What Is a Dinosaur Tooth? The Most Common Fossil and the Most Informative

Enamel is the hardest tissue any vertebrate produces and resists weathering, transport and chemical attack far better than bone, so a tooth survives conditions that destroy a skeleton. More importantly, dinosaurs replaced their teeth throughout life rather than growing one permanent set as mammals do, with new teeth forming continuously in the jaw beneath the functional ones and pushing them out as they wore. A single large predator might shed thousands of teeth across a lifetime, so the fossil record contains vastly more teeth than animals, and a site producing hundreds of theropod teeth may represent very few individuals. That replacement pattern also explains why shed teeth are found scattered at feeding sites, frequently alongside bones bearing bite marks, since a tooth lost while biting into a carcass ends up buried with it. The rate of replacement can be measured from growth lines inside the tooth, and in some herbivores it was remarkably fast, with individual teeth replaced every few weeks under the heavy wear of processing tough vegetation.

Tooth form corresponds closely to diet and the correspondence is reliable enough to identify feeding habits from isolated finds:

• •Blade-like teeth with serrated edges, curved backwards, for slicing flesh and holding struggling prey, characteristic of theropods and comparable in construction to a steak knife
• •Conical unserrated teeth, better for gripping than cutting, found in fish eaters including spinosaurs and in many marine reptiles
• •Spoon-shaped and pencil-shaped teeth in sauropods, used for stripping and raking vegetation rather than chewing it, with the food processed by the gut instead
• •Dental batteries in hadrosaurs and ceratopsians, where hundreds of teeth are packed into interlocking columns forming a single continuous grinding or shearing surface that renewed itself from below
• •Leaf-shaped serrated teeth in many early herbivorous dinosaurs, suited to cropping soft plants
• •Complete absence of teeth in several groups including ornithomimosaurs and modern birds, replaced by a beak, which evolved independently many times

The serrations on a theropod tooth, called denticles, are structures of real engineering interest. Each is a small projection along the cutting edge, and at the base of each sits a rounded space that distributes stress and stops cracks propagating, which is the same principle used in engineering to prevent tearing at the end of a slot. Internal structure includes bundles of fibres in the dentine oriented to resist the forces the tooth experiences, and the enamel is arranged in layers. The combination allows a tooth to slice through flesh and withstand contact with bone without shattering, and to keep working while cracks develop, since a tooth that will be replaced anyway does not need to last. Denticle size, density and shape differ between groups sufficiently that isolated teeth can frequently be assigned to a family, and considerable work has gone into building identification keys, though the limits of that approach are real and identifications from isolated teeth are treated cautiously.

Beyond shape, teeth carry two further layers of evidence. Microwear, meaning the pattern of microscopic scratches and pits on the enamel surface, records what an animal ate in the days before it died, since pits indicate hard objects and parallel scratches indicate a shearing motion on abrasive material, and the technique is used on fossil and living animals alike so that patterns can be calibrated. It has been applied to hadrosaurs to demonstrate a chewing motion involving movement of the upper jaw outwards, which is a mechanism no living animal uses. Stable isotopes preserved in enamel record the composition of the water an animal drank and the plants it ate, which supports inferences about migration, about whether species drank from the same sources, and about local climate. Growth lines within the tooth, laid down daily, permit replacement rates to be counted directly. Together these turn a single isolated tooth into evidence about diet, behaviour, environment and physiology, which is a great deal from an object a few centimetres long.

Enamel outlasts bone and dinosaurs replaced teeth continuously, so a single predator shed thousands and the record holds far more teeth than animals. Shape tracks diet reliably, from serrated blades for slicing to interlocking grinding batteries of hundreds of teeth. Rounded spaces beneath the serrations stop cracks spreading. Microscopic wear records the last few days of eating and isotopes in enamel record the water drunk.