Sometime after he calculated the size of a specimens from a new supermassive dinosaur species he discovered in 2005, paleontologist Ken Lacovara nabbed one of his son's plastic dino toys and stood on the sidewalk outside of his house in New Jersey. He held the plastic sauropod up to his eye, trying to make a mental calculation of how an actual Dreadnoughtus schrani would have looked, standing next to the house. He decided that with its head stretched out across the driveway, the tail of the 25-meter-long Dreadnoughtus would have reached well into the backyard.
The genus name comes from the discovery team's feeling that something this big would have, well, dread naught. "Sometimes herbivores don't get their due as being really tough, badass animals," Lacovara says. "At 65 tons in life, Dreadnoughtus wouldn't be afraid of anything." It is more than seven times as massive as a Tyrannosaurus rex. Its name is also a nod to the world's first steel battleships, called dreadnoughts.
The fossil, being announced today in Scientific Reports, will represent one of the largest animals ever to walk on Earth. It is also the most complete fossil of a supermassive dinosaur ever found. With further study it could yield some new insights into how these late Jurassic giants moved and grew, and how their bodies evolved their extraordinary size. "It's an interesting discovery because of the scale and of the extent of the bones preserved," says Kristi Curry Rogers, a paleontologist at Macalester College in Minnesota who specializes in sauropods. Dreadnoughtuses are sauropods, a long-necked, herbivorous group of dinosaurs that includes apatosaurs. Not all sauropods were giant but some of world's biggest land animals were sauropods. (Scientific American and Scientific Reports are both parts of Nature Publishing Group.)
Lacovara's team, including paleontologists from institutes in Argentina's Chubut Province, found two D. schrani fossils in that nation's Patagonia region. The larger and more complete one has 70 percent of the types of bones believed to be in the dinosaur’s body, excluding the skull. The scientific record's next-most complete giant dinosaur fossil, a Futalognkosaurus dukei, has about 27 percent of the relevant bone types. The identities of some giant dinos are deduced from less than 10 percent of their skeletons.
Supermassive sauropods are generally poorly preserved. Paleontologists think that is because their huge bodies are not likely to become completely covered with sediment after death. (Lacovara thinks his Dreadnoughtuses died in a sediment-filled flood, making their corpses mostly inaccessible to scavengers that might otherwise scatter their bones.) Not many bones of the same type are found across giant sauropod species, which makes it difficult to compare bones and untangle evolutionary relationships. For example, to decide how two species are related, paleontologists might want to compare their femurs—but that's a nonstarter if there aren't femurs available for both. Basic questions, such as whether massive body size evolved once or many times in the family tree, remain unanswered. "Their paper and the fact that they have this fairly complete, large dinosaur is a step in the right direction," says Jeffrey Wilson, a paleontologist at the University of Michigan. Neither he nor Rogers worked on the Dreadnoughtus.
The Scientific Reports paper aims only to announce the discovery of the animal, so it doesn't yet answer those questions. The article, however, may help others do so: It contains a pdf with 3-D laser-scanned models of the bones. Anyone with Adobe Reader can open the file, see the model, rotate it and zoom in. For certain studies, such data may be enough to eliminate a costly trip to see the bones in person. A number of museums have begun publishing data like this for their collections, but Lacovara thinks this is the first time such information has appeared with a new species.
Many paleontologists applauded the discovery by offering to lend a hand with the bones: three U.S. labs cleaned them; volunteers spent thousands of hours making 3-D scans of the specimens. From discovery to publication took nearly 10 years. "Digging up a sauropod is like taking out a mortgage," Lacovara says, although he credits someone else for the joke.
Good thing Lacovara's house and Dreadnoughtus will never actually meet. "It would leave footprints the size of dishwashers in my nicely manicured lawn," he says. "I would have mixed feelings."