What dinosaur teeth reveal about diet and evolution

What did dinosaurs eat? Teeth provide important clues to understanding the ecology of dinosaurs, which became extinct approximately 66 million years ago. Their shape, structure and patterns of wear can help scientists reconstruct how these animals obtained and processed their food.

But fossil teeth do not tell their stories in isolation. By comparing them with the teeth of living animals, researchers can identify similarities and differences that shed light not only on dinosaur diets, but also on the evolutionary processes that shaped feeding adaptations in very different groups of animals.

Takafumi Kato, a professor in the Department of Dinosaur Paleontology at Okayama University of Science who specializes in mammalian evolutionary history, explains what dinosaur teeth can tell us about diet, adaptation and evolution.

Q: Let's start with the basics. How do scientists determine whether a dinosaur was herbivorous or carnivorous?

Kato: When I talk to visitors at our Museum of Dinosaur Research, I often use the Tyrannosaurus as an example. When you see its sharp teeth, you naturally get the impression that they were suited for eating meat. Along the edges of those pointed teeth are serrations. Their shape resembles a steak knife designed to cut through thick pieces of meat. These characteristics are among the reasons we believe the Tyrannosaurus ate meat.

Of course, diet is not determined from teeth alone. Among living mammals, very few have teeth with this type of serration. Some seals have teeth that may look somewhat similar at first glance, but they differ from the serrated teeth of dinosaurs.

Q: Dinosaur teeth were repeatedly replaced, like those of sharks, weren't they?

Kato: Yes. In many dinosaurs, teeth were replaced repeatedly throughout life. In the Tyrannosaurus, for example, an old tooth would eventually fall out after being used and worn. Meanwhile, a replacement tooth was already developing underneath it, ready to emerge and take its place.

Q: What about the teeth of herbivorous dinosaurs?

Kato: There are several patterns among plant-eating dinosaurs. Living iguanas, for example, are herbivorous reptiles that eat leaves, flowers and fruits. Their small teeth have numerous fine serrations along the edges. You could call them serrations, but they are shaped in a way that is well suited for cutting plant material.

Fossil teeth with a remarkably similar form have also been found. They are spatula-shaped, with serrated edges on both sides and a slightly raised central portion. These are the teeth of the Iguanodon. Although the animals differ greatly in size, the morphology of the teeth and other evidence indicate that the Iguanodon was a plant eater.

Q: Couldn't teeth with serrations like these also suggest a carnivorous diet?

Kato: The shape and function of these serrations differ from those of carnivorous dinosaurs. Iguanodon teeth are broad and leaf-shaped, with ridges on their surfaces. When the upper and lower teeth came into contact, they formed large wear surfaces. This structure was well suited for cutting and crushing plant material.

Q: Ah! Another striking example among herbivorous dinosaurs is the teeth of the Parasaurolophus, a hadrosaur displayed at the Museum of Dinosaur Research.

Kato: Yes, their dental structure is quite distinctive. As the teeth were worn down by grinding plant material, new teeth continually joined the functional chewing surface. In other words, replacement teeth kept coming into use one after another. This structure is known as a dental battery.

When examined individually, the teeth resemble elongated versions of Iguanodon teeth. They are shaped somewhat like long, narrow leaves. In the lower jaw, newer teeth emerging lingually from below progressively joined the chewing surface as older teeth wore down. As the teeth that had been functioning first became worn, newer teeth that emerged later took over their role.

If we look more closely at dental structure, we also find an interesting similarity between hadrosaurs such as the Parasaurolophus and the teeth of deer.

Q: Deer?

Kato: Yes. In the Parasaurolophus, teeth at different stages of wear were arranged across the chewing surface. Tissues of different hardness, including enamel and dentin, combined to create an uneven surface well suited for grinding plant material.

Interestingly, the enamel patterns in the parts of the teeth that come into contact with food first, as well as the outlines formed as the teeth moved past one another, closely resemble the enamel contours seen in the molars of deer and cattle.

Dinosaurs and modern mammals belong to completely different groups. Yet when their teeth become highly specialized for the same function — efficiently grinding plant material — similar features can emerge in tooth shape and patterns of wear, even in completely unrelated lineages.

Q: Why does that happen?

Kato: When two animals share a similar characteristic, one possibility is that they inherited it from a common ancestor. But even in completely different evolutionary lineages, such as the Parasaurolophus and deer, similar forms and mechanisms can evolve when animals adapt to perform the same function — in this case, efficiently grinding food. This is called convergent evolution.

Q: Why do the teeth of living mammals show such a wide variety of forms compared with those of reptiles?

Kato: Wild animals live in extremely demanding environments. Herbivores, for example, seem to be eating almost constantly. They need to consume that much food simply to maintain their bodies.

When food resources are scarce, even a slight advantage in the efficiency with which an animal can grind food may allow it to obtain more nutrition from the same amount of food than its competitors. Small differences in efficiency can therefore translate into differences in the probability of survival.

Living mammals generally have higher metabolic rates than living reptiles and require more energy. Some reptiles, on the other hand, can maintain relatively low metabolic rates and tolerate long periods without food. Some snakes, for example, can survive for months without eating. However, this does not mean that dinosaur metabolism was necessarily the same as that of living reptiles.

In mammals, teeth became differentiated into incisors, canines and molars, each performing different functions. The precise occlusion of the upper and lower teeth allows mammals to cut, crush and grind food very efficiently. Such mechanisms are thought to have been advantageous in supporting their relatively high metabolic demands.

As mammals adapted to different foods, their teeth became increasingly specialized. As a result, today we can often classify mammals in considerable detail based on their teeth alone.

Q: That makes fossil teeth particularly valuable, doesn't it?

Kato: Absolutely. To study fossils, we also need to study animals living today. Comparison with living species is essential.

We need to ask what living animals eat and what shapes their teeth have. Then, by carefully examining the similarities and differences between fossil teeth and the teeth of living animals, we can uncover a great deal about animals that lived in the past.