Ancient arachnid: 100-million-year-old spider found trapped in amber

Terry Joseph
February 7, 2018

Besides having a flagellum or tail - believed to have been used by the invertebrate as a sensory organ - Chimerarachne stands out from much older arachnids of 300 million years ago in having silk-producing spinnerets.

Even though the two studies placed these new specimens in slightly different spots on the spider family tree, the differences are minor, Selden says.

But from the point of view of Gonzalo Giridet's team at Harvard University, who conducted the other study, Chimerarachne yingi would be a Uraraneida itself and would have gotten extinct without leaving descendants.

But waaay back in the age of the dinosaurs, spider-like creatures roamed the earth with "long, whippy" tails. Credit: University of Kansas.

These early arachnids, scientifically classified as Chimerarachne yingi, contain the spinneret organs that modern spiders use to create their spectacular, varied, and complex aerial webs.

The creatures would have likely lived in the bark of resin-producing trees during the mid-Cretaceous period. What's fantastic is that the amber process preserves parts that wouldn't be conserved through regular fossilization.

Fossil hunters found the extraordinary creatures suspended in lumps of amber that formed 100m years ago in what is now Myanmar.

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The odd creature shares certain characteristics with modern spiders - including fangs, four walking legs and silk-producing organs at its rear - however, it also has a long tail, or flagellum - a feature that living spiders lack.

Fun fact: the combination of primitive and advanced traits in C. yingi is so unusual that the two teams of researchers behind the dueling studies disagree on what the animal is, evolutionarily-speaking.

The fossils are now so well preserved that, one can easily observe the head, fangs, male pedipalps, their legs and spinner rest at their back. Chimerarachne shared a common ancestor with the true spiders and resembles a member of the most primitive group of modern living spiders, the mesotheles, which are found today only in China, Japan, and Southeast Asia.

Spider fossils with whip-like tails are challenging what scientists previously thought they knew about the origin of arachnids. Another distinctive feature is that uraraneids had plates on their bellies instead of the squishy abdomens seen in spiders. Their body length is around 2.5 millimeters (0.1 inches) and their tail size is 3 millimeters (0.2 inches) which is longer than the body. It is estimated that the queue functioned as an antenna for detecting the environment. Scientists may have just discovered your worst nightmare.

Professor Paul Selden, who was involved in the discovery of Attercopus three decades ago, said: The new fossils are like the missing link from older animals to modern spiders.

"We haven't found them", he says in the University of Kansas statement, "but some of these forests aren't that well-studied, and it's only a tiny creature".

The finding has been described in a paper appearing in Nature Ecology and Evolution by an worldwide team, including Paul Selden of the Paleontological Institute and Department of Geology at the University of Kansas.

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