Mariana Ruiz Villareal

An artist's conception shows a pair of Alamosaurus sanjuanensis dinosaurs.

Here's a trivia question for your dino-crazy kids: What's the biggest dinosaur to roam North America? Paleontologists report that it's Alamosaurus sanjuanensis, one of many breeds of long-necked, long-tailed sauropods to roam the continent 69 million years ago.

Montana State University's Denver Fowler and the State Museum of Pennsylvania's Robert Sullivan make that judgment on the basis of two huge vertebrae and a femur that they collected in New Mexico between 2003 and 2006. Based on the bones' proportions, they figure that Alamosaurus could be around the same size as South America's giant sauropods, such as the 70-ton Argentinosaurus.

If  Fowler and Sullivan are correct, that'd make Alamosaurus twice as heavy as paleontologists thought it was just a few years ago. Their research was published Tuesday in Acta Palaeontologica Polonica. 

"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 in an MSU news release issued Tuesday. "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."

There's more at stake here than mere bragging rights. "Our findings show that Alamosaurus was originally described based on immature material, and this is a problem, as characteristics that define a species are typically only fully gained at adult size," said Fowler, a doctoral student at MSU's Museum of the Rockies. "This means that we might be misinterpreting the relationships of Alamosaurus and possibly other sauropod dinosaurs too."

Researchers from MSU and the Pennsylvania museum are continuing to collect Alamosaurus bones to resolve the size question as well as other details about the dinosaurs' life and death. To keep up with the research — and perhaps eventually find out whether Alamosaurus pushes aside Argentinosaurus and its Russian rival, Ruyangosaurus, check in with the Facebook page for the Horner Paleo Lab at the Museum of the Rockies. You can also check out this video about the Alamosaurus quest:

Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.