Size and placement of developing anterior teeth in immature Neanderthal mandibles from Dederiyeh Cave,Syria: Implications for emergence of the modern human chin

Evolutionary and functional significance of the human chin has long been explored from various perspectives including masticatory biomechanics, speech, and anterior tooth size. Recent ontogenetic studies have indicated that the spatial position of internally forming anterior teeth partially constrains adult mandibular symphyseal morphology. The present study therefore preliminarily examined the size and placement of developing anterior teeth in immature Neanderthal mandibles of Dederiyeh 1 and 2, compared with similarly‐aged modern humans (N = 16) and chimpanzees (N = 7) whose incisors are comparatively small and large among extant hominids, respectively. The Dederiyeh 1 mandible is described as slightly presenting a mental trigone and attendant mental fossa, whereas Dederiyeh 2 completely lacks such chin‐associated configurations. Results showed that, despite symphyseal size being within the modern human range, both Dederiyeh mandibles accommodated overall larger anterior dentition and displayed a remarkably wide bicanine space compared to those of modern humans. Dederiyeh 2 had comparatively thicker deciduous incisor roots and more enlarged permanent incisor crypts than Dederiyeh 1, but both Dederiyeh individuals exhibited a total dental size mostly intermediate between modern humans and chimpanzees. These findings potentially imply that the large deciduous/permanent incisors collectively distended the labial alveolar bone, obscuring an incipient mental trigone. It is therefore hypothesized that the appearance of chin‐associated features, particularly of the mental trigone and fossa, can be accounted for partly by developmental relationships between the sizes of the available mandibular space and anterior teeth. This hypothesis must be, however, further addressed with more referential samples in future studies. Am J Phys Anthropol 156:482–488, 2015. © 2014 Wiley Periodicals, Inc.     

Interspecies difference in placement of developing teeth and its relationship with cross-sectional geometry of the mandibular symphysis in four primate species including modern humans

The form of the anthropoid mandibular symphysis has recently been addressed in association with spatial requirements for the forming anterior teeth. To evaluate potential relationships between the symphyseal shape and teeth further, the growth patterns of the symphyseal region and the positioning of the tooth crypts were examined using CT data, comparing four primate species (modern humans, chimpanzees, Japanese monkeys, and hamadryas baboons) with varied symphyseal curvature and tooth size. First, results showed that interspecies differences in overall mandibular shape including symphyseal inclination and bicanine width are consistently expressed throughout postnatal ontogeny, although local symphyseal configurations related to the superior transverse torus (STT) tended to change considerably during growth in chimpanzees. Second, the four species were found to exhibit differentiated formation positions of the incisor and canine crypts. In particular, I2 developed between I1 and C in humans with a broad bicanine space and small teeth, whereas it was positioned posterior to I1 and above C in the cercopithecines with an extremely narrow bicanine space. In chimpanzees, despite the large bicanine width, I1 and I2 grew with a large antero-posterior overlap owing to their large size. These results indicate that the dental positioning is determined in concert with the size balance of the available mandibular space and forming teeth. Finally, the positions/contours of I2 crypt were shown to correspond strongly with the STT across the taxa. This suggests that interspecies differences in symphyseal shape should be interpreted partially by the species-specific positional relationships of the developing anterior teeth.     

Mental foramen and mental nerve: changes with age

In a study of 525 dry mandibles and dissections in 50 cadavers, the mental foramen (MF) was found: single in 94.67% of the cases and multiple in 5.33%. Its shape was round in 34.48% with an average diameter of 1.68 mm and oval in 65.52% with an average long diameter of 2.37 mm. In 43.66% the MF was located in front of the apex of the root of the second premolar. In children before tooth eruption, the MF is somewhat closer to the alveolar margin; during the eruption period, the MF descends to half way between the margins, and in adults with the teeth preserved, the MF is somewhat closer to the inferior border. With loss of teeth and bone resorption the MF moves upwards closer to the alveolar border. In extreme cases of resorption the MF and the adjacent part of the mandibular canal are open at the alveolar margin. In the dissections the findings were similar. The mental nerve emerged from the MF closer to or at the alveolar border, according to the degree of resorption. In extreme degrees of resorption, the mental nerve and the final part of the inferior alveolar nerve were found directly under the gums. In these cases, the vestibular grooves became very shallow, and the mucosa passed directly from the cheeks over the alveolar ridge. Practical implications of the changes of the MF and mental nerve are discussed.     

Crossing the Red Sea: phylogeography of the hamadryas baboon, Papio hamadryas hamadryas

The hamadryas baboon (Papio hamadryas hamadryas) is found both in East Africa and western Arabia and is the only free-ranging nonhuman primate in Arabia. It has been hypothesized that hamadryas baboons colonized Arabia in the recent past and were possibly even transported there by humans. We investigated the phylogeography of hamadryas baboons by sequencing a portion of the control region of mtDNA in 107 baboons from four Saudi Arabian populations and combing these data with published data from Eritrean (African) P. h. hamadryas. Analysis grouped sequences into three distinct clades, with clade 1 found only in Arabia, clade 3 found only in Africa, but clade 2 found in both Arabian and African P. h. hamadryas and also in the olive baboon, P. h. anubis. Patterns of variation within Arabia are neither compatible with the recent colonization of Arabia, implying that baboons were not transported there by humans, nor with a northerly route of colonization of Arabia. We propose that hamadryas baboons reached Arabia via land bridges that have formed periodically during glacial maxima at the straits of Bab el Mandab in the southern Red Sea. We suggest that the genetic differentiation of Arabian from African populations suggests that Arabian populations have a higher conservation status than recognized previously.     

A clinical and anatomical study of the location of the mental foramen in adult Chinese mandibles

One hundred mandibles of adult Chinese cadavers of both sexes without missing teeth, alveolar bone resorption and malposition of teeth were studied. The anatomical location of each mandibular mental foramen was measured by using a combination of three previous methods. Our results showed that the location of the mental foramen below the apex of the lower second premolar (relation IV: 58.98%) was the most common. On average, the distance between the most anterior portion of the anterior border of the mental foramen and the mandibular symphysis was 28.06 mm, between the most anterior portion of the anterior border of the mental foramen and the posterior border of the ramus 74.14 mm, between the inferior border of the mental foramen and the lower border of the mandibular body 14.70 mm, between the superior border of the mental foramen and the bottom of the lower second premolar socket 2.50 mm. The distance across the mental foramen between the alveolar crest and the lower border of the mandibular body was 30.29 mm. Our results were compared with those of other investigators. The significance of identifying the anatomical location of the mental foramen in dental practice is discussed.     

Neandertal mandibles from the Sima de las Palomas del Cabezo Gordo,Murcia, southeastern Spain

The Middle Paleolithic levels of the Sima de las Palomas have yielded eight partial mandibles (Palomas 1, 6, 7, 23, 49, 59, 80, and 88). Palomas 7, 49, 80, and 88 are immature, and Palomas 49, 59, 80, and 88 are among the latest Neandertals (～40,000 cal BP). Palomas 1 is geologically older (～50,000–60,000 cal BP), and the other three were found ex situ. The mandibles exhibit a suite of characteristics that align them with the Neandertals among later Pleistocene humans, including symphyseal morphology, symphyseal orientation, corpus robusticity, distal mental foramen position, retromolar space presence, wide immature dental arcade, and high‐coronoid process with an asymmetrical mandibular notch. However, Palomas 6 lacks a retromolar space, Palomas 59 has a narrow lateral corpus, and Palomas 80 has a mesial mental foramen and open mandibular foramen. The Palomas mandibles therefore help to document that the late Middle Paleolithic of southern Iberia was the product of Neandertals. They also reinforce the presence of variability in both metric and discrete aspects of Neandertal mandibular morphology, both within and across samples, some of which may be temporal and/or geographic in nature. Am J Phys Anthropol, 2010. © 2009 Wiley‐Liss, Inc.     

Indication of higher salivary α‐amylase expression in hamadryas baboons and geladas compared to chimpanzees and humans

Background Little is known about salivary α‐amylase expression in primates. Methods We compared saliva of gelada and hamadryas baboons, chimpanzees and humans using SDS‐PAGE and immunoblotting. Results and conclusions Amylase expression was increased in hamadryas baboons (P = 0.0376) compared to humans and might indicate dietary starch use in Cercopithecines.     

The anterior buccal mandibular depressions: ontogeny and phylogeny

The frequency of an anterior buccal depression in the mandible (ABMD), or a mental fossa, is reported on 970 human mandibles of various groups and different ages, as well as in 38 mandibles of nonhuman primates. The ontogenetic and phylogenetic significance of the results relevant to development of a chin in Homo sapiens is discussed. The ABMD is also compared with the occurrence of a lingual mandibular depression.     

门齿孔位置在中国古人类化石与现代人群的表现及其演化意义

魏敦瑞在研究周口店北京直立人化石时发现,位于上颌骨硬腭表面的门齿孔位置在周口店标本靠后,而在现代人靠近齿槽。此后,门齿孔位置作为具有演化意义的形态特征被用于古人类学研究。迄今,对门齿孔位置在中国古人类化石表现的专门研究仅有周口店一件标本,而在现代中国人的数据尚属空白。鉴于此,本文对门齿孔位置在中国古人类化石以及现代中国人标本进行了观察、测量和数据统计。在此基础上,结合世界其他地区古人类数据资料,本文对门齿孔位置在中国古人类化石的表现特点及其演化意义进行了探讨。本研究发现,从更新世早期到更新世晚期,门齿孔位置在中国古人类呈现由后向前的总体变化趋势。更新世早期和中期直立人(郧县曲远河口、周口店)的门齿孔位置都比较靠后;中更新世晚期的部分中国古人类(大荔、长阳、华龙洞)的门齿孔位置前移,并与现代人接近,而金牛山和巢县门齿孔位置比较靠后,位于直立人范围;在更新世晚期,所有中国古人类都比较靠前,位于现代人变异范围。本文对现代人标本的观测显示,门齿孔位置在现代中国人比较靠前。现代人门齿孔大小及形态存在较大变异,这种表现特点在一定程度上影响对门齿孔位置及演化意义的判定。几乎全部现代人标本门齿孔前缘呈...     

The Early Aurignacian human remains from La Quina-Aval (France)

There is a dearth of diagnostic human remains securely associated with the Early Aurignacian of western Europe, despite the presence of similarly aged early modern human remains from further east. One small and fragmentary sample of such remains consists of the two partial immature mandibles plus teeth from the Early Aurignacian of La Quina-Aval, Charente, France. The La Quina-Aval 4 mandible exhibits a prominent anterior symphyseal tuber symphyseos on a vertical symphysis and a narrow anterior dental arcade, both features of early modern humans. The dental remains from La Quina-Aval 1 to 4 (a dm₁, 2 dm₂, a P⁴ and a P₄) are unexceptional in size and present occlusal configurations that combine early modern human features with a few retained ancestral ones. Securely dated to ∼33 ka ¹⁴C BP (∼38 ka cal BP), these remains serve to confirm the association of early modern humans with the Early Aurignacian in western Europe.     

Mandibular precedence in the prenatal development of four permanent teeth.

As shown in 62 pairs of dental opponents from 32 grossly normal human fetuses in the 75-378 mm crown-rump range, mandibular precedence is the rule for 11, 12, C and M1, a trend in agreement with mandibular precedence for deciduous teeth through dm1 and in the gingival emergence of the same permanent teeth during postnatal development.     

High Prevalence of Simian T-Lymphotropic Virus Type L in Wild Ethiopian Baboons

Simian T-cell leukemia viruses (STLVs) are the simian counterparts of human T-cell leukemia viruses (HTLVs). A novel, divergent type of STLV (STLV-L) from captive baboons was reported in 1994, but its natural prevalence remained unclear. We investigated the prevalence of STLV-L in 519 blood samples from wild-living nonhuman primates in Ethiopia. Seropositive monkeys having cross-reactive antibodies against HTLV were found among 22 out of 40 hamadryas baboons, 8 of 96 anubis baboons, 24 of 50 baboons that are hybrids between hamadryas and anubis baboons, and 41 of 177 grivet monkeys, but not in 156 gelada baboons. A Western blotting assay showed that sera obtained from seropositive hamadryas and hybrid baboons exhibited STLV-L-like reactivity. A PCR assay successfully amplified STLV sequences, which were subsequently sequenced and confirmed as being closely related to STLV-L. Surprisingly, further PCR showed that nearly half of the hamadryas (20 out of 40) and hybrid (19 out of 50) baboons had STLV-L DNA sequences. In contrast, most of the seropositive anubis baboons and grivet monkeys carried typical STLV-1 but not STLV-L. These observations demonstrate that STLV-L naturally prevails among hamadryas and hybrid baboons at significantly high rates. STLV-1 and -2, the close relative of STLV-L, are believed to have jumped across simian-human barriers, which resulted in widespread infection of HTLV-1 and -2. Further studies are required to know if STLV-L is spreading into human populations.     

Incongruity between Affinity Patterns Based on Mandibular and Lower Dental Dimensions following the Transition to Agriculture in the Near East,Anatolia and Europe

While it has been suggested that malocclusion is linked with urbanisation, it remains unclear as to whether its high prevalence began 8,000 years earlier concomitant with the transition to agriculture. Here we investigate the extent to which patterns of affinity (i.e., among-population distances), based on mandibular form and dental dimensions, respectively, match across Epipalaeolithic, Mesolithic, and Neolithic samples from the Near East/Anatolia and Europe. Analyses were conducted using morphological distance matrices reflecting dental and mandibular form for the same 292 individuals across 21 archaeological populations. Thereafter, statistical analyses were undertaken on four sample aggregates defined on the basis of their subsistence strategy, geography, and chronology to test for potential differences in dental and mandibular form across and within groups. Results show a clear separation based on mandibular morphology between European hunter-gatherers, European farmers, and Near Eastern transitional farmers and semi-sedentary hunter-gatherers. In contrast, the dental dimensions show no such pattern and no clear association between the position of samples and their temporal or geographic attributes. Although later farming groups have, on average, smaller teeth and mandibles, shape analyses show that the mandibles of farmers are not simply size-reduced versions of earlier hunter-gatherer mandibles. Instead, it appears that mandibular form underwent a complex series of shape changes commensurate with the transition to agriculture that are not reflected in affinity patterns based on dental dimensions. In the case of hunter-gatherers there is a correlation between inter-individual mandibular and dental distances, suggesting an equilibrium between these two closely associated morphological units. However, in the case of semi-sedentary hunter-gatherers and farming groups, no such correlation was found, suggesting that the incongruity between dental and mandibular form began with the shift towards sedentism and agricultural subsistence practices in the core region of the Near East and Anatolia.     

Who made the Aurignacian and other early Upper Paleolithic industries?

The Aurignacian is typically taken as a marker of the spread of anatomically modern humans into Europe. However, human remains associated with this industry are frustratingly sparse and often limited to teeth. Some have suggested that Neandertals may, in fact, be responsible for the Aurignacian and the earliest Upper Paleolithic industries. Although dental remains are frequently considered to be taxonomically undiagnostic in this context, recent research shows that Neandertals possess a distinct dental pattern relative to anatomically modern humans. Even so, it is rare to find mandibles or maxillae that preserve all or most of their teeth; and, the probability of correctly identifying individuals represented by only a few teeth or a single tooth is unknown. We present a Bayesian statistical approach to classifying individuals represented exclusively by teeth into two possible groups. The classification is based on dental trait frequencies and sample sizes for ‘known’ samples of 95 Neandertals and 63 Upper Paleolithic modern humans. In a cross validation test of the known samples, 89% of the Neandertals and 89% of the Upper Paleolithic modern humans were classified correctly. We then classified an ‘unknown’ sample of 52 individuals: 34 associated with Aurignacian or other (non-Châtelperronian) early Upper Paleolithic industries, 15 associated with the Châtelperronian, and three unassociated. Of the 34 early Upper Paleolithic-associated individuals, 29 were assigned to modern humans, which is well within the range expected (95% of the time 26-33) with an 11% misclassification rate for an entirely modern human sample. These results provide some of the strongest evidence that anatomically modern humans made the Aurignacian and other (non-Châtelperronian) early Upper Paleolithic industries.     

Relationship between canine dimorphism and mandibular morphology in the hamadryas baboon and the Japanese monkey

To examine morphological interrelationships between canine size and mandibular corpus shape, inter-sex comparisons were made in the hamadryas baboon and the Japanese monkey, known to display extreme and moderate canine dimorphism, respectively. Results of adult comparisons showed that all mandibular dimensions were significantly larger in the males than in the females in both species. In the hamadryas baboon, the males also exhibited a higher ratio of anterior to posterior corpus height than the females. This sex difference in corpus shape was not significant in the Japanese monkey, indicating lack of involvement of canine dimorphism. Analysis of mandibular growth patterns in the hamadryas baboon demonstrated that significant sexual size difference did not occur before incisor eruption, and that the anteriorly high corpus of the adult male mandible was associated with a rapidly increasing symphyseal height after incisor eruption. It was also shown that the female canine started to erupt shortly after incisor eruption, while the forming male canine continued to stay near the mandibular base and developed further in size until eruption. The relative positions of the incisors kept shifting upwards even after eruption in the males, while they hardly changed in the females. It is therefore suggested that the prolonged development and size increase of the male canine is accompanied by further enlargement of the symphysis, resulting in the higher anterior corpus of the adult males compared to the adult females. The results thus indicate the importance of understanding the spatial relationships of the developing teeth in interpreting mandibular morphology.     

Dental eruption schedules of wild and captive baboons

Dental eruption schedules previously used to age wild baboons have in the past derived from studies of captive animals housed under standard conditions and fed standard laboratory diets. This paper reports for the first time eruption schedules derived from wild baboons, the yellow baboons (Papio hamadryas cynocephalus) of Mikumi National Park, Tanzania, and compares these schedules with those of other baboon subspecies inhabiting both similar and dissimilar environments. Eighteen males and twelve females from the Viramba groups, ranging in age from 21 to 103 months, were trapped, and dental impressions and notes were made of the state of eruption of each tooth. Eruption of all teeth were delayed at Mikumi relative to the baboon standards derived from the captive animals at the Southwest Foundation for Biomedical Research, San Antonio, Texas. Teeth of the canine-premolar 3 complex and third molars were most delayed, erupting up to a year and a half later than their counterparts from captive animals. Comparison with data on hamadryas baboons from Erer-Gota in Ethiopia revealed that both the hamadryas and yellow subspecies of baboons, with different genetic backgrounds and living under markedly different environmental conditions, followed the same schedule. This constancy of developmental schedules suggests that these Mikumi data may reasonably be used as standards for other wild baboon populations and that acceleration of dental maturation, as well us maturation of other somatic systems in captivity, is another manifestation of the short-term adaptive plasticity of the baboon species as a whole.     

Does space in the jaw influence the timing of molar crown initiation? A model using baboons (Papio anubis) and great apes (Pan troglodytes, Pan paniscus)

Radiographic and histological studies of baboon (Papio hamadryas, P. anubis) and chimpanzee (Pan troglodytes) permanent tooth development have found that periods of molar crown mineralization overlap markedly in chimpanzees but are staggered in baboons. Here we test the hypothesis that these intertaxon differences in molar initiation are primarily due to the space available in the mandibles of each species for these teeth. This study includes radiographic, linear measurement, and three-dimensional (3D) coordinate landmark data taken from baboon (Papio anubis n=51) and great ape (Pan paniscus n=43, P. troglodytes n=60) mandibles and permanent molars across a broad developmental range for each taxon. Unexpectedly, 3D multivariate statistical shape analysis of the molar crypt, crown, and root data shows that all three species trajectories of molar row shape change are indistinguishable from each other. Qualitative analysis of these 3D data reveals subtle and inconclusive intergeneric differences in the space maintained between adjacent molars during growth. The space distal to each newly initiated molar is slightly greater in the baboon. Bivariate analyses comparing molar row and mandibular corpus proportions in Papio and Pan fail to show clear or consistent taxonomic differences in the ratio of space afforded developing molars in the alveolar bone. Thus, there is a poor correlation between mandibular proportion and both intermolar spacing and 3D molar development pattern. Contrary to earlier studies, these results suggest that pattern of molar crown initiation and temporal overlap of adjacent mineralizing crowns is not significantly different between Papio and Pan. This may be due in part to the inclusion here of not only 3D molar crown data but also 3D molar crypt data. This study strongly refutes the hypothesis that space available in the mandible directly underlies different times of permanent molar crown initiation between Papio and Pan.     

Human deciduous mandibular molar incremental enamel development

Quantitative studies of incremental markings retained within human enamel have reconstructed the duration and rate (crown and cusp formation times, initiation and completion, daily enamel secretion rates) of permanent tooth development. This approach has provided one way of estimating human age‐at‐death, and facilitated comparative dental studies of primate evolution. Similar applications from deciduous enamel are inhibited because developmental reconstructions from incremental markings for these teeth are less frequently reported in the literature. This study quantified the duration and rate of enamel development for mesial (protoconid, metaconid) and distal cusps (hypoconid, entoconid) for first (dm1) and second (dm2) deciduous mandibular molars from an archaeological sample of modern human juveniles. Crown formation time can be calculated from the dm1 protoconid because growth initiates and completes in this cusp, and from the dm2 protoconid combined with the final period of hypoconid growth. The dm1 postnatal crown formation time included the time taken for the tubercle of Zuckerkandl to develop, and differed slightly compared to radiographic methods. The majority of dm1 protoconid cuspal (occlusal region) enamel formed before birth. The dm2 entoconid enamel formed mainly after birth. Birth reduced daily enamel secretion rates, changed the visibility of incremental markings, and disrupted enamel growth for 3 to 8 days. Findings presented here can contribute to age‐at‐death estimates for human infants aged 13‐postnatal months or less, and should facilitate comparisons of primate deciduous incremental enamel development in an evolutionary context. Regression equations are included so that cuspal formation time can be estimated from enamel thickness. Am J Phys Anthropol, 2011. © 2010 Wiley‐Liss, Inc.     

Human–hamadryas baboon (Papio hamadryas) conflict in the Wonchit Valley,South Wollo,Ethiopia

Understanding the extent of human–primate conflict is crucial to the development of conservation and management strategies. We carried out this study in an unprotected area of central Ethiopia to examine the magnitude of human–hamadryas baboon (Papio hamadryas) conflict and to assess the attitude of local farmers towards baboons in Wonchit Valley. In 2014, we interviewed 119 adult respondents using a structured questionnaire. Local farmers considered hamadryas baboons to be the major pest in the area. All respondents reported that hamadryas baboons caused crop raiding and small livestock predation in the region. Respondents reported that a shortage of fruit producing wild trees and ready availability of crops were the main causes of conflict between farmers and hamadryas baboons. We found that hamadryas baboons damaged cereal crops at dusk and dawn during full moonlight, and most (89.9%) respondents claimed that they were not interested in hamadryas baboon conservation. Our results indicate that human–hamadryas baboon conflict has a strongly negative impact on both baboon conservation and local farmers. We suggest that to mitigate the human–hamadryas baboon conflict, job opportunities such as beekeeping should be introduced in the region.