Research from Montana State University's Museum of the Rockies and the State Museum of Pennsylvania say the bones belonged to the sauropod dinosaur Alamosaurus sanjuanensis, a long-necked plant eater previously thought to reach 60 feet in length, an MSU release said Wednesday.
The sheer size of the bones, found between 2003 and 2006, surprised the scientists.
"We used to think that a fully grown Alamosaurus measured around 60 feet long and weighed about 30 tons; but a 2009 study ... found that a femur thought to belong to an adult was still growing," MSU researcher Denver W. Fowler said. "This told us that Alamosaurus got even bigger, but we didn't imagine that it could get quite this big."
Researchers said the size of the new fossil bones puts Alamosaurus in the same size league as other giant sauropods from South America, including the 70-ton Argentinosaurus, widely considered before now to have been the biggest dinosaur of all.
"Over the past 20 years, Argentinean and Brazilian paleontologists have been unearthing bigger and bigger dinosaurs, putting the rest of the world in the shade," Fowler said. "However, our new finds not only show that Alamosaurus is newly recognized as the biggest dinosaur from North America, but also that it was right up there with the biggest South American species: the U.S. is back in the fight for the No.1 spot."