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305 Million-Year-Old Fossil A Glimpse Into The Origins Of Spiders

Digital visualization of Idmonarachne brasieri based on laboratory-based scans of the fossil. i

Digital visualization of Idmonarachne brasieri based on laboratory-based scans of the fossil. Proceedings of the Royal Society B hide caption

toggle caption Proceedings of the Royal Society B
Digital visualization of Idmonarachne brasieri based on laboratory-based scans of the fossil.

Digital visualization of Idmonarachne brasieri based on laboratory-based scans of the fossil.

Proceedings of the Royal Society B

Scientists have discovered a well-preserved 305 million-year-old arachnid that is "almost a spider" in France. In a new journal article, they say the fossil sheds some light on the origins of "true" spiders.

Idmonarachne brasieri, from the Late Carboniferous period and found in Montceau-les-Mines, France.

Idmonarachne brasieri, from the Late Carboniferous period and found in Montceau-les-Mines, France. Proceedings of the Royal Society B hide caption

toggle caption Proceedings of the Royal Society B

The main point of distinction: This newly discovered arachnid very likely could produce silk but lacked the spinnerets used by true spiders to, well, spin it, the scientists say. The researchers say it belongs to a "sister group" to the real-deal spiders.

The species, which they described in a new article in the journal Proceedings of the Royal Society B, is named Idmonarachne brasieri. That's after Idmon, the father of Arachne in Greco-Roman mythology. Appropriately, Arachne was a master weaver who was transformed into a spider.

The paper says Idmonarachne "does not fit comfortably into the established orders." National Geographic reports that it "acts as a bridge between early spider-like creatures brewing up blobs of silk and the skilled weavers that we see today."

Here's more from National Geographic on the comparatively clumsy beginnings of spiderly silk production:

"While delicately constructed webs seem synonymous with spiders, we know from the fossil record that the ability to secrete silk came before the ability to carefully control it. Spider relatives called uraraneids, which lived from 385 million years ago through the time of Idmonarachne, could produce silk but could not build webs."

University of Manchester's Russell Garwood, who was one of the article's authors, told the BBC, "This fossil is the most closely related thing we have to a spider that isn't a spider."

The specimen was found in a deposit in Montceau-les-Mines in France and then included in what the article's co-author described as a "box of fossils" borrowed by the University of Kansas, as the BBC reported. It had been sitting there for decades — the BBC says the box came from Paris' Museum National d'Histoire Naturelle in the 1980s.

The scientists used laboratory and synchrotron scans of the fossil to produce digital 3-D imagery of Idmonarachne. The arachnid predated the first appearance of the dinosaurs by some 80 million years.

As the BBC reports, "The 1.5 cm creature lived alongside the oldest known ancestors of modern spiders but its lineage is now extinct."

There was a rich landscape of arachnids in the Late Carboniferous period — according to the journal article, "the period may have been a time of generally higher arachnid diversity than today."

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