Scientists cannot agree on the maximum size of these giant dinosaurs. Brachiosaurus is usually said to be the biggest, weighing 77 tonnes. A recently described dinosaur, provisionally called Ultrasaurus, is thought to have been about 30 m long and to have weighed as much as 130 tonnes. This would make it by far the heaviest land animal ever to have existed. Even the mighty blue whale is small in comparison to these huge prehistoric creatures.
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