Arachnids in amber

Two papers published online this week in Nature Ecology & Evolution report a new arachnid fossil with a curious mixture of ancient and modern features, including multi-segmented spinnerets - the silk-spinning organs characteristic of the modern spider.

Spiders have been an extremely successful lineage, but some aspects of the species’ development remain unclear. Two papers authored by different groups illuminate these origins with four specimens of a 100-million-year-old proto-spider, all preserved in Burmese amber. Bo Wang and colleagues present two fossils, including the type specimen, Chimerachne yingi (C. yingi). The genus name translates to 'chimaera spider', reflecting the mix of primitive and modern features in this spider relative. A second paper, from Gonzalo Giribet and colleagues, presents two more C. yingi fossils.

C. yingi is 200 million years younger than the first spider ancestor, and has some features that look quite different from modern-day spiders including a long tail-like appendage called a telson, which we see today in scorpions. In contrast, however, C. yingi preserves multi-segmented spinnerets for silk-spinning just like modern spiders.

Due to its combination of ancient and modern features, the two papers disagree on where C. yingi should sit in the evolutionary tree: Giribet and colleagues place it within an order of extinct spider relatives (Uraraneida), while Wang and colleagues conclude it could be one of the first true spiders (Araneae).

doi: 10.1038/s41559-017-0449-3

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