Ancient spiders, preserved in amber

Two arachnids 100 million years old have been found exquisitely preserved in amber in Myanmar, shedding light on the evolution of spiders.

The creatures, formally named Chimerarachne yingi, bear some characteristics of modern spiders, but also some typical of a closely related but long extinct arachnid order, known as the Uraraneida.

The first Uraraneida fossil was discovered in New York state in the US in 1987 and was initially misidentified as a spider. Comparison with fossils subsequently unearthed showed that this newly classified branch of arachnids differed from spiders – the Araneae – in several structural ways, notably in the positioning of silk-producing spigots, and a tail-like appendage, known as a telson, at the end of the abdomen.

In two papers published in the journal Nature Ecology and Evolution, teams led by researchers from the Nanjing Institute of Geology and Palaeontology at the Chinese Academy of Sciences, report that C. yingi represents “a key transition stage in spider evolution”.

The species has a typical Uraraneidan telson, but also boasts trademark Araneaen structures, including well defined spinnerets for silk production.

C. yingi, write the researchers, “most likely represents the earliest branch of the Araneae”.

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