Tyrannosaurus rex

One of the most famous dinosaurs, Tyrannosaurus rex roamed the Earth during the final stretch of the Cretaceous period, from around 68-70 million years ago until 66 million years ago when an asteroid impact killed off the non-avian dinosaurs. The name Tyrannosaurus rex means "Tyrant Lizard King", which is an apt description. Tyrannosaurus was a large bipedal carnivore. Current size estimates place it at around 12 - 13 m in length from head to tail, around 4 m tall at the hips, and weighing around 5 - 8 tonnes - with some estimates being even higher.

While T. rex is the most well-known, it is not the only recognized Tyrannosaurus species. The other, T. mcraeensis, was discovered more recently and is a similar size but features a longer skull and narrower chin. In this article, we'll use "Tyrannosaurus" to specifically refer to T. rex.

Tyrannosaurus lived in what is now the western North America - places like Montana, Wyoming, and South Dakota - with some specimens found in Canada. At the time, this was an island continent called Laramidia, with much of the territory resembling a large floodplain. The climate was generally warm and humid.

Several relatively complete T. rex specimens have been found, including rare patches of skin. T. rex is known from a number of relatively complete specimens, including some patches of skin. While it's accepted that many dinosaurs - especially early Tyrannosaurus relatives - had feathers, it's unclear how much (if any) plumage Tyrannosaurus itself had. Fossilized skin impressions show scaly skin with no direct evidence of feathers, but this doesn't rule them out entirely. Feathers and scales aren't mutually exclusive, and these impressions come from limited areas of the body.
The large size of Tyrannosaurus might explain a reduction in feather coverage - a coating of plumage would have made it more difficult to cool off after chasing prey. Like today's large mammals such as elephants and rhinos, T. rex may have lost much of its insulation to help regulate body temperature.

Tyrannosaurus is also famous for its short, 2-fingered arms. The exact function of these arms (if any) is unclear. They might have shrunk as the skull grew larger, helping balance the body, so that T. rex did not become top-heavy. However, their thick bone structure suggests they could still handle significant force.

Tyrannosaurus had a large, strong skull. Despite the presence of some openings, called fenestrae, which helped to reduce weight, the skull as a whole was large & robust - up to around 5ft long. The nasal bones were fused together (a feature of the Tyrannosaur group, comprising of T. rex and some of its close relatives). The skull was T-shaped - wide at the rear, with a long narrow snout. This helped to give T. rex very good binocular vision, allowing them to effectively judge distances and hunt prey. Their binocular overlap (the area both eyes can see, allowing depth perception) was around 55 degrees, which is more than modern hawks. They also had huge eyes - one of the largest of all known terrestrial animals. Generally speaking, the absolute size of an eye is more important than its size relative to the animal - a bigger eye lets more light in, allowing for better vision. So, contrary to what you may remember from Jurassic Park, this was definitely not an animal that couldn't see you if you didn't move!

Even if it couldn't see you, it would also have easily been able to sniff you out - T. rex had a long nasal cavity, and seems to have had a large olfactory bulb in the brain. This is estimated by reconstructing the shape of the brain by looking at the space in the skull which it occupied. This would have allowed it to smell carcasses from far away. Studies of Tyrannosaurus ears also suggest it had a well-developed sense of hearing, especially for low-frequency sounds. This would be useful as low-frequency sounds travel well over long distances & through dense vegitation - making them important for tracking prey as well as mating.

Tyrannosaurus boasted around 60 large teeth. At the front of the upper jaw were 8 premaxillary teeth - these were short compared to the other teeth, relatively uniform in length, and shaped like incisors. The rear side of these teeth were flattened, such that if you sliced the tooth in half and looked down at it, it would resemble a capital "D". The teeth also curved backwards. These features strengthened the teeth and reduced the likelihood of them breaking/snapping. The rest of the teeth were strong also, and were significantly thicker than those of other carnivorous dinosaurs relative to their length. These teeth varied in length, up to around 1ft long, with some of the longest ones in the middle and smaller ones towards the back of the mouth. They were serrated - like a steak knife, though these serrations were much smaller - which helped to tear into meat.

Tyrannosaurus teeth were also very deeply rooted - the root was about twice as long as the crown (the part you could see). These adaptations all helped to give Tyrannosaurus its famously powerful bite, estimated to have been the largest known in any terrestrial animal. The teeth were also replaced regularly - around every 2 years - meaning an adult Tyrannosaurus would have gone through hundreds, even a thousand, teeth in its lifetime!