Tyrannosaurus rex is the most famous dinosaur of all - a 12-metre, 8-tonne predator with teeth the size of bananas. But was it a fearsome active hunter, or really just a giant scavenger feasting on dead animals? Palaeontologist Jack Horner famously argued the scavenger case, pointing to features like tiny arms, slow legs for its size, and a powerful sense of smell. Others have pointed to the massive crushing jaws, forward-facing eyes, and evidence of healed wounds on prey animals (which means they survived a T. rex attack - proof T. rex was attacking living prey). Today most experts agree the answer is both: T. rex was an opportunist - it hunted when it could and scavenged when it could, much like a modern lion or hyena.
All tyrannosaurs had small arms, but T. rex's were the most extreme - only about 1 metre (3 feet) long on an animal that was 12 metres (40 feet) long overall. For many years their purpose was a mystery. Modern research has revealed that the arms were not weak: they had large attachment points for muscles, heavy bones for their size, and a limited range of motion that suggests they were used for holding rather than reaching. The current best guess is that T. rex used its arms to hold struggling prey against its body while its jaws did the killing - although some scientists still argue the arms may have been a leftover feature with no major function.
Tyrannosaurus rex with tiny arms
Estimates have fallen over time. Older guesses put T. rex at up to 70 kmh (43 mph), but biomechanical models published since 2017 - factoring in the strain a 7-8 tonne body would put on the leg bones - now suggest a top speed of just 17-25 kmh (10-15 mph). Adult T. rex probably could not actually run; it walked very fast, with both feet briefly leaving the ground only in young, lighter individuals. That was still fast enough to catch many of its prey species like Triceratops and Edmontosaurus, which were not built for speed either. Smaller theropods such as Ornitholestes were significantly faster.
Tyrannosaurus and Ornitholestes
Enormous. T. rex's jaws could measure up to 1.2 metres (4 feet) long, and bite-force studies estimate it could crush down with around 35,000-57,000 newtons (3,600-5,800 kilograms of force) - the strongest bite of any land animal ever measured. That is roughly 5-6 times stronger than a saltwater crocodile's bite and over 50 times stronger than a human's. A single T. rex bite could shear through bone. Such enormous power is strong evidence against a pure scavenger lifestyle - scavengers do not need to crush living prey, only to tear apart dead animals.
Tyrannosaurus rex jaws
Yes - exceptionally good, in fact. T. rex's eyes faced forward, giving overlapping fields of view from both eyes (called binocular vision) that allowed it to judge distance accurately. A 2006 study by palaeontologist Kent Stevens estimated T. rex's depth-perception range at about 13 times better than a human's, and its visual acuity at far greater than that of a modern hawk. Such precise eyesight is the hallmark of an active predator - scavengers can afford to be near-sighted. Combined with its bite force and brain size, T. rex's eyes are strong evidence for active hunting.
T. rex field of view
Yes - and T. rex had one of the most powerful noses ever evolved. CT scans of T. rex skulls have revealed enormous olfactory bulbs - the brain regions that process smell - relative to its body size. Among dinosaurs, only the smaller scavenger Saurornitholestes beats T. rex in this measure. A super-strong nose helps scavengers locate dead animals from miles away, but it is also useful for hunters - lions, sharks, and wolves all rely on smell to find prey. So T. rex's nose is consistent with both lifestyles, supporting the modern view that it was both hunter and scavenger.
Prominent nostrils of T. rex