Dreadnoughtus schrani, as it might have looked 77 million years ago (Image: Jennifer Hall)

They just keep getting bigger. The latest dinosaur to be discovered was 26 metres long and seven times as heavy as Tyrannosaurus rex . Named Dreadnoughtus schrani by the team who found it, the bones belonged to the largest known land animal whose size can be reliably calculated. And it wasn’t even fully grown.

Video: Assembling the bones of the largest land dinosaur

The 77-million-year-old Dreadnoughtus skeleton was found in south-west Patagonia, Argentina, in 2005, and has taken several years to analyse. While other giants from Patagonia are known from a handful of bones, almost half of the Dreadnoughtus skeleton has been recovered. What’s more, the fossilised bones are in such good condition – even revealing where muscles attached – that the skeleton could provide unprecedented insights into the biology, movement and evolution of the group of huge plant-eating dinosaurs it belonged to, called the titanosaurian sauropods.


“Knowing what muscles exist and their size and power is fundamental to formulating reliable hypotheses for how these animals moved,” says Kenneth Lacovara of Drexel University in Philadelphia, Pennsylvania, who led the team that discovered Dreadnoughtus.

The supermassive fossil was discovered in 2005 in Patagonia (Image: Ken Lacovara)

So many of the specimen’s bones are known that Lacovara’s team could estimate its weight precisely. Their figure – 59.3 tonnes – means Dreadnoughtus was considerably heavier than Elaltitan lilloi which, at 42.8 tonnes, is the next-largest sauropod with a weight that has been reliably calculated. By comparison, well-known sauropods such as Brachiosaurus and Diplodocus are minnows, at 34 and 15 tonnes respectively.

“The most important thing is that the specimen is relatively complete, especially when compared to other gigantic dinosaur species we know,” says Matthew Carrano at the Smithsonian Institution National Museum of Natural History in Washington DC. “Although sauropods are often thought to have all looked pretty similar, once you see the anatomy it’s clear that there’s an enormous variety of shapes and sizes. And understanding exactly how they are built is one of the key things to understanding how they functioned and evolved.”

Exquisite preservation

“The relative completeness of Dreadnoughtus and the exquisite preservation of its bones will help improve our understanding of many questions,” says Lacovara. These include how quickly and how large sauropods grew, what muscles they had and where they were attached, their bodily proportions, and their body temperatures.

Lacovara has a wealth of other questions, too. “How tightly did they regulate temperature? What were their caloric requirements? Could they kneel down? What kind of genitals did they have and how did they have sex? These are questions to which we have no answer or, at best, a foggy understanding.”

Experiments are already under way in his lab to look for answers. One involves biomechanical analysis of how Dreadnoughtus moved, with the help of three-dimensional virtual models of the animals. “The other involves robotic experiments on 3D-printed Dreadnoughtus bones,” says Lacovara. “Because the bones beautifully preserve muscle scars where muscles were inserted, the musculature of a supermassive dinosaur can now be reconstructed in unprecedented detail.”

“Ultimately, Dreadnoughtus may be able to help us understand the upper size limits to life on land, in terms of the physical constraints imposed by bone and muscle strength, blood pressure and feeding requirements,” says Paul Barrett at the Natural History Museum in London.

The other big surprise was that Dreadnoughtus may actually have grown still larger than the current fossil. “Shockingly, at the time of death, the 59-tonne Dreadnoughtus was still growing fast,” says Lacovara. He could tell it wasn’t fully mature because its shoulder bones had yet to fuse together, as is seen in adult sauropods, and its bones generally lacked the cellular features seen in adults.

Journal reference: Scientific Reports, DOI: 10.1038/srep06196