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