These are the sharp-toothed, ferocious meat-eating dinosaurs of popular imagination – the ultimate predators built purely to kill. Or are they? Collectively known as theropods, they range from bus-sized to chicken-sized, and include the outlandish parrot-faced, feathered, toothless and ostrich-like.

It is estimated that carnivores made up only about one per cent of the dinosaur population. This figure is typical of similar ecosystems today.

Giganotosaurus carolinii
Giganotosaurus skeleton (reconstructed cast). Argentina, Creataceous, 112 89 million years ago. Image: Stuart Humphreys
© Australian Museum

Teeth – all the better to eat you with

The wolf probably didn’t expect to have his words to Little Red Riding Hood immortalised alongside dinosaurs. But he did have a good point – teeth of meat-eaters are adapted for killing and eating specific types of animals, be they small girls in red capes, or insects, fish, reptiles and mammals. We can determine the likely diet of a meat-eating dinosaur by making comparisons with living animals.

Which theropods ate flesh?

Velociraptor (and other dromaeosaurs), Allosaurus, Giganotosaurus, Tyrannosaurus, Albertosaurusand Carcharodontosaurus had sharp teeth typical of modern flesh-eaters. They also had serrations on at least one tooth-edge. Serrations help cut through flesh and bone by a ‘grip and rip’ action. Different teeth reveal the different eating styles of flesh-eaters. For instance, Giganotosaurus teeth were quite narrow and long with effective cutting edges for slicing; Allosaurus had relatively short, small teeth to cope with impacts that may have occurred when attacking large prey; and Tyrannosaurus had teeth that were robust, conical and variable in size to crunch bone.

Modern knives provide useful comparisons to flesh-eating teeth. You may have noticed how much easier it is to cut meat with a serrated knife rather than a butter knife (and that serrated knives do not require constant sharpening like other slicing knives).

Bite forces

Tyrannosaurus rex reconstructed head
Tyrannosaurus rex, head (model based on skull reconstruction). Image: Stuart Humphreys
© Australian Museum

We know the teeth of T. rex were suited to crunching through flesh and bone. But were the jaws and skull capable of such a forceful bite? Modern technology helps provide the answer.

Experts use computer modelling techniques to analyse anatomical and biomechanical data from skull and muscle tissue. Of great importance are data on how the jaw works, how the muscles and bones contribute to bite strength, how stress is dispersed through the skull and the ability of the lower jaw to resist bending.

Interestingly, fossil evidence of a different kind supports views of T.rex as a powerful bone cruncher. A large 44-cm-long coprolite (fosil poo) attributed to this species contains many bone fragments – nearly half of which are undigested.

Which theropods ate fish?

Suchomimus and Spinosaurus had cone-shaped teeth similar to modern fish-eaters. These teeth were able to hook and pierce fish that tend to be slippery and hard to grasp. The teeth of Spinosaurus were typical of fish-eaters, a fossil from Brazil shows it had a more diverse diet – a tooth was discovered embedded in a pterosaur vertebra. Whether Spinosaurus had scavenged a dead animal or caught a flying pterosaur is not known.

Which theropods ate insects?

Archaeopteryx (a bird, and so a theropod) had the small jaws and sharp teeth characteristic of living insect-eaters. These are useful for piercing tough exoskeletons of insects but can also be used to catch small lizards, fish and mammals. This is why it is hard to tell the difference between a true insect-eater and a small flesh-eater from fossils.

Archaeopteryx lithographica skull cast
Archaeopteryx skull, reconstructed cast. F134185. Based on fossils from Germany, Late Jurassic, 155 - 150 million years ago. Image: Robert Jones
© Australian Museum

The odd ones out

Just when you thought you could tell a meat-eater by its sharp teeth and claws! The theropods described here have unusual features that make it difficult to determine what they ate. They include the beaked and toothless oviraptorosaurs, the ostrich-like filter-feeding ornithomimosaurs and the enigmatic therizinosaurs.

Modern animals that have similar feeding apparatuses include:

  • The Green Sea Turtle, which has a beak and skull of similar to those of oviraptorosaurs.
  • The Flamingo, which has a beak with filaments used for filter-feeding, similar to those of ornithomimosaurs.

Examples of 'odd' theropods:

  • Therizinosaurus cheloniformis is a theropod with an impressive hand claw that looks savage but was possibly used for stripping vegetation, or ripping open termite mounds like echidnas and goannas do today. Therizinosaurus probably had a large, heavy build which suggests it was quite slow, and a beak with small teeth.
  • Oviraptorosaurs like Ingenia yanshini were meat-eaters with no teeth. They had relatively large heads with short, deep beaks and jaw muscles powerful enough to crush bones. They may also have eaten plants, molluscs and eggs.
  • Struthiomimus altus had beak-like jaws with no teeth. It may have fed by filtering food from sediments, like other ornithomimosaurs.
  • Ornithomimus edmontionicus fossils have been found with some soft tissues of their jaws preserved. These tissues are like those of some living water birds, such as flamingos, that eat by straining food from sediment.

Did you know: Dino klutzes?

Theropods have the greatest number of limb injuries of all dinosaurs. This does not mean they were the most accident prone, but suggests they led very active lifestyles and that injuries were a big risk to a bipedal hunter.