Tooth use and the physical properties of food

For decades, natural historians and comparative anatomists have acknowledged the form/function relationship between an animal's dentition and its food. Historically, anthropologists have cited this relationship to explain adaptations observed in modern species as well as to infer the diets of extinct animals found in the fossil record. Anthropologists have described morphological differences between species that permit dietary niche partitioning which allows closely related primates to co-exist within a single ecosystem. For example, Robinson¹ postulated that the anatomical differences between Australopithecus and Paranthropus are the result of their adaptations to different diets. Jolly's² seed-eating hypothesis suggested that early hominids' morphological divergence from apes resulted from their specialized feeding on small and hard grass seeds. Early work by Kay³ suggested that Sivapithecus' thick molar enamel was an adaptation to habitually eating resistant food items such as hard nuts or seeds enclosed in tough pods.     

Frequency and chronological distribution of linear enamel hypoplasia in a North American colonial skeletal sample

A skeletal sample of 44 individuals born and raised in early 18th century frontier settlements of Northeastern United States is examined for the frequency and chronological distribution of linear enamel hypoplasia (LEH) on the maxillary and mandibular incisors and canines. The prevalence of LEH ranged from 31% on the I² to 66% on the mandibular C and the mean number of defects ranged from .59 on the I² to 1.08 on the mandibular C. These frequencies were generally lower than those reported for two later samples: the Monroe County Poorhouse sample and the Hammon-Todd sample. Individuals in these latter two samples were derived from the lowest socioeconomic stratum of their respective populations. Frequency differences are explained within the context of the changing availability of resources that resulted from the rise of industrialization, urbanization, and wage labor which took place during the 18th and 19th centuries. The frequency of LEH was low prior to 1.5 years of age and may result from attrition and/or decreased susceptibility in the relevant area of the crown or from low morbidity or high mortality. Peak frequencies are observed in all age categories ranging from 2.5 to 3.0 years up to 4.0 to 4.5 years and are too late to result from weaning. Instead, they may reflect the susceptibility of nonimmune children to diseases that were common in colonial North America. As the majority of these diseases were not fatal, most victims who survived may have had one or more LEHs as visible proof of their earlier encounter(s). © 1996 Wiley-Liss, Inc.     

Tooth chipping can reveal the diet and bite forces of fossil hominins

Mammalian tooth enamel is often chipped, providing clear evidence for localized contacts with large hard food objects. Here, we apply a simple fracture equation to estimate peak bite forces directly from chip size. Many fossil hominins exhibit antemortem chips on their posterior teeth, indicating their use of high bite forces. The inference that these species must have consumed large hard foods such as seeds is supported by the occurrence of similar chips among known modern-day seed predators such as orangutans and peccaries. The existence of tooth chip signatures also provides a way of identifying the consumption of rarely eaten foods that dental microwear and isotopic analysis are unlikely to detect.     

MANDIBULAR DENTAL ONTOGENY OF RINGED SEALS (PHOCA HISPIDA)

X-rays of mandibles from ringed seal fetuses ( n = 15), newborns ( n = 12), and young-of-the-year ( n = 11), collected up to early June, were examined for the presence, location, and eruption patterns of deciduous and permanent teeth. The presence of a neonatal line and cementum in permanent canines was determined microscopically. Fetuses sampled in October-November had only unerupted, deciduous tooth germs, but by late January there were robust, deciduous teeth at il-2 pc2-4 and small permanent teeth at 11-2 Cl PCl-5. In newborns collected in early April, 109 of 143 (76%) deciduous teeth were resorbed completely. The remaining 34 deciduous teeth were partially resorbed; six (18%) had erupted and likely would be shed. By late April young-of-the-year had no deciduous teeth remaining. In newborns 54% of the permanent teeth (102/188) were erupted < 2 mm, and by late May the permanent dentition was erupted fully. The neonatal line first appeared in the canine teeth of young-of-the-year collected in mid-April and was 100% present after early May. There was no cementum apparent on any canine collected up to early June. Two seals were missing one and two permanent incisors, respectively. No supernumerary teeth or morphological variants were observed.     

Deciduous tooth dimensions in fetal rhesus monkeys from mothers with induced diabetes

Thirty-four measurements of the deciduous dentition in 21 fetal rhesus monkeys from diabetic mothers (FDM) and 36 nondiabetic fetuses were compared in order to assess the effects of induced maternal diabetes on the teeth of third-trimester fetuses. After exclusion of 14 variates due to significant age-related variation, univariate statistical analysis suggested a trend toward smaller teeth in the FDMs. Multivariate discriminant function analysis indicated not only a clear separation between the two groups, with molar breadths and some incisor lengths and breadths serving as the best discriminators, but also that the deciduous dental dimensions in FDMs are smaller than in nondiabetic fetuses.     

Ontogenic changes and sexual dimorphism in the head, mouth and teeth of the lesser spotted dogfish

Male Scyliorhinus canicula possess a longer and narrower mouth than females resulting in pronouced sexual dimorphism with respect to the mouth length/mouth width ratio (0.49 and 0.43, respectively). Significant sexual differences in the girth of the head and pre-oral, pre-branchial and head lengths were also recorded. Males were found to have longer teeth than females. Reasons for these differences are discussed.     

Additional mandibles of Rangwapithecus gordoni,an early Miocene catarrhine from the Tinderet localities of Western Kenya

Two catarrhine mandibles and five isolated teeth have been discovered from Early Miocene localities in Western Kenya. One mandible comes from the well‐known locality of Songhor whereas the other is from a newly discovered locality, Lower Kapurtay, located near Songhor. The mandibles both can clearly be assigned to the species Rangwapithecus gordoni based on molar morphology, which is unique among Early Miocene catarrhines. The isolated specimens can be assigned to Rangwapithecus based on their similarities in morphology to the homologues preserved in the two mandibles. These specimens provide important new information about the dentognathic morphology of Rangwapithecus, which is described in detail. The mandible from Songhor (KNM‐SO 22228) represents the first definitive female mandible of Rangwapithecus. The Lower Kapurtay mandible (KNM‐KT 31234) appears to be male but is much smaller than another recently described male mandible of this species (KNM‐SO 17500) and the type maxilla (KNM‐SO 700). These specimens enable a reassessment of the attributions of all other mandibles and isolated lower teeth of Rangwapithecus, and we present a complete hypodigm of the mandibular and lower dental material for the species. Finally, we provide some additions to the diagnosis of Rangwapithecus gordoni based on previously unknown morphology. Am J Phys Anthropol 153:341–352, 2014. © 2013 Wiley Periodicals, Inc.     

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.     

Identification of a derived dental trait in the papionini relative to other old world monkeys

Variation in the shape of teeth provides an immense amount of information about the evolutionary history and adaptive strategy of a mammalian lineage. Here, we explore variation in the expression of a purported molar lingual remnant (the interconulus) across the Old World Monkeys (Primates: Cercopithecidae) with the aim of elucidating a component of the adaptive radiation of this family. This radiation is characterized by a wide geographic range (Asia and Africa) as well as diverse dietary niches. While all of the cercopithecids are distinguished by their derived bilophodont molars, the colobines have evolved taller and more pointed cusps compared with the cercopithecines. We investigate whether the interconulus also correlates with phylogenetic affinity and/or dietary adaptation. We assess the frequency and range of interconulus expression in 522 specimens representing seven species of Old World Monkeys (Cercopithecus mitis, n = 78; Macaca fascicularis, n = 85; Macaca mulatta, n = 70; Papio hamadryas, n = 55; Colobus guereza, n = 76; Presbytis melalophos, n = 82; Presbytis rubicunda, n = 76). Results show that the interconulus has a significantly higher frequency and degree of expression in Tribe Papionini and exhibits ordered metameric variation with greatest expression in the third molars. Given the rarity of the interconulus in other closely related taxa, and its morphological distinction from the purportedly homologous features in other primates, we interpret the high degree of expression of the interconulus to be a trait derived in papionins that originated in the Miocene baboon/macaque ancestor. Am J Phys Anthropol, 155:422–429, 2014. © 2014 Wiley Periodicals, Inc.