There's a new contender for the "biggest dinosaur" title, with the imposing name of Dreadnoughtus, but even its lead discoverer says that size isn't everything. What matters the most is the completeness of this Argentinian titanosaur's skeleton — which should help scientists figure out how these ancient monsters lived, and not just how big they were.
"It offers us the best window that we have so far into the anatomy and the biology of these supermassive land animals," Drexel University paleontologist Kenneth Lacovara told NBC News. Lacovara is the lead author of a paper about the find, published Thursday in Scientific Reports.
Dreadnoughtus schrani takes its name from the giant battleships of the early 20th century (plus a nod to entrepreneur Adam Schran, who helped fund the research). The plant-eating dinosaurs weren't quite as big as dreadnoughts, but they definitely ranked among the largest battleships of the Late Cretaceous Era, about 77 million years ago.
Lacovara and his colleagues estimate that the creature measured about 85 feet (26 meters) long, 30 feet (9 meters) tall, and weighed about 65 tons (59 metric tons). That weight is the equivalent of a dozen elephants, or seven tyrannosaurs. And an analysis of Dreadnoughtus' microscopic bone structure suggests that it could have gotten even bigger. "When it died, it was still growing," Lacovara said.
So was this the world's biggest dinosaur? Asking that question is a good way to start an argument. Some researchers say they've come across fossils from bigger dinosaurs, with Argentinosaurus' weight estimated at 70 to 90 tons. In May, a different team of paleontologists reported finding bones from a dinosaur that they claimed was bigger than Argentinosaurus.
Lacovara says those other estimates are based on a mere smattering of bones, or on analyses that haven't yet been subjected to peer review. In contrast, the estimate of Dreadnoughtus' size and weight was based on measurements of more than 100 separate elements, including most of the tail vertebrae, a yard-long (meter-long) neck vertebra, numerous ribs and nearly all the bones from the forelimbs and hindlimbs.
Researchers unearthed about 45 percent of the skeleton's full complement of bones, representing 70 percent of the bone types found below the skull (for example, a left rib without the mirror-image right rib). A smaller, less complete skeleton of the same species was also found at the site in Argentina's southern Patagonia region, during a series of excavations conducted between 2005 and 2009.
The researchers made crucial measurements of the bigger dinosaur's thigh bone (femur) and upper arm bone (humerus) that led to the 65-ton weight estimate. Lacovara said no other dinosaur measured in that way has been judged to be as big. Other dinosaurs may well have been bigger. It's just that the evidence isn't as solid, at least in Lacovara's view.
"I can say that we have the largest land animal that we can confidently affix a number to," he said. "I cannot confidently say that we have the largest land animal."
Looking beyond the debate over size, Lacovara said the relative completeness of the Dreadnoughtus skeleton, plus the "exquisite" preservation of the bones, will help paleontologists fine-tune their image of super-sized dinosaurs. The picture that's emerging is already different from what Lacovara and his colleagues were expecting.
"It had a tail that was shorter than we expected, and a neck that was longer than we expected," he said. "Its tail was more muscular than we expected."
To flesh out that picture, Lacovara's team made laser scans of every bone and fed the 3-D imagery into a computer. Researchers are playing around with those virtual 3-D bones, plus virtual muscles, to figure out the biomechanics behind Dreadnoughtus' massive frame.
They're also using 3-D printers to create one-tenth-scale models of the dinosaur skeleton, and working with a roboticist at Drexel to manipulate the models. "We can in a real sense test these models of joint movement," Lacovara said.
The researchers are even making their 3-D scans freely available on the Internet as PDF files, so that anyone in the world can download virtual copies of the Dreadnoughtus bones. "I'm excited about this because it's part of the open-access movement that is really democratizing science," Lacovara said.
At the same time, Lacovara's team is trying to demineralize some of the fossil bones and recover enough ancient protein for sequencing, just as other researchers have done with bones from Tyrannosaurus rex. Although it's too early to report how that effort has turned out, "I can say that we're getting some promising data from this," Lacovara said.
Researchers are already starting to draw conclusions from the way Dreadnoughtus was built. "The one thing everyone can agree on is that these animals must have been very efficient," Lacovara said.
For example, why did Dreadnoughtus have a 37-foot-long (11-meter-long) neck? "It gives the animals access to a huge eating envelope while standing in one place," Lacovara said. The creatures could spend an hour or so clearing out one patch of vegetation, take just a few steps, and then clear out another patch. That level of efficiency would have been important for an animal that had to take in about a half-ton of food every day.
There's another advantage to having a long neck: That would have made it easier for Dreadnoughtus to shed its considerable body heat. "Long limbs and a long neck and a long tail give you a lot of surface area per volume," Lacovara said.
And that's just the beginning. Lacovara said he and his colleagues already have four more studies nearly ready to go. So stay tuned for more tales of the titanosaur.
"It's a big animal," Lacovara said. "There's a lot to talk about."
In addition to Lacovara, the authors of "A Gigantic, Exceptionally Complete Titanosaurian Sauropod Dinosaur from Southern Patagonia, Argentina" include Matthew Lamanna, Lucio Ibiricu, Jason Poole, Elena Schroeter, Paul Ullmann, Kristyn Voegele, Zachary Boles, Aja Carter, Emma Fowler, Victoria Egerton, Alison Moyer, Christopher Coughenour, Jason Schein, Jerald Harris, Ruben Martinez and Fernando Novas.