Tanya M. Smith

Griffith University · Australian Research Centre for Human Evolution

Studies of climate variation commonly rely on chemical and isotopic changes recorded in sequentially-produced growth layers, such as in corals, shells and tree rings, as well as in accretionary deposits—ice and sediment cores, and speleothems. Oxygen isotopic compositions (δ18O) of tooth enamel are a direct method of reconstructing environmental va...

Studies of climate variation commonly rely on chemical and isotopic changes recorded in sequentially-produced growth layers, such as in corals, shells and tree rings, as well as in accretionary deposits—ice and sediment cores, and speleothems. Oxygen isotopic compositions (δ18O) of tooth enamel are a direct method of reconstructing environmental va...

Studies of climate variation commonly rely on chemical and isotopic changes recorded in sequentially-produced growth layers, such as in corals, shells and tree rings, as well as in accretionary deposits - ice and sediment cores, and speleothems. Oxygen isotopic compositions (d18O) of tooth enamel are a direct method of reconstructing environmental...

The regular incremental secretion of enamel and dentine can be interrupted during periods of stress resulting in accentuated growth lines. These accentuated lines, visible under light microscopy, provide a chronology of an individual's stress exposure. Previously, we showed that small biochemical changes along accentuated growth lines detected by R...

Objectives: Intra-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. Material...

Variability in resource availability is hypothesized to be a significant driver of primate adaptation and evolution, but most paleoclimate proxies cannot recover environmental seasonality on the scale of an individual lifespan. Oxygen isotope compositions (δ ¹⁸ O values) sampled at high spatial resolution in the dentitions of modern African primate...

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 el...

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 t...

Age at lower first molar (M1) emergence is a commonly used proxy for inferring life-history scheduling in fossil primates, but its utility is dependent on knowing to what extent extant populations vary in this datum and how this variation correlates with the scheduling of life-history variables. Here, we address the first of these issues among exta...

Human brains are three times larger, are organized differently, and mature for a longer period of time than those of our closest living relatives, the chimpanzees. Together, these characteristics are important for human cognition and social behavior, but their evolutionary origins remain unclear. To study brain growth and organization in the homini...

Dentine‐ and enamel‐forming cells secrete matrix in consistent rhythmic phases, resulting in the formation of successive microscopic growth lines inside tooth crowns and roots. Experimental studies of various mammals have proven that these lines are laid down in subdaily, daily (circadian), and multidaily rhythms, but it is less clear how these rhy...

The fossil record of middle and late Miocene Eurasian hominoids has expanded considerably over the past few decades, particularly with the recovery of numerous isolated teeth and jaws. Scholars have turned to assessments of internal tooth structure and growth to make sense of the evolutionary radiations of these primates as well as their affinities...

Scholars have debated the taxonomic identity of isolated primate teeth from the Asian Pleistocene for over a century, which is complicated by morphological and metric convergence between orangutan (Pongo) and hominin (Homo) molariform teeth. Like Homo erectus, Pongo once showed considerable dental variation and a wide distribution throughout mainla...

Scholars endeavor to understand the relationship between human evolution and climate change. This is particularly germane for Neanderthals, who survived extreme Eurasian environmental variation and glaciations, mysteriously going extinct during a cool interglacial stage. Here, we integrate weekly records of climate, tooth growth, and metal exposure...

Seasonal variation in rainfall and temperature are major determinants of ecosystem structure and productivity and influence physical processes such as erosion rates and glaciation. By extension, seasonality can drive evolutionary change, and is hypothesized to have influenced early human subsistence and technological development. Rainfall patterns...

The progressive character of tooth formation records aspects of mammalian life history, diet, seasonal behavior and climate. Tooth mineralization occurs in two stages: secretion and maturation, which overlap to some degree. Despite decades of study, the spatial and temporal pattern of elemental incorporation during enamel mineralization remains poo...

Virtual sections of enamel mineral density. Virtual buccal enamel sections extracted from synchrotron scanned tooth volumes at 45μm resolution. Brighter pixels indicate dense, highly mineralized enamel, and darker pixels indicate less dense, poorly mineralized enamel. In file name, day of animal death is indicated first, followed by scan batch (1 o...

Animation of synchrotron mineral density imaging. Animation showing 3D density data collected from synchrotron imaging of a single first molar. Red colors indicate dense, highly mineralized enamel, and blue colors indicate less dense, poorly mineralized enamel. Visualization produced using VGStudio MAX 3.0 software. (AVI)

Description of additional methods used in this study. This text provides additional detail on synchrotron mineral density measurement, flattening and standardizing virtual enamel sections, estimating initiation and extension, calcein labeling, model conversion between different tooth types, and MCMC methods for estimating mineral density increase o...

Dynamic model of mineral density increase. Animation showing mineral density increase described by the mineralization model. Dark blue colors indicate no mineral addition, while warmer colors (light blue, yellow, red) indicate higher rates of mineral deposition. Mineral density increase has been Gaussian blurred for the purposes of visualization, w...

Definitions of terms used. This file contains a list of definitions for terms commonly employed by this manuscript. An associated reference list is provided. (PDF)

Genetic evidence for anatomically modern humans (AMH) out of Africa before 75 thousand years ago (ka) and in island southeast Asia (ISEA) before 60 ka (93-61 ka) predates accepted archaeological records of occupation in the region. Claims that AMH arrived in ISEA before 60 ka (ref. 4) have been supported only by equivocal or non-skeletal evidence....

Nursing behavior is notoriously difficult to study in arboreal primates, particularly when offspring suckle inconspicuously in nests. Orangutans have the most prolonged nursing period of any mammal, with the cessation of suckling (weaning) estimated to occur at 6 to 8 years of age in the wild. Milk consumption is hypothesized to be relatively const...

Numerous studies have investigated molar development in extant and fossil hominoids, yet relatively little is known about orangutans, the only great ape with an extensive fossil record. This study characterizes aspects of dental development, including cuspal enamel daily secretion rate, long-period line periodicities, cusp-specific molar crown form...

Early life stress can disrupt development and negatively impact long-term health trajectories. Reconstructing histories of early life exposure to external stressors is hampered by the absence of retrospective time-specific biomarkers. Defects in tooth enamel have been used to reconstruct stress but the methods used are subjective and do not identif...

Developmental defects in teeth (accentuated lines and hypoplasias) have played a critical role in studies of childhood disease, nutrition, weaning, environmental variation, and early mortality. While these enigmatic structures have been lauded for their potential insights into human evolution, few studies have examined defects in individuals of kno...

Until recently, our understanding of the evolution of human growth and development derived from studies of fossil juveniles that employed extant populations for both age determination and comparison. This circular approach has led to considerable debate about the human-like and ape-like affinities of fossil hominins. Teeth are invaluable for unders...

Enamel thickness has played an important role in studies of primate taxonomy, phylogeny, and functional morphology, although its variation among hominins is poorly understood. Macaques parallel hominins in their widespread geographic distribution, relative range of body sizes, and radiation during the last five million years. To explore enamel thic...

During childhood, systemic physiological stresses such as illness, disease, and malnutrition can disrupt the growth of dental enamel. These disruptions are often recorded in the form of linear enamel hypoplasia (LEH). Many researchers have analyzed the frequency and timing of LEH formation in Neanderthal populations as they relate to ideas about Ne...

Modern humans differ from wild great apes in gestation length, weaning age, interbirth interval, sexual maturity, and longevity, but evolutionary anthropologists do not know when these distinctive life-history conditions evolved. Dental tissues contain faithful records of birth and incremental growth, and scholars suggest that molar eruption age, t...

Modern humans differ from wild great apes in gestation length, weaning age, interbirth interval, sexual maturity, and longevity, but evolutionary an- thropologists do not know when these distinctive life-history conditions evolved. Dental tissues contain faithful records of birth and incremental growth, and scholars suggest that molar eruption age,...

Early-life dietary transitions reflect fundamental aspects of primate evolution and are important determinants of health in contemporary human populations. Weaning is critical to developmental and reproductive rates; early weaning can have detrimental health effects but enables shorter inter-birth intervals, which influences population growth. Unco...

Understanding dental development in chimpanzees, our closest living relatives, is of fundamental importance for reconstructing the evolution of human development. Most early hominin species are believed to show rapid ape-like patterns of development, implying that a prolonged modern human childhood evolved quite recently. However, chimpanzee develo...

The Aterian fossil hominins represent one of the most abundant series of human remains associated with Middle Stone Age/Middle Paleolithic assemblages in Africa. Their dates have been revised and they are now mostly assigned to a period between 90 and 35 ka. Although the Aterian human fossil record is exclusively Moroccan, Aterian assemblages are f...

Dental enamel thickness has received considerable attention in ecological models of the adaptive significance of primate morphology. Several authors have theorized that the degree of enamel thickness may reflect selective pressures related to the consumption of fallback foods (dietary items that may require complex processing and/or have low nutrit...

Orangutans (Pongo) are the only great ape genus with a substantial Pleistocene and Holocene fossil record, demonstrating a much larger geographic range than extant populations. In addition to having an extensive fossil record, Pongo shows several convergent morphological similarities with Homo, including a trend of dental reduction during the past...

Contexts and age of the new dental human fossils from Middle Pleistocene deposits at Thomas Quarry I (Casablanca, Morocco) - The Thomas Quarry I locality became famous in 1969 with the discovery of a human half-mandible in a cave. From 1988 onwards, modern controlled excavations took place within the framework of the Franco-Moroccan co-operative pr...

Studies of dental development have reported conflicting results regarding whether Neanderthal growth and development was similar to that of modern humans. The discovery of a partial permanent maxillary juvenile dentition (OR-1) from the Obi-Rakhmat Grotto, Uzbekistan, provides the opportunity to assess dental development and age at death in a Paleo...

Contexts and age of the new dental human fossils from Middle Pleistocene deposits at Thomas Quarry I (Casablanca, Morocco) – The Thomas Quarry I locality became famous in 1969 with the discovery of a human half-mandible in a cave. From 1988 onwards, modern controlled excavations took place within the framework of the Franco-Moroccan co-operative pr...

A comparative study has been made of human and great ape molar tooth enamel. Nanoindentation techniques are used to map profiles of elastic modulus and hardness across sections from the enamel-dentin junction to the outer tooth surface. The measured data profiles overlap between species, suggesting a degree of commonality in material properties. Us...

Dental enamel thickness continues to feature prominently in anthropological studies of ape and human evolution, as well as studies of preventative oral care and treatment. Traditional studies of enamel thickness require physical sectioning of teeth for linear and scaled measurements. Recent applications of microtomographic imaging allow scientists...

Humans have an unusual life history, with an early weaning age, long childhood, late first reproduction, short interbirth intervals, and long lifespan. In contrast, great apes wean later, reproduce earlier, and have longer intervals between births. Despite 80 y of speculation, the origins of these developmental patterns in Homo sapiens remain unkno...

The Thomas Quarry I locality was made famous in 1969 with the discovery of a human half-mandible in a cave. In 1985, further investigations revealed the presence of a Lower Acheulean assemblage in lower units of the section. From 1988 onwards, modern controlled excavations took place within the framework of the Franco-Moroccan co-operative project...