Tyrannosaurus rex

***Tyrannosaurus rex*** (from the Greek words ***tyrannos/τύραννος*** = tyrant + ***sauros/σαῦρος***  = lizard + ***rex*** = king), also known as ***Tyrannosaurus*** and colloquially known as ***T. rex***, was a large carnivorous theropod dinosaur that lived from 68 to 66 million years ago during the latest Cretaceous age known as the Maastrichtian.

*Tyrannosaurus* is perhaps the most well known prehistoric animal that has ever lived and has been depicted in nearly every form of media involving dinosaurs. There have been around 50 individuals of this taxon found since its discovery in the early 1900s. The most complete specimen of *Tyrannosaurus rex*, Sue, is around 90% complete and measures 12.4 meters (40 feet) long, stands nearly 4 meters (13 feet) tall at the hips and weighed about 8.8 tonnes (9.7 short tons) in life, making it among the largest terrestrial predators in Earth's history.

## noted tyrannosaurs

Rexy

Rex

Chomper

## Description

*Tyrannosaurus rex* was one of, if not the largest land carnivores of all time. The largest known specimen, RSM P2523.8 (AKA "Scotty"), and largest (Smurfette) in life would have measured 12.9-15meters (42.6-50 ft) long, stood 4-6meters (13-20ft) tall at the hips and top of head, and weighed 8870 kg (9.8 short tons). Though most individuals would have weighed between 7 and 8 tonnes and been between 11 and 12 m long. Although *T. rex* is currently the largest known terrestrial predator in terms of weight, theropods such as *Spinosaurus* and potentially *Giganotosaurus,*surpassed *Tyrannosaurus* in terms of height and length. It is believed that Scotty and Sue are among the oldest of their kind currently known at 28 years old or more.

*T. rex's* skull could measure up to 1.5 m (5 ft) long and was very robust. The base was much wider than its snout, and would have given it excellent binocular vision. Its mouth was wide compared to most other theropods and resembled a U-shape. The skull had several openings in it, known as fenestra, that would have lightened the skull and likely held soft tissue such as muscle or blood vessels. The fenestra on top of its head would likely have served as a way to cool the dinosaur down in a similar way to crocodiles. The mandible (jaw) of *Tyrannosaurus* could measure 1.2 m (4 ft) in length and was quite robust, which was to compensate for the animal's devastating bite force. The most recent studies have shown that *T. rex*was capable of opening its jaws a maximum of 63-80 degrees wide, not as wide as the Allosaurus, but wide enough to kill an Iguanodon or severely wound a ceratopsian.
The neck of *T. rex* formed a natural S-shaped curve like that of other theropods, but was relatively short and would have been very muscular in order to support its massive head. The forelimbs were only around the size of an adult human's arms but would have been anchored by very strong muscles and, unlike theropods such as *Carnotaurus* and its relatives, were not vestigial and would have had some use in life, although the exact purpose for them is not entirely known. Unlike more basal theropods, *Tyrannosaurus'*hands bore only two usable digits, though there is a third vestigial one that was so small it would not have even shown through the skin. The two visible digits would have been tipped with sharp claws. In contrast to the forelimbs, the hind limbs were among the longest in proportion to body size of any theropod and incredibly robust in order to support the animal's massive size. Its feet resembled those of terrestrial birds with three longer toes that would have impacted the ground and one vestigial hallux "dewclaw" that would have never touched the Earth. Each toe was tipped with massive slightly hoof-esque claws.

The tail was heavy and long, sometimes containing over forty vertebrae, in order to balance the large head and torso. To compensate for the immense bulk of the animal, many bones throughout the skeleton were hollow like birds and other theropods, reducing its weight without significant loss of strength. Its torso was wide and deep and would have resembled a "barrel-chest" in life. This body would have supported most of the animal's internal organs, with aid from its gastralia (belly ribs). Since *Tyrannosaurus* was a saurischian dinosaur, the pubis in its hip would have pointed forward and away from the backward-facing ischium.

The teeth of *T. rex* displayed some heterodonty (differences in shape). The teeth in the premaxilla (front upper jaw) were relatively small and closely packed, D-shaped in cross-section, had reinforcing ridges on the rear surface, were incisiform (their tips were chisel-like blades) and curved backwards, which all would have reduced the risk of the teeth breaking when *Tyrannosaurus* bit and pulled. The remaining teeth were robust, like "lethal bananas" rather than daggers as seen in more basal theropods, more widely spaced and also had reinforcing roots. The teeth in the middle of the maxilla were the largest in its mouth. The largest tooth found so far is 30.5 centimeters (12 in.) long including the root, making it the largest tooth of any carnivorous dinosaur and one of the largest teeth in general.