Doubts have surfaced over the excavation in the 1980s of ancient ruins in Taiwa, Miyagi Prefecture, by a disgraced archaeologist who earlier this month admitted fabricating his "discoveries" at another site in the prefecture, sources close to the case said.

The sources said Saturday that Shinichi Fujimura, 50, former deputy chief of the Tohoku Paleolithic Institute, discovered archaeologically important stone implements during the excavation -- but only when he was alone at the site.

Fujimura's discoveries led to the estimated date of the site, named Nakamine C, being pushed back, making it between 140,000 and 370,000 years old. It was initially believed to date from the Heian Era, which spanned the eighth to 12th centuries.