Are Teeth Fossils? How They Form & What They Reveal

Teeth are fossils, and they are among the most abundant and informative types discovered. A fossil is the preserved remains or traces of a once-living organism, and the inherent durability of teeth makes them well-suited for preservation, often surviving to become part of the geological record.

The process that turns a tooth into a fossil is a specific type of fossilization called permineralization. After an animal dies and its tooth is buried in sediment, groundwater saturated with dissolved minerals seeps into its porous structures. Over millions of years, these minerals, like silica or calcite, crystallize and fill the microscopic spaces within the dentin and root, turning the tooth to stone.

A tooth’s high potential for fossilization comes from its enamel. This outer layer is the hardest substance in the vertebrate body, composed almost entirely of a dense mineral called hydroxyapatite. This composition makes enamel highly resistant to decomposition and chemical weathering, allowing it to survive long after softer tissues and even bones have disintegrated.

The Fossilization Process of Teeth

Fossilization begins when a tooth is quickly covered by sediment, such as sand, silt, or mud. Rapid burial protects the tooth from scavengers and surface weathering. Shielded from oxygen and decay, the tooth can begin its long alteration process, and the surrounding environment will dictate the fossil’s final appearance.

Groundwater flowing through the sediment carries a unique mineral signature. As this water permeates the tooth, it deposits these minerals into the porous dentin and the root’s interior. This infilling process adds mineral weight and density, petrifying the tooth while retaining its original shape and surface details.

The color of the fossil is determined by the minerals in the sediment. Sediments rich in iron will stain a tooth shades of brown, red, or orange, while phosphate-heavy environments often produce black or dark gray teeth. A tooth found in limestone might be light gray or tan. Fossil teeth are almost never white because their color is a direct record of the geological context where they were preserved.

Information Gleaned from Fossil Teeth

Fossilized teeth reveal much about an ancient animal’s life and environment. The tooth’s physical shape is a strong indicator of diet. Carnivores, like Tyrannosaurus rex, had sharp, serrated teeth for tearing flesh, while herbivores that ate tough plants, like Triceratops, possessed broad, flat molars for grinding.

Microscopic wear patterns on the enamel surface offer even more specific dietary clues. Abrasive foods, such as nuts or gritty tubers, leave behind tiny pits in the enamel. In contrast, animals that consumed softer foods like leaves or fruit tend to have fine, linear scratches on their teeth. Scientists can also perform a chemical analysis of the fossilized enamel, studying carbon isotopes to determine the specific types of plants an herbivore ate.

Beyond diet, teeth help identify extinct species. For some animals, like the Megalodon shark, fossil teeth are often the only remains found, making them the primary evidence of the species’ existence. The unique size, shape, and serrations of these teeth allow paleontologists to distinguish them from others. The degree of wear on a tooth can also suggest the animal’s relative age at its time of death, with heavily worn teeth indicating an older individual.

Identifying a Fossil Tooth

Several characteristics distinguish a fossil tooth from a modern one. Unlike modern teeth, which are white or off-white, a fossilized tooth is almost always discolored from the minerals it absorbed. This results in shades of black, gray, brown, or tan. A pure white tooth is unlikely to be a fossil unless it has been leached by groundwater after fossilization.

Weight and texture provide further clues. A fossil tooth is significantly heavier than a modern tooth of the same size because it has been infused with minerals, giving it a dense, stone-like feel. A modern tooth is much lighter by comparison. The surface of a fossil’s enamel may still feel smooth, but the overall object has the heft of a rock.

The location of the find also provides context. Fossils are preserved in sedimentary rock, which is often exposed in creek beds, riverbanks, beaches, and construction sites. If a tooth is found in a layer of rock or in an area known for other fossils, it is likely ancient. Finding a shark tooth many miles inland is a strong sign it is a fossil from a time when that area was underwater.