Archaeological bones or teeth-who wins the race? A geochemical reappraisal to evaluate the potential for palaeoscience research

Abstract

The palaeoclimatic reconstruction based on sediment archives, spores and pollens, and invertebrate fossil records is widely explored in palaeoscience research. However, the disappearance or collapse of many civilisations due to climatic shifts over the geological timescale underscores the need to expand the realm of Palaeosciences to include archaeological remains. In this context, the bones and teeth from human and animal remains found in archaeological sites have become essential records for palaeoscientific research. These remains, which originate from a range of cultural and environmental contexts beyond necropolis sites, offer isotopic and chemical clues about past climatic conditions, mobility and diets. Although the primary focus of this study is on human remains, the conclusions are generally applicable to faunal materials, which raises the main question: which tissue—bone or tooth—offers more trustworthy insights for palaeoscientific research? The present study critically evaluates the potential of archaeological bones and teeth for reconstructing palaeoclimatic and palaeodietary landscapes, seeking a better asset for palaeoscientists. The teeth, particularly the enamel part, have been found here superior due to their higher degree of preservation owing to the mineral content and resistance to diagenetic changes. Therefore, the ability of fossilised teeth to consistently retain elemental and isotopic signals—a well-established characteristic based on biomineralisation science—makes them invaluable repositories for reconstructing palaeoenvironmental conditions and palaeodietary practices.

In contrast, the bones, due to their porous structure and organic matrix, are more susceptible to post-mortem alterations and environmental contamination. Such secondary processes occurring in the fossilised bone raise doubts about the quality of information recorded from their chemical analyses. Therefore, their utilisation in palaeoscience poses some limitations and requires special care. The holistic overview of the temporal resolution, preservation quality and contextual integrity of both tissues reveals that the teeth provide a more precise snapshot of early-life environmental conditions, such as childhood diet and geographic origin. In contrast, the bones provide narratives into broader temporal patterns with relatively less precision. Although the significance of bones in reconstructing past climates and human adaptations cannot be ruled out, the teeth win the race for providing more accurate and high-resolution insights into early-life conditions.

INTRODUCTION

Palaeoscience is an interdisciplinary field that reconstructs past environmental and climatic conditions through geological, biological and archaeological records (Jansen et al., 2007). It utilises diverse proxies—including geochemical, biological, archaeological, sedimentological and ice core data—to uncover Earth’s climatic history. These proxies are essential not only for understanding long-term environmental changes and human–environment interactions but also for informing future climate predictions (Birks et al., 2010). Among archaeological remains, bones and teeth are particularly valuable as they retain biogeochemical signatures over millennia. Stable isotope ratios (such as δ¹³C, δ¹⁵N and δ¹⁸O) and trace element (TE) concentrations (e.g., Sr, Ba, Zn) preserved in skeletal tissues provide direct insights into ancient diets, mobility patterns and palaeoenvironmental conditions (Katzenberg & Harrison, 1997). The analysis of bioapatite and collagen in these remains helps decode dietary patterns, subsistence strategies and physiological stress in past populations, making them vital for palaeodietary and palaeoenvironmental studies (Lee-Thorp, 2002).

Numerous case studies have highlighted the utility of both human and faunal remains in palaeoclimate reconstruction. Although the present study focuses on human archaeological samples, faunal remains have also proven to be significant archives of palaeoenvironmental change. For example, stable isotope analyses of Late Pleistocene horse remains in North America revealed substantial dietary and habitat-use shifts in response to climatic fluctuations (MacFadden, 2000). Similarly, dental studies on prehistoric ungulates in Europe have demonstrated how changing vegetation patterns influenced their morphology and geographical distribution (Janis et al., 2000). In the Arctic, isotopic evidence from ancient caribou remains has shed light on past migratory adaptations to shifting vegetation zones (Guthrie, 1990). These faunal studies not only validate geochemical methods but also offer broader ecological perspectives that enhance the interpretation of human data.

Beginning approximately 11,700 years ago, the Holocene epoch encompasses a wide range of cultural development on the Indian subcontinent, from the Mesolithic to the Medieval era. Significant shifts in social organisation, settlement patterns and subsistence practices characterise it. Human and animal remains, found at archaeological sites throughout India, are being examined more and more using geochemical methods in an effort to reconstruct earlier lifestyles over this extensive time period. The Indian summer monsoon gradually weakened after approximately 7,000 years BP, which corresponded with cultural shifts in the Harappan civilisation, according to an oxygen isotope analysis of animal bioapatites from the archaeological site of Bhirrana in northwest India (Sarkar et al., 2016). Using ancient DNA and stable isotope analysis (δ¹³C and δ¹⁵N), multidisciplinary research at Roopkund Lake has revealed the presence of genetically distinct groups, including individuals of Mediterranean ancestry, who arrived in the Indian Himalayas around the ninth century CE (Harney et al., 2019). While Late Pleistocene mammalian enamel from central India reflects environmental shifts at the Holocene threshold (Mehra et al., 2024), carbon and oxygen isotope data from human tooth enamel at Chalcolithic Inamgaon offer insights into palaeodiet, weaning practices and ecological conditions across three cultural periods, forming a valuable isotopic baseline for prehistoric western India (Mahajan et al., 2021). Stable isotope analysis and radiocarbon dating of human skeletal remains from the Sinauli burial site in the Ganga-Yamuna Doab suggest a warm, semi-arid climate and a diet dominated by C₄ plants. In addition to suggesting regional adaptation to agro-pastoral lifeways (Sharma et al., 2024) and supporting a date of the second millennium BCE, the results of isotopic studies of nineteenth-century people at Ajnala have shown C3-based diets and geographic origins (Sehrawat et al., 2020). Skeletal analyses at Porunthal, in southern India, provide information on population health and burial customs from the Iron Age to the Early Historic Period (Talanki et al., 2015). Our understanding of population dynamics, palaeodiet, mobility and environmental change in ancient South Asia is enhanced by situating isotopic and TE research within the framework of Holocene archaeology, as these geographically varied and chronologically anchored studies demonstrate.

The current study intends to assess whether teeth or bones are more trustworthy markers for reconstructing the palaeodiet and palaeoclimate in light of this. This evaluation takes into account each of their isotopic signatures, potential for preservation, and the applicability of current analytical developments.

HUMAN BONES AS PALAEOCLIMATE INDICATORS

Composition and structure

Human bone is composed of ~60% inorganic material, ~30% organic substances and ~10% water (Figure 1) (Morgan et al., 2008). The inorganic part includes hydroxyapatite, with substitutions like carbonate, fluoride, chloride, magnesium, strontium, sodium and potassium that influence bone solubility and homeostasis (Brommage & Neuman, 1979; Doi et al., 1979; McConnell et al., 1971). The organic component consists mainly of Type I collagen (~95%) and non-collagenous proteins (~5%), along with bone cells (~2%) (Feng, 2009). Collagen’s triple-helix structure provides tensile strength and forms the scaffold for mineral deposition.

Figure 1.

The diagram illustrates the chemical composition of human bone, which is primarily made up of inorganic material (~60%), organic material (~30%), and water (~10%). The inorganic fraction consists primarily of hydroxyapatite (~95%) with minor other elements (~5%), while the organic portion is predominantly bone matrix (~98%) composed of collagen (~95%) and non-collagenous proteins (~5%), along with bone cells (~2%). Diagram modified after © 2025 Sushil Humagain, M.Sc. Medical Microbiology. Author and Editor at OnlineScienceNotes.com; Content Creator at MicrobeNotes.com; Science Teacher at GEMS School, Dhapakhel, Nepal. All rights reserved.

Human bones share a broadly similar chemical composition with those of many animal species, comprising approximately 60%–70% inorganic mineral (primarily hydroxyapatite), 20%–30% organic matrix (mainly Type I collagen) and a small percentage of water. However, interspecies differences in the mineral-to-matrix ratio, degree of mineral crystallinity and remodelling dynamics are well documented. For instance, rodents generally exhibit lower mineralisation levels, whereas animals such as dogs and pigs tend to have slightly higher mineral content than humans (Aerssens et al., 1998).

Density variations also distinguish human and animal bones. Large quadrupeds like horses and cattle typically possess denser cortical bone due to the biomechanical demands of quadrupedal locomotion. In contrast, human cortical bone, adapted for bipedal movement, is generally less dense. Moreover, commonly used animal models in research, such as rats and rabbits, tend to have lower overall bone mass and elevated rates of bone remodelling, which render their mechanical properties less analogous to those of the human skeleton (Aerssens et al., 1998).

From a microstructural perspective, human bones are characterised by a well-developed Haversian system, marked by secondary osteons and relatively high porosity—particularly in trabecular bone—resulting from continuous remodelling throughout life. In contrast, bones from several animal species, such as sheep and pigs, often exhibit a more lamellar or plexiform structure with fewer secondary osteons, especially in species with slower or minimal remodelling rates. These interspecies microstructural differences are crucial to consider when selecting suitable animal models for biomechanical and biomedical research, as they significantly impact bone strength, healing response and overall mechanical behaviour (Aerssens et al., 1998).

In life, bones constantly remodel, replacing old tissue with new to maintain strength and function. With death, these protective processes cease, leaving the skeleton exposed to environmental influences. Depending on conditions, bones may either undergo preservation, retaining much of their original structure, or diagenesis, where chemical and physical changes alter their composition over time.

Preservation and diagenesis

Bones are one of the most enduring biological tissues in nature. However, they can be subjected to secondary alteration, owing to ~9.2% porosity due to the breakdown of soft tissues within blood vessels and osteocyte lacunae (Figueiredo et al., 2010). Thus, the archaeological bones, as well as the fossils, may undergo water interaction, microbial colonisation and ion exchange, which significantly reduces their preservation potential and allows them to undergo diagenesis (Hedges & Millard, 1995).

Based on the burial place, the preservation potential of human bones is associated with several extrinsic factors, such as soil pH, local hydrological conditions, presence of organic matter in the soil, and microbial activities.

Soil pH- This chemical parameter of soil highly controls bone preservation. Experimental studies have shown that acidic soils (3.5 < pH < 4.5) are more corrosive than alkaline soils (7.5 < pH < 8.0) (Nicholson, 1996; Nielsen-Marsh et al., 2007). Human bones in acidic environments experience rapid mineral dissolution, as bioapatite is most stable at a pH of 7.8 (Berna et al., 2004) but begins to dissolve when pH drops to <6.0 (White & Hannus, 1983).

Hydrological conditions- Water plays a key role in bone preservation and modification. Hydrological conditions around buried bones fall into three categories: diffusive (minimal water movement), recharge (fluctuating wet-dry cycles) and flow (constant water movement) (Hedges & Millard, 1995; Nielsen-Marsh et al., 2000). Cyclical wetting, drying, freezing and thawing are particularly damaging, leading to cracks and flaking (Fernández-Jalvo et al., 2010; Pfretzschner & Tütken, 2011; Pokines et al., 2016). Absorbing and desorbing rates of water in archaeological bones are relatively higher in comparison to fresh bone due to their porosity (Turner-Walker, 1993). When water passes through a bone, it can dissolve and remove the mineral content of the bone. The speed at which these minerals are leached (removed) depends on: pH of water and volume of water inside the bone.

Soil organic matter- Humic substances in soil contribute to secondary alterations in bone by interacting with its organic and mineral components. These compounds, originating from decomposing plant material, form stable complexes with metal ions and can bond with bone collagen, resulting in partial demineralisation (van Klinken & Hedges, 1995). In moist soil conditions, bones in direct contact with humic substances often develop a darker colouration and undergo partial mineral loss (Turner-Walker, 1993, 2008).

Microbial activities- This is another major factor in bone diagenesis. Microorganisms (e.g., fungi, bacteria and aquatic microorganisms) can penetrate bone through various pathways (such as vascular canals, cracks and surface erosion), leading to bioerosion (Bell et al., 1991; Davis, 1997; Hackett, 1981; Jackes et al., 2001; Marchiafava et al., 1974; Pesquero et al., 2010, 2018; Turner-Walker, 2012). These microbial-induced alterations compromise bone integrity by accelerating collagen degradation and structural weakening.

It is interesting to note that bone collagen degradation can occur through both biological and chemical processes. Microbe-induced collagenases are the biological track of collagen destruction after mineral removal (Child, 1995a, 1995b; Marchiafava et al., 1974). The environmental factors, such as temperature, soil pH and burial duration, influence the chemical mode of collagen degradation. Extreme pH levels and higher temperatures accelerate collagen loss, although bones with extensive cross-linking can retain collagen over a more extended time period (Collins et al., 1995; Smith et al., 2002).

PALAEOSCIENCES RESEARCH ON ARCHAEOLOGICAL BONES

Pre-analytical processes

Before any removal techniques can be applied, it is imperative to identify the types of secondary alterations present in archaeological human bones and teeth. Secondary alterations can occur due to various factors, including environmental conditions, post-depositional processes and anthropogenic influences.

Bones and teeth undergo various post-mortem changes, including microbial decomposition, where microorganisms degrade organic components, often visible as biofilms or discolouration (Mays, 2010). Chemical alterations like leaching or mineralisation affect their composition, which is identifiable through techniques such as X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). Although physical changes, such as abrasion, weathering, or mechanical damage, can be initially observed by macroscopic inspection, scanning electron microscopy (SEM) provides high-resolution information about the type, extent and location of these changes, which helps piece together the taphonomic past. Additionally, taphonomic processes like scavenging and burial conditions modify bone structure, assessed through comparisons with known taphonomic signatures (Behrensmeyer, 1978).

Techniques for identifying secondary alterations

Analysis of skeletal remains involves multiple techniques to identify alterations. Visual inspection is the first step, noting colour changes, surface texture, and signs of erosion or damage. Microscopy, including light microscopy and SEM, reveals microstructural changes on bone and tooth surfaces (Jeong et al., 2019). Spectroscopic methods, such as FTIR and XRD, offer quantitative data on chemical composition, enabling the detection of changes, including secondary mineral formation. Histological analysis of thin bone sections allows observation of cellular-level alterations and helps assess the extent of microscopic changes (Vacková et al., 2022). After identifying the presence of secondary alterations, it becomes essential to eliminate these modifications to obtain accurate results in paleoclimate and paleodiet reconstruction.

Techniques for secondary alteration removal

Once secondary alterations have been identified, various techniques can be employed to remove or mitigate their effects. These techniques can be broadly categorised into physical, chemical and biological methods.

Physical techniques

Cleaning of skeletal remains involves several careful techniques. Mechanical cleaning uses tools like dental picks, scalpels, or brushes to gently remove surface debris, taking care not to harm the bone (Mays, 2010). Ultrasonic cleaning utilises high-frequency sound waves to dislodge contaminants without causing damage, making it an effective method for cleaning delicate surfaces. Abrasive techniques may be used with mild materials to remove surface alterations, but must be applied cautiously to avoid further damage (Vacková et al., 2022).

Chemical techniques

Chemical cleaning of bones involves various controlled treatments. Weak acids like acetic or citric acid effectively dissolve mineral deposits without harming the bone matrix. Hydrogen peroxide is used to remove organic stains, but must be applied carefully to avoid collagen degradation. Chelating agents such as EDTA bind and remove calcium carbonate deposits while preserving bone integrity. Alkaline solutions like sodium bicarbonate help neutralise acidic conditions and restore pH balance.

Biological techniques

Biological cleaning methods use targeted agents to remove organic contaminants from bones. Bioremediation involves microorganisms that degrade organic matter, aiding in the cleaning process (Mays, 2010). Enzymatic treatments, such as proteases, break down organic residues like collagen without damaging the mineral matrix. For biofilm removal, surfactants or enzymes are applied, often in conjunction with physical or chemical methods, to eliminate microbial layers effectively. After removing secondary alterations through various pre-treatment protocols, the next step is to reconstruct past environmental and dietary conditions through analytical processes such as isotopic analysis and TE analysis.

Analytical process I-isotopic analysis

Isotopic analysis of the archaeological bones is a powerful tool for reconstructing past diets, migration patterns and palaeoenvironmental conditions. The analyses of the stable isotope composition of carbon, nitrogen, oxygen and strontium within bone collagen and bioapatite can provide significant insights into ancient subsistence strategies, climatic conditions and geographic mobility.

Implications for palaeodiet reconstruction

The isotopic composition of carbon and nitrogen in bone collagen reflects the dietary intake of individuals because these isotopes are incorporated into body tissues through food consumption and metabolic processes. Carbon isotopes can distinguish between diets based on C3 plants (e.g., wheat, rice) and C4 plants (e.g., maize, millet), as well as the consumption of marine versus terrestrial resources. C₃ plants, common in temperate regions, have δ¹³C values between −34‰ and −19‰, while C₄ plants, which thrive in arid and tropical environments, range from −16‰ to −10‰ (Agrawal et al., 2012). Individuals consuming primarily C₄ plants, such as maize or millet, exhibit more enriched δ¹³C values compared to those reliant on C₃ plants like wheat and rice (Vogel & van der Merwe, 1977). Similarly, marine diets show higher δ¹³C values (around −12‰ to −14‰) compared to terrestrial diets, as marine ecosystems have distinct carbon cycling patterns (Walker & DeNiro, 1986). For example, a higher ¹³C/¹²C ratio indicates a diet rich in C4 plants or marine resources. Nitrogen isotopes, on the other hand, are used to identify the trophic level of the diet. Higher ¹⁵N/¹⁴N ratios typically suggest a diet that includes more animal protein, as nitrogen isotopes become enriched with each step up the food chain. By analysing these isotopes in bone collagen, researchers can infer the types of foods consumed and the relative contributions of different food sources to the diet (Ambrose & Norr, 1993; Walker & DeNiro, 1986).

Application in palaeoclimate reconstruction

The oxygen isotope composition (δ¹⁸O) of archaeological bones reflects paleotemperature and precipitation because bone apatite (Ca₅(PO₄)₃(OH)) and collagen incorporate oxygen from body water, which in turn derives from drinking water and dietary sources. The δ¹⁸O values in environmental water vary with climatic conditions, as heavier oxygen isotopes (¹⁸O) are preferentially retained in precipitation during warm periods and become depleted in colder climates due to temperature-dependent fractionation (Dansgaard, 1964). This fractionation follows the Rayleigh distillation process, where δ¹⁸O decreases with increasing latitude and altitude due to the progressive condensation of water vapour (Rozanski et al., 1993). Since vertebrates record these isotopic signatures in their bones and teeth, δ¹⁸O analysis enables paleoclimate reconstructions by estimating past temperature and precipitation regimes. For instance, Luz et al. (1984) demonstrated that δ¹⁸O in human and animal bones corresponds to regional meteoric water δ¹⁸O, which is temperature-dependent. Similarly, Longinelli (1984) used δ¹⁸O from fossil mammal bones to estimate ancient climatic conditions. These studies confirm that oxygen isotopes in archaeological bones serve as reliable proxies for paleotemperature and hydrological conditions.

Implications for understanding human mobility

Strontium isotope ratios (⁸⁷Sr/⁸⁶Sr) in bones are widely used in archaeology and bioanthropology to trace human mobility and geographic origins because strontium in human tissues reflects the isotopic composition of local geology through the food chain. Strontium isotopes vary geographically due to the differing ages and compositions of bedrock, with older rocks generally having higher ⁸⁷Sr/⁸⁶Sr ratios due to the radiogenic decay of ⁸⁷Rb (rubidium) over time (Bentley, 2006). Plants from the soil absorb these ratios, enter the food chain, and are incorporated into human bones and teeth, replacing calcium in hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂). Since tooth enamel forms in early childhood and remains unchanged, it preserves childhood ⁸⁷Sr/⁸⁶Sr signatures, while bones remodel over time, reflecting the strontium composition of the individual’s later years (Price et al., 2002). By comparing skeletal strontium ratios with local bioavailable strontium from soils and water, researchers can identify individuals who were local or non-local to an archaeological site, thus reconstructing migration patterns (Montgomery, 2010). Notable applications include studies on prehistoric migration in Europe (e.g., Neolithic and Viking populations) and the mobility of ancient civilisations such as the Maya and the Inca (Knudson et al., 2004).

The combined use of carbon, nitrogen, oxygen and strontium isotopic analyses allows for a comprehensive understanding of past human lifestyles, including their dietary choices, migration patterns and responses to climatic changes.

Analytical method II: TE analysis

The analysis of TE in human skeletal remains is valuable in bioarchaeology, as it offers deep insights into past human diet, health, social status, occupations and daily activities (Simpson et al., 2021). The concentration of TE in the human bones depends on the chemistry of extracellular fluids, which is mainly the reflection of dietary habits, that is, the foods they consume. The elements get incorporated into these foods from the soil and ultimately return to the soil after human death, followed by burial (Kabata-Pendias & Mukherjee, 2007).

Implications for palaeodiet reconstruction

TE analysis is a valuable method in palaeodietary research, offering insights into ancient human and animal diets based on the elemental composition of skeletal remains. Elements such as strontium (Sr), barium (Ba), zinc (Zn) and lead (Pb) are commonly analysed to infer trophic levels, dietary sources and environmental exposure. These elements are incorporated into bones and teeth through food and water intake, making them reliable indicators of long-term dietary habits (Burton & Price, 1990).

Strontium and barium are particularly useful for distinguishing plant-based from animal-based diets. Since these elements are more abundant in plants and decrease in concentration as they move up the food chain, individuals consuming a diet rich in plants tend to have higher Sr/Ba ratios, whereas those consuming more animal protein exhibit lower ratios (Price et al., 2002). This pattern allows researchers to differentiate between agricultural populations with mixed or meat-based diets and hunter-gatherer groups that relied heavily on plant resources. Similarly, zinc levels are used as a marker for meat consumption, as higher concentrations of Zn are associated with carnivorous diets. At the same time, herbivores tend to exhibit lower levels of this element (Kohn et al., 1996).

Beyond dietary reconstruction, TE can provide information on environmental exposure and cultural practices. Lead, for instance, has been linked to anthropogenic pollution and food storage methods, with elevated Pb levels often found in populations that use lead-based cookware or are exposed to contaminated water sources (Montgomery et al., 2007).

HUMAN TEETH AS PALAEOCLIMATE INDICATORS

Composition and structure

The human tooth consists of four main layers—enamel, dentin, pulp and cementum—each with unique structures and functions (Figure 2). Enamel, the outermost layer, is the hardest biological material, composed of ~96% inorganic hydroxyapatite and ~4% organic material and water. Its tightly packed rods make it highly resistant to mechanical forces, though brittle (Chen et al., 2025). Beneath the enamel lies dentin, which forms the bulk of the tooth. It contains ~70% inorganic material, 20% organic (mainly Type I collagen), and 10% water, providing flexibility and reducing fracture risk. Dentin also contains tubules that transmit nerve signals and fluids, contributing to sensitivity.

Figure 2.

Diagram of tooth structure and its chemical composition. The image illustrates the major anatomical components of a tooth, including enamel, dentin, pulp, gum, cementum, blood vessels, periodontal ligament, lateral canals, and nerve. The corresponding chemical composition of enamel (~96% inorganic, ~4% organic, and water), dentin (~70% inorganic, ~30% organic and water), and cementum (~45%–50% inorganic, ~50%–55% organic and water) is also provided, highlighting the variation in mineral content across different tooth tissues. Tooth diagram modified after ©2013 Encyclopaedia Britannica, Inc.

The pulp, located at the centre, is a soft, vascularised tissue composed of nerves, blood vessels, fibroblasts and odontoblasts. It supports the dentin by providing nutrients, sensory function and repair through secondary dentin formation (Ghannam et al., 2023). Cementum, a thin calcified layer covering the tooth root, anchors it to the alveolar bone via the periodontal ligament. It consists of 45%–50% hydroxyapatite and 50%–55% collagen and continues to grow throughout life, adapting to occlusal changes (Bosshardt & Selvig, 1997). Each layer’s chemical composition reflects its function: enamel offers mechanical protection, dentin ensures shock absorption, pulp supports sensory and regenerative roles, and cementum aids in tooth attachment. Water, present in varying amounts, supports ion transport and structural integrity (Ten Cate, 2019).

Preservation and diagenesis

The preservation and diagenesis of human teeth are critical areas of study in bioarchaeology and forensic science, as they provide insights into the environmental and biological factors that influence the long-term survival of dental remains. Human teeth, due to their mineralised structure, are among the most durable biological tissues, often surviving in archaeological contexts where other skeletal elements are degraded. However, despite their durability, teeth undergo chemical and physical changes after death (diagenesis), which can affect their composition and structural integrity.

Factors affecting human tooth preservation

The exceptional preservation of teeth is mainly due to their high mineral content, primarily hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂), which is highly resistant to degradation. Enamel, the most mineralised tissue, is particularly robust and provides an excellent archive for chemical and isotopic analyses. The survival of teeth in archaeological and fossil contexts depends on multiple factors, including the burial environment, soil chemistry, microbial activity and post-mortem exposure to environmental elements.

One key factor influencing preservation is the pH and mineral composition of the surrounding soil. Acidic environments accelerate enamel dissolution, while alkaline conditions favour mineral retention. In waterlogged or anaerobic conditions, teeth tend to be better preserved due to limited microbial activity (Collins et al., 2002). In contrast, high microbial activity in organic-rich soils can lead to the degradation of dentin and pulp faster than enamel.

Temperature fluctuations and mechanical stress also play a role in preservation. Teeth buried in permafrost conditions or desert environments are often found in near-pristine conditions due to minimal chemical alteration. On the other hand, burial in fluctuating wet-dry conditions can lead to cracking and hydrolytic breakdown of organic components.

Diagenesis of human teeth

One of the most common diagenetic changes in teeth is mineral replacement and recrystallisation. Over time, the original bioapatite in enamel and dentin can undergo ion substitution, where elements such as fluoride (F⁻), strontium (Sr²⁺) and uranium (U⁺) replace calcium (Ca²⁺) and phosphate (PO₄³⁻) ions in hydroxyapatite (Imran et al., 2024). While this process increases hardness, it can distort the original isotopic composition, affecting studies on diet, migration, and environmental reconstructions.

Another form of chemical diagenesis is carbonate leaching, where carbonates are lost due to acidic soil conditions, altering carbon (δ¹³C) and oxygen (δ¹⁸O) isotope ratios used in radiocarbon dating. The presence of microbial activity accelerates this process, as bacteria produce organic acids that dissolve hydroxyapatite, increasing porosity and making the tooth structure more fragile (Kendall et al., 2018).

Physical diagenetic changes in teeth include microcracking, fragmentation and recrystallisation, which primarily affect dentin and cementum due to their higher organic content. Enamel, being highly mineralised, is more resistant to structural diagenesis but can still undergo over time (Gehler et al., 2011; Pellegrini et al., 2011; Tütken et al., 2008; Tütken & Vennemann, 2011).

Over long-time scales, fossilised teeth may undergo secondary mineral deposition, where original hydroxyapatite is gradually replaced by minerals such as calcite, silica, or iron oxides, leading to increased density and loss of original microstructural details. The incorporation of TE, such as strontium or lead, from the burial environment into the tooth’s mineral matrix is a common feature of diagenetic processes, complicating interpretations of biogeochemical data (Hoppe et al., 2003).

This replacement alters the physical and chemical properties of teeth, making it necessary to use analytical techniques such as FTIR, SEM, Laser Ablation-Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), Raman spectroscopy, and XRD to assess the degree of diagenetic change before conducting further research.

The accurate analysis of human teeth for stable isotope studies, TE composition, and paleoclimate reconstruction requires rigorous pre-treatment procedures to remove diagenetic alterations. Diagenesis can lead to contamination from secondary minerals, organic matter, microbial degradation, and groundwater infiltration, which can distort original isotopic and elemental signals. Therefore, pre-treatment is essential to ensure the reliability of data obtained from archaeological and palaeontological specimens.

PALAEOSCIENCE RESEARCH ON ARCHAEOLOGICAL TEETH

Pre-analytical processes

To mitigate diagenetic effects, researchers selectively analyse enamel over dentin and cementum due to enamel’s high mineral content and lower susceptibility to diagenesis (Lacruz et al., 2017). Before chemical treatments, the teeth samples undergo physical cleaning to remove visible contaminants:

Ultrasonic Cleaning: Teeth are sonicated in deionised water or ethanol to remove surface debris and sediment (Esposito et al., 2024).

Mechanical Abrasion: Gently grinding with abrasive paper, aluminium shot blaster, or by gentle abrasion is used to remove outermost enamel layers that may have undergone diagenetic alterations (Esposito et al., 2024; Ventresca et al., 2018).

Fracturing and Micro-Milling: For isotope analysis, enamel powder is obtained using a micro-milling technique to avoid cross-contamination with dentin.

Chemical pre-treatment is a critical step in preparing ancient and fossilised tooth samples for isotopic, TE and palaeobiological analysis.

Acid treatment for carbonate removal

Acetic acid (CH₃COOH, 0.1M–1.0M) is commonly used to remove secondary carbonates from fossilised teeth while preserving the primary phosphate composition. For enamel, a 0.1M–0.5M concentration is recommended due to its higher mineralisation, whereas 0.5M–1.0M is used for dentin, which is more porous and susceptible to diagenetic alteration (Ventresca et al., 2018 ).

Organic contamination removal

Microbial activity can affect δ¹⁵N values and degrade proteins in dentin and cementum, making pre-treatment crucial. Hydrogen peroxide is used to oxidise organic matter, but overexposure may damage collagen (Valdes et al., 2019). Sodium hypochlorite effectively removes microbial residues and humic acids, especially in protein-based isotope studies. Ethanol or methanol rinses are also used to eliminate lipids and contaminants, ensuring accurate δ¹⁵N analysis.

Analytical process I-isotopic analysis

Isotopic analysis of archaeological human teeth is a powerful tool in bioarchaeology, enabling the reconstruction of various aspects of ancient life, including diet, migration patterns and environmental conditions. Due to their highly mineralised structure, teeth are more resistant to diagenetic alteration compared to other skeletal elements, allowing them to retain authentic isotopic signatures over long periods.

Implications for reconstructing diets

Isotopic analysis has played a crucial role in understanding the dietary patterns and food sources of ancient populations. Carbon isotope ratios (¹³C/¹²C) help distinguish between C3 (e.g., wheat, rice) and C4 (e.g., maize, millet) plant consumption, reflecting shifts in agricultural practices. For example, studies have shown that the transition from hunter-gatherer subsistence to agriculture-rich diets was marked by increased consumption of C4 crops, such as maize in prehistoric North America (van der Merwe & Vogel, 1978). Similarly, nitrogen isotopes (¹⁵N/¹⁴N) can indicate an individual’s trophic level, distinguishing between plant-based and protein-rich diets, such as those reliant on marine or terrestrial animal protein sources.

Applications in tracking habitat migration

A combination of strontium (⁸⁷Sr/⁸⁶Sr) and oxygen (¹⁸O/¹⁶O) isotope ratios allows researchers to trace the movements of ancient populations and individuals. Strontium isotopes reflect the geological composition of a region’s bedrock, which is absorbed into human teeth through water and food consumption during childhood. By comparing the strontium signatures in teeth with local geological baselines, researchers can determine whether individuals lived in one location or migrated from elsewhere. Additionally, oxygen isotopes vary with climate and altitude, providing further evidence of geographic origins. This approach has been used to study the migration of individuals during the Roman Empire and Viking expansions, revealing movement patterns across vast regions (Montgomery et al., 2007).

Applications in environmental and climatic reconstruction

The analysis of oxygen isotopes (¹⁸O/¹⁶O) in teeth provides crucial information about past climatic conditions and environmental changes. Because oxygen isotope values are influenced by drinking water sources, they can indicate whether individuals lived in warm, temperate, or cold climates. This technique has been employed to investigate climate shifts and their impact on human societies, including droughts and temperature fluctuations that may have influenced population movements and settlement patterns (Pellegrini et al., 2016). By integrating oxygen isotope data with archaeological and historical records, researchers can gain a better understanding of how climate impacted ancient civilisations.

Overall, isotopic analysis of human teeth provides a high-resolution record of past human life, offering key insights into dietary habits, mobility and climate adaptations. By applying multi-isotope approaches and integrating them with archaeological and historical data, researchers continue to uncover the complex interactions between humans and their environments throughout history.

COMPARATIVE ANALYSIS: BONE VS. TOOTH

Reliability of isotopic signatures

In terms of the reliability of isotopic signatures, teeth are more authentic due to their higher preservation potential, owing to high mineral content and resistance to diagenetic alteration. Enamel’s dense crystalline structure preserves isotopic signals from childhood, providing a stable ‘snapshot’ of early life conditions that is less prone to post-mortem changes (Hillson, 2005). In contrast, bones are porous because of the lesser abundance of hydroxyapatite as well as their collagen content, which makes them more prone to post-burial diagenetic alteration responsible for obscuring or altering the earlier records (Hedges, 2002). In particular, the strontium and oxygen isotopic data recorded from archaeological teeth samples are highly valuable to determine the geographic origins and environmental conditions, while bone carbon and nitrogen isotopic measurements of bone specimens can be used to reconstruct diet after careful consideration of diagenetic contamination (Bentley, 2006; Evans et al., 2012).

Temporal resolution

The temporal resolution of the proxies is one crucial parameter in Palaeosciences research. It is the ability to provide information about specific time periods in an individual’s life. Hence, the temporal resolution can significantly affect how precisely the isotopic data reflect an individual’s diet, mobility and environmental interactions at particular life stages.

Teeth offer high temporal resolution, particularly because each tooth forms at specific, known periods in life. Once tooth enamel is formed, it remains unchanged throughout the individual’s life, preserving a permanent isotopic record from that specific period of formation. This allows teeth to act as biological time capsules, reflecting the diet and environment of the individual during infancy, childhood and adolescence, depending on which tooth is analysed. This high resolution makes teeth particularly useful for tracing early-life conditions, such as geographic origin (via strontium and oxygen isotopes), childhood diet (via carbon and nitrogen isotopes) and early migration patterns (Evans et al., 2012).

Bone, in contrast, has low temporal resolution because it is a living tissue that undergoes continuous remodelling throughout life. The isotopic signatures in bone reflect the diet and environment from approximately the last 10–20 years of life, depending on the bone type and the individual’s age at death. Bone isotopic composition is essentially an average of the individual’s diet and environmental conditions over that time period, rather than a snapshot of any specific age.

Preservation and contextual integrity

Teeth, particularly enamel, preserve far better than bone in archaeological contexts due to their highly mineralised structure, making enamel resistant to decay and diagenetic alterations (Hillson, 1996). While dentin and cementum are more susceptible to post-mortem changes, teeth still survive better than bone, especially in harsh burial environments like acidic soils or waterlogged areas (Hedges et al., 1995). In contrast, bone’s porous structure makes it vulnerable to microbial activity, chemical leaching and diagenetic changes that alter its isotopic composition (Trueman et al., 2008). Bone is particularly prone to degradation from environmental factors like moisture and pH, leading to significant isotopic information loss (Hedges, 2002).

Teeth generally exhibit higher contextual integrity than bones in isotopic studies due to their resistance to diagenesis, particularly in the enamel, which preserves original isotopic compositions (Montgomery, 2010). Once formed, enamel remains stable, portraying a reliable picture of early-life conditions, such as childhood diets and migration, with minimal post-burial alteration (Kohn, 2008). In contrast, bone continuously remodels throughout life, meaning its isotopic signals reflect an average of the last decade or so of an individual’s life, making it less useful for studying specific life stages (Hedges et al., 1995). Additionally, bone’s porous nature makes it more susceptible to contamination from groundwater and soil ions, complicating the retrieval of accurate biogenic information (Trueman et al., 2008).

CONCLUSIONS

For palaeoscientific research, this study supports the long-held but empirically supported belief that teeth—especially enamel—are more trustworthy than bones. Particularly from early-life stages, they can preserve isotopic signatures with greater fidelity and temporal precision due to their high mineral content and resistance to diagenetic alteration. In contrast, bones are more likely to become contaminated because of remodelling, porosity and environmental interactions, even though they can be used to reconstruct dietary and mobility patterns in later life.

This is not merely a theoretical distinction. Case studies from Holocene South Asia demonstrate the value of prioritising teeth. An understanding of high-altitude migration that would probably be hidden in bone by post-depositional alteration was provided by femur bone collagen-based carbon and nitrogen isotope analyses at Roopkund Lake, which showed the presence of Mediterranean people who perished in the Indian Himalayas circa the ninth century CE and a mixed C₃-C₄ diet. Similarly, isotopic analysis of human enamel at the Sinauli burial site provided insight into agro-pastoral lifeways in the second millennium BCE Ganga-Yamuna Doab, revealing a semi-arid climate and a diet high in C₄ plants. These examples demonstrate how dental tissues offer information that is both culturally and environmentally significant, in addition to providing improved preservation.

Therefore, this study supports the conclusion that archaeological teeth are the more reliable, high-resolution archive for reconstructing early-life conditions in past human populations, even though bones still have value in palaeodietary and palaeoclimate studies—especially when collagen is well-preserved.