Teeth are the most common vertebrate fossil in the rock record, and it’s not even close. Whole skeletons are exceptionally rare by comparison. Because teeth survive millions of years better than almost any other body part, they end up being the primary evidence paleontologists have for understanding extinct animals, ancient climates, evolutionary relationships, and even the daily lives of individual creatures.
Why Teeth Survive When Bones Don’t
The outer layer of a tooth, enamel, is made of a mineral called carbonated hydroxyapatite. Bone and the inner layers of teeth contain this same mineral, but enamel is far more densely packed and contains less organic material. That density makes enamel highly resistant to the chemical and physical changes that break down biological tissues after burial, a process geologists call diagenesis. Fossilized tooth enamel remains relatively unchanged over millions of years, preserving its original chemical signature in ways that bone simply cannot match.
This durability means that for many extinct species, teeth are the only fossils that exist. A single tooth can be enough to identify a new species, estimate body size, reconstruct diet, determine where an animal lived, and even pin down when it died. That’s an extraordinary amount of information from one small piece of anatomy.
Built-In Calendars: Daily Growth Lines
Teeth don’t form all at once. They grow in layers, and each layer leaves a visible mark. In the inner tooth tissue (dentine), these marks are called incremental lines of von Ebner, and in most vertebrates they form once per day. Think of them like tree rings, but on a daily rather than annual scale.
Paleontologists have confirmed this daily rhythm in crocodilians, the closest living relatives of dinosaurs, using chemical labeling experiments. Because dinosaur teeth show the same type of layering, researchers can count these lines to calculate exactly how many days it took a dinosaur tooth to develop. Since many dinosaurs replaced their teeth continuously throughout life, growth line counts also reveal how quickly old teeth were shed and new ones grew in. This kind of precision, measuring an extinct animal’s biology in days rather than millennia, is something almost no other fossil can provide.
Decoding Diet and Evolution
Tooth shape is one of the most reliable indicators of what an animal ate. Flat, broad molars suggest grinding plant material. Sharp, blade-like teeth point to slicing meat. And the details matter far beyond these basics.
In early mammal evolution, one tooth design proved transformative: the tribosphenic molar, a complex shape capable of both crushing and shearing. Marsupials, placentals, and their close relatives all share this versatile molar type, and it’s widely considered a key driver of their early diversification and evolutionary success. Interestingly, research published in Nature revealed that tribosphenic molars actually evolved independently in two separate groups on different continents during the Jurassic and Early Cretaceous periods, one in the southern landmasses and one in the north. Without fossil teeth preserving these shapes, that entire chapter of mammalian history would be invisible.
In human evolution, enamel thickness has been a central measurement for decades. Palaeoanthropologists use relative enamel thickness to track dietary shifts across hominin species. Thicker enamel generally makes a tooth crown stronger and more resistant to fracture from hard or abrasive foods. The robust australopiths (like Paranthropus boisei) had stronger molars than the more gracile australopiths (like Australopithecus afarensis), who in turn had stronger molars than chimpanzees. These differences help researchers reconstruct what our distant ancestors were eating and how their diets changed over millions of years.
Chemical Time Capsules
Because enamel resists chemical alteration so well, it preserves the isotopic signatures of whatever an animal was eating and drinking during the years that tooth formed. Two isotope systems are especially useful.
Strontium isotope ratios in enamel reflect the local geology where an individual’s food was grown. Oxygen isotope values reflect the water an individual drank, which varies with air temperature, altitude, latitude, and rainfall patterns. When a tooth’s isotopic values don’t match the geology and water of the place where the body was buried, that individual likely grew up somewhere else. This technique has been used to track migration patterns in ancient humans, revealing which members of a community were born locally and which arrived from distant regions.
These same methods work on animal teeth millions of years old. Researchers can reconstruct ancient rainfall patterns, seasonal temperature swings, and the geographic ranges of extinct species, all from the chemistry locked inside a single tooth.
Estimating Body Size From a Single Tooth
For many extinct predators, teeth are among the few fossils available, and paleontologists have developed methods to work backward from tooth measurements to full body size. The giant shark Otodus megalodon is a famous example. The most widely used approach relies on the proportional relationship between tooth crown height and total body length in the modern great white shark, the closest ecological comparison available.
One landmark 1996 study used the total height of a specific upper tooth (root and crown together) to estimate megalodon’s maximum adult size at about 15.9 meters, roughly 52 feet. More recent methods sum the widths of all teeth in a jaw to calculate body length, operating on the principle that the ratio of total tooth width to body length stays proportional across related species. These estimates have been refined over the years, but the core insight remains: a handful of teeth can tell you how large an animal was, even when no other part of the skeleton survives.
Dating Fossils Directly
Radiocarbon dating stops working at around 50,000 years ago. For the vast stretch of the Pleistocene, which covers most of the evolutionary history of our genus Homo, a technique called electron spin resonance coupled with uranium-series dating fills the gap. It works specifically on the carbonated hydroxyapatite in tooth enamel, making teeth one of the only fossils that can be dated directly rather than relying on the age of surrounding sediments.
The method measures radiation damage that accumulates in enamel over time, along with the uptake of uranium after burial. It’s not without complications (the rate of uranium absorption can affect accuracy), but for periods beyond 50,000 years ago, it is often the only way to get a direct age from a fossil. A large portion of what we know about when and where early humans lived depends on dates pulled from their teeth.
Ancient DNA and Proteins in Dental Calculus
Teeth hold one more surprise: dental calculus, the hardite mineralized plaque that builds up on tooth surfaces during life. This calcified plaque traps particles from everything that entered the mouth, and once mineralized, it preserves them for thousands of years.
Researchers extracting proteins and DNA from ancient calculus have identified hundreds of distinct proteins in a single sample, including proteins from oral bacteria, human immune system components, and even food residues. In one study, researchers found proteins from cattle milk, evidence of specific bacterial species associated with gum disease, and markers of active immune responses like complement proteins and hemoglobin from bleeding gums. Mitochondrial DNA recovered from calculus can reveal an individual’s maternal lineage. Bacterial DNA maps the ancient oral microbiome, showing which pathogens people carried.
This makes a single tooth with intact calculus a record of diet, disease, immune function, ancestry, and even occupation. Combined with the isotopic and structural information locked in the enamel and dentine beneath it, a tooth becomes one of the most information-dense objects in the entire fossil record.