Features of the fossil link the plant-eater to well-known giant sauropods such as Diplodocus from North America and Brachiosaurus from Africa. (Related pictures: Dino With "Vacuum Mouth" Revealed [November 15, 2007].)
"But you should imagine it as representing some other additional lineage in this major group, which we didn't know about at all," Naish said.
Getting an accurate picture of what Xenoposeidon looked like from a single piece of backbone is impossible, the researcher admitted.
"You can't tell from the shape of the vertebra whether it was a long, low animal like Diplodocus, or whether it was an altogether shorter, stockier animal like Brachiosaurus," Naish said.
If built like a brachiosaur, the dinosaur would have measured some 15 meters (50 feet) long and weighed 7.6 tons, the researchers estimated.
If instead it resembled more lightly framed diplodocoids, Xenoposeidon would have stretched 20 meters (66 feet) nose to tail and weighed about 2.8 tons, the study said.
More Finds to Come?
Fossil collector Philip James Rufford originally discovered the odd vertebra in the early 1890s near Hastings in southeast England.
The fossil was briefly reviewed by paleontologists, then hidden away for 113 years at the Natural History Museum.
Researchers don't know whether other remains of the fossil creature survived, since the museum didn't keep a record of the exact location of the find.
That's not uncommon, Naish said. Hundreds of dinosaurs and other long-extinct animals are known from a single fossil specimen. (Related: "New Species of Ancient Sea Creature Discovered—Under Ping-Pong Table" [September 29, 2006].)
But attaching a name to the newly described sauropod bone should increase the chances of future Xenoposeidon discoveries.
"Hopefully this will mean that other sauropod experts will know what to look for, and they will have this [fossil] in mind when they look at other unusual vertebrae," Naish said.
As many new dinosaur species are described from museum fossil collections as from freshly unearthed specimens, he pointed out.
"There are paleontologists who say, If you want to find new species, don't go out in the field, just go and look at old collections," Naish added.
Natural History Museum dinosaur researcher Paul Barrett said in a statement that the museum's fossil collection contains thousands of dinosaur specimens, which are studied by researchers from all over the world.
"Because of their work," he added, "dinosaur bones are being constantly reassessed, and our collections still offer us lots of surprises."
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