The well-preserved 150-million-year-old specimen of the herbivorous dinosaur Stegosaurus stenops – now in the Natural History Museum, London, UK – would have weighed 1,560 kg in life, similar to the size of a small rhino, according to a group of paleontologists led by Dr Charlotte Brassey from the Museum’s Department of Earth Sciences.
Stegosaurus stenops. Image credit: Nobu Tamura / CC BY-SA 3.0.
Calculating body mass in animals that have been dead for many millions of years has been difficult for paleontologists.
There are two methods: one relies on researchers taking measurements of limb bones and extrapolating body mass from a large dataset of living animals, while the other produces a 3D model of the animal and applies densities to body segments to calculate mass. However, both often have varying results.
Dr Brassey and her colleagues are the first to combine both methods to calculate the body mass of an extinct creature to get an accurate measurement.
They used this approach on a specimen of the Jurassic dinosaur Stegosaurus stenops, which was found in the Upper Jurassic Morrison Formation near Shell, Wyoming, in 2003.
They have calculated that the dinosaur would have weighed 1,560 kg, similar in weight to a small rhino.
“This finding identifies just how important exceptionally complete specimens like this are for scientific research and collections,” said team member Prof Paul Barrett of the Natural History Museum, who is the senior author of the paper published in the journal Biology Letters.
Dr Susannah Maidment of Imperial College London, a co-author of the paper, said: “our study is the first to attempt different methods on the same animal, and has highlighted how and why different body mass estimation methods come up with different results.”
Since the specimen arrived at the Natural History Museum in December 2013 and before it went on permanent public display one year later, the team created the 3D model of the skeleton by scanning, photographing and measuring each of its 360 bones.
“Because this incredible specimen is so complete, we have been able to create a 3D digital model of the whole fossil and each of its 360 bones, which we can research in excellent detail without using any of the original bones,” said Dr Brassey, who is the first author of the paper.
“We also took the skeleton’s leg bone circumference and compared it to a modern animal of similar size, and came up with matching estimates for the dinosaur’s weight.”
In addition to the findings in this study, the data will underpin a series of future scientific studies, which will uncover more about the unusual lifestyle of Stegosaurus.
“Now we know the weight, we can start to find out more about its metabolism, feeding requirements and the growth rates of Stegosaurus,” Prof Barrett explained.
“We can also use the same techniques on other complete fossils to find out much more about the wider ecology of dinosaurs.”
_____
Charlotte A. Brassey et al. Body mass estimates of an exceptionally complete Stegosaurus (Ornithischia: Thyreophora): comparing volumetric and linear bivariate mass estimation methods. Biology Letters, published online March 4, 2015; doi: 10.1098/rsbl.2014.0984
