An anachronistic Clarkforkian mammal fauna from the Paleocene Fort Union Formation (Great Divide Basin, Wyoming, USA)

The Clarkforkian (latest Paleocene) North American Land Mammal Age (NALMA) remains a relatively poorly sampled biostratigraphic interval at the close of the Paleocene epoch that is best known from the Bighorn Basin of northwestern Wyoming. A period of global warming between the cooler early and middle Paleocene and the extreme warming of the early Eocene, the Clarkforkian witnessed significant floral and faunal turnover with important ramifications for the development of Cenozoic biotas. The combination of warming global climates with mammalian turnover (including likely intercontinental dispersals) marks the Clarkforkian and the succeeding Wasatchian (Earliest Eocene) NALMAs as periods of intense interest to paleobiologists and other earth scientists concerned with aspects of biostratigraphy and with the biotic effects of climate change in the past. In this paper we describe a new Clarkforkian mammalian fauna from the Great Divide Basin of southwestern Wyoming with some surprising faunal elements that differ from the typical suite of taxic associations found in Clarkforkian assemblages of the Bighorn Basin. Several different scenarios are explored to explain this "anachronistic" assemblage of mammals from southern Wyoming in relation to the typical patterns found in northern Wyoming, including the concepts of basin-margin faunas, latitudinal and climatic gradients, and a chronologically transitional fauna. We suggest that the observed faunal and biostratigraphic differences between southern and northern Wyoming faunas most likely result from latitudinal and associated climatic differences, with floral and faunal changes being reflected somewhat earlier in the south during this period of marked climate change

An anachronistic Clarkforkian mammal fauna from the Paleocene Fort Union Formation (Great Divide Basin

The Clarkforkian (latest Paleocene) North American Land Mammal Age (NALMA) remains a relatively poorly sampled biostratigraphic interval at the close of the Paleocene epoch that is best known from the Bighorn Basin of northwestern Wyoming. A period of global warming between the cooler early and middle Paleocene and the extreme warming of the early Eocene, the Clarkforkian witnessed significant floral and faunal turnover with important ramifications for the development of Cenozoic biotas. The combination of warming global climates with mammalian turnover (including likely intercontinental dispersals) marks the Clarkforkian and the succeeding Wasatchian (Earliest Eocene) NALMAs as periods of intense interest to paleobiologists and other earth scientists concerned with aspects of biostratigraphy and with the biotic effects of climate change in the past. In this paper we describe a new Clarkforkian mammalian fauna from the Great Divide Basin of southwestern Wyoming with some surprising faunal elements that differ from the typical suite of taxic associations found in Clarkforkian assemblages of the Bighorn Basin. Several different scenarios are explored to explain this "anachronistic" assemblage of mammals from southern Wyoming in relation to the typical patterns found in northern Wyoming, including the concepts of basin-margin faunas, latitudinal and climatic gradients, and a chronologically transitional fauna. We suggest that the observed faunal and biostratigraphic differences between southern and northern Wyoming faunas most likely result from latitudinal and associated climatic differences, with floral and faunal changes being reflected somewhat earlier in the south during this period of marked climate change

Tracing fetal and childhood exposure to lead using isotope analysis of deciduous teeth

We report progress in using the isotopic composition and concentration of Pb in the dentine and enamel of deciduous teeth to provide a high resolution time frame of exposure to Pb during fetal development and early childhood. Isotope measurements (total Pb and 208Pb/206Pb, 207Pb/206Pb ratios) were acquired by laser ablation inductively coupled mass spectrometry at contiguous 100 micron intervals across thin sections of the teeth; from the outer enamel surface to the pulp cavity. Teeth samples (n=10) were selected from two cohorts of children, aged 5–8 years, living in NE England. By integrating the isotope data with histological analysis of the teeth, using the daily incremental lines in dentine, we were able to assign true estimated ages to each ablation point (first 2–3 years for molars, first 1–2 years for incisors+pre-natal growth). Significant differences were observed in the isotope composition and concentration of Pb between children, reflecting differences in the timing and sources of exposure during early childhood. Those born in 2000, after the withdrawal of leaded petrol in 1999, have the lowest dentine Pb levels (0.4 µgPb/g) with 208Pb/206Pb (mean ±2σ: 2.145–2.117) 208Pb/206Pb (mean ±2σ: 0.898–0.882) ratios that can be modelled as a binary mix between industrial aerosols and leaded petrol emissions. Short duration, high intensity exposure events (1–2 months) were readily identified, together with evidence that dentine provides a good proxy for childhood changes in the isotope composition of blood Pb. Our pilot study confirms that laser ablation Pb isotope analysis of deciduous teeth, when carried out in conjunction with histological analysis, permits a reconstruction of the timing, duration and source of exposure to Pb during early childhood. With further development, this approach has the potential to study larger cohorts and appraise environments where the levels of exposure to Pb are much higher

An anachronistic Clarkforkian mammal fauna from the Paleocene Fort Union Formation (Great Divide Basin, Wyoming, USA)

The Clarkforkian (latest Paleocene) North American Land Mammal Age (NALMA) remains a relatively poorly sampled biostratigraphic interval at the close of the Paleocene epoch that is best known from the Bighorn Basin of northwestern Wyoming. A period of global warming between the cooler early and middle Paleocene and the extreme warming of the early Eocene, the Clarkforkian witnessed significant floral and faunal turnover with important ramifications for the development of Cenozoic biotas. The combination of warming global climates with mammalian turnover (including likely intercontinental dispersals) marks the Clarkforkian and the succeeding Wasatchian (Earliest Eocene) NALMAs as periods of intense interest to paleobiologists and other earth scientists concerned with aspects of biostratigraphy and with the biotic effects of climate change in the past. In this paper we describe a new Clarkforkian mammalian fauna from the Great Divide Basin of southwestern Wyoming with some surprising faunal elements that differ from the typical suite of taxic associations found in Clarkforkian assemblages of the Bighorn Basin. Several different scenarios are explored to explain this "anachronistic" assemblage of mammals from southern Wyoming in relation to the typical patterns found in northern Wyoming, including the concepts of basin-margin faunas, latitudinal and climatic gradients, and a chronologically transitional fauna. We suggest that the observed faunal and biostratigraphic differences between southern and northern Wyoming faunas most likely result from latitudinal and associated climatic differences, with floral and faunal changes being reflected somewhat earlier in the south during this period of marked climate change

Are there two distinct types of hypocone in Eocene primates? The 'pseudohypocone' of notharctines revisited

Upper molars of modern humans and most extant primates have four cusps that have evolved from the original tribosphenic tooth of therian mammals. These include the three cusps of the original trigon (e.g., paracone, metacone, and protocone), and the addition of the distolingual cusp or hypocone. Among Eocene primates of the family Adapidae, a distinction has long been made between a "true" hypocone associated with the lingual cingulum (adapine form) and a "pseudohypocone" associated with the distal margin of the protocone (notharctine form). The developmental processes underlying these two types of distolingual cusp are unknown, and the validity of the distinction is based on phylogenetic utility and homology rather than cusp position, as in other mammalian groups. To address this issue we use micro-computed tomography to reveal the morphology of the hypocone and associated cusps and crests on the enamel-dentine junction (EDJ). The EDJ preserves the initial steps of tooth crown development and can be used to clarify detailed aspects of crown morphology in variably worn or damaged fossil teeth. Our study sample includes both adapine species from Europe and notharctines from North America. We confirm that the pseudohypocone found among notharctines is a true cusp since it forms as a dentine horn during crown development. Our results also confirm that these two forms of hypocone are developmentally distinct and have evolved convergently in these two primate clades. A review of the paleontological literature suggests that, in spite of the fact that homoplasy is rampant among mammalian clades with respect to the development of the hypocone, only among the notharctines do we find an alternative name for this cusp

Enamel formation and growth in non-mammalian cynodonts

The early evolution of mammals is associated with the linked evolutionary origin of diphyodont tooth replacement, rapid juvenile growth and determinate adult growth. However, specific relationships among these characters during non-mammalian cynodont evolution require further exploration. Here, polarized light microscopy revealed incremental lines, resembling daily laminations of extant mammals, in histological sections of enamel in eight non-mammalian cynodont species. In the more basal non-probainognathian group, enamel extends extremely rapidly from cusp to cervix. By contrast, the enamel of mammaliamorphs is gradually accreted, with slow rates of crown extension, more typical of the majority of non-hypsodont crown mammals. These results are consistent with the reduction in dental replacement rate across the non-mammalian cynodont lineage, with greater rates of crown extension required in most non-probainognathians, and slower crown extension rates permitted in mammaliamorphs, which have reduced patterns of dental replacement in comparison with many non-probainognathians. The evolution of mammal-like growth patterns, with faster juvenile growth and more abruptly terminating adult growth, is linked with this reduction in dental replacement rates and may provide an additional explanation for the observed pattern in enamel growth rates. It is possible that the reduction in enamel extension rates in mammaliamorphs reflects an underlying reduction in skeletal growth rates at the time of postcanine formation, due to a more abruptly terminating pattern of adult growth in these more mammal-like, crownward species

3D-Geomorphometrics tooth shape analysis in hypodontia

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 20 PCs. 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

Elemental models of primate nursing and weaning revisited

ObjectivesIntra-tooth patterns of trace elements barium (Ba) and strontium (Sr) have been used to infer human and nonhuman primate nursing histories, including australopithecine and Neanderthal juveniles. Here, we contrast the two elemental models in first molars (M1s) of four wild baboons and explore the assumptions that underlie each.Materials and MethodsLaser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was employed to create comprehensive calcium-normalized barium and strontium (Ba/Ca, Sr/Ca) maps of M1 enamel and dentine at 35 micron resolution.ResultsPostnatal Ba/Ca values were typically high, peaking ~0.5 years of age and then decreasing throughout M1 crown formation; all four individuals showed minimal Ba/Ca values between ~1.2–1.8 years, consistent with field reports of the cessation of suckling. Enamel Sr/Ca did not support patterns of previous LA-ICP-MS spot sampling as the enamel rarely showed discrete Sr/Ca secretory zonation. Increases in Sr/Ca appeared in coronal dentine beginning ~0.3 years, with varied peak value ages (~0.7–2.7 years) and no evidence of a predicted postweaning decline.DiscussionInferences of baboon weaning ages from initial Ba/Ca minima are more congruent with behavioral observations than Sr/Ca maxima; this is consistent with studies of captive macaques of known weaning ages. Elemental variation is more apparent in the coronal dentine than the enamel of these baboons, which may relate to its more rapid mineralization and protection from the oral environment. Inferences of nursing histories from enamel Sr/Ca patterns alone should be reconsidered, and elevated values of Ba/Ca and Sr/Ca in teeth formed after weaning require further study

Determinants of childhood lead exposure in the postleaded petrol era: The Tooth Fairy cohort from Newcastle upon Tyne

Lead is an environmental contaminant causing irreversible health effects in children. We used dentine lead levels as a measure of early-life lead exposure and explored determinants of lead exposure in children living in Newcastle upon Tyne, a historically industrialised UK city, in a cohort born since legislation was introduced to remove lead from petrol, paint and water pipes. The “Tooth Fairy study” cohort comprised 69 children aged 5–8 years. We collected upper deciduous incisors from children and questionnaire data from their parents in 2005. We measured lead levels in pre- and postnatal enamel and dentine using laser ablation inductively coupled plasma mass spectrometry, and assessed associations between dentine lead levels and residential, dietary, lifestyle and socio-economic characteristics. Dentine lead levels were low (mean 0.26 μg/g, range 0.06–0.77); however, we observed considerable variability in dentine lead levels within and between children suggestive of differing exposure levels and/or exposure sources across this population. Variables earlier documented to be associated with childhood lead levels were not found to be significant determinants of dentine lead levels in this study. Exposure pathways should continue to be investigated to enable targeted interventions and prevention of lead-induced health impacts in vulnerable populations