A recently-discovered, more than 300 million-year-old, eight-legged arachnid fossil is the closest relative to modern-day spiders ever discovered, but despite having spider-like legs and mouths, it is not actually a member of order Araneae, according to a new study.
According to BBC News and the Guardian, the creature was no bigger than a postage stamp, had large fangs, and was somewhat portly in shape. However, it lacked several important features that all true spiders possess, including the spinnerets used by the arachnids to spin silk.
In addition, CT scans of the fossils (which were originally found in France several decades ago) revealed that the newly-identified species had an odd plated and segmented abdomen, and that it lacked the long tail-like flagellum found in earlier spider-like arachnids known as the Uraraneids. The new species has been identified as the Idmonarachne brasieri, the researchers said.
“This fossil is the most closely related thing we have to a spider that isn’t a spider,” University of Manchester paleobiologist Russell Garwood, lead author of a study on the new species published Wednesday in the journal Proceedings of the Royal Society B, confirmed to BBC News.
The creature lived in the late Carboniferous period and belongs to a now-extinct lineage. Credit: Garwood et al
Secret to spiders’ success may be spinnerets, scientists say
When the remains of the arachnid were first discovered at a site near Montceau-les-Mines in eastern France, half of it was found to be entombed in rock and could not be identified, so the fossil was placed in storage. Now, several decades later, Garwood and his colleagues used CT scans to complete a detailed reconstruction of what the creature looked like.
The 3D scans revealed that arachnids shed their flagellum at some point during the evolutionary process, and that this took place before at least some members of the group developed spinnerets, the Manchester paleobiologist told the Guardian. As such, his team reported that the new species likely diverged from the spider like after Attercopus and before modern spiders evolved.
“The earliest known spider is actually from the same fossil deposit,” Garwood told BBC News, “and it definitely has spinnerets. So what we’re actually looking at is an extinct lineage that split off the spider line some time before 305 million years ago” and evolved alongside spiders.
Based on their analysis of the Idmonarachne brasieri, and comparisons with other arachnids, the study authors have come to the conclusion that spinnerets are, as Garwood told the Guardian, the “key innovation of spiders” and are “probably responsible for their massive success.” After all, as the newspaper noted, there are at least 45,000 known species of spiders, and the eight-legged creatures can be found on every continent except Antarctica.
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Image credit: Garwood et al 2016/
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