentition of pharyngeal bones in Abramis brama bream. As development rate accelerates, the number of teeth reduces to the formula 5-4. When development rate is retarded, this number increases to the formula 6-5. Moreover, an additional minor row of teeth (1.6–5.1, 2.6–5.2) is formed. The observed changes in tooth numbers exceed the known variability in natural populations of bream. It is assumed that heterochronies lead to the changes in the number of teeth.     

Effect of thyroid hormones on the development of pharyngeal dentition in roach <Emphasis Type="Italic">Rutilus rutilus</Emphasis> (Cyprinidae,Cypriniformes)

Development of teeth on the pharyngeal bones of roach Rutilus rutilus and the effect of thyroid hormones on this development are investigated. The addition of exogenous triiodothyronine leads to accelerated development of the teeth, but the deficit of triiodothyronine (provoked by the addition of thiourea in the media) stimulates the retardation of this development. Change of developmental rate of the organism leads to change in the definitive state of the pharyngeal teeth formula. Owing to accelerated development, the number of teeth significantly decreases, and the formulas 5–5, 5–4, and 4–4 appear instead of the typical formula 6–5 in the control group and in the fish from natural populations. Retarded development of the organism leads to increased frequency of occurrence of the formula 6–6. The directed asymmetry in the numbers of pharyngeal teeth with the formula (6–5), most likely, is connected with different types of teeth development on the left and right pharyngeal bones.     

Tooth microstructure tracks the pace of human life-history evolution

A number of fundamental milestones define the pace at which animals develop, mature, reproduce and age. These include the length of gestation, the age at weaning and at sexual maturity, the number of offspring produced over a lifetime and the length of life itself. Because a time-scale for dental development can be retrieved from the internal structure of teeth and many of these life-history variables tend to be highly correlated, we can discover more than might be imagined about fossil primates and more, in particular, about fossil hominids and our own evolutionary history. Some insights into the evolutionary processes underlying changes in dental development are emerging from a better understanding of the mechanisms controlling enamel and dentine formation. Our own 18-20-year period of growth and development probably evolved quite recently after ca 17 million years of a more ape-like life-history profile.     

Pattern and pace of dental eruption in Tarsius

This article uses data on the dental eruption pattern and life history of Tarsius to test the utility of Schultz's rule. Schultz's rule claims a relationship between the relative pattern of eruption and the absolute pace of dental development and life history and may be useful in reconstructing life histories in extinct primates. Here, we document an unusual eruption pattern in Tarsius combining early eruption (relative to molars) of anterior replacement teeth (P2 and incisors) and relatively late eruption of the posterior replacement teeth (C, P3, and P4). This eruption pattern does not accurately predict the "slow" pace of life documented for Tarsius [Roberts: Int J Primatol 15 (1994) 1-28], nor aspects of life history directly associated with dental development as would be expected using Schultz's rule. In Tarsius, the anterior teeth and M1 erupt at an early age and therefore are not only fast in a relative sense but also fast in an absolute sense. This seems to be related to a developmental anomaly in the deciduous precursor teeth, which are essentially skipped. This decoupling among dental eruption pattern, dental eruption pace, and life history pace in Tarsius undermines the assumptions that life histories can accurately be described as "fast" or "slow" and that dental eruption pattern alone can be used to infer overall life history pace. The relatively and absolutely early eruption of the anterior dentition may be due to the utility of these front teeth in early food acquisition rather than with the pace of life history.     

鲤咽齿个体发生及其与近缘种间关系的比较研究

鲤具鲤科咽齿个体发生的共同性征,又呈现其种的独特性状.主要特性;(1)主列齿相连3齿胚几乎同时出现、同时脱落,形成3个相连齿种同时置换的特殊模式;(2)主列齿发生中曾出现4枚齿,替换3代后A_4齿退化消失,最终齿式1.1.3-3.1.1,成为迄今3列咽齿的鱼类中齿数最少的种类.鲤与其近缘种间系统关系比较结果;依最近缘属顺次排列为中鲤、原鲤、肥鲤;而最近缘的亚科为肥亚科.       

雌性宽肋盘腹蛛的种内形态变异(蜘蛛目,蝗蟷蛛科)

通过研究同一种群雌性宽肋盘腹蛛Cyclocosmia latusicosta Zhu,Zhang & Zhang,2006,发现该种个体间在体长、步足长度、齿堤齿的形态与数量、圆盘肋数及纳精囊长宽之比等方面变异较大;宽肋盘腹蛛与里氏盘腹蛛Cyclocosmia ricketti(Pocock,1901)的区别主要是圆盘印痕中央是否存在纽扣状突起.     

Schultz's unruly rule: dental developmental sequences and schedules in small-bodied, folivorous lemurs

Schultz's rule (as reconstructed by Smith) states that there is a relationship between the pattern (or relative order) of eruption of molar versus secondary (replacement) teeth and the overall pace (or absolute timing) of growth and maturation. Species with 'fast' life histories (rapid dental development, rapid growth, early sexual maturation, short life spans) are said to exhibit relatively early eruption of the molars and late eruption of the secondary replacement teeth (premolars, canines, incisors), whereas species with 'slow' life histories are said to exhibit relatively late eruption of the molars and early eruption of the secondary dentition. In a recent review, B.H. Smith noted that primates with tooth combs might violate this rule because tooth combs tend to erupt early, regardless of the pace of life history. We show that exceptions to Schultz's rule among lemurs are not limited to the relative timing of eruption of the tooth comb. Rather, among lemurs, some species with extremely accelerated dental development exhibit a pattern of eruption of molars and of secondary teeth in direct opposition to the expectations of Schultz's rule. We focus particularly on the pattern (order) and pace (absolute timing) of dental development and eruption in Avahi and Lepilemur - two relatively small, nocturnal folivores with rapid dental development. These taxa differ markedly in their eruption sequences (the premolars erupt after M2 and M3 in Lepilemur but not Avahi ). We offer an explanation for the failure of Schultz's rule to predict these differences. Schultz's rule presumes that eruption timing is dependent on the size of the jaw and that, therefore, molar crown formation and eruption will be delayed in species with slow-growing jaws. We show that a variety of processes (including developmental imbrication) allows the crowns of permanent teeth to form and to erupt into jaws that might appear to be too small to accommodate them.     

Dentition in Pacific walrus (Odobenus rosmarus divergens) calves of the year

The oral cavity and teeth were examined in Pacific walrus calves of the year that died or were harvested on Cape Vancarem and Koluchin Island, the Chukchi Sea, in September to October 2010. The order of gingival eruption of teeth, the resultant dental formula in calves of the year and 1.5-year-old animals, and the dental formula after alveolar eruption of teeth were determined. The number of teeth after gingival eruption in calves of the year did not depend on their body length and sex. The loss of some teeth, mainly incisors, was recorded in individuals aged 5?C6 months. Already at early developmental stages, functional teeth were found to differ significantly from other (rudimentary) teeth in their weight, total size, and the size of apical foramen. Some individuals had milk teeth, which were either gingivally erupted or partly remained within soft tissues. Cases of aberration in dentition that require additional studies were recorded.     

Variation of tooth number in mammalian dentition: connecting genetics,development, and evolution

A major question in modern biology is how gene mutations affect development and are translated into macroevolutionary changes in morphology. Variations in tooth number, a strategy used by many mammals to develop specialized dentitions, has been an important factor for species diversification. Changes in the number of teeth tend to occur in the reverse of the order teeth are formed during development, which also characterizes the general pattern of tooth loss observed during the evolution of placental mammals. To understand how changes at the molecular level affect the distinct stages of tooth development, we analyzed the ontogenesis of tooth growth arrest in sciurids and mice and in single and double knockout mutant mice. We show that the complexity of the genetic network that governs tooth development can change during ontogenetic trajectory, and these changes may be related to macroevolutionary changes. Furthermore, we show that the variation in tooth number in the affected members of human families bearing mutations in the MSX1 and PAX9 genes can help to understand how the genetic variations within a population can modulate evolutionary changes in dental patterning.     

The study of animal bones from archaeological sites. By Raymond E. Chaplin. ix + 170 pp., figures,tables, bibliography,index. Seminar press,London. 1971. $5.75 (cloth)

A review of the literature reveals a long history of disagreement on the interpretation of the lower deciduous and permanent dentition of the Indriidae. This disagreement has centered on the existence and/or replacement of a canine as a member of the indriid toothcomb. The presence of a pair of canines in the toothcomb of lemurids and lorisids has rarely been questioned, and there is no evidence to indicate that this interpretation is incorrect. There has, however, been no consistency nor substantiating evidence presented for any interpretation of the indriid toothcomb. By comparing the morphology of the teeth of the lemurid, lorisid, and indriid toothcomb, both deciduous and permanent, comparing the mode of dental development in these three families, identifying the indriid lower deciduous dentition, and by relating the data to an ontogenetic and phylogenetic framework, this study proposes: (1) in all three families, the lateral teeth of the toothcomb are canines, (2) the dental formula for the lower deciduous teeth of indriids is 1.1.4, (3) the dental formula for the lower permanent teeth of indriids is 1.1.2.3, and (4) that decrease in number of incisors during primate evolution was most likely I1 to I2 to I3.     

Development of the dentition in Alligator mississippiensis: upper jaw dental and craniofacial development in embryos, hatchlings, and young juveniles, with a comparison to lower jaw development

Development of the upper dentition in Alligator mississippiensis was investigated using a close series of accurately staged and aged embryos, hatchlings, and young juveniles up to 11 days posthatching, as well as some young and old adult specimens. Studies from scanning electron microscopy, light microscopy, acetate and computer reconstructions, radiography and macroscopy were combined to elucidate the details of embryonic dental development, tooth initiation pattern, dentitional growth, and erupted functional dentition. The results were compared with those from the lower jaw and related to the development of other craniofacial structures. Approximately 17 early teeth in each jaw half develop as surface teeth, of which 13 project for 1 to 12 days before sinking into the mesenchyme. The first three teeth initiate directly from the oral epithelium at Ferguson stages 14-15 (days 15-19 after egg laying), before there is any local trace of dental lamina formation. All other teeth develop from a dental prolamina or lamina; and with progressive lamina development, submerged teeth initiate from the aboral end leading to the formation of replacement teeth. All teeth form dentin matrix, but 12 early teeth do not form enamel. Approximately 20 embryonic teeth are resorbed, 6 are transitional, and 42 function for longer periods after hatching. The embryonic tooth initiation pattern (illustrated by defining a tooth position formula) does not support the previous models of Odontostichi, Zahnreihen, and Tooth Families, each of which postulates perfect regularity. Up to three interstitial tooth positions develop between sites of primary tooth initiation, and families with up to five generations at hatching are at first arbitrarily defined.     

Review of Chinese Oligaphorurini (Collembola, Onychiuridae) with descriptions of two new Palaearctic species

A checklist of Chinese Oligaphorurini is given. Two new Chinese species, Micraphorura changbaiensissp. n. and Oligaphorura pseudomontanasp. n., are described from Changbai Mountain Range. Micraphorura changbaiensis sp. n. has the same dorsal pseudocelli formula and number of papillae in Ant. III sensory organ as Micraphorura uralica, but they can be easily distinguished by number of chaetae in Ant. III sensory organ, ventral pseudocelli formula, ventral parapseudocelli formula, number of pseudocelli on subcoxa 1 of legs I-III, dorsal axial chaeta on Abd. V and number of chaetae on tibiotarsi. Oligaphorura pseudomontana sp. n. is very similar to the species Oligaphorura montana having an increased number of pseudocelli on body dorsally, well marked base of antenna with 1 pseudocellus and 3 pseudocelli outside, subcoxa 1 of legs I-III with 1 pseudocellus each, dorsally S-chaetae formula as 11/011/22211 from head to Abd. V, S-microchaeta present on Th. II-III, claw without inner teeth and with 1+1 lateral teeth, and unguiculus with basal lamella; but they can be separated easily by the number of pseudocelli on Abd. V and VI terga, parapseudocelli on the body, number of chaetae on Th. I tergum, and number of chaetae on tibiotarsi. A key to Chinese species of Oligaphorurini is provided in the present paper.     

Homologies of the anterior teeth in Indriidae and a functional basis for dental reduction in primates

In a recent paper Schwartz ('74) proposes revised homologies of the deciduous and permanent teeth in living lemuriform primates of the family Indriidae. However, new evidence provided by the deciduous dentition ofAvahi suggests that the traditional interpretations are correct, specifically: (1) the lateral teeth in the dental scraper of Indriidae are homologous with the incisors of Lemuridae and Lorisidae, not the canines; (2) the dental formula for the lower deciduous teeth of indriids is 2.1.3; (3) the dental formula for the lower permanent teeth of indriids is 2.0.2.3; and (4) decrease in number of incisors during primate evolution was usually in the sequence I3, then I2, then I1. It appears that dental reduction during primate evolution occurred at the ends of integrated incisor and cheek tooth units to minimize disruption of their functional integrity.     

The size and morphology of the Nasioi dentition

Dental impressions were obtained on 240 Nasioi, a Melanesian population living on the island of Bougainville. Odontometric data are presented for both the permanent and deciduous teeth, and the former teeth are also examined morphologically. The results show that the Nasioi have large permanent teeth like other Australoid populations whereas the deciduous teeth are only of moderate size. The coefficients of variation are large in the permanent teeth compared to other populations but the sexual dimorphism in tooth size and variability is not remarkable. Morphologically, the permanent teeth of the Nasioi are characterized by a cusp number pattern, a high frequency of the Dryopithecus + pattern on the first mandibular molar, few individuals with a Cusp of Carabelli, and a moderate expression of shovelled-shaped anterior teeth.     

昆明裂腹鱼骨骼系统解剖

常规方法和透明骨法制备昆明裂腹鱼的骨骼标本,记录观测结果并拍照,对其骨骼系统进行描述。其特征为脊椎数目在46～47之间,肋骨在18～19之间,咽骨上有三排咽齿,齿式呈2:3:5式。骨骼系统的形状和变化可以为裂腹鱼亚属的分类及演化提供分类方面的基础资料。     

FGF8-mediated signaling regulates tooth developmental pace during odontogenesis

The developing human and mouse teeth constitute an ideal model system to study the regulatory mechanism underlying organ growth control since their teeth share highly conserved and well-characterized developmental processes, and their developmental tempo varies notably. In the current study, we manipulated heterogenous recombination between human and mouse dental tissues and demonstrated that the dental mesenchyme dominates the tooth developmental tempo and FGF8 could be a critical player during this developmental process. Forced activation of FGF8 signaling in the dental mesenchyme of mice promoted cell proliferation, prevented cell apoptosis via p38 and perhaps PI3K-Akt intracellular signaling, and impelled the transition of the cell cycle from G1- to S-phase in the tooth germ, resulting in the slowdown of the tooth developmental pace. Our results provide compelling evidence that extrinsic signals can profoundly affect tooth developmental tempo, and the dental mesenchymal FGF8 could be a pivotal factor in controlling the developmental pace in a non-cell-autonomous manner during mammalian odontogenesis.     

First Fossil Evidence for the Advance of Replacement Teeth Coupled with Life History Evolution along an Anagenetic Mammalian Lineage

In mammals that grow up more slowly and live longer, replacement teeth tend to appear earlier in sequence than in fast growing mammals. This trend, known as ‘Schultz''s Rule’, is a useful tool for inferring life histories of fossil taxa. Deviations from this rule, however, suggest that in addition to the pace of life history, ecological factors may also drive dental ontogeny. Myotragus balearicus is an extinct insular caprine that has been proved to be an excellent test case to correlate morphological traits with life history. Here we show that Myotragus balearicus exhibits a slow signature of dental eruption sequence that is in agreement with the exceptionally slow life history of this species, thus conforming to ‘Schultz''s Rule’. However, our results also show an acceleration of the absolute pace of development of the permanent incisors in relation to that of the posterior teeth. The rodent-like incisors of Myotragus balearicus erupted early not only in relative but also in absolute terms (chronological age), suggesting that feeding characteristics also plays an important role in dental ontogeny. This is in agreement with ecological hypotheses based on primates. Our study documents a decoupling of the pace of development of teeth in mammals that is triggered by different selection pressures on dental ontogeny. Moreover, we show that Myotragus kopperi from the early Pleistocene (a direct ancestor of the late Pleistocene-Holocene M. balearicus) follows the pattern of first incisor replacement known in living bovids. Hence, the advance in the eruption sequence of the first incisors occurs along the Myotragus evolutionary lineage over a period of about 2.5 Myr. To our knowledge, this is the first fossil evidence of an advance of the emergence of the permanent first incisor along an anagenetic mammalian lineage.     

Dentition and tooth replacement pattern in Chalcides (Squamata; Scincidae)

This study was undertaken as a prerequisite to investigations on tooth differentiation in a squamate, the Canarian scincid Chalcides. Our main goal was to determine whether the pattern of tooth replacement, known to be regular in lizards, could be helpful to predict accurately any stage of tooth development. A growth series of 20 laboratory-reared specimens, aged from 0.5 month after birth to about 6 years, was used. The dentition (functional and replacement teeth) was studied from radiographs of jaw quadrants. The number of tooth positions, the tooth number in relation to age and to seasons, and the size of the replacement teeth were recorded. In Chalcides, a single row of pleurodont functional teeth lies at the labial margin of the dentary, premaxillary, and maxillary. Whatever the age of the specimens, 16 tooth positions were recorded, on average, in each quadrant, suggesting that positions are maintained throughout life. Replacement teeth were numerous whatever the age and season, while the number of functional teeth was subject to variation. Symmetry of tooth development was evaluated by comparing teeth two by two from the opposite side in the four jaw quadrants of several specimens. Although the relative size of some replacement teeth fitted perfectly, the symmetry criterion was not reliable to predict the developmental stage of the opposite tooth, whether the pair of teeth compared was left-right or upper-lower. The best fit was found when comparing the size of successive replacement teeth from the front to the back of the jaw. Every replacement tooth that is 40-80% of its definitive size is followed, in the next position on the arcade, by a tooth that is, on average, 20% less developed. Considering teeth in alternate positions (even and odd series), each replacement tooth was a little more developed than the previous, more anterior, one (0.5-20% when the teeth are from 10-40% of their final size). The latter pattern showed that tooth replacement occurred in alternate positions from back to front, forming more or less regular rows (i.e., "Zahnreihen"). In Chalcides, the developmental stage of a replacement tooth in a position p can be accurately predicted provided the developmental stage of the replacement tooth in position p-1 or, to a lesser degree, in position p-2 is known. This finding will be particularly helpful when starting our structural and ultrastructural studies of tooth differentiation in this lizard.     

Somatic variation in living, wild ring-tailed lemurs (Lemur catta)

While understanding somatic variability among wild primates can provide insight into natural patterns of developmental plasticity, published data for living populations are rare. Here we provide such information for two distinct wild populations of Lemur catta. Variants observed include microtia, athelia, and female virilization. Dental variants observed include individuals with supernumerary teeth, rotated teeth, maxillary incisor agenesis, and severe malocclusion. There was a sex bias in incisor agenesis, with 5 of 7 examples (71%) found in males. The frequency of dental variants in our sample is lower than that seen in many other lemuriformes, as well as other primates. This may be a product of their less derived dental formula and/or their relatively fast dental development. Amassing such data is a critical first step to assess if wild primate populations are exhibiting normal variability or are being affected by potential inbreeding and/or environmental effects.     

POSTCANINE ROOT SYSTEM IN TRITYLODONTS

<正> Inspired by Dr. Tom Rich's letter inquiring the structure of the roots of tritylodont cheekteeth, we initiated this study. At first, only several isolated teeth were exposed. Later on, jaws and partial skull carrying the dentition have been included.The generic identification of the materials is based mainly on the morphology of the upper postcanine crowns. Among the four genera dealt with in this work, Yunnanodon is unique in having a cusp formula of 2-3-2:2 buccal, 3 median and 2 lingual cusps. From the smaller and a little medially situated posterior cusp of the lingual row, Lufengia could be separated from the other two genera.Bienotheroides is supposed to be distinguished by a cusp formula of 2-2-2, as those in the later tritylodonts: Stereognathus, Bocatherium, etc. However, in fact, this cusp pattern exists only in the type species, B. wanhsienensis. Another species, B. zigongensis from a lower horizon, namely, Lower Shaximiao Formation of Sichuan and Wucaiwan Formation of Xinjiang, possesses a cusp formula of 2-3-3, much similar to that of Bienotherium. Consequently, the localities and horizons are taken as a measure of discriminating those specimens with similar crown pattern, especially the lower postcanine teeth.