Perikymata Counts Research Articles

Linear enamel hypoplasia in Homo naledi reappraised in light of new Retzius periodicities.

Among low-latitude apes, developmental defects of enamel often recur twice yearly, linkable to environmental cycles. Surprisingly, teeth of Homo naledi from Rising Star in South Africa (241-335 kya), a higher latitude site with today a single rainy season, also exhibit bimodally distributed hypoplastic enamel defects, but with uncertain timing and etiology. Newly determined Retzius periodicities for enamel formation in this taxon enable a reconstruction of the temporal patterning of childhood stress. Using high resolution casts of 31 isolated anterior teeth from H. naledi, 82 enamel defects (linear enamel hypoplasia [LEH]) were identified. Seventeen teeth are assigned to three individuals. Perikymata in the occlusal wall of enamel furrows and between the onsets of successive LEH were visualized with scanning electron microscopy and counted. Defects were measured with an optical scanner. Conversion of perikymata counts to estimates of LEH duration and inter-LEH interval draws upon Retzius periodicities of 9 and 11 days. Anterior teeth record more than a year of developmental distress, expressed as two asymmetric intervals centered on 4.5 and 7.5 months bounded by three LEH. Durations, also, show bimodal distributions, lasting 3 or 12 weeks. Short duration LEH are more severe than long duration. Relative incisor/canine rates of formation are indistinguishable from modern humans. We invoke a disease and dearth model, with short episodes of distress reflecting onset of disease in young infants, lasting about 3 weeks, followed by a season of undernutrition, possibly intensified by secondary plant compounds, spanning about 12 weeks, inferably coincident with austral winter.

Short and long period growth markers of enamel formation distinguish European Pleistocene hominins

Characterizing dental development in fossil hominins is important for distinguishing between them and for establishing where and when the slow overall growth and development of modern humans appeared. Dental development of australopiths and early Homo was faster than modern humans. The Atapuerca fossils (Spain) fill a barely known gap in human evolution, spanning ~1.2 to ~0.4 million years (Ma), during which H. sapiens and Neandertal dental growth characteristics may have developed. We report here perikymata counts, perikymata distributions and periodicities of all teeth belonging to the TE9 level of Sima del Elefante, level TD6.2 of Gran Dolina (H. antecessor) and Sima de los Huesos. We found some components of dental growth in the Atapuerca fossils resembled more recent H. sapiens. Mosaic evolution of perikymata counts and distribution generate three distinct clusters: H. antecessor, Sima de los Huesos and H. sapiens.

Insights on patterns of developmental disturbances from the analysis of linear enamel hypoplasia in a Neolithic sample from Liguria (northwestern Italy)

ObjectiveTo assess developmental disturbances through the analysis of linear enamel hypoplasia (LEH) frequency and to infer environmental stress and life history within Neolithic communities from Liguria (Italy). Materials43 unworn/minimally worn permanent anterior teeth of 13 individuals recovered from nearby caves and dated to c. 4800−4400 cal. BCE. MethodsLEH defects were identified with high-resolution macrophotos of dental replicas, age at LEH was calculated via perikymata counts. LEH defects matched between two or more teeth were considered as systemic disturbances. LEH frequency by age classes was analyzed via GLZ and Friedman ANOVA. ResultsNumber of matched defects per individual range between 2–12. The mean LEH per individual was highest in the 2.5–2.99 age category, with a significant increase relative to earlier growth stages, followed by a decline. ConclusionLEH may reflect life-history in the local ecology of Neolithic Liguria, where several individuals with osteoarticular tuberculosis have been recorded. Disease burden may have triggered developmental disturbances around the time of weaning. Age at first defect was negatively correlated with age at death and positively with the total number of defects, suggesting that early stress may have affected survivorship. SignificanceThe study contributes to the reconstruction of ecological pressures among Neolithic people of Liguria, and informs on environmental challenges during the Neolithic adaptive expansion. LimitationsThe visual examination of macrophotos is prone to observer error; mid-crown tends to display more visible LEH due to tooth architecture. Suggestions for further researchApply different quantitative methods to examine severity and duration of disturbances.

Developmental stress in South African hominins: Comparison of recurrent enamel hypoplasias in Australopithecus africanus and Homo naledi

Discovery of a new hominin (Homo naledi) in the same geographical area as Australopithecus africanus creates the opportunity to compare developmental dental stress in higher latitude hominins with low that in latitude apes, among whom repetitive linear enamel hypoplasia (rLEH) recurs seasonally at about 6 or 12 months. In contrast to equatorial Africa, a single rainy/dry cycle occurs annually in non-coastal southern Africa. It is predicted that LEH will recur annually but not differ in duration between ancient and more recent hominins. Data were collected from epoxy casts of anterior teeth attributed to H. naledi (18 incisors, 13 canines) and A. africanus (29 incisors, 8 canines) using a digital microscope, surface scanner and scanning electron microscope. The location, number, width, depth and distance between defects (including perikymata counts and spatial measurements) of 136 LEH events were compared among crown moieties (deciles 4–6 and 7–9), tooth types and taxa. Enamel defects are concentrated in the cervical half of anterior crowns, and in similar numbers in each taxon. Contrary to expectations, H. naledi show bimodal LEH durations reconstructed at about 2 and 8 weeks compared to just 4 weeks in A. africanus. Both taxa show bimodally recurrent episodes of LEH centring on 2 and, more commonly and severely, 6 months. A combination of two independent annual stressor types, one disease and one seasonal, could explain the observations. These estimations of duration and recurrence of developmental stress require evaluation using actual perikymata periodicity for H. naledi and more refined understanding of palaeoenvironments for both taxa.
 Significance: 
 
 Seasonal stress is a central concern in the biological and health sciences. Because of the innate way that enamel is deposited, the timing of stress in the childhood of apes, modern humans and their fossil ancestors can be measured with a precision of about 1 week.
 Application of this method to South African Pliocene Australopithecus africanus and Mid-Pleistocene Homo naledi reveals that, unexpectedly, both forms show semi-annual stress – a finding that is tentatively attributed to two independent annual stressors, possibly disease and malnutrition.

Applying standard perikymata profiles to Pongo pygmaeus canines to estimate perikymata counts between linear enamel hypoplasias

Recently, studies have interpreted regular spacing and average number of perikymata between dental enamel defects in orangutans to reflect seasonal episodes of physiological stress. To estimate the amount of time between developmental defects (enamel hypoplasia), studies have relied on perikymata counts. Unfortunately, perikymata are frequently not continuously visible between defects, significantly reducing data sets. A method is presented here for estimating the number of perikymata between defects using standard perikymata profiles (SPP) that allow the number of perikymata between all pairs of defects across a tooth to be analyzed. The SPP method should allow the entire complement of defects to be analyzed within the context of an individual's crown formation time. The average number of perikymata were established per decile and charted to create male and female Pongo pygmaeus SPPs. The position of the beginning of each defect was recorded for lower canines from males (n = 6) and females (n = 17). The number of perikymata between defects estimated by the SPP was compared to the actual count (where perikymata were continuously visible). The number of perikymata between defects estimated by the SPPs was accurate within three perikymata and highly correlated with the actual counts, significantly increasing the number of analyzable defect pairs. SPPs allow all defect pairs to be included in studies of defect timing, not just those with continuously visible perikymata. Establishing an individual's entire complement of dental defects makes it possible to calculate the regularity (and potential seasonality) of defects.

Lateral enamel growth in human incisors from Çatalhöyük in Turkey

Whereas the differences in lateral enamel growth between fossil and modern populations have been well documented in recent years, few studies report on the variability in perikymata counts and distribution between modern human populations. There is a need for information on modern human populations from a wide range of geographical regions and archaeological populations to determine whether existing patterns are representative. The aim of this paper is to document enamel surface microstructures in human teeth from a previously unknown region and time period comprehensively. Perikymata counts and distribution are assessed in a large sample of relatively unworn permanent incisors from the mid-Holocene site of Çatalhöyük in Turkey. All four incisor types exhibit total perikymata counts that are intermediate between values for modern samples from northern Europe and South Africa. The perikymata distribution followed the modern human pattern of a marked decrease in spacing in the cervical half of the crown. The existence of regional differences in perikymata number and distribution demonstrates the importance of documenting enamel microstructures in a wider range of modern human populations, both geographically and chronologically.

Perikymata distribution on anterior teeth of Miocene Lufengpithecus lufengensis from Yunnan, Southern China.

The present study investigated the distribution of perikymata on anterior teeth of Miocene Lufengpithecus lufengensis so as to broaden the comparative data of developmental variation within and among hominoids. We also compared perikymata-spacing pattern of Lufengpithecus lufengensis with hominins and extant African great apes to understand the implication of dental development. A total of 30 anterior teeth (including 6 I1, 10 I2, and 14 C) of Lufengpithecus lufengensis were examined using a scanning electron microscope and Keyence VHX-600EOS digital microscope to document the number and distribution of perikymata on their labial surfaces. The labial crown height of each tooth was divided into 10 equal deciles and the total perikymata number in each decile was recorded. The mean number of perikymata per millimeter was then calculated for each decile. SPSS statistical software was used to perform analyses of these data, including t-tests for sexual dimorphism and plots showing the perikymata distribution in Lufengpithecus lufengensis. Perikymata counts of Lufengpithecus lufengensis in the first three deciles are fewer than the remaining deciles, and with perikymata becoming increasingly more closely packed as growth progresses from cusp to cervix, but decrease in density in the cervical decile. Besides, total labial perikymata counts of canines tend to display very significant sexual dimorphism. Lufengpithecus lufengensis anterior teeth are more similar in their distribution of labial perikymata to those of Australopithecus than those of other hominins and extant African great apes from previous studies.

Perikymata numbers and enamel extension rates in the incisors of three archaeological modern human populations from two caves located in Spain: Maltravieso Cave (Cáceres) and Mirador Cave (Burgos)

Abstract A number of authors have studied the variability of total perikymata counts on permanent incisors in different modern human populations, finding that some populations show a significantly lower number of perikymata than others. However, little is known about the overall variability of these traits in archaeological populations of modern humans. Our aim was to broaden the available data on total perikymata counts on incisors, and to further discuss enamel extension rate variability in modern human incisors. Our sample consisted of 15 incisors from three different archaeological populations belonging to the Holocene: two populations from Mirador Cave (Sierra de Atapuerca, Burgos) assigned to two different chronological periods, and a population from Maltravieso Cave (Caceres). We refer to these populations as the MTV–MIR sample. Perikymata were counted from several images obtained using an environmental scanning electron microscope (ESEM). Our results suggest the total number of perikymata of the MTV–MIR incisors fall most comfortably within the distribution of counts reported for modern Europeans and Inuit rather than those representing southern African samples of incisors. Furthermore, the percentage of the perikymata numbers in the last five deciles into which the crowns were divided (the cervical half) did not show statistically significant differences when compared to the other modern human populations. This suggests that enamel extension rates among modern human incisors share a common pattern, which might differ from that present in other species. More data from other modern and archaeological sub-Saharan African samples are needed to test whether low perikymata counts are exclusive to the southern African group or are indeed truly representative of sub-Saharan African populations as a whole today and in the past.

"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.

Chronology and periodicity of linear enamel hypoplasia among Late/Final Jomon period foragers: Evidence from incremental microstructures of enamel

This study estimates age-at-defect formation and periodicity of linear enamel hypoplasia (LEH) using incremental microstructures of enamel. Results are compared to previous studies and between sites from different regions of Japan (Costal Honshu, Inland Honshu, and Hokkaido). High resolution impressions were collected from the dental remains of 32 individuals from nine archaeological sites. Casts were produced from these impressions and studied under an engineer's measuring microscope. LEH were identified based on enamel surface depressions and accentuated perikymata. Age-at-defect formation was estimated using histological methods. LEH periodicity was estimated using counts of perikymata between defects. Age-at-defect formation ranged between 1.1 and 5.8 years, while interquartile ranges were between 2.9 and 4.1 years. LEH periodicity ranged between 0.1 and 1.7 years, with an average of 0.2 years. There were no significant differences in average age-at-defect formation between regions. Significantly higher LEH periodicities were observed among Jomon foragers from Hokkaido and Inland Honshu compared to Coastal Honshu. Earlier ages-at-defect formation and lower stress periodicities were found by this study compared to earlier research. These differences are attributed to the inclusion of individuals with intact tooth crowns and use of objective, microscopic methods to identify LEH. The interquartile ranges for ages-at-defect formation are consistent with isotopically estimated ages for reductions in breast milk consumption. The lack of differences in average age-at-defect formation between geographic groups may reflect similar environmental stress burdens associated with this process. Comparatively shorter intervals between defects among Late/Final Jomon foragers from Coastal Honshu suggest elevated ecological stress burdens among this sample.

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.

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.

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.

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.

Identification of a single birth cohort in Kenyapithecus kizili and the nature of sympatry between K. kizili and Griphopithecus alpani at Paşalar

The sample of the less common hominoid species at Paşalar, Kenyapithecus kizili, is characterized by a number of unusual attributes. All ten of the upper central incisors attributed to this species show a distinct, identical pattern of two linear enamel hypoplasias. The two hypoplasias occur on the same portion of the labial crown face, revealing that the two hypoplasia-causing events occurred at the same stage of development in all individuals. The morphology of the two hypoplasias and the amount of time between them, as determined by both their separation and counts of perikymata, are also the same on all teeth. In addition, all of the approximately 70 teeth assigned to K. kizili appear to come from young adults based on degrees of wear; there are no younger or older individuals (diagnostic morphology at most tooth positions would be evident even with heavy wear). Thus, all of the K. kizili individuals (minimum number of individuals is nine: seven males, two females) appear to have died at essentially the same age. It is concluded that the most plausible interpretation of all these features is that the incisor hypoplasias were caused by the same two events in all the K. kizili individuals and that these individuals therefore represent a single birth cohort. As such, and because they died at essentially the same age, they would also have died at the same time, which is consistent with the catastrophic nature of the Paşalar deposits. The number of coincidences needed to explain all of the attributes of the K. kizili sample if these animals were born in, and died in, different years seems highly improbable. Moreover, the lack of a typical age-class structure for the K. kizili sample, or any age-class structure at all beyond the one age class of young adult, strongly suggests that the species was not resident in the area that contributed to the Paşalar accumulation, and that K. kizili was not permanently sympatric with the other Paşalar hominoid, Griphopithecus alpani. Rather, the nine K. kizili individuals must have been transients in, or recent immigrants to, the area at the time of the events that led to the formation of the site. Recent observations on social associations in male chimpanzees offer at least a possible interpretive framework to explain this unprecedented occurrence in the primate fossil record.

Variation in modern human premolar enamel formation times: Implications for Neandertals

A recent study demonstrated that variation in enamel cap crown formation in the anterior teeth is greater than that in the molars from two geographically distinct populations: native indigenous southern Africans and northern Europeans. Eighty southern African and 69 northern European premolars (P3 and P4) were analyzed in the present study. Cuspal, lateral, and total enamel formation times were assessed. Although cuspal enamel formation times were not consistently different between the two populations, both lateral and total enamel formation times generally were. Bonferroni-corrected t-tests showed that southern Africans had significantly shorter lateral enamel formation time for five of the six cusps, as well as significantly shorter total enamel formation time for these same cusps. An analysis of covariance performed on the lingual cusps of the upper third and fourth premolars showed that differences in enamel formation times between these populations remained when crown height was statistically controlled. A further goal of this study was to ascertain, based on perikymata counts, what Neandertal periodicities would have to be in order for their teeth to have lateral enamel formation times equivalent to either southern Africans or northern Europeans. To this end, perikymata were counted on 32 Neandertal premolars, and the counts were inserted into regression formulae relating perikymata counts to periodicity for each population and each tooth type. Neandertal enamel formation times could be equivalent to those of southern Africans or northern Europeans only if their hypothetical periodicities fall within the range of periodicities for African apes and modern humans (i.e., 6–12 days). The analysis revealed that both populations could encompass Neandertal timings, with hypothetical periodicities based on the southern African population necessitating a lower range of periodicity (6–8 days) than those based on the northern European population (8–11 days).

Age at first molar emergence in Lufengpithecus lufengensis and its implications for life-history evolution

The late Miocene hominoid Lufengpithecus from Yunnan Province, China, is crucial for understanding hominoid evolution in Asia. Given that age at first permanent molar emergence is a key life-history trait in primates, the present study determined the age at death of the Lufengpithecus lufengensis juvenile PA868, which was in the process of erupting its first molar. Using a perikymata periodicity of 7–11 days, along with estimation of cusp formation time and the postnatal delay of crown mineralization, perikymata counts obtained from the permanent central incisor and canine germs indicate that the age at death of PA868 was 2.4–4.5 years based on the central incisor germ, and 2.5–4.7 years based on the canine germ. The age at the first molar emergence was actually slightly younger (by about 0.3 years), as demonstrated by tiny wear facets on this tooth, which indicate that gingival emergence had occurred sometime before death. The average age at first molar emergence of Lufengpithecus lufengensis PA868 is estimated to be 3.2–3.3 years, with a range of 2.1–4.4 years. In comparison to extant primates and other fossil hominoids, the life history of Lufengpithecus lufengensis is similar to that of extant great apes and the Miocene hominoids Afropithecus turkanensis and Sivapithecus parvada, as well as Plio-Pleistocene Australopithecus, and different from monkeys, gibbons, and modern humans.

Dental development and life history in Anapithecus hernyaki

The sample of Anapithecus from Rudabánya, Hungary, is remarkable in preserving a large number of immature individuals. We used perikymata counts, measurements of root length and cuspal enamel thickness, and observations of the sequence of tooth germs that cross match specific developmental stages in Anapithecus to construct the first composite picture and time scale for dental development in a pliopithecoid (Catarrhini, Primates). We conclude that the age of eruption of M1 in Anapithecus was similar to various macaque species (∼1.45 months), but that M2 and M3 emergence were close to 2.2 and 3.2 years, respectively (both earlier than expected for similarly sized cercopithecoids). There may have been little difference in individual tooth formation times between cercopithecoids and Anapithecus, but the degree of molar overlap during M1, M2, and M3 crown development, which is extreme in Anapithecus, is fundamentally different. Overall dental development in Anapithecus was very rapid. Old World monkeys appear derived in lacking significant molar overlap, and hominoids may be derived in having longer tooth formation times, both resulting in longer overall dental development times. This is consistent with the general conclusion that the Pliopithecoidea is an outgroup to the Cercopithecoidea and the Hominoidea. On the other hand, rapid dental formation in Anapithecus may be an apomorphy indicative of an unusually rapid life history or unique pressures related to diet and maturation. Folivory and/or predation pressure may be responsible for generating selection to more rapidly erupt permanent teeth and possibly attain adult body masses in Anapithecus. Whatever the case, Anapithecus, with an M3 emergence of ∼3.2 years, is dramatically faster than any extant catarrhine of similar body mass. This represents yet another unusual attribute of this poorly known fossil catarrhine.

Enamel and dentine development and the life history profile of Victoriapithecus macinnesi from Maboko Island, Kenya

Two permanent lower second molar teeth (KNM-MB 19841 and KNM-MB 27844) attributed to Victoriapithecus macinnesi were prepared for histological analysis. A further five male and three female canine teeth were replicated with a silicone impression material and perikymata counts subsequently made on epoxy casts over the whole crown surface. Daily enamel cross striations averaged 6 microm apart in both cuspal and lateral enamel of the molars and the total crown formation times were approximately 1.24 years in the molars and, using the same periodicity determined from the molars, 1.84 and 1.36 years respectively in the male and female canines. Rates of dentine formation matched those known for extant macaques and were used to calculate root extension rates, which averaged 11.5 microm per day over the whole 8 mm root length of KNM-MB 19841. The period between M2 initiation and gingival emergence was estimated to be approximately 1.95 years in Victoriapithecus which is greater than estimates for Cebus albifrons and Chlorocebus aethiops, (which are similar in body mass to Victoriapithecus), but less than estimates made here for several macaque species. A speculative picture of dental development in Victoriapithecus emerges that is slower than that known for modern vervet monkeys and may have been more similar to that in some smaller modern macaque species.

Hypothesis for the causes and periodicity of repetitive linear enamel hypoplasia in large, wild African (Pan troglodytes and Gorilla gorilla) and Asian (Pongo pygmaeus) apes.

Repetitive linear enamel hypoplasia (rLEH) is often observed in recent large-bodied apes from Africa and Asia as well as Mid- to Late Miocene sites from Spain to China. The ubiquity and periodicity of rLEH are not understood. Its potential as an ontogenetic marker of developmental stress in threatened species (as well as their ancient relatives) makes rLEH an important if enigmatic problem. We report research designed to show the periodicity of rLEH among West African Pan troglodytes (12 male, 32 female), Gorilla gorilla (10 male, 10 female), and Bornean and Sumatran Pongo pygmaeus (11 male, 9 female, 9 unknown) from collections in Europe. Two methods were employed. In the common chimpanzees and gorillas, the space between adjacent, macroscopically visible LEH grooves on teeth with two or more episodes was expressed as an absolute measure and as a ratio of complete unworn crown height. In the orangutans, the number of perikymata between episode onsets, as well as duration of rLEH, was determined from scanning electron micrographs of casts of incisors and canines. We conclude that stress in the form of LEH commences as early as 2.5 years of age in all taxa and lasts for several years, and even longer in orangutans; the stress is not chronic but episodic; the stressor has a strong tendency to occur in pulses of two occurrences each; and large apes from both land masses exhibit rLEH with an average periodicity of 6 months (or multiples thereof; Sumatran orangutans seem to show only annual stress), but this needs further research. This is supported by evidence of spacing between rLEH as well as perikymata counts. Duration of stress in orangutans averages about 6 weeks. Finally, the semiannual stressor transcends geographic and temporal boundaries, and is attributed to regular moisture cycles associated with the intertropical convergence zone modified by the monsoon. While seasonal cycles can influence both disease and nutritional stress, it is likely the combination of seasonal variation in fruiting cycles with specific stressors (malaria and/or intestinal parasites, especially hookworm) that results in this widespread phenomenon. This seasonal stress is sufficiently common and of long duration (6 weeks on average in orangutans) that we think rLEH may reflect significant stress in recent and, inferentially, fossil apes. Increasing seasonality may have impinged negatively on later Miocene apes, especially if they lacked a clear birth peak or seasonality in their reproductive cycles.