Asked by James (aged eight)

At 43 foot (13 metres) long and weighing up to nine tons (heavier than one and a half African elephants), Tyrannosaurus Rex was one of the largest meat-eating dinosaurs to have lived, but not the biggest dinosaur ever. Spinosaurus aegyptiacus was even longer at up to 59 feet (18 metres), and possibly twice as heavy. However, the largest dinosaurs were herbivores, not meat-eaters.

The largest dinosaur we know about from good fossils was the long-necked sauropod Argentinosaurus huinculensis, which was possibly 98 feet (30 metres) long (longer than three London buses end-to-end) and weighed over 90 tons (almost as much as 17 African elephants). Another sauropod dinosaur called Amphicoelias altus may have been larger, but the fossil bones of this creature are lost. Working out the size of dinosaurs is very difficult, because we very rarely find complete skeletons. Normally we only have a few bones available to estimate overall size and weight, so there may be many different estimates.

Dr Stig Walsh, Senior Curator of Vertebrate Palaeobiology, National Museums Scotland

Microraptor

This tiny raptor, resembling an odd-shaped pigeon, lived in the early cretaceous period. It measured no more than a foot from head to tail and weighed less than a kilogram.

Raptorex

Gracing the Earth 60 million years before T-rex, raptorex is the smallest tyrannosaur discovered so far, weighing less than 154lb (70kg), much less than it’s famous cousin.

Europasaurus

Sauropods are usually considered to be extremely large, but the under-a-ton sauropod europasaurus was comparable in size to a modern ox, averaging about ‘only’ 3m (10ft) in length.

Nemicolopterus

This pterosaur is the smallest known ‘flying dinosaur’. It had a wingspan of 25cm (10 inches) and weighed about 0.1kg (0.2lb). It came about 50 million years before the quetzalcoatlus, the largest pterosaur of all time.

Lariosaurus

Lariosaurus is the smallest marine reptile discovered to date. It was about 0.6m (2ft) long and weighed 9kg, becoming extinct at the end of the Triassic period.

The T-Rex may have been one of the largest meat-eating dinosaurs, but it might not have been a predator at all

Tyrannosaurus rex – from Greek and Latin words meaning ‘tyrant’, ‘lizard’ and ‘king’ – was one of the largest carnivorous dinosaurs to walk the earth. It lived about 85 to 65 million years ago, in lightly forested North American river valleys and plains. The
T-Rex stood more than four metres tall and 12 metres
long, weighing in at five to seven metric tons. Some
fossil evidence shows that the female T-Rex may have been the larger of the sexes, although there’s no way to know for sure. Its banana-shaped, serrated teeth gripped flesh and its massive jaw crushed bones as it downed more than 200 kilos of meat in one gulp. Likely prey included the Triceratops horridus and the Torosaurus, each about the size of an elephant.

There have been several nearly complete Tyrannosaurus rex skeletons found since the first bones were discovered in 1894, some of which included soft tissue. From these, palaeontologists have learned that the T-Rex had a lot of bird-like traits. It likely had a one-way air sac system that kept its lungs constantly full of fresh air, hollow bones to lighten its body weight, and binocular, colour sight. It also had a wishbone, or furcula. Some palaeontologists believe that our assumptions of scaly, lizard-like skin might not be entirely accurate and that
T-Rex could’ve even had feathers.

Controversy about the T-Rex centres on whether it was a predator or a scavenger, as well as whether it moved slowly or quickly. Many palaeontologists believe that the Tyrannosaurus rex was strictly a predator, but those who question this assumption point to its short, weak arms with two-fingered hands, large legs suited for walking distances and a strongly developed sense of smell. These seem more in line with what we know of scavengers rather than predators. Others argue that muscle scars found on skeletons show that the T-Rex had strong arms. They also believe that their binocular sight and hollow bones indicate a faster-moving predator. However, predators today will sometimes scavenge if fresh prey isn’t around, so T-Rex could’ve actually been both.