for National Geographic News
Over a hundred millions years ago, one small spider wove its intricate silken weba task spiders are thought to have performed for hundreds of millions of years. This spider lived during the Cretaceous period in what is now Lebanon, and shared its world with some of the largest dinosaurs to have ever existed.
But on this rare occasion one small piece of that delicate web became trapped in oozing, tar-like, tree resin, which later hardened to form amber. One hundred thirty million years or so would pass before fossil hunters dug it up, and now that miraculously fossilized spider's web is described for the first time in today's issue of the science journal Nature.
The fossil, described by Samuel Zschokke, a spider biologist at the University of Basel in Switzerland, is the oldest direct evidence of spiderwebs.
"Spiders are amongst the rarest of all fossils," commented William Shear, an entomologist at Hampden-Sydney College in Virginia. "We almost never find web fossils, and this is undoubtedly the oldest," he said.
Spiders don't fossilize well, as they have no hard skeleton and are not typically found near bodies of water, which readily accumulate the sediments ideal for preservation.
Polished and Put Aside
Though spider thread preserved in amber has been found before, previous specimens have dated from much more recent periodstypically from amber beds some 20 to 30 million years old, deposited long after the extinction of the dinosaurs. But the newly described fossil spiderweb dates roughly 90 million years older than the previous oldest known specimen.
The piece of amber was found in Jezzine, Lebanon, by German fossil hunter Dieter Schlee in 1969 in amber beds that date to between 127 and 132 million years ago. The amber beds are from the early Cretaceous period and are the oldest beds known to contain fossilized insects.
Though Schlee noted that the fossil might contain a piece of web, it wasn't his area of expertise, so the fossil was polished and put aside in a Stuttgart museum, without the recognition it deserved.
That was until Zschokke recently paid a visit to the museum, and asked staff if he could examine their amber collection. What he found on inspection with a microscope astounded him.
The tiny thread of silk is just four millimeters (0.15 inch) long and just three micrometers in diameter (a micrometer is one-thousandth of a millimeter and approximately one twenty-five-thousandth of an inch). That's many times thinner than a human hair.
The thread was only noticed because it is coated in larger glue droplets, deposited by many species of spider. All spiders known to weave delicate circular net-like orb webs are spiders of the superfamily Araneoidea who produce this kind of glue coated "viscid" silk. The thread shows "a striking resemblance to recent araneoid spider threads," said Zschokke.
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