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Teeth – all the better to eat with

Most of us don’t look at a fern or tree and think ‘mmm food’ so we may not appreciate the range of food options plant-eating dinosaurs had. How can we work out what plants a dinosaur munched on? One way is to compare dinosaur teeth and jaws to those of living plant-eaters whose diets we know.

Which dinosaurs didn’t chew their food?

Sauropods (long-necked plant-eaters) couldn’t chew. They had no cheeks to keep food in their mouths and no grinding back teeth. Instead, they had peg-like teeth that raked and sliced leaves from trees. Some may have swallowed stones to help break up food in their stomach. Sauropod teeth differed between species. For instance, Camarasaurus had spatula-shaped teeth useful for raking tough vegetation. Diplodocus had thin teeth more suited to stripping soft leaves from plants.

gastroliths real from sauropod
Sauropod gastroliths (stomach stones). USA, Late Jurassic, 156 - 146 million years ago. Many sauropods have been found with stones that may once have been in their stomachs. Clues to the stones' function can be found by studying the stomachs of living animals like crocodiles. Crocodiles, emus and chickens deliberately swallow stones to use in the stomach to break up food because they cannot chew. Image: Robert Jones
© Australian Museum

Which dinosaurs chewed their food?

Iguanodon, Centrosaurus, Probactrosaurus and Edmontosaurus (and other hadrosaurs) chewed plants with their grinding back teeth. They probably had cheeks to prevent food from falling out during chewing. These dinosaurs didn’t chew like us and other mammals (the only living animals that can chew) because they had a different jaw structure. Their side-to-side chewing motion resulted from an expansion of the upper jaw when the mouth closed. Most mammalian plant-eaters chew with a sideways movement of the lower jaw.

What’s on the menu?

Plant fossils indicate what food was available to dinosaurs. They also show how food options changed over time. Ferns, horsetails, club-mosses, conifers, cycads and ginkgoes dominated Triassic and Jurassic menus. The Cretaceous saw an expansion of options with flowering plants becoming dominant and grasses appearing towards the end of the period.

The ‘solid’ evidence

It may not sound pleasant, but we get excited over stomach contents, partially digested meals and poo – particularly if they once belonged to a dinosaur! Rare fossils of these items reveal specific diets in ways that plants and teeth cannot. For instance, the ankylosaur Minmi was found with seeds and leaves in its gut contents, whereas twigs, berries and tough plants were found in the stomach region of a hadrosaur. A 66-million-year-old sauropod coprolite (fossil poo) from India contained traces of grass – the earliest evidence yet for this plant.

Producing methane

Plant-eating dinosaurs were, in all likelihood, champion farters! Plants are hard to digest, requiring a lot of time and plenty of bacteria to break them down. One ‘end’ product of this is the gas methane.