SYDNEY, Australia — Lightning Ridge is a town about 450 miles inland from Australia’s eastern coast, yet as he mined for opal there 35 years ago, Bob Foster would find remnants of fish bones and mussels.

Forty feet below the surface, where water might have flowed some 100 million years ago, animals died and their bones became encrusted with colorful stone.

Mr. Foster and his fellow miners would smash those bones apart to see if opal, Australia’s national gemstone, lay beneath. One day he came across a semicircle-shaped bone that he thought might be a horse hoof but turned out to be the vertebrae of a dinosaur that was previously unknown.

Now it is named Fostoria, after him.

After years of studying the remains Mr. Foster found, scientists reported the discovery of the plant-eating species on Monday in the Journal of Vertebrate Paleontology.