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Nephila jurassica, with a 5mm scale bar

What's the News: Researchers have unearthed the largest fossilized spider yet, announced in a study

online today in Biology Letters. The fossil, a Jurassic Period ancestor of the modern orb-weaver spider, gives scientists a glimpse not only into the evolutionary history of orb-weaver spiders, but how these ancient arachnids might have impacted the evolution of insect species that could be snared in the webs. How the Heck:

The fossil, found preserved in volcanic ash in the Daohugou fossil beds in northeastern China, dates back 165 million years. The researchers dubbed the species Nephila jurassica .

At about an inch long, the spider's body isn't unusually large, but its leg span, at nearly six inches, is the largest seen in a fossil spider.

This spider was female, suggesting the size disparity seen in modern orb-weaver spiders---with females dwarfing the males---may have begun at least 165 million years ago.

Silk spinning organs, called spinnerets, preserved on the fossilized spider's legs suggest that, like its modern counterparts, Nephila jurassica spun big, durable webs.

The spider's formidable prey-catching ability likely drove the evolution of the medium-to-large insects it fed on, as those species scrambled to survive, the researchers wrote.

What's the Context:

Until now, the earliest known fossil from the Nephila genus was 34 million years old; this find pushes back the origin of the genus 130 million years from what researchers previously thought.

Modern orb-weaver spiders live in tropical climes, so this fossil suggests that the region where it was found may have had a much muggier climate during the Jurassic than it does today.

The oldest fossil spiders ever found are nearly twice as old as this specimen, dating back 310 million years.

While its size is remarkable for a fossilized spider, Nephila jurassica's legspan is only half as big as that of the world's largest living spiders, the evocatively named goliath bird-eater and giant huntsman.

Reference: Paul A. Selden, ChungKun Shih and Dong Ren. "A golden orb-weaver spider (Araneae: Nephilidae: Nephila) from the Middle Jurassic of China." Biology Letters online before print, April 20, 2011. DOI: 10.1098/rsbl.2011.0228

Image: Selden et al. paper