Hamish Sawers, of Ardgowan School, asks :-

What was the largest dinosaur?

Alison Cree, a zoologist at Otago University, responded.

The largest dinosaurs belong to a group called the sauropods. Sauropods lived from about 200 million years ago to 65 million years ago. They were enormous creatures with long necks, long tails and massive, pillar-like legs. They walked on land on all four legs and were herbivores (plant-eaters).

Scientists can talk about size in different ways - height, length and weight, for example. Nobody knows for sure which was the heaviest dinosaur because the skeletons are often incomplete and guesses have to be made about the weight of tissues, like muscle, that don't preserve. One of the largest sauropods with a well-preserved skeleton was Brachiosaurus. It had front legs that were longer than its rear legs, and an enormous neck. Its head was held about 13 metres high (that's more than twice as high as a giraffe) and estimates of weight range up to about 80 tonnes (that's 80,000 kilograms, about 13 times as heavy as a large elephant). Some other sauropods like Supersaurus and Seismosaurus (seismos means earthquake) may have been even heavier - perhaps 100 tonnes - but only a few bones have been found.

Not all dinosaurs were the "fearfully great" reptiles that their name implies. Some were only about 1 metre long. Dinosaur bones have been found in New Zealand and one was possibly a sauropod about 10-12 m long. An artist's impression of what it looked like featured on a 45c stamp a few years ago.

New Zealand's distinctive tuatara (Sphenodon) is not a dinosaur but a type of reptile called a sphenodontian. Sphenodontians are related to lizards, and first appeared about 230 million years ago. About 30 extinct species have been described. Like its ancient relatives, the modern tuatara has retained a body shape rather like a lizard, and a relatively small body size (up to 600 mm long).