After nine years of excavation and study, paleontologists have unveiled one of the largest creatures ever to walk the Earth. The most complete skeleton of a giant titanosaur will provide new insights into how these giants lived large.

The new dinosaur is named Dreadnoughtus schrani, a reference to the armored battleship and a tribute to the dinosaur's perceived fearlessness. Details on the dinosaur are announced Thursday in the journal Scientific Reports.

View Images Art: Emily M. Eng, NG Staff Source: Matthew C. Lamanna, Carnegie Museum of Natural History

In life, Dreadnoughtus would have been about 86 feet (26 meters) long and weigh nearly 60 tons, heavier than a Chieftan tank, Drexel University paleontologist Ken Lacovara and colleagues calculate. That's so big, the scientists write, that adults of the species would have been "nearly impervious to attack" by predators that stalked the same floodplains between 84 million and 66 million years ago.

Among the largest of dinosaurs, titanosaurs like Dreadnoughtus were hefty herbivores with tiny heads, long necks, and tapering tails. This body type marks titanosaurs as part of a group called sauropods, to which classic dinosaurs such as Apatosaurus also belonged. Sauropods spent their days feeding high and low, plucking greens from patches of ferns and trees alike, as they browsed the prehistoric salad bar.

What makes Dreadnoughtus a remarkable new addition to this prehistoric family is the amount of material recovered from the dinosaur. The remains, representing two individual animals, include both the humerus and femur of Dreadnoughtus, and Lacovara and colleagues used the circumference of these bones to estimate the dinosaur's weight.

So far, Lacovara says, "Dreadnoughtus has the largest calculable mass of any land animal."

View Images The humerus, or upper arm bone, of Dreadnoughtus shows muscle scarring. Photograph by Robert Clark, Excel Magazine, Drexel University

A Big Find

At first, though, Dreadnoughtus didn't seem so impressive. "In 2005, we were prospecting in the desert [of southern Argentina]," Lacovara says, "and the first day of that field season I found a collection of bones." They just looked like a pile of fragments, but when Lacovara and collaborators returned to the site, they started uncovering big limb bones.

"By the end of the day we had ten bones exposed," Lacovara says. "At that point we were pretty excited." Four field seasons later, the team had excavated 145 bones.

Altogether the bones represent about 45 percent of a complete skeleton, and because some of the bones have mirror images on the other side of the body, Lacovara and colleagues were able to reconstruct about 70 percent of a Dreadnoughtus skeleton. The best large titanosaur find previously, Futalognkosaurus, was only about 27 percent complete.

"Now we can start talking intelligently about the body proportions of these giant titanosaurs," says Western University of Health Sciences paleontologist Mathew Wedel.

View Images Emily M. Eng, NG Staff

And Dreadnoughtus could have grown even bigger than the new estimate. "Since the authors provide data that illustrate that Dreadnoughtus was still growing when it died," says Macalester College paleontologist Kristi Curry Rogers, "we can be fairly certain that there were other heavier dinosaurs out there."

Mysterious Lives

But size isn't everything. "If we want to really begin to understand how these big dinosaurs grew, and how long it took them to reach their massive sizes, these are the perfect kinds of data to begin with," Curry Rogers says. Having two individuals is a good start, she says, but scientists will need to find more of the dinosaurs to begin piecing together their lifestyles.

"There are so many fundamental things we don't know about sauropods," Lacovara says, such as the arrangement of their muscles and how they moved. Turning to muscle scars on the bones of Dreadnoughtus, Lacovara and others are figuring out the dinosaur's muscle anatomy and how those soft tissues translated to movement.

This is just the sort of effort other paleontologists are hoping to see. "It's all about building toward a more complete picture of the living animal," Wedel says.

View Images The 5.6-foot (1.7-meter) scapula of Dreadnoughtus is the longest yet reported for any titanosaur. Photograph by Robert Clark, Excel Magazine, Drexel University

For now, though, Lacovara is glad to see Dreadnoughtus finally emerge after all the years of fieldwork and study. "This is like Christmas and my birthday and my wedding combined."

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