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Integrated developmental and elemental information in teeth provide a unique framework for documenting breastfeeding histories, physiological disruptions, and neurotoxicant exposure in humans and our primate relatives, including ancient hominins. Here we detail our method for detecting the consumption of mothers' milk and exploring health history through the use of laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) mapping of sectioned nonhuman primate teeth. Calcium‐normalized barium and lead concentrations in tooth enamel and dentine may reflect milk and formula consumption with minimal modification during subsequent tooth mineralization, particularly in dentine. However, skeletal resorption during severe illness, and bioavailable metals in nonmilk foods, can complicate interpretations of nursing behavior. We show that explorations of the patterning of multiple elements may aid in the distinction of these important etiologies. Targeted studies of skeletal chemistry, gastrointestinal maturation, and the dietary bioavailability of metals are needed to optimize these unique records of human health and behavior. [ABSTRACT FROM AUTHOR]

Assessment of tooth morphology is an important part of the diagnosis and management of hypodontia patients. Several techniques have been used to analyze tooth form in hypodontia patients and these have shown smaller tooth dimensions and anomalous tooth shapes in patients with hypodontia when compared with controls. However, previous studies have mainly used 2D images and provided limited information. In the present study, 3D surface-imaging and statistical shape analysis were used to evaluate tooth form differences between hypodontia and control patients. Eighteen anatomical landmarks were recorded on the clinical crown of the lower left first permanent molar of 3D scanned study models of hypodontia and control subjects. The study sample group comprised of 120 hypodontia patients (40 mild, 40 moderate, and 40 severe hypodontia patients) and 40 age- and sex-matched controls. Procrustes coordinates were utilized to scale and superimpose the landmark coordinate data and then were subjected to principal component analysis (PCA). Subsequently, differences in shape as well as size were tested statistically using allometric analysis and MANOVA. Significant interaction was found between the two factor variables "group" and "sex" (p< 0.002). Overall expected accuracies were 66 and 56% for females and males, respectively, in the cross-validated discriminant-analysis using the first 20PCs. Hypodontia groups showed significant shape differences compared with the control subjects (p< 0.0001). Significant differences in tooth crown shape were also found between sexes (p< 0.0001) within groups. Furthermore, the degree of variation in tooth form was proportional to the degree of the severity of the hypodontia. Thus, quantitative measurement of tooth shape in hypodontia patients may enhance the multidisciplinary management of those patients. [ABSTRACT FROM AUTHOR]

Abstract: Dental development was reconstructed in several individuals representing four species of catarrhine primates—Symphalangus syndactylus, Hylobates lar, Semnopithecus entellus priam, and Papio hamadryas—using the techniques of dental histology. Bar charts assumed to represent species-typical dental development were constructed from these data and estimated ages at first and third molar emergence were plotted on them along with ages at weaning, menarche, and first reproduction from the literature. The estimated age at first molar emergence appears to occur at weaning in the siamang, lar gibbon, and langur, and just after weaning in the baboon. Age at menarche and first reproduction occur earlier relative to dental development in both cercopithecoids than in the hylobatids, suggesting that early reproduction may be a derived trait in cercopithecoids. The results are examined in the context of life history theory. [Copyright &y& Elsevier]

The use of dental development to chart and understand life history evolution has been one of the most fruitful lines of research in palaeontology and biological anthropology for many years. My aim here is to present an overview of the current state of this research using examples from my own research and that of my colleagues. My focus will be on the levels at which we understand life history variation and the appropriate levels at which both our questions and our methods can inform our work. Life history variables, e.g. gestation, age at weaning, age at first reproduction, and lifespan, vary between individuals within populations, between populations within species, between species, and between clades above the species level. Dental development can be seen to operate at two basic levels - the formation of individual teeth and the formation of the dentition. The formation of teeth is one step removed from life history, as the primary purpose of its components (e.g. daily secretion rate of enamel and dentine, angle of the striae of Retzius, combining to form extension rate) is to create a functional unit of a certain size, constrained by the time (life history) in which it develops. The formation of the dentition is more closely related to life history, as the development and eruption of teeth must match the pace of overall growth of the individual. The questions we ask about life history and the measures we make of aspects of dental development need to be aligned in order to be meaningful. Exciting new techniques allow us to look at life history variation between individuals; other methods are required to allow us to look at life history at higher levels, including not just eruption of teeth, particularly molars, but also their development relative to each other across the growth period. [ABSTRACT FROM AUTHOR]

The origin of determinate growth in mammals is associated with other important mammalian characters, including diphyodont dentition, lactation and endothermy. These characters likely evolved in the extinct cynodont and basal mammaliaform lineages of the Triassic and early Jurassic, with Morganucodon hypothesised to be the most basal mammaliaform to have both determinate growth and diphyodonty. Histological techniques to assess periodic enamel increments have not previously been applied to cynodonts and mammaliaforms, and are likely to improve understanding of their dental replacement and growth patterns. We prepared histological thin sections of postcanines of three cynodonts (Thrinaxodon, Scalenodon, Diademodon), molars of Morganucodon, and teeth from crown mammals and diapsids (e.g. Crocodylus, Canis, Tupaia). Using polarized light microscopy we assessed measures relating to dental growth patterns, including daily secretion rates of enamel, and crown and root extension rates. Two orders of incremental lines, analogous to daily prism cross-striations and longer period striae of Retzius of mammalian enamel, were observed in all cynodont and mammaliaform specimens. Daily secretion rate was lower in cynodont and mammaliaform enamel than in crown mammal teeth of comparable size. Very high mean crown extension rates were observed, both in diapsids and cynodonts (e.g. Crocodylus: 33.9μm/day; Thrinaxodon: 104.2μm/day), with cynodont extension rates at least double those of crown mammals with comparably sized teeth. Enamel thus extended extremely rapidly in thin 'sheath'-like layers in diapsids and cynodonts. In contrast, crown extension rate in Morganucodon is much lower (7.8μm/day), more closely resembling the crown mammals used for comparison. Low extension- and daily secretion rates suggest lower differentiation rates and secretory function of ameloblasts in Morganucodon. If this is coupled with reduced function of osteoblasts, it may suggest reduced rates of bone growth during molar formation. These patterns would be consistent with the hypothesis of determinate growth patterns in Morganucodon and of more indeterminate growth in cynodont species. [ABSTRACT FROM AUTHOR]

In 2013 we presented a model for identifying nursing behavior from primate teeth based on rapid postnatal concentration changes in the non-essential trace element barium. Here we leverage the permanent neonatal (birth) line in the enamel of several dozen primate M1 cusps to compare pre- and postnatal trends in barium, zinc, strontium, and oxygen, as each element is believed to evince developmental patterning. Barium and zinc are the most consistent biomarkers of nursing initiation; a majority of M1 cusps shows concentration increases from prenatal to postnatal enamel, whereas strontium shows decreases or no change with similar frequency. Exceptions to the pattern of barium increase occurred in cusps that had been mineralizing for less than three weeks, suggesting that subsequent enamel maturation has only a minor impact on detecting real time events. Oxygen isotope compositions (δ18O) show rapid and marked fluctuations (∼1–2‰) within two weeks of birth in 93% of M1 cusps (n = 27/29). This is likely due to measurements of hypomineralized perinatal enamel and physiological changes in the body water of newborn infants. Ongoing work integrating elemental concentration gradients with isotopic variation will help establish the degree to which milk intake may cause elevated δ18O in teeth. We show that chemical identification of pre-to postnatal transitions may be robust to slight planar deviations that commonly obscure growth increments under light microscopy, and could help validate the identification of potential neonatal lines, making this approach a useful complement to bioarchaeological studies and public health investigations. • M1 cusps often show Ba/Ca and Zn/Ca concentration increases in enamel after birth. • These trends appear in cusps that began calcification at least 3 weeks before birth. • Perinatal patterns of Sr/Ca are more variable than those of Ba/Ca and Zn/Ca. • Oxygen isotopes (δ18O) nearly always show marked perinatal fluctuations (∼1–2‰). • Chemical identification of birth will aid bioarchaeology and public health studies. [ABSTRACT FROM AUTHOR]