Nigersaurus: 500 teeth and a vegetarian diet. Photo by Mike Hettwer, courtesy of Project Exploration. ©2007 National Geographic.

Discovered in 1999 in the Sahara desert by National Geographic Explorer-in-Residence Paul Sereno of  the University of Chicago, Nigersaurus taqueti was a vegetarian originally known only by a few distinctive hand bones. But further excavation has fleshed (boned?) him out.

Nigersaurus, whose closest relative was Diplodocus, measured 30 feet from head to toe, and was barely able to lift its head above its back, says Sereno, forcing it to chow down like a Mesozoic cow, mowing through ferns, horsetails and other vegetation. A broad, straight muzzle let its mouth work close to the ground. But Nigersaurus differed from every other known herbivorous dino in having more than 50 columns of teeth, lined up in almost military formation along the front of its squared-off jaw. A CT scan of the jaw bones revealed up to nine "spares" stacked behind each cutting tooth, so that when one wore out, another could drop down and take its place. "Among dinosaurs," Sereno said, "Nigersaurus sets the Guinness record for tooth replacement."

Nigersaurus’ backbone was more air than bone, with vertebrae so paper-thin it's difficult to understand how he stood up.