Dinosaurs on the attack

The ability to overpower another animal requires a combination of strength, speed, balance and weaponry. Most theropods relied on such skills and assets to find food, although some appeared to have adapted to life as filter-feeders or plant-eaters.

Most theropods 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

It's important to remember that most living carnivores prefer to hunt the old, sick or young, as these make the easiest and safest prey 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 guts of larger 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.
• 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.
• Velociraptor mongoliensis was a small and agile meat-eater. One fossil specimen from Mongolia preserves an individual locked in combat with its presumed prey Protoceratops. There is no evidence that it hunted in packs, although some if its close relatives did. This species had many bird-like characteristics, including long arms, feathers and a wishbone. It also 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.
• Tyrannosaurids generally have robust strong skulls, massive jaws and heavy chunky bodies. These probably helped deal with impacts from struggling prey and provided enough power to crush bone. However, the tyrannosaur Alioramus altai, from Mongolia, had a body unlike other members of the family. 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 speed instead of brute strength.

Claws for killing?

Utahraptor, Velociraptor and Deinonychus each had a specialised second toe (the innermost toe contacting the ground) 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 suggest it acted more like a grappling hook and latched onto prey.

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, which 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 mutually opposable first and third fingers that could grip small prey – an unusual feature seen in only a few other 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.

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 may have been used for stripping vegetation, or ripping open termite mounds like echidnas and goannas do today. Therizinosaurus had a large, heavy build, which suggests it was quite slow, and a beak with only small teeth.
• Struthiomimus altus had beak-like jaws with no teeth. It likely fed on plants and insects, like other ornithomimosaurs did.
• 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 sediments in lake and riverd.

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