What did they eat?
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). 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 pegshaped. 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 bonecrunching 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 crocodilelike 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 spoonshaped 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 closelypacked 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.
“The best evidence usually comes from studying teeth and jaws”