Measuring nearly 1 inch (2.5 centimeters) in length, the 165-million-year-old fossil was uncovered in 2005 by farmers in Inner Mongolia (see map)—a region teeming with fossils from the middle Jurassic period.

"Compared to all other spider fossils, this one is huge," said study co-author ChungKun Shih, a visiting professor at Capital Normal University in Beijing, China.

(Related blog post: "Seven of the Biggest Beasts of All Time.")

"When I first saw it, I immediately realized that it was very unique not only because of its size, but also because the preservation was excellent," Shih said.

Fine volcanic ash preserved the specimen's exquisite features, such as mouthparts and hairlike structures that covered its