Spider with a tail discovered in 100m-year-old amber

6 Feb 2018

Dorsal view of entire Chimerarachne yingi specimen. Image: University of Kansas

Those with arachnophobia might want to look away now, as scientists have unearthed an incredible 100m-year-old spider that actually had a tail.

In an area of modern-day Myanmar, a remarkable fossilised discovery has led to the addition of an entirely new (yet now extinct) species of arachnid that didn’t have just eight legs, but an extra ‘ninth’ one in the form of a tail.

Believed to have existed during the Cretaceous age approximately 100m years ago, the new spider species appeared relatively normal at first by modern standards, with fangs, four walking legs and silk-producing spinnerets at its rear.

But the spider – encased in fossilised tree sap known as amber – also had a long tail. No other living spider has a tail, although some relatives of spiders, the vinegaroons, do have an anal flagellum.

In a paper published to Nature Ecology & Evolution, the international research team revealed that it found four new specimens of the species, each of which measures just 2.5mm in body length, while the tail adds an extra 3mm.

Northern Myanmar has become something of a hotbed for palaeontology as much of the amber coming from there into China is being sold by merchants to researchers, including this latest sample.

This spider confirms a prediction made a few years ago by the researchers when they described a similar tailed arachnid, which resembled a spider but lacked spinnerets.

These animals, from the much older Devonian (about 380m years ago) and Permian (about 290m years ago) periods, formed the basis of a new arachnid order, the Uraraneida, which lies along the line to modern spiders.

“The ones we recognised previously were different in that they had a tail but don’t have the spinnerets,” said Paul Selden of the research team.

“That’s why the new one is really interesting, apart from the fact that it’s much younger – it seems to be an intermediate form. In our analysis, it comes out sort of in between the older one that hadn’t developed the spinneret, and modern spider that has lost the tail.”

Spider picture

How the spider would have looked. Image: University of Kansas

Didn’t spin webs

The new creature has been called Chimerarachne after the Greek mythological Chimera, a hybrid creature composed of the parts of more than one animal.

As for what its day-to-day life would have been like, the researchers can only guess.

“We can only speculate that, because it was trapped in amber, we assume it was living on or around tree trunks,” Selden said, adding that unlike modern spiders – and despite its ability to produce silk – it likely didn’t produce webs.

“Spinnerets are used to produce silk but for a whole host of reasons – to wrap eggs, to make burrows, to make sleeping hammocks or just to leave behind trails.”

Given its size, the team believes there is still a chance its ancestors could be living in the south-east Asian rainforest today.

Colm Gorey was a senior journalist with Silicon Republic