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