The iconic T. rex dinosaur grew bigger and faster than previously estimated, according to British and US scientists.
Scientists digitally modelled flesh on five mounted T. rex skeletons and showed that the meat-eating lizard kings were up to a third bigger and grew two times as fast into adults than previous research had suggested.
The findings, led by Professor John Hutchinson of The Royal Veterinary College, London, and Peter Makovicky, curator of dinosaurs at The Field Museum of Natural History in Chicago, are published in the journal PloS One .
One of the skeletons included in the study was "Sue", the largest and most complete T. rex specimen ever found, on display at The Field Museum.
The 67-million-year-old dinosaur was discovered in 1990 on an Indian reservation in South Dakota by American palaeontologist Sue Hendrickson.
Named after its finder, Sue was previously thought to be about the size of a big elephant or rhinoceros, standing 3.5 metres high and 13 metres from head to tail.
Her living weight was guessed to be 6400 kilograms, or about six and a half tonnes.
But the latest methods found she would have tipped the scales at well over nine tonnes.
"We knew she was big but the 30 per cent increase in her weight was unexpected," says Makovicky.
Using digital modelsThe technique used mounted skeletons to derive body mass estimates, instead of models created to scale.
The team made three-dimensional laser scans of the skeletons to form a template for digital models that would add simulated flesh.
They devised three different levels of the approximate amount of flesh the creatures likely had, to figure the size of a thin, hungry animal up to a well-fed one.
"Previous methods for calculating mass relied on scale models, which can magnify even minor errors, or on extrapolations from living animals with very different body plans from dinosaurs," says Makovicky.
"We overcame such problems by using the actual skeletons as a starting point for our study."
By establishing new sizes for the other four specimens studied, the researchers also found that the creatures likely grew faster than initially thought.
"We estimate they grew as fast as 1790 kilograms per year during the teenage period of growth, which is more than twice the previous estimate," says lead author Hutchinson.
That would mean the land-roaming carnivores expanded by about 5 kilograms per day during their peak growth spurt, more than double their 2004 estimate of 2.1 kilograms per day.