Giant sauropod dinosaur may not be as large as thought

Using new three dimensional modelling, scientists have found that the giant sauropod dinosaur, Dreadnoughtus, discovered by palaeontologists in South America in 2014, was not as large as thought earlier.

The mass of the Dreadnoughtus was more likely to be between 30 and 40 tonnes, considerably less than original estimates of around 60 tonnes, the findings showed.

"Estimating the body mass of an extinct animal from approximately 77 million years ago of this size from only its fossilised bones is extremely challenging and relies on the availability of certain data from living animals and modelling techniques," said one of the researchers Karl Bates from the University of Liverpool in Britain.

"The original method used to calculate the mass of the animal is a common one and has been used successfully on many specimens. The highest estimates produced for this particular giant, however, did not quite match up," Bates added.

Found in Patagonia, the huge fossil had almost all of the major bones intact, allowing scientists to confidently estimate its overall size - measuring in at 26 metres long.

Preserved in rock, it was thought that the animal was close to maturity but not fully grown when it died, and may have grown to be even larger. Also, it was perceived that the long necked, plant-eating dinosaur was the biggest to ever walk the earth.

To estimate the mass of Dreadnoughtus scientists originally used a scaling equation that predicts body mass based on the size of thigh and arm bones. This method produced a range of estimates with the average being a colossal 60 tonnes.

In the new study, the researchers re-evaluated this estimate after it became clear that other sauropod dinosaurs, only marginally smaller than the giant, weighed considerably less than 60 tonnes. The team used a three-dimensional skeletal modelling technique to examine body mass more directly.

This method involves mathematically reconstructing a 'skin' volume around bones of Dreadnoughtus on a computer and then expanding that skin outline to account for muscle, fat and other tissues.

The size of expanded skin outline is based on similar data from living animals. By exploring a range of expansions the team could more accurately predict how heavy Dreadnoughtus could realistically have been.

"Using digital modelling and a dataset that took in species, alive and dead, we were able to see that the creature couldn't be as large as estimated," Bates said.

The research was published in the Royal Society journal Biology Letters.