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A paleontologist who investigated three-dimensional tooth complexity and its relationship to diet in different mammalian lineages.^[ref]

An epithelial cell producing enamel during tooth development. Loss of the enamel-producing cellular layer after eruption limits replacement of worn crown enamel.

A body fossil preserves evidence of an organism's body or a part of it, such as a tooth, bone, shell or leaf. Preservation can retain original material, a mineralized structure, an impression or a cast. A body fossil therefore need not be an intact body or contain the original organic substances.

A trace fossil, such as a footprint or burrow, records activity rather than the body itself. Both are biological evidence, but they answer different questions: a tooth can constrain anatomy, whereas a trackway can constrain movement. Decay experiments show why preserved anatomy requires care: some characters disappear before others, biasing the apparent similarities used in phylogenetics.^[ref]

A specialized shearing tooth. In Carnivora the principal opposing pair is the upper fourth premolar and lower first molar; other predatory lineages can specialize different teeth.

The dental crown is the coronal part of a tooth, anatomically distinguished from its root. Its external covering and surface geometry are adapted to contact and food processing. The visible clinical crown can differ from the anatomical crown when the gingival margin changes.

Small wear features on tooth surfaces used to infer food processing near the end of the wear record. Diet, external grit, preparation and post-mortem damage must be distinguished.

A dentinal tubule is a microscopic channel in dentine, within the mineralized material formed by odontoblasts. The tubule network records the paths of odontoblast processes as dentine is deposited. A tubule is a structural channel; whether a prepared specimen contains fluid, a cellular process or an empty space depends on the tissue and its preparation.^[ref]

Elephant ivory provides a useful structural example. In a2017 study, observations of different cut planes and computed tomography using synchrotron radiation connected visible tubule profiles with their three-dimensional trajectories. A tube cut across, along or obliquely does not present the same two-dimensional profile. Consequently, a collection of oval profiles in a section need not consist of isolated oval cavities.^[ref]

A deliberately simplified transport example makes the channel size matter. For steady laminar flow through a straight circular tube, the Hagen-Poiseuille equation gives $Q=\pi r^4\Delta p/(8\mu L)$, where $r$ is tube radius, $L$ length and $\mu$ fluid dynamic viscosity. Doubling $r$ would multiply $Q$ by16 at fixed pressure difference and length. Real dentinal tubules branch, vary in width and may be obstructed, so this ideal calculation illustrates sensitivity to geometry rather than predicting a whole tooth's permeability.

A mineralized dental tissue formed by odontoblasts. It differs developmentally and structurally from the outer enamel coating of a typical human tooth crown.

A replacement pattern with two successive generations for the replaced tooth classes. It should not be taken to mean every tooth in the jaw is replaced exactly once.

A fossil is preserved evidence of past life in a geological context. A body fossil retains evidence of an organism's body, such as a tooth, bone or leaf; a trace fossil, such as a footprint or burrow, records activity. Complete replacement by minerals is not required for something to be a fossil.^[ref]

Fossilization can preserve different kinds of information. Permineralization fills spaces in biological material with minerals, while an impression may retain only external shape. These pathways help explain why the fossil record samples some anatomy characters much better than others, and why a transitional fossil is assessed through a combination of characters rather than overall resemblance.

The gingiva is the gum tissue surrounding the teeth and covering the supporting alveolar region. It contributes a protective interface around each tooth. Its attached portions differ mechanically from the more mobile buccal mucosa.

A horse is an equine mammal within Perissodactyla, with limbs specialized for terrestrial locomotion. Its fossil history supplies unusually rich evidence for changes in diet, tooth wear and crown height. Those changes represent branching lineages rather than one predetermined ladder toward the modern animal.

Continued growth of a tooth, distinguished from a tall but finite reserve crown in hypsodonty.

A high-crowned tooth construction supplying a reserve against wear. It differs from hypselodonty, and is not by itself proof of a grass diet.

An anterior tooth class specialized in diverse ways for cropping, cutting or gnawing.

Mechanical processing of food by repeated jaw and tooth movements. It changes food particle size and surface area before subsequent digestion.

A paleontologist who studied horse dietary change, comparing dental wear with the evolution of tooth crown height.^[ref]

A posterior tooth class important in many forms of food processing. Molar form varies with lineage, position and wear.

Paleontology investigates past life through fossils and their geological context. It combines anatomy, ecology, evolution and evidence about burial and preservation to infer what extinct organisms were like and how life changed.

The connection between evidence and history is the central challenge. A fossil may preserve a tooth but lose its surrounding soft tissues; absence of a visible character need not mean the living organism lacked it. Taphonomy therefore informs both reconstruction of individual organisms and interpretation of the fossil record.

Experiments following carcass decay test that inference directly: anatomically selective loss can remove derived characters and produce stemward slippage in a phylogenetics analysis.^[ref]

Skeletal anatomy can reconstruct likely resource use and test hypotheses about competition, but it cannot by itself measure the strength of an interaction between fossil populations. Resource partitioning among living sympatric primate species provides a useful source of comparative predictions. It does not establish that every difference among coexisting fossil species was caused by competition: differences may predate coexistence, reflect other selective pressures, or merely determine which species can occur together.

The first requirement is to establish the relevant community. fossils from one formation may have accumulated over many thousands of years or represent animals transported from different habitats. Stratigraphy, dating, sedimentology and taphonomy must therefore establish plausible coexistence at an ecologically relevant scale. Species boundaries, skeletal associations, age, sex and the number of individuals also need attention. A mixed collection of several time-separated populations cannot be treated as one living primate group, and an isolated limb should not be confidently assigned to a hominin species solely because its teeth occur nearby.

For diet, I would measure tooth size and proportions, crown shape, shearing edges, enamel thickness, jaw geometry and muscle attachment regions. Functional morphology connects these observations to potential food processing: slicing leaves, crushing relatively hard items and resisting repeated chewing loads impose different demands. Body size affects both mechanics and energetic requirements, so comparisons need allometry rather than assuming that a larger tooth necessarily reflects a different food category. Phylogenetic relationships also matter because inherited resemblance can produce apparent ecological overlap independently of recent competitive interactions.

These measurements estimate capability better than habitual consumption. Paranthropus boisei has a powerful chewing apparatus and very large postcanine teeth, yet a dental-microwear study found comparatively low surface complexity and anisotropy in the seven specimens preserving suitable surfaces. ^[ref] This contradicted a straightforward inference of habitual hard-object feeding from robust anatomy alone. It is compatible with the importance of mechanically demanding fallback foods, or other uses of the apparatus, without uniquely demonstrating either explanation. A morphology selected during rare food shortages need not correspond to the last meals recorded by dental microwear.

Enamel chemistry provides a partially independent test. Carbon-isotope measurements indicated substantial use of C4-based resources by Paranthropus boisei. ^[ref] This helps distinguish it from a consumer relying predominantly on C3-derived resources, but does not specify the plant part, exact food species or necessarily every intermediate step through a food web. Grasses and sedges can share the broad photosynthetic signature. Isotopic overlap therefore need not mean identical diets, just as different wear patterns need not imply complete separation. The strength of the reconstruction comes from combining evidence that integrates different biological timescales and different aspects of resource use.

For locomotion, I would examine joint shape, limb proportions, phalangeal curvature, grip-related structures, the shoulder, pelvis, vertebral column and articular surfaces. These can constrain leaping, climbing, suspension, quadrupedal walking or habitual bipedalism and hence access to canopy levels, support diameters and terrestrial resources. However, a locomotor category is not a diet. Animals with similar locomotor competence may choose different foods, while animals with different locomotion may compete for the same ground-level resource. Wear, preservation and reconstruction uncertainty need to be propagated rather than assigning every specimen to a single categorical lifestyle.

Hominins make this caution especially important. A bipedal lower limb need not imply complete abandonment of climbing. Comparative analysis of the juvenile scapula of Australopithecus afarensis supported retained climbing-related features and showed why ontogeny matters in comparison with living apes. ^[ref] This informs possible resource access, but does not quantify time spent climbing or competitive effects on another species. A fossil community containing an australopith, a species of Homo and other primates could consequently share some resources while partitioning others. The anatomical mosaic should be retained in the model rather than compressed into a single “terrestrial” score.

An explicit model clarifies what is missing. In one conventional competition model:${\alpha }_{ij}$ is an ecological competition coefficient, defined relative to the chosen density units and model assumptions. It represents the effect of another population on population $i$, not simply their morphological resemblance. Estimating it requires information about density, resource limitation and demographic responses that skeletal shape rarely provides. The same niche overlap could accompany negligible competition when food is abundant and severe competition during a bottleneck. Conversely, strong present-day partitioning could be a legacy of past competition rather than evidence that competition was always weak.

I would therefore construct quantitative, uncertainty-aware estimates of dietary and locomotor overlap, calibrated against living primates with measured behaviour. The calibration should include species occupying similar environments but differing in abundance or competitive context, and test predictions on species excluded from model fitting. A morphospace can summarize measurements, but distance in it is not automatically ecological distance. Closely related species, correlated skeletal measurements and multiple teeth from one individual cannot be counted as independent demonstrations.

To test competition more directly, compare putatively interacting species across intervals or localities with and without the competitor, while accounting for habitat, climate, ancestry and body size. Divergence specifically associated with overlap would support ecological character displacement more strongly than a difference observed at one site. Comparable shifts in abundance, resource availability or population performance would strengthen the inference, although fossil abundance itself is affected by preservation and collection. Several independent lines of evidence are needed to distinguish competition from environmental filtering or an inherited ecological difference.