T.rex is, without a doubt, the most infamous dinosaur of all time, and for good reason says Will Newton. This giant carnivore stood more than twice as tall as an average human, weighed nearly twice as much as an elephant, and had the strongest bite of any animal ever…
What was T.rex?
T.rex, or Tyrannosaurus rex to give it its scientific name, is a species of large theropod dinosaur that lived during the Late Cretaceous (76-66 million years ago) in what is now western North America, back when the continent was split in two by an inland sea.
There were many other tyrannosaurs that lived during the Cretaceous, such as Albertosaurus, Tarbosaurus, and Gorgosaurus, but T.rex was by far the largest of the lot and, arguably, the most successful of its time. In fact, T.rex is widely regarded as the largest and most ferocious terrestrial predator that has ever lived.
Like other tyrannosaurs, T.rex was bipedal - meaning it walked (and ran) on two legs - and had a giant, heavyset skull balanced by a long tail. Its body and legs were strongly built too, giving it the speed and bulk it needed to hunt the giant herbivores that also shared its environment.
The only parts of T.rex that weren’t massive and menacing were its comically small arms, which measured just 90cm in length, or about 30cm more than an adult human’s arm. What use are arms, though, when your primary weapon is a pair of 1.5m-long jaws lined with 60 serrated teeth, each up to 20cm long and specially designed to tear flesh and crush bones…
How big was T.rex?
T.rex was massive. One of the largest and most complete specimens ever discovered, nicknamed Sue, measures 12.4m in length and stands 3.96m tall at the hips. Another specimen known as Scotty is even longer, with a reported length of 13m. Both Sue and Scotty are estimated to have weighed around 8.5 tons, which is roughly the weight of 100 adult male humans, or one small combine harvester.
Some palaeontologists think Sue and Scotty represent abnormally large individuals and that most T.rexes were less than 12m-long and weighed between five and seven tons. However, others think that there may have been even larger individuals. These palaeontologists have used computer modelling to work out that the largest T.rex ever might have been 70% heavier and 25% longer than the largest T.rex known today.
So far, only 30 or so individual T.rexes have been found. According to the authors of a recent computer modelling study, a tiny sample size such as this makes it statistically unlikely that Sue and Scotty are the largest of their kind. In their opinion, there are even larger specimens out there, waiting to be dug out of the ground. They also say that there are some isolated bits of T.rex bone in museum collections that hint at larger individuals.
Where did T.rex live?
As mentioned above, T.rex lived in what is now western North America, ranging from Canada in the north to New Mexico in the south.
A lot of the most notable T.rex remains have been found in a series of rocks known as the Hell Creek Formation. These rocks, located near Jordan, Montana, preserve lots of other fossils too, including those of plants, and paint a picture of a subtropical, forested environment. T.rex remains have also been found in rocks from semi-arid plains and even coastal environments.
T.rex shared its environment with lots of other dinosaurs, but notably few other large-bodied predators. Typically, rocks containing the remains of dinosaurs preserve a handful of similarly-sized predators that likely competed with one another. However, in the Hell Creek Formation there’s just T.rex, which is perhaps testament to its status as the apex predator of its environment.
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What did T.rex eat?
There weren’t many things off the menu for a fully-grown T.rex. As a hypercarnivore, T.rex’s diet consisted almost entirely of meat, with a few bones sprinkled in here and there for good nutritional measure.
According to several studies, T.rex would have needed to consume around140kg of meat per day to survive, which is roughly the weight of two adult humans. That said, during particularly bountiful seasons, T.rex may have eaten more than double that amount!
T.rex was, of course, not feasting on humans during the Late Cretaceous. Instead, the so-called ‘King of the Tyrant Lizards’ hunted other dinosaurs, primarily the giant herbivores that shared its environment, such as Triceratops, Edmontosaurus, and Ankylosaurus.
T.rex also ate others of its own kind, at least occasionally. There’s evidence of T.rex-inflicted bite marks on the bones of other T.rexes, suggesting they may have had a particular taste for one another.
While T.rex was well equipped to take down the likes of Triceratops, Edmontosaurus, and Ankylosaurus, hunts wouldn’t have been easy. Triceratops, in particular, are known for their bulk, aggression, and speed, as well as the three deadly horns that protrude from their faces.
Edmontosaurus, on the other hand, travelled in huge herds and were no doubt a force to be reckoned with en masse. Ankylosaurus weren’t fast, nor did they travel in large groups, but covered in a layer of virtually impenetrable dermal plates and armed with a bone-breaking tail club, they may have been the toughest prey T.rex faced.
Was T.rex a hunter or a scavenger?
For years, palaeontologists have fiercely debated whether T.rex was a hunter, as is popularly depicted, or a scavenger.
The famous palaeontologist Jack Horner has been a major proponent of the latter view, based on several different lines of evidence. Horner has claimed that T.rex’s incredible sense of smell and its ability to crush bones with its powerful jaw are signs that it likely scavenged the carcasses left by other predators. Horner has also argued that T.rex’s arms were ‘too small’ to hold onto its prey during a hunt.
Other palaeontologists have opposed Horner’s views, arguing that it likely used its jaws, rather than its arms, to subjugate its prey. These palaeontologists also point to evidence of healed, T.rex-inflicted wounds on the bones of Edmontosaurus and Triceratops as signs that it was an active hunter that targeted living prey. A healed wound is a sign of an unsuccessful hunt, but a hunt nonetheless.
While debate still rages on about T.rex’s lifestyle, most palaeontologists seem to agree that it was both an active hunter and an occasional scavenger, just like a lot of large carnivores living today.
Why were T.rex’s arms so small?
They may be the butt of a lot of jokes, but T.rex’s comically small arms have been the focus of many scientific studies.
It’s widely thought that T.rex’s arms are a product of evolution. As the heads of tyrannosaurs grew and their jaws became increasingly more powerful, the need for a pair of grasping front limbs diminished. There’s also an argument that small arms helped T.rex balance - if its arms were any longer it may have been too front-heavy.
If this hypothesis is true, and that the arms of tyrannosaurs were slowly but surely decreasing in size, then it’s possible that - had the dinosaurs not become extinct - armless superpredators even larger than T.rex may have eventually evolved.
While they may have been small, T.rex’s arms were surprisingly muscular, suggesting they did have some kind of function.
There have been a number of theories as to what T.rex may have used its arms for, including helping itself get off the ground, scratching at prey, and even dancing. Yes, T.rex may have waved its arms around in an attempt to attract a mate - although we suspect dances like the Macarena were probably beyond its limited abilities…
How fast was T.rex?
As dinosaurs go, T.rex wasn’t particularly fast. In fact, according to several studies that have examined its skeleton and plugged the data into some biomechanical models, T.rex would have struggled to outrun an average human at peak physical fitness.
T.rex is thought to have relied on explosive bursts of speed to catch its prey, reaching max speeds of 30 km/h during a hunt. This isn’t quite as fast as some of its prey - for example, Triceratopsmay have been able to run as fast as 35 km/h - but as an ambush predator, T.rex was a master of stealth and may have been able to bridge the gap before its prey even knew it was there.
Interestingly, young T.rex are thought to have been significantly quicker than their parents. This would have allowed them to occupy a slightly different ecological niche and hunt smaller, nimbler prey while avoiding competition with the adults.
Why did T.rex become extinct?
It’s a common misconception that all of the dinosaurs went extinct at the same time, but that couldn’t be further from the truth.
So far, roughly 700 species of dinosaurs have been discovered and described. These dinosaurs are known from the Triassic, Jurassic, and Cretaceous periods of the Mesozoic Era and, in a lot of cases, are separated in time by millions of years.
To put this into perspective, imagine Stegosaurus for a moment - the famous, Jurassic-aged herbivore known for the plates on its back and the spikes on its tail. This dinosaur lived from 155 to 145 million years ago and nearly 100 million years before T.rex appeared. This means that it was a fossil by the time that T.rex was stalking the forests and plains of western North America. It also means that T.rex is closer in age to us, humans, than it is to Stegosaurus.
T.rex, unlike Stegosaurus, lived right up until the end of the ‘Age of Dinosaurs’ and actually witnessed the infamous dinosaur-killing asteroid impact firsthand. Living just a few hundred miles from where the impact happened in the Gulf of Mexico, T.rex was probably one of the first species to face extinction, with hundreds, perhaps thousands of individuals eviscerated by the initial blast from the impact.
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The asteroid impact took place 66 million years ago and claimed the lives of countless different species of animals, not just the dinosaurs. In total, around 75% of all species on Earth vanished after this catastrophic event, making it one of the deadliest mass extinctions of all time.