A few years ago, scientists uncovered the largest-ever fossil of spider: a female representative of a never-before-seen species that was buried in volcanic ash during the age of the dinosaurs.
Now the researchers say they have found an adult male spider to match, but the discovery complicates the original interpretation of the species. The scientists have proposed a new genus — Mongolarachne — to describe the extinct creature.
When researchers first found the female spider in northern China, they named it Nephila jurassica, putting it in the Nephila genus of golden silk orb-weavers, which still exist today and have been known to ensnare birds and bats in their huge wheel-shaped webs. (Ewww! See Photos of Bat-Eating Spiders in Action)
"It was so much like the modern golden orb weaver," said Paul Selden, a paleontologist with the University of Kansas. "We couldn't find any reason not to put it in the same genus of the modern ones."
With soft, squishy bodies, spiders don't typically turn up in the fossil record, but several hundred have been found in the volcanic deposits at the Daohugou fossil beds in Inner Mongolia, Selden said.
Volcanic ash is famous for preserving more ephemeral pieces of the past, from bodies buried in their death poses at Pompeii to 2.7-billion-year-old raindrop impressions found in South Africa. Researchers think these spiders were likely swept to the bottom of a sub-tropical lake and covered in fine ash after a volcano blew its lid.
Unlike insects, spiders are typically pretty good at staying away from water, Selden explained.
"It would take something like a volcanic eruption to blow them into the bottom of the lake and bury them," Selden told LiveScience. "That's the sort of scenario we imagine."
And in that volcanic rock layer at Daohugou, the researchers found another spider that looked remarkably similar to Nephila jurassica, except it was male. There were several clues in the newfound fossil, however, that suggest this ancient arachnid just doesn't fit the bill for Nephila.