The new animal resembles a spider in having fangs, male pedipalps and silk-producing spinnerets at its rear. However, it also bears a long flagellum or tail. No living spider has a tail. Photo: Dinghua Yang, KU

There are more than 47,000 known species of living spiders around the world – but none resemble the 100-million-year-old arachnid creature recently found encased in amber in Myanmar.

What makes this fossil discovery so unique? The spider-like animal had a tail longer than its body length, according to an international team of researchers from China, Germany, the UK and U.S.

The “spider cousin” – which has been named Chimerarachne yingi after the Greek mythological creature Chimera, who was composed of parts from several animals – had features from both modern spiders, as well as ancient arachnids.

It had eight legs and fangs, typical of most modern spiders, and measured about 2.5 millimeters long, with a tail extending to 3 millimeters long – something that no modern spider is equipped with. It also had silk spinnerets, although the researchers are doubtful that C. yingi wove webs.

The researchers cannot confirm what the unique tail would have been used for, but they speculate it may have helped them navigate their surroundings. They are also unsure whether the arachnid was venomous or not.

“Any sort of flagelliform appendage tends to be like an antenna,” said Paul Selden, study author, of the Paleontological Institute and Department of Geology at the University of Kansas. “It’s for sensing the environment. Animals that have a long whippy tail tend to have it for sensory purposes.”

A total of four of the tiny specimens were recovered, and date back to the mid-Cretaceous period.

The new find supports a prediction made by Selden and colleagues nearly 10 years ago as a result of fossil evidence that portrayed a similar tailed arachnid as C. yingi, but didn’t have the spinnerets. These animals were from the much older Devonian (380 million years ago) and Permian periods (290 million years ago) according to Selden. The evidence formed the basis of a new arachnid order – the Uraraneida – which lies along the line to modern spiders.

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

Because the C. yingi specimens were found trapped in amber, the researchers believe the arachnid lived near tree trunks, possibly under bark or in the moss near the foot of a tree. The creature likely lived for about 200 million years side-by-side with “true” spiders.

There’s a slight chance – although unlikely – that the animal still exists somewhere in the rainforests of southeast Asia, the researchers note.

“It makes us wonder if these may still be alive today. We haven’t found them, but some of these forests aren’t that well-studied, and it’s only a tiny creature,” said Selden.

The discovery was published in Nature Ecology & Evolution.