There are three main groups of dinosaurs. Very generally, ornithischians and sauropods were plant-eaters while theropods were meat-eaters (this is a legacy of evolutionary history, similar to how today’s hoofed animals are herbivores and cats are carnivores).
How do we know what dinosaurs eat?
But there are many exceptions, so how do scientists know what a species ate? Although the contents of the gut or dung can provide clues to diet, the best evidence usually comes from studying teeth and jaws.
Omnivorous dinosaurs had a combination of sharp and blunt tooth types: pointed for piercing and cutting; rounded for pounding and crushing. Just as mammals can have incisors, canines and molars, dinosaur teeth had a variety of forms, too – such as leaf, cone and peg-shaped. While early dinosaurs such as Plateosaurus (‘broad lizard’) were often generalists, later species became more specialist.
Carnivorous dinosaurs such as Allosaurus had a type of tooth that curved backwards with a serrated edge for tearing and carving flesh, called a ziphodont (‘sword-tooth’).
Some large theropods, notably tyrannosaurs, had chunkier teeth to better withstand bone-crunching stress – Tyrannosaurus rex (T. rex) had a predicted bite force of 35,000-65,000 Newtons, around twice what’s measured in saltwater crocodiles.
Other theropods were adapted to a more specialised diet: Spinosaurus (‘spine lizard’) had a crocodile-like snout and (possibly unserrated) teeth for catching fish, for example, whereas Therizinosaurus (‘scythe lizard’) had enormous claws but was actually a vegetarian. While the jaws of most carnivores opened and closed like scissors, those of herbivores typically had a wider range of motion – including side-to-side for chewing.
Herbivorous dinosaurs had an array of tooth types. Sauropods like Diplodocus (‘double beam’) had pencil-shaped teeth that worked as a rake for stripping tree branches, and Brachiosaurus (‘arm lizard’) had spoon-shaped teeth for chopping plant matter.
The most complex dentition belonged to duck-billed hadrosaurs like Edmontosaurus (‘Edmonton lizard’), whose jaws contained a battery of hundreds of closely-packed teeth – each of the 60 or so tooth positions had up to five replacements stacked below the top one.
These batteries formed a flat, rough surface for grinding, and were made from several hard materials (like enamel, dentine and cement) that were self-sharpening and resisted wear. Triceratops and other ceratopsians also had tooth batteries, but instead of the rasp-like arrangement seen in hadrosaurs, their stacks worked like overlapping shears.
While a mammal’s teeth are replaced once or twice over its lifetime, fish and reptiles (including dinosaurs) grow teeth continually. And as in sharks, if a tooth broke or fell out, a dinosaur waited for a new one – in the carnivorous theropod Majungasaurus (‘Mahajanga lizard’) that only took about two months.
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