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Abstract: Data are presented to demonstrate that the circumpulpal dentine of deciduous teeth can be used to reconstruct a detailed record of childhood exposure to lead. By combining high spatial resolution laser ablation ICP-MS with dental histology, information was acquired on the concentration of lead in dentine from in utero to several years after birth, using a true time template of dentine growth. Time corrected lead analyses for pairs of deciduous molars confirmed that between-tooth variation for the same child was negligible and that meaningful exposure histories can be obtained from a single, multi-point ablation transect on longitudinal sections of individual teeth. For a laser beam of 100μm diameter, the lead signal for each ablation point represented a time span of 42days. Simultaneous analyses for Sr, Zn and Mg suggest that the incorporation of Pb into dentine (carbonated apatite) is most likely controlled by nanocrystal growth mechanisms. The study also highlights the importance of discriminating between primary and secondary dentine and the dangers of translating lead analyses into blood lead estimates without determining the age or duration of dentine sampled. Further work is in progress to validate deciduous teeth as blood lead biomarkers. [Copyright &y& Elsevier]

Abstract: Fossil elephantids are often assigned chronological ages based on tooth eruption and wear in extant elephants. Differences in body mass are likely to be accompanied by shifts in life history strategies, however, and hypotheses about these shifts cannot be tested using relative age. A better understanding of interspecific differences in the duration of tooth formation would help test hypotheses about life history variation. In this study, periodic incremental features visible in the enamel of histological thin sections of molar plates were used to estimate the rate and duration of plate formation in an insular dwarf, Palaeoloxodon cypriotes, which is smaller than extant elephants, and Mammuthus columbi, which is larger. Polarized light microscopy and image analysis software were used to determine the daily secretion rate of enamel and plate extension rate, the rate at which the plate increases in height each day, utilizing the daily incremental features, the cross striations, and accentuated lines representing the forming front of enamel at a particular time during plate formation. Estimates were made of total plate formation time from crown height and extension rate. Histological sections were prepared from molar fragments from each species. Five sections were prepared in the same plane from the large M. columbi plate. The daily secretion rate, 2–5 μm, is similar in both elephants, but the extension rate is higher in the larger M. columbi. The initial extension rate is estimated to be 62.5 μm per day, but drops to around 32.3 toward cervical portion of the plate. In P. cypriotes, the initial extension rate is estimated to be 34.4 μm per day, dropping to 12 μm per day and then rising to 23.3 μm per day in the cervical region. Estimated plate formation time is around 10.6 years for 180.9 mm of height in M. columbi and 5.9 years for 51.1 mm of height in P. cypriotes. M. columbi thus forms a taller plate by increasing both extension rate and the duration of formation. These differences could be allometric, with higher crowned teeth forming more rapidly than low crowned teeth, or they could be related to differences in life history strategies between taxa. [Copyright &y& Elsevier]

The condylarths, or archaic ungulates, are a paraphyletic mammalian group including a number of fossil taxa whose relationships are unresolved. Included are two genera from the Paleocene and Eocene of North America, Meniscotherium and Phenacodus. Some workers place both genera in the family Phenacodontidae, while others exclude the highly dentally derived Meniscotherium. In this study, we use growth increments in histological thin sections to examine the timing of crown formation in five molars of Meniscotherium and one each of Phenacodus intermedius and Phenacodus trilobatus. We also use perikymata counts on an additional six molars of Meniscotherium. Although estimated body mass and molar dimensions in Meniscotherium are smaller than in either species of Phenacodus, molar formation times are longer, ranging from 0.71 to 1.44 years. Both Phenacodus molars take less than a year to form. Crown extension rates, the rate at which the crown grows in height, are as low as 3-15 µm per day in Meniscotherium, but range from 13 to 54 µm per day in Phenacodus. Although striae periodicities and daily enamel secretion rate are similar in both genera, the differences in the crown extension rate and overall timing of crown formation suggest differences in life histories and raise questions about the phylogenetic relationship of the two genera. [ABSTRACT FROM AUTHOR]

• Peak frequencies of enamel formation disturbances identified through statistics. • Peak frequencies occur in the sample at c. four, nine, eleven, and twelve months. • These peak frequencies may relate to developmental milestones at population level. • Statistical approaches for future comparative studies, including on peak duration. The objectives are 1) to calculate the position of highly accentuated lines in dental enamel of a group of individuals from Shahr-i-Sokhta, a thriving urban centre in Bronze Age South West Asia; 2) to identify peak frequencies of physiologically stressful periods during early childhood of these individuals; and 3) to relate these peak frequencies to developmental milestones at population level. We analysed highly accentuated lines in the enamel of nine (n = 9) permanent mandibular first molars of nine individuals from the 5th millennium before the present urban and long-distance-trading complex, Shahr-i Sokhta (Iran). Age at death ranged between 4.5 years and 18−20 years. Permanent mandibular first molar enamel begins to mineralise before birth, and is normally completed sometime between 2.1–3.3 years, giving us insight to early childhood physiological stress, the ages at which it occurs, and any peaks in the frequencies in highly accentuated line formation, through histological sections investigated using transmitted light microscopy. Highly accentuated line peak frequencies occur in the sample at c. four, nine, eleven, and twelve months. After 1 year of age, no more peaks occur. The peak frequencies coincide with the timing timing of the type of developmental milestones which may have exposed the individuals to an increased pathogen load, injury, or sub-optimal diet. We note similarity in peak timings in the few published, disparate populations, suggest a potential link with attainment of developmental milestones connected with morbidity, and propose reporting standardised statistics to enable exploration of differences between populations in terms of postnatal health-related stress. [ABSTRACT FROM AUTHOR]