Pig enamel revisited – Incremental markings in enamel of wild boars and domestic pigs

The nature and periodicity of incremental markings in pig enamel is currently debated. To broaden the basis for a correct interpretation of growth marks in pig enamel, we analyzed their periodicity in teeth of wild boars and domestic pigs. For that, the numbers of enamel incremental markings were recorded in ground sections and compared with crown formation times for the respective teeth derived from literature data on tooth development and eruption in Sus scrofa. Our study revealed that laminations with a daily periodicity are the dominant incremental feature of pig enamel. In wild boar M₃s, daily enamel secretion (apposition) rates ranged between a minimum of 6.1?µm in the inner and a maximum of 30.6?µm in the outer enamel.Long-period (supra-daily) incremental markings were present as perikymata at the outer enamel surface (OES). Contrary to the situation in primate enamel, in pig enamel the long-period incremental lines terminating in perikyma grooves were mostly structurally indistinguishable from the daily laminations. Typically, five sub-daily increments were present between successive laminations. The incremental pattern in pig enamel can be misinterpreted if the laminations are mistaken for long-period markings (striae of Retzius) and the sub-daily growth marks for daily prism cross-striations. The findings of the present study demonstrate the critical importance of correctly characterizing the incremental markings and their periodicity in enamel, and caution against an uncritical transfer of the interpretation of the nature of incremental markings in primate enamel to other mammalian taxa.     

Analysis and significance of linear enamel hypoplasia in Plio-Pleistocene hominins

This study of linear enamel hypoplasia (LEH) in Plio-Pleistocene hominins builds on a previous study (Guatelli-Steinberg [2003] Am. J. Phys. Anthropol. 120:309-322) that focused on LEH in early South African hominins. The present study is more comprehensive, encompassing dental specimens of hominins from East Africa as well, including early Homo. As a developmental defect of enamel, LEH is used in anthropological contexts to reveal information about physiological stress. However, intrinsic aspects of enamel development and morphology can affect the expression of LEH, complicating efforts to understand the significance of these defects. In this study, the analysis of LEH is conducted with respect to enamel development and morphology. It is predicted that Paranthropus should have fewer defects on its canine teeth than Australopithecus and Homo, owing to its abbreviated period of enamel formation. This prediction is supported: Paranthropus has statistically significantly fewer defects per canine than Australopithecus and Homo. The previous study demonstrated that despite the wider spacing of perikymata on the teeth of South African Paranthropus, defects on the canine teeth of this genus were not wider than those of Australopithecus. A multiple linear regression analysis in that study, as well as a separate analysis in the present study, indicate that the number of perikymata within defects is a better predictor of defect width than perikymata spacing. In this study, it was additionally found that the average number of perikymata within Australopithecus defects is statistically significantly greater than it is in Paranthropus, thus explaining why Paranthropus defects are not wider than those of Australopithecus. The biological significance of this difference in the number of perikymata within the defects of Australopithecus and Paranthropus is considered in light of several factors, including: 1) the possibility that other intrinsic attributes of enamel morphology may be involved (specifically the faster extension rates of Paranthropus that result in shallower defects), 2) generic differences in the canalization of enamel development, and 3) generic differences in the duration of disruptions to enamel growth.     

Macroscopic and microscopic analyses of linear enamel hypoplasia in Plio-Pleistocene South African hominins with respect to aspects of enamel development and morphology

This study uses macroscopic and microscopic methods to analyze the expression of linear enamel hypoplasia (LEH) in Plio-Pleistocene South African hominins. LEH is a developmental defect of enamel that is used in many anthropological contexts as a physiological stress indicator. Previous research has not settled the question as to whether differences in LEH expression exist between Paranthropus and Australopithecus and if they exist, to what extent these differences might be explained simply by taxonomic differences in enamel development and morphology rather than by differential stress experience. In this study, the analysis of LEH is conducted with respect to differences between Paranthropus and Australopithecus in aspects of enamel development and morphology that are thought to influence LEH expression. Two factors impacting LEH expression are considered: the duration of enamel formation, and the spacing of perikymata. It is predicted that if the first factor strongly influences the expression of LEH, then there should be fewer defects per tooth in Paranthropus because of its abbreviated crown formation spans (and fast extension rates) relative to Australopithecus. It is also predicted that because Australopithecus has more densely packed perikymata in comparable regions of the crown than Paranthropus, this taxon should, on average, have narrower defects than Paranthropus. To address these questions, 200 Australopithecus and 137 Paranthropus teeth were examined for LEH, and the analysis of defect width with respect to perikymata spacing was conducted on tooth impressions examined under a scanning electron microscope using INCA (Oxford Instruments) measurement software. Data support the first prediction: Australopithecus does have significantly more defects per canine tooth than Paranthropus. Data do not support the second prediction in large part because several Australopithecus specimens have wide groove defects in which perikymata are not visible and enamel is irregular. Such wide grooves are not predicted by perikymata spacing such that alternative explanations, including taxonomic differences in ameloblast sensitivity and the duration/severity of disruptions to enamel growth, must be considered.     

Did the lateral enamel of Neandertal anterior teeth grow differently from that of modern humans?

The formation of lateral enamel in Neandertal anterior teeth has been the subject of recent studies. When compared to the anterior teeth of modern humans from diverse regions (Point Hope, Alaska; Newcastle upon Tyne, England; southern Africa), Neandertal anterior teeth appear to fall within the modern human range of variation for lateral enamel formation time. However, the lateral enamel growth curves of Neandertals are more linear than those of these modern human samples. Other researchers have found that the lateral enamel growth curves of Neandertals are more linear than those of Upper Paleolithic and Mesolithic modern humans as well. The statistical significance of this apparent difference between Neandertal and modern human lateral enamel growth curves is analyzed here. The more linear Neandertal enamel growth curves result from the smaller percentage of total perikymata located in the cervical halves of their teeth. The percentage of total perikymata in the cervical halves of teeth is therefore compared between the Neandertal sample (n=56 teeth) and each modern human population sample: Inuit (n=65 teeth), southern African (n=114 teeth), and northern European (n=115 teeth). There are 18 such comparisons (6 tooth types, Neandertals vs. each of the three modern human populations). Eighteen additional comparisons are made among the modern human population samples. Statistically significant differences are found for 16 of the 18 Neandertal vs. modern human comparisons but for only two of the 18 modern human comparisons. Statistical analyses repeated for subsamples of less worn teeth show a similar pattern. Because surface curvature is thought to affect perikymata spacing, we also conducted measurements to assess surface curvature in thirty teeth. Our analysis shows that surface curvature is not a factor in this lateral enamel growth difference between Neandertals and modern humans.     

Accessing Developmental Information of Fossil Hominin Teeth Using New Synchrotron Microtomography-Based Visualization Techniques of Dental Surfaces and Interfaces

Quantification of dental long-period growth lines (Retzius lines in enamel and Andresen lines in dentine) and matching of stress patterns (internal accentuated lines and hypoplasias) are used in determining crown formation time and age at death in juvenile fossil hominins. They yield the chronology employed for inferences of life history. Synchrotron virtual histology has been demonstrated as a non-destructive alternative to conventional invasive approaches. Nevertheless, fossil teeth are sometimes poorly preserved or physically inaccessible, preventing observation of the external expression of incremental lines (perikymata and periradicular bands). Here we present a new approach combining synchrotron virtual histology and high quality three-dimensional rendering of dental surfaces and internal interfaces. We illustrate this approach with seventeen permanent fossil hominin teeth. The outer enamel surface and enamel-dentine junction (EDJ) were segmented by capturing the phase contrast fringes at the structural interfaces. Three-dimensional models were rendered with Phong’s algorithm, and a combination of directional colored lights to enhance surface topography and the pattern of subtle variations in tissue density. The process reveals perikymata and linear enamel hypoplasias on the entire crown surface, including unerupted teeth. Using this method, highly detailed stress patterns at the EDJ allow precise matching of teeth within an individual’s dentition when virtual histology is not sufficient. We highlight that taphonomical altered enamel can in particular cases yield artificial subdivisions of perikymata when imaged using X-ray microtomography with insufficient resolution. This may complicate assessments of developmental time, although this can be circumvented by a careful analysis of external and internal structures in parallel. We further present new crown formation times for two unerupted canines from South African Australopiths, which were found to form over a rather surprisingly long time (> 4.5 years). This approach provides tools for maximizing the recovery of developmental information in teeth, especially in the most difficult cases.     

华南化石猩猩前部牙齿釉面横纹与牙冠形成时间研究

釉面横纹的分布与数目可以反映牙齿生长发育的时间和速率变化, 在化石研究中能为复原个体生活史提供重要依据。本研究运用扫描电子显微镜观察华南化石猩猩门齿、犬齿釉面横纹分布与数目, 并估算门齿和犬齿牙冠形成时间, 结果如下: 牙冠从牙尖至牙颈方向釉面横纹分布密度有疏密变化, 牙尖釉面横纹密度小于10条/mm, 中间至牙颈釉面横纹密度较尖部增大, 大约10-15条/mm; 犬齿釉面横纹数目多于门齿, 雄性犬齿釉面横纹数目多于雌性; 根据釉面横纹计数及其生长周期的组织切片观察结果, 估算门齿牙冠形成时间大约为2.97-6.66年, 犬齿雄性长于雌性, 分别为6.25-11.31年和4.28-7.29年。与一些古猿、早期人类、现代人以及现生大猿比较, 华南化石猩猩釉面横纹整体密度稍大于南方古猿和傍人, 小于黑猩猩、大猩猩、现代人和禄丰古猿; 除侧门齿外, 华南化石猩猩釉面横纹数目明显多于南方古猿、傍人和现代人, 与大猩猩接近; 华南猩猩前部牙齿牙冠形成时间与现生大猿、禄丰古猿差别不大, 与现生猩猩最相近, 长于南方古猿和傍人。     

禄丰古猿牙齿釉质发育不全的观察研究

对出自禄丰石灰坝的26个禄丰古猿下颌齿列的246枚恒齿进行了观察研究,发现禄丰古猿具有普遍的带状釉质发育不全（LEH）现象,个体LEH比例为100%,恒齿LEH比例为85%。乳齿几乎没有LEH现象,第一恒臼齿的LEH比例也很低仅57%。根据牙齿萌出顺序及现代大猿的牙齿发育年龄特征,作者推断2—3岁之前的幼儿古猿很少出现釉质发育不全现象,这可能与母体的营养关照有关。禄丰古猿的LEH的发生频率具有明显的季节性,结合中新世晚期气候变化特征、古猿的生态环境、生活习性及食性特征分析,作者推测：季节性营养不良可能是造成禄丰古猿釉质发育不全的主要原因。     

Perikymata spacing and distribution on hominid anterior teeth

We documented the spacing and distribution of perikymata on the buccal enamel surface of fossil hominin anterior teeth with reference to a sample of modern human and modern great ape teeth. A sample of 27 anterior teeth attributed to Australopithecus (5 to A. afarensis, 22 to A. africanus) and of 33 attributed to Paranthropus (6 to P. boisei, and 27 to P. robustus) were replicated and sputter-coated with gold to enable reflected light microscopy of their surface topography. Anterior teeth were then divided into 10 equal divisions of buccal crown height. The total perikymata count in each division of crown height was recorded using a binocular microscope fitted with a vernier micrometer eyepiece. Then the mean number of perikymata per millimeter was calculated for each division. Similar comparative data for a modern sample of 115 unworn human anterior teeth and 30 African great ape anterior teeth were collected from ground sections. Perikymata counts in each taxon (together with either known or presumed periodicities of perikymata) were then used to estimate enamel formation times in each division of crown height, for all anterior tooth types combined. The distributions of these estimates of time taken to form each division of crown height follow the same trends as the actual perikymata counts and differ between taxa in the same basic way. The distinction between modern African great apes and fossil hominins is particularly clear. Finally, we calculated crown formation times for each anterior tooth type by summing cuspal and lateral enamel formation times. Estimates of average crown formation times in australopiths are shorter than those calculated for both modern human and African great ape anterior teeth. The data presented here provide a better basis for exploring differences in perikymata spacing and distribution among fossil hominins, and provide the first opportunity to describe four specimens attributed to Homo in this context. Preliminary data indicate that differences may exist among the species attributed to early Homo, especially between Homo ergaster and Homo rudolfensis on the one hand, and Homo habilis sensu strico on the other.     

Variation in perikymata counts between repetitive episodes of linear enamel hypoplasia among orangutans from Sumatra and Borneo

The goal of this study is to evaluate whether repetitive linear enamel hypoplasia (rLEH) in apes is ecologically informative. LEH, which appears as grooves of thinner enamel often caused by malnutrition and/or disease, is a permanent record of departures from developmental homeostasis in infant and juvenile apes. Orangutans were selected for the study as they are a threatened species, have a remarkably high prevalence of rLEH, and because Sumatra is deemed a better habitat for orangutans than is Borneo, facilitating an ecological comparison. Objectives are to determine: a) whether periodicity of rLEH in orangutans corresponds to monsoon‐mediated cycles in precipitation or food; and b) whether patterning of rLEH supports the view that Borneo is an inferior habitat. This study compares the counts of perikymata between adjacent LEH from 9 Sumatran and 26 Bornean orangutans to estimate the periodicity of rLEH. A total of 131 nonredundant inter‐LEH perikymata counts were transformed to natural log values to reveal clusters of counts in a multiplicative series. Using a value of 10 days to form one perikyma, rLEH tends to recur semiannually in both populations. However, Sumatran orangutans show significantly fewer semiannual intervals and more annually recurring episodes. Bornean orangutans show mostly semiannual intervals and are more variable in inter‐LEH perikymata counts. It is concluded that: a) developmental conditions for infant orangutans in Sumatra protect them somewhat from seasonal and environmental variation; b) temporal patterning of rLEH indicates that Borneo is the poorer habitat for orangutans; and c) the study of rLEH can be ecologically informative. Am J Phys Anthropol 154:125–139, 2014. © 2014 Wiley Periodicals, Inc.     

Missing defects? A comparison of microscopic and macroscopic approaches to identifying linear enamel hypoplasia

Linear enamel hypoplasia (LEH), the presence of linear defects of dental enamel formed during periods of growth disruption, is frequently analyzed in physical anthropology as evidence for childhood health in the past. However, a wide variety of methods for identifying and interpreting these defects in archaeological remains exists, preventing easy cross‐comparison of results from disparate studies. This article compares a standard approach to identifying LEH using the naked eye to the evidence of growth disruption observed microscopically from the enamel surface. This comparison demonstrates that what is interpreted as evidence of growth disruption microscopically is not uniformly identified with the naked eye, and provides a reference for the level of consistency between the number and timing of defects identified using microscopic versus macroscopic approaches. This is done for different tooth types using a large sample of unworn permanent teeth drawn from several post‐medieval London burial assemblages. The resulting schematic diagrams showing where macroscopic methods achieve more or less similar results to microscopic methods are presented here and clearly demonstrate that “naked‐eye” methods of identifying growth disruptions do not identify LEH as often as microscopic methods in areas where perikymata are more densely packed. Am J Phys Anthropol 153:463–472, 2014. © 2013 Wiley Periodicals, Inc.     

Prevalence and the duration of linear enamel hypoplasia: a comparative study of Neandertals and Inuit foragers

As a dental indicator of generalized physiological stress, enamel hypoplasia has been the subject of several Neandertal studies. While previous studies generally have found high frequencies of enamel hypoplasia in Neandertals, the significance of this finding varies with frequencies of enamel hypoplasia in comparative samples. The present investigation was undertaken to ascertain if the enamel hypoplasia evidence in Neandertals suggests a high level of physiological stress relative to a modern human foraging group, represented here by an archaeological sample of Inuit from Point Hope, Alaska. Unlike previous studies, this study focused specifically on linear enamel hypoplasia (LEH), emphasizing systemic over localized causes of this defect by considering LEH to be present in an individual only if LEH defects occur on two anterior teeth with overlapping crown formation periods. Moreover, this study is the first to evaluate the average growth disruption duration represented by these defects in Neandertals and a comparative foraging group. In the prevalence analysis, 7/18 Neandertal individuals (from Krapina and southern France) and 21/56 Neandertal anterior teeth were affected by LEH, or 38.9% and 37.5% respectively. These values do not differ significantly from those of the Inuit sample in which 8/21, or 38.1% of individuals, and 32/111, or 28.8% of anterior teeth were affected. For the growth disruption duration analysis, 22 defects representing separate episodes of growth disruption in Neandertals were compared with 22 defects in the Inuit group using three indicators of duration: the number of perikymata (growth increments) in the occlusal walls of LEH defects, the total number of perikymata within them, and defect width. Only one indicator, the total number of perikymata within defects, differed significantly between the Inuit and Neandertal groups (an average of 13.4 vs. 7.3 perikymata), suggesting that if there is any difference between them, the Inuit defects may actually represent longer growth disruptions than the Neandertal defects. Thus, while stress indicators other than linear enamel hypoplasia may eventually show that Neandertal populations were more stressed than those of modern foragers, the evidence from linear enamel hypoplasia does not lend support to this idea.     

“Missing perikymata”—fact or fiction? A study on chimpanzee (Pan troglodytes verus) canines

Recently, a lower than expected number of perikymata between repetitive furrow‐type hypoplastic defects has been reported in chimpanzee canines from the Fongoli site, Senegal (Skinner and Pruetz: Am J Phys Anthropol 149 (2012) 468–482). Based on an observation in a localized enamel fracture surface of a canine of a chimpanzee from the Taï Forest (Ivory Coast), these authors inferred that a nonemergence of striae of Retzius could be the cause for the “missing perikymata” phenomenon in the Fongoli chimpanzees. To check this inference, we analyzed the structure of outer enamel in three chimpanzee canines. The teeth were studied using light‐microscopic and scanning‐electron microscopic techniques. Our analysis of the specimen upon which Skinner and Pruetz (Am J Phys Anthropol 149 (2012) 468–482) had made their original observation does not support their hypothesis. We demonstrate that the enamel morphology described by them is not caused by a nonemergence of striae of Retzius but can be attributed to structural variations in outer enamel that result in a differential fracture behavior. Although rejecting the presumed existence of nonemergent striae of Retzius, our study provided evidence that, in furrow‐type hypoplastic defects, a pronounced tapering of Retzius increments can occur, with the striae of Retzius forming acute angles with the outer enamel surface. We suggest that in such cases the outcrop of some striae of Retzius is essentially unobservable at the enamel surface, causing too low perikymata counts. The pronounced tapering of Retzius increments in outer enamel presumably reflects a mild to moderate disturbance of the function of late secretory ameloblasts. Am J Phys Anthropol 157:276–283, 2015. © 2015 Wiley Periodicals, Inc.     

Linear enamel hypoplasia in gibbons (Hylobates lar carpenteri)

This study describes the expression of linear enamel hypoplasia (LEH), a sensitive dental indicator of physiological stress, in Thailand gibbons (Hylobates lar carpenteri). Previous studies of enamel hypoplasia in hominoids have focused on great apes, with little attention given to the expression of this stress indicator in gibbons. In that gibbons differ from both monkeys and great apes in numerous life history features, LEH expression in gibbons might be expected to show significant differences from both. In this study, 92 gibbon specimens from two sites in Thailand were compared with several samples of monkeys and great apes in their expression of LEH. The intertooth distribution of LEH in gibbons was compared to that of chimpanzees and rhesus monkeys. Gibbon populations from both sites exhibit LEH frequencies intermediate between those of the monkey samples, in which LEH prevalence is usually low, and those of the great ape samples, in which LEH prevalence is high. Gibbons differ significantly from monkeys, but not great apes, in the number of individuals whose teeth record multiple stress events. Multiple episodes of stress are rarely recorded in the teeth of monkeys, while multiple stress events occur with higher frequency in gibbons and great apes. Taxonomic variation in the duration of crown formation, the prominence and spacing of perikymata on dental crowns, life history features, and/or experience of physiological stress may explain these patterns. The intertooth distribution of LEH in gibbons is, for different reasons, unlike that of either chimpanzees or rhesus monkeys. The mandibular canines of gibbons have significantly more LEH than any of their other teeth. Aspects of crown morphology, perikymata prominence/spacing, enamel thickness, and crown formation spans are potential causes of taxonomic variation in the intertooth distribution of LEH.     

Reconstruction of periodicity of repetitive linear enamel hypoplasia from perikymata counts on imbricational enamel among dry‐adapted chimpanzees (Pan troglodytes verus) from Fongoli,Senegal

Periodicity of repetitive linear enamel hypoplasia (rLEH) in apes from high latitudes with single wet and dry seasons annually has not been described. We reconstruct periodicity and duration of rLEH in canine teeth from three recently deceased chimpanzees from Fongoli, Senegal with a marked seven‐month dry season. High‐resolution dental molds were taken in the field for magnified imaging with digital microscopy. Photomontages allowed counting of perikymata between episodes of rLEH for reconstruction of periodicity and duration of physiological stress. Where rLEH spans the imbricational enamel, the number of events is consistent with years required to form canine imbricational enamel; i.e., periodicity of rLEH seems circannual. We predicted perikymata counts between rLEH events ranging from 52 to 61 based on reported “long counts” of 7–6 days. Counts ranged from 29.5 to 44, individual mean of 36.7. This discrepancy could be explained by recurrent stress with a periodicity of 7.2–8.4 months, or by long counts of 10 days per stria. Neither is supported in the literature. Since we find evidence of rLEH with circannual periodicity, we postulate the existence of non‐emergent imbricational striae. Based on evidence that stress at Fongoli recurs annually, we reconstruct stress duration of 2–3 months, longer than reported for chimpanzees living in other habitats, which we attribute to heat stress and food shortage near shrinking waterholes. We conclude that canine teeth from a small mortality cohort of chimpanzees at Fongoli preserve a faithful record of dry season stress in an extreme environment. Am J Phys Anthropol, 2012. © 2012 Wiley Periodicals, Inc.     

Plasticity and constraint in response to early‐life stressors among late/final jomon period foragers from Japan: Evidence for life history trade‐offs from incremental microstructures of enamel

This study evaluates two hypotheses that address how Late/Final Jomon period people responded to early‐life stress using linear enamel hypoplasia (LEH) and incremental microstructures of enamel. The first hypothesis predicts that Jomon people who experienced early‐life stressors had greater physiological competence in responding to future stress events (predictive adaptive response). The second hypothesis predicts that Jomon people traded‐off in future growth and maintenance when early investment in growth and survival was required (plasticity/constraint). High resolution tooth impressions were collected from intact, anterior teeth and studied under an engineer's measuring microscope. LEH were identified based on accentuated perikymata and depressions in the enamel surface profile. Age of formation for each LEH was estimated by summing counts of perikymata and constants associated with crown initiation and cuspal enamel formation times. The relationship between age‐at‐first‐defect formation, number of LEH, periodicity between LEH, and mortality was evaluated using multiple regression and hazards analysis. A significant, positive relationship was found between age‐at‐death relative to age‐at‐first‐defect formation and a significant, negative relationship was found between number of LEH relative to age‐at‐first‐defect formation. Individuals with earlier forming defects were at a significantly greater risk of forming defects at later stages of development and dying at younger ages. These results suggest that Late/Final Jomon period foragers responded to early‐life stressors in a manner consistent with the plasticity/constraint hypothesis of human life history. Late/Final Jomon period individuals were able to survive early‐life stressors, but this investment weakened responses to future stress events and exacerbated mortality schedules. Am J Phys Anthropol 155:537–545, 2014. © 2014 Wiley Periodicals, Inc.     

Estimating striae of Retzius periodicity nondestructively using partial counts of perikymata

Accurate age estimations for enamel formation and the timing of enamel hypoplasia have traditionally only been available through histological analyses of dental thin sections, which is a difficult and destructive process. However, an association between striae of Retzius periodicity, crucial for accurate aging, and the total number of striae in imbricational enamel has been reported in the literature. This means periodicity can be estimated nondestructively but is reliant on all perikymata being visible along the crown surface. Therefore, crowns with worn or damaged surfaces may not be able to be assessed, potentially limiting sample sizes. We tested this relationship in a modern New Zealand sample and investigated whether reliable associations might be identified using only partial perikymata counts from the cervical half of the crown. Using mandibular canines (n = 11), the distribution of perikymata per decile was recorded using high definition replica surfaces. Thin sections of the same crowns were used to assess periodicity histologically along with striae of Retzius distributions. A strong correlation between total striae numbers and periodicity was also identified in our sample. Furthermore, we report strong correlations that allow periodicity to be estimated from perikymata counts using only 10% of crown height when certain deciles are used. Based on these findings, we propose a simple matrix that can be developed for nondestructively estimating periodicity based on the range of perikymata counts in the sixth to ninth deciles. Am J Phys Anthropol 154:251–258, 2014. © 2014 Wiley Periodicals, Inc.     

Brief communication: The distribution of perikymata on Qafzeh anterior teeth

Recent studies have suggested that Neandertals and modern humans differ in the distribution of perikymata (enamel growth increments) over their permanent anterior tooth crowns. In modern humans, perikymata become increasingly more compact toward the cervix than they do in Neandertals. Previous studies have suggested that a more homogeneous distribution of perikymata, like that of Neandertals, characterizes the anterior teeth of Homo heidelbergensis and Homo erectus as well. Here, we investigated whether Qafzeh anterior teeth (N = 14) differ from those of modern southern Africans, northern Europeans, and Alaskans (N = 47–74 depending on tooth type) in the percentage of perikymata present in their cervical halves. Using the normally distributed modern human values for each tooth type, we calculated Z‐scores for the 14 Qafzeh teeth. All but two of the 14 Qafzeh teeth had negative Z‐scores, meaning that values equal to these would be found in the bottom 50% of the modern human samples. Seven of the 14 would be found in the lowest 5% of the modern human distribution. Qafzeh teeth therefore appear to differ from those of modern humans in the same direction that Neandertals do: with generally lower percentages of perikymata in their cervical regions. The similarity between them appears to represent the retention of a perikymata distribution pattern present in earlier members of the genus Homo, but not generally characteristic of modern humans from diverse regions of the world. Am J Phys Anthropol 2010. © 2009 Wiley‐Liss, Inc.     

Enamel incremental periodicity in the pig-tailed macaque: A polychrome fluorescent labeling study of dental hard tissues

Bromage and Dean originally outlined a nondestructive method for the study of enamel formation and concluded that early hominids resembled the extant apes more closely than they did modern humans in their rates of growth and maturation. The method used assumed that an enamel circadian rhythmicity was referable to a longer near-weekly period represented by perikymata (periodic surface growth features). This assumption became a matter of debate and discussion. In this study, developing teeth in Macaca nemestrina were labeled with polychrome fluorescent dyes. Examination of the distribution of these dyes in two sectioned teeth provides experimental confirmation of enamel circadian periodicity.     

Enamel extension rate patterns in modern human teeth: Two approaches designed to establish an integrated comparative context for fossil primates

Enamel extension rates (EERs), the rates at which ameloblasts differentiate, determine how fast tooth crowns grow in height. Studies of fossil primate (including hominin) enamel microstructure usually focus on species differences in enamel formation time, but they have also begun to address species-level variation in enamel extension rates. To improve our ability to compare EERs among primate species, a better understanding how EERs vary within species is necessary. Using a large and diverse modern human histological sample, we find that initial EERs and patterns of EER change along the enamel-dentine junction (EDJ) vary in relation to EDJ length. We also find that enamel formation time varies in relation to EDJ length, but that it does so independently of initial EERs. These results suggest that EDJ length variation within a species sample can affect interspecific comparisons not only of EERs but also of enamel formation times. Additionally, these results lend within-species support to the hypothesis, based on comparisons among hominin species, that EERs and crown formation times can vary independently (Dean, 2009). In a second approach, we analyzed EER changes specifically in the lateral enamel of two modern human population samples as these changes relate to the distribution of perikymata. As surface manifestations of internal enamel growth increments, perikymata provide a valuable source of information about enamel growth in fossils. We find that EER declines in the lateral enamel are associated with an increase in perikymata density from first to last-formed lateral enamel. Moreover, variation in the extent of EER decline among individuals is associated with variation in the distribution of perikymata along their enamel surfaces. These latter findings suggest that the distribution of perikymata on the enamel surface provides information about rates of EER decline in lateral enamel, at least in modern humans.     

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.