Dinosaur - Tyrannosaurus rex

T. rex is one of the most popular and enduring dinosaurs of all, starring in movies and children’s shows as well as featuring in pop culture memorabilia.

Introduction

Pronounced Ty-ran-oh-sore-us rex

Tyrannosaurus means 'tyrant lizard' in Greek and rex means 'king' in Latin.

Tyrannosaurus rex commonly known as T. rex, was the largest tyrannosaur and the last of its family. It is one of the best studied tyrannosaurs due to the number of specimens found. As of 2020, there have been over 42 specimens (5-80% complete by bone count) discovered, including several almost complete skeletons.

Teeth from what is now documented as a Tyrannosaurus rex were found in 1874 by Arthur Lakes near Golden, Colorado.

The famous fossil hunter Barnum Brown found the first partial skeleton of T. rex in eastern Wyoming in 1900; he then found another partial skeleton in 1902 in Hell Creek, Montana The species was named in 1905 by Henry Fairfield Osborn, president of the American Museum of Natural History at the time.

In the 1960s, there was renewed interest in Tyrannosaurus.

The 1990s saw numerous discoveries, with nearly twice as many finds as in all previous years, including two of the most complete skeletons found to date: Sue and Stan.

In 2000, crews organised by Jack Horner discovered five Tyrannosaurus skeletons near the Fort Peck Reservoir.

Identification

T. rex was one of the largest known carnivorous dinosaurs, 4 metres tall at the hips and 12.3 metres long. It had strong legs and a long tail (to counterbalance the large head)

T. rex had a very large head (1.5 metres long) and powerful jaws (1.2 metres long) with adults having sixty (60) 30cm long teeth (including the roots).

T. rex adults could have weighed up to about 8,000 kilograms.

T. rex is famous for its very short arms. The reduced length of the arms is believed to be due to the enlargement of the massive heads of the tyrannosaurids. An increase in head size relative to the body requires a decrease in arm length to retain a balance, along with a counter-balancing tail.

Habitat

Tyrannosaurus rex remains have been discovered in different ecosystems, including inland and coastal subtropical, and semi-arid plains. T. rex lived in areas with high humidity and semi-tropical temperatures.

Distribution

T. rex lived 68-66 million years ago during the Late Cretaceous period, in what is now Canada and the USA. There have been no specimens of T. rex reported outside of North America.

Feeding and diet

Tyrannosaurus rex was a carnivore, but may also have been an opportunistic scavenger. T. rex likely specialised in bringing down large dinosaurs, like the herbivores Edmontosaurus and Triceratops but probably also ate other tyrannosaurs. It is believed that unrelated individuals of different age and speed could have fed at the same meal.

These giant predators used their strong and powerful jaws to crunch through flesh, bone and marrow. Their D-shaped teeth were serrated (like a steak knife) and 30 cm long, including the root. They had no chewing teeth, they chomped, tore and swallowed. This is known as a puncture-pull feeding strategy.

According to a 2012 study in the Canadian Journal of Earth Sciences, not all the teeth had the same function. The 2012 study found that T. rex’s 'front teeth gripped and pulled; its side teeth tore flesh, and its back teeth diced chunks of meat and forced food into the throat. T. rex's teeth were wide and dull (rather than being flat and daggerlike), allowing the teeth to withstand the forces exerted by struggling prey.'

Other behaviours and adaptations

Tyrannosaurus rex had sturdy and quite long legs and its forelimbs were reduced, a feature typical of all advanced tyrannosaurs. The function of the forelimbs is still not clear. Like other tyrannosaurs, it had a huge head with large cutting, serrated teeth. Its brain was tiny in comparison with its huge body.

Scientific studies show that T. rex had binocular vision slightly better than that of modern hawks.

Their maximum speed could have been up to 40km/hr.

Fossils description

Over 40 specimens of Tyrannosaurus rex have been identified, some of which are nearly complete skeletons, and at least one specimen has been reported with fossilised soft tissue and protein remains

Evolutionary relationships

Tyrannosaurus rex is a member of the family Tyrannosauridae and subfamily Tyrannosaurinae. Also, in this subfamily are the genera Alioramus, Teratophoneus, Daspletosaurus, Zhuchengtyrannus and Tarbosaurus

Some scientists think that T. rex and the very closely related Tarbosaurus should both be in the same genus (Tyrannosaurus, which was named before Tarbosaurus). However, compared toTarbosaurus, T. rex had a shorter, more robust skull and less teeth. Studies comparing nerve pathways in skulls of the two species also show significant differences, supporting the idea that Tarbosaurus and Tyrannosaurus are separate genera.

It is possible that Tarbosaurus had evolutionary precedence, and spawned Tyrannosaurus rex when some hardy individuals crossed the Siberian land bridge into North America about 67 million years ago when the seaway between Asia and North America receded.

T. rex's skeletal features showed that the dinosaur king was more like two tyrannosaurs in Asia, Tarbosaurus and Zhuchengtyrannus, than it was to North American tyrannosaurs. However, these findings are still preliminary, and other experts maintain that T. rex evolved in North America.