Dinosaurs on the attack
The ability to overpower another animal requires a combination of strength, speed, balance and weaponry. Most theropod dinosaurs relied on such skills and assets to find food, although some appeared to have adapted to life as filter-feeders or plant-eaters - hardly conforming to the vision of theropods as fearsome hunters.
Most theropod dinosaurs have the same general body plan – powerful lightweight frames, two relatively long legs, stiff counter-balancing tails and sharp claws – for the purpose of hunting.
However, theropods also vary in body size, arm length, skull structure and claw shape. This suggests they used different methods to overpower prey. By looking closely at these features, and comparing them to those of modern predators, we can detect what these methods may have been.
How do living predators attack?
Living predators vary widely in size and weaponry and use different techniques to attack prey. Some of these techniques may be similar to those used by dinosaurs. Examples include:
- Cheetah: devastating speed and physical agility
- Lion: hunt in packs using stalking tactics and the element of surprise, before using speed and strength
- Crocodile: relies primarily on ambush and physical strength, with enormous bite pressure and huge teeth
- Eagle: strong gripping claws, great eyesight, speed and agility
- Snakes: some species rely on venom injected through fangs to immobilise prey
It's important to remember that most modern carnivores prefer to hunt the old, sick or young, as these are the easiest and safest options. This suggests that big theropods were probably not hunting large healthy adult herbivores. Fossil evidence supports this as remains of juveniles have been found with bite marks or as preserved meals inside the gut of theropods.
How did different theropods attack?
- Some theropods like Albertosaurus and Giganotosaurus possibly attacked with a ‘bite and slice’ technique rather than going for an outright kill. This may have helped them prey on large sauropods.
- Coelophysis bauri was a small theropod with a slender, lightweight skeleton and very long tail, for speed and agility in attack. A mass burial of over a dozen of these dinosaurs suggests they may have lived in packs.
- The long forelimbs and curved claws of the spinosaur Suchomimus may have been used for ‘fishing’
- Sinornithosaurus was an active and agile species that may have hunted in groups. It was probably adapted for leaping as its rigid tail acted as a counterbalance, allowing pinpoint accuracy and freeing the powerful feet claws. Whether this helped in attacking prey or leaping among tree branches is difficult to say. Recent research (published in 2010) suggests it may even have been venomous as it had similar teeth and jaw structures to modern rear-fanged snakes. Depressions on the side of its face could have housed a venom gland, and these connected to depressions above the tooth row that fed venom to long grooved teeth in the upper jaw.
- Velociraptor was a small and agile meat-eater. One fossil specimen from Mongolia preserves it locked in death with its prey Protoceratops. There is no evidence that it hunted in packs, although some if its close relatives did. Velociraptor had many bird-like characteristics, including long arms, feathers and a wishbone. It had a specialised claw on the second toe that it held off the ground when walking. This claw may have been used to pierce or hold on to prey.
- Tyrannosaurs generally have chunky bodies, short strong skulls, massive jaws and heavy robust bodies. These probably helped deal with heavy impacts from fighting with prey and provided power to crunch through bone. However, the tyrannosaur Alioramus altai, found in Mongolia and announced in 2009, had a body unlike other tyrannosaurs. It had a long thin head, weak jaw, and slender light-weight body, These features are far more suitable for hunting smaller prey and using stealth and speed instead of brute strength. Alioramus also had air sacs in the vertebrae, similar to those found in living birds. Air fills these cavities during inhalation and then flows to the lungs during exhalation, providing lungs with a constant stream of fresh air. In birds, this highly efficient breathing system extracts over twice as much oxygen per breath as a mammal.
Claws for killing?
Utahraptor, Velociraptor, Megaraptor and Deinonychus each had a specialised second toe with a massive claw used for killing prey. This toe had a joint that enabled it to move in a large arc, providing additional downward striking power to the claw. Although most scientists think this specialised claw was used to wield a killer slash, some believe it was designed to act like a grappling hook and latch onto prey. What do you think?
Claws for catching?
Suchomimus had long forelimbs with curved hand-claws. These were suited for scooping fish from the water towards its mouth, possibly like some bears do today. Dilophosaurus also had long arms and strong claws, and may have used these to help catch prey.
Another theropod that probably used its long forelimbs and claws for catching food was Bambiraptor. It had opposable fingers that could grip small prey – an unusual feature in dinosaurs.
Claws for subduing?
Allosaurus had large, strong claws on its hands and feet that may have held or subdued prey while it used its jaws and teeth to kill. These kinds of claws are typical of larger theropods.
Some large theropods such as Carnotaurus and Tyrannosaurus rex had large hand claws but very short arms that did not reach their mouths. These forelimbs may have been small, but the muscles were very strong. The arm length may be due to the massive heads of these theropods. An increase in head size relative to the body required a decrease in arm size to retain balance.
Which theropods didn't attack?
The theropods described here have unusual features that suggest they did not stalk and attack live prey.
- 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.
- 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: Who was smarter – predator or prey?
Evidence suggests that theropods were probably smarter than their prey. Their brain casts are often twice as big as herbivores of the same size
Fran Dorey , Exhibition Project Coordinator