Milly Gaines
Scientists use a variety of methods to reconstruct the diets of fossil hominins, including stable isotope analysis of amino acids, molar cusp shapes, microscopic wear patterns on tooth surfaces, and the community composition of non-hominin fossil remains. Stable isotope analysis of carbon, nitrogen, and oxygen isotopes in fossil teeth and bones can provide insights into the dietary behaviours and ecologies of past hominin populations. The specific shapes of molar cusps and microscopic wear patterns on teeth can suggest adaptations to different diets, such as leaf- or fruit-based diets. Additionally, the community composition of non-hominin fossil remains at a site can help reconstruct the paleoenvironments in which our ancestors foraged. More recently, zinc isotope analysis has emerged as a new tool for studying the diets of fossil hominins and other Pleistocene mammals, providing information on the types of food consumed.
| Characteristics | Values |
|---|---|
| Stable isotope analysis | Carbon and nitrogen isotope analysis of the structural protein collagen in bones and dentin |
| Zinc isotope analysis of tooth enamel | |
| δ15Namino acid and δ13Camino acid analysis | |
| Isotope ratios from fossil teeth and bone | |
| Isotope ratios of individual amino acids | |
| Isotope ratios of fossil teeth from a Southeast Asian cave setting | |
| Isotope ratios of faunal remains | |
| Isotope ratios of individual amino acids | |
| Isotope ratios of bulk materials | |
| Isotope ratios of bone remains | |
| Isotope ratios of fossil teeth | |
| Isotope ratios of collagen-bound nitrogen | |
| Isotope ratios of modern animals | |
| Microscopic wear patterns on tooth surfaces | Reflect the fracture-resistance properties of the foods eaten in the weeks before death |
| Molar cusp shapes | Suggest adaptations to a leaf- or fruit-based diet, or to a more general one |
| Community composition of non-hominin fossil remains | Help reconstruct the paleoenvironments in which our ancestors foraged |
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What You'll Learn
Stable isotope analysis of teeth and bones
The stable isotope ratios of fossil teeth and bone represent a broad signature of the foods consumed at the time those tissues were formed. For example, δ15Namino acid is emerging as an indispensable method for dietary reconstruction, but it has a limited ability to independently determine the proportional contributions of terrestrial versus aquatic resources, which can lead to erroneous estimations of trophic positions. This limitation can be reduced in hominin dietary studies by measuring the local δ15N values of freshwater fish, terrestrial plants, terrestrial meat, and seafood.
Another example is δ13Camino acid, which, when studied in pigs fed varying proportions of terrestrial and marine proteins, showed that valine, an essential amino acid, tended to be 13C depleted in bone collagen and 13C enriched in muscle tissue relative to diets. This reinforces the need to define tissue-specific δ13Camino acid offsets to reconstruct consumer diets and resource use accurately.
The accuracy and precision of isotopic analyses depend on the quality of gas chromatography separation, interface design, and isotopic calibration. During runs, it is crucial to monitor the isotopic drift of analytical standards and reference materials, such as modern bones, and to ensure that scale normalization for the samples being measured is based on two or more reference analytes.
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Microscopic wear patterns on tooth surfaces
The analysis of microscopic wear patterns on the occlusal surfaces of fossil hominid teeth can provide valuable information about their diet and chewing behaviour. The occlusal surface of teeth, or the grinding surface, can record an individual's life history, with the wear facet pattern indicating the mechanisms used for crushing, shearing, and grinding food. For example, the molars of A. afarensis show diverse functional areas, suggesting a varied diet. On the other hand, the molars of A. africanus and P. robustus exhibit rapid flattening of crown relief, indicating hard-object feeding.
In a study published in 2016, researchers examined the microscopic scratches on the cheek surfaces of teeth from 167 fossil specimens of Paranthropus and early Homo species. They found that contrary to previous isotopic evidence, the scratch patterns on the teeth of P. aethiopicus and P. boisei indicated that they did not chew significant amounts of abrasive foods. Instead, these species may have consumed less abrasive, brittle plants. Meanwhile, the scratch patterns on H. ergaster teeth suggested a diet of more abrasive foods than previously thought.
Three-dimensional analysis of wear patterns on hominid teeth can provide additional insights into the relationship between diet, chewing behaviour, and early hominid evolution. High-resolution optical topometry enables the measurement of parameters on 3D computer models of teeth, allowing for the comparison of various occlusal morphologies and the interpretation of function. This approach can help to identify species-specific dietary patterns and understand early hominid evolution.
While microscopic wear pattern analysis provides valuable information, it is essential to consider its limitations. Most interpretations of tooth wear patterns are based on two-dimensional analyses, which may not capture the complex wear patterns on hominid teeth fully. Additionally, the lack of reliable tracers in paleodietary studies can make it challenging to determine the exact timing of dietary changes and the species involved.
To overcome these limitations, scientists have developed new methods such as zinc isotope analysis. By analyzing zinc isotopes in fossil tooth enamel, researchers can expand their knowledge of the diets of fossil hominids and other Pleistocene mammals. This method has been successfully applied to fossils for the first time, offering the potential to study dietary behaviours over 100,000 years ago.
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Molar cusp shapes
Molar cusp shape is a critical aspect of reconstructing the diets of fossil hominids. Teeth are the most durable part of the skeletal system and are the dominant part of the hominin fossil record. Molar teeth, in particular, stand out due to their functional importance, good preservation, and direct association with diet and environmental changes.
The shape of molar cusps can indicate adaptations to specific diets. For example, the specific shapes of molar cusps may suggest adaptations to a leaf- or fruit-based diet or a more general one. Living primates that eat leaves, for example, have longer crests and more sloping occlusal surfaces than those that prefer hard foods.
However, it is important to note that tooth shape does not always correspond to preferred food items. Other lines of evidence, such as microwear textures, are needed to understand food preferences. For instance, hard seeds and bones tend to leave complex, pitted surface textures, while tough leaves and meat more often leave anisotropic textures with long, parallel scratches.
The evolution of molar cusp shape over time has been a subject of interest. Molar teeth underwent significant changes, including variations in enamel thickness, the relative size of the first, second, and third molars, and mean crown area. These changes were especially pronounced between 2.5 and 1.8 million years ago, with tooth size rapidly declining after a steady increase.
To understand the evolution of molar cusp shape, researchers have utilized databases of molar teeth from fossil hominids, including measurements of cuspal enamel thickness, dentin horn angle, and section width. By analyzing these data with fracture stress and geological age, insights into the functional performance and dietary habits of fossil hominids can be gained.
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Amino acid stable isotope ratio analysis
Amino acids are essential nitrogenous molecules that play a critical role in nutrient exchange in living organisms. All organisms synthesize proteins from the same set of 20 amino acids, which are also used to form other biomolecules or oxidized to produce energy. Distinct metabolic processes control the isotope patterns among individual amino acids in consumers and their food sources. By studying these patterns, researchers can gain valuable insights into the dietary habits of fossil hominids.
One of the key advantages of using amino acid stable isotope ratios is their robustness to degradation and residue issues. Bone structures are susceptible to environmental fluctuations, such as humidity and temperature changes, which can accelerate amino acid degradation. However, amino acid stable isotope ratios are less affected by these factors compared to bulk stable isotope ratios. This is because amino acids bound in tissue proteins can be extracted and isolated, even in the presence of degradation and exogenous materials introduced during conservation treatments.
The δ15Namino acid method, in particular, has become indispensable for dietary reconstruction. It helps determine trophic positions and food sources by analyzing the stable isotope ratios of specific amino acids, such as phenylalanine. However, it has limited ability in independently determining the proportional contributions of terrestrial versus aquatic resources, which can lead to errors in estimating trophic positions. To address this limitation, researchers have suggested measuring local δ15N values of various food sources, such as freshwater fish, terrestrial plants, and meat.
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Nitrogen isotope analysis
The nitrogen isotope analysis is based on the understanding that different types of plants have distinct nitrogen isotope signatures, which are then reflected in the tissues of the organisms that consume them. This method is particularly useful for distinguishing between the consumption of terrestrial and aquatic resources, as these sources can have significantly different nitrogen isotope ratios.
One example of the application of nitrogen isotope analysis is in the study of Neanderthal dietary preferences. Researchers have used this technique to compare the diets of Neanderthals and early modern humans, shedding light on their ecological behaviors and food sources.
Additionally, nitrogen isotope analysis has been essential in understanding the dietary habits of ancient hominin populations. For instance, by analyzing the nitrogen isotope ratios in fossil hominin remains, scientists can determine the relative contributions of different food sources, such as freshwater fish, terrestrial plants, and meat, to their diets.
However, there are some limitations to this method. Nitrogen isotope analysis is most effective for tissues that are well-preserved, and it is challenging to apply this technique to fossils older than 100,000 years. The timeframe is even further reduced to a few thousand years in regions with humid or arid climates, such as Africa and Asia, which are crucial areas of interest for human evolution.
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Frequently asked questions
The most common method used to reconstruct the diets of fossil hominids is the analysis of stable isotope ratios, specifically carbon and nitrogen, in the structural protein collagen in bones and dentin. Nitrogen isotope analysis helps determine whether animal or plant food was consumed.
Stable isotope analysis has a limited ability to determine the proportional contributions of terrestrial versus aquatic resources. This can lead to incorrect estimations of trophic positions.
New methods include the analysis of zinc isotopes in fossil tooth enamel. This method has been used to study the diet of fossil hominids and other mammals from the Pleistocene era.
Other methods include studying the shape of molar cusps, microscopic wear patterns on tooth surfaces, and the community composition of non-hominin fossil remains.
