Teeth are the most durable biological structures in the vertebrate body, making them invaluable records of an animal’s life history. Composed primarily of crystalline calcium phosphate in the form of enamel and dentin, these biominerals are highly resistant to decay and degradation. This durability allows teeth to survive long after soft and skeletal tissues have vanished, especially in the fossil record. Studying dental anatomy and chemistry provides a wealth of information, from the animal’s diet and migratory patterns to its place on the evolutionary tree.
Decoding Diet and Lifestyle Through Dental Morphology
An animal’s diet is immediately reflected in the shape and structure of its teeth, a relationship known as dental morphology. Carnivores, such as cats and dogs, possess sharp, bladelike carnassials—specialized premolars and molars that shear muscle and tendon. They also feature large, pointed canines for puncturing and gripping prey, and their jaw movement is restricted to a vertical motion.
In contrast, herbivores have evolved complex grinding surfaces to process tough, fibrous plant material. Grazing animals like cows and horses often exhibit hypsodonty, characterized by high-crowned molars that compensate for the extreme wear caused by abrasive grasses. These molars display intricate patterns of enamel ridges (lophs or selenes) that increase grinding efficiency.
Omnivores, including humans and bears, possess a generalized dentition with low-crowned molars featuring rounded cusps, referred to as bunodonty. This shape accommodates a varied diet by allowing for both crushing plant matter and tearing meat. Scientists can further analyze microscopic wear patterns on the enamel surface using dental microwear analysis.
This analysis differentiates between tiny scratches (suggesting tough, fibrous foods like grass) and pits (left by consuming brittle items such as nuts or hard seeds). Because the enamel surface changes rapidly, the microwear pattern often reflects the animal’s diet from only the last few days or weeks of its life. This short-term snapshot of foraging behavior complements the long-term dietary picture provided by the tooth’s shape.
Determining Age and Longevity from Dental Structures
Teeth contain a highly accurate biological clock that reveals an animal’s longevity. The most precise method for determining absolute age in many mammals is by counting the annual growth layers, or annuli, found in the dental cementum. Cementum is a bone-like tissue that covers the tooth root and is continuously deposited throughout the animal’s life.
Similar to tree rings, cementum layers appear as alternating light and dark bands when examined under a microscope. The darker, thinner band usually forms during winter or resource scarcity, while the lighter, thicker band forms during the growing season. Counting these paired bands provides a reliable estimate of the animal’s age in years, which is valuable for wildlife management and population ecology studies.
A less precise method involves assessing the degree of tooth wear and eruption. As an animal ages, constant grinding leads to the progressive attrition of the enamel and dentin surfaces. For juveniles, the sequence of permanent tooth eruption provides an initial age estimate. Molar wear offers a relative age for older individuals, but wear patterns are heavily influenced by diet, making the cementum annuli count the superior technique for definitive age determination.
Uncovering Health and Nutritional History
The formation of tooth enamel permanently records periods of physiological stress. Scientists look for defects known as enamel hypoplasia, which manifest as pits, grooves, or lines on the tooth surface. These defects form when the cells creating enamel are temporarily disrupted by severe illness, malnutrition, or environmental stress during the tooth’s developmental stage.
Because teeth develop at predictable rates, the location of a hypoplastic line on the crown can be mapped to a specific time in the animal’s life, pinpointing the exact age when the stress event occurred. For example, hypoplasia on the first molar in white-tailed deer fawns often correlates with nutritional stress during weaning. Analyzing patterns of infection, such as abscesses or periodontal disease, also provides insight into the animal’s overall health status.
The chemical composition of a tooth reveals long-term nutritional and environmental history through stable isotope analysis. Elements like carbon and nitrogen from the diet are incorporated into the tooth’s collagen and enamel, reflecting the animal’s position in the food chain and the types of plants consumed. Analyzing oxygen and strontium isotope ratios indicates the chemistry of the water the animal drank, which is tied to local geology and climate. Since enamel forms during childhood and is metabolically inert, it provides a fixed chemical signature of the animal’s geographic origin and early life movements.
Tracing Ancestry and Evolutionary Relationships
The resilience of dental material means teeth are the most common and informative remains found in the fossil record, often serving as primary evidence for extinct species. Subtle variations in the number, size, and arrangement of teeth, summarized by the dental formula, are used to classify species and distinguish evolutionary lineages. For instance, placental mammals are thought to have an ancestral dental pattern of three incisors, one canine, four premolars, and three molars in each quadrant.
The specific patterns of cusps—the bumps and ridges on the chewing surfaces of molars—are highly conserved and genetically controlled, making them reliable markers for establishing phylogenetic links. Evolutionary trends in cusp complexity, such as the transition from a simpler triangular to a more complex rectangular molar pattern, trace the adaptive radiation of mammals. These minute differences are used by paleontologists to link a fossil specimen to its closest relatives and reconstruct the complex branches of the tree of life.