Researchers have found a link between today's eight-legged spiders and an ancient group of arachnids that also possessed tails, according to two studies published in the latest issue of Nature Ecology & Evolution.
Four fossils of the tiny crawlers were found largely intact, encased in Burmese amber that were recovered from Myanmar by researchers. The BBC reports the "cousin" of the spider — called a Chimerarachne yingi — lived about 100 million years ago during the Cretaceous Period.
"We have known for a decade or so that spiders evolved from arachnids that had tails, more than 315 million years ago," Russell Garwood of The University of Manchester, a co-researcher on the study, told the BBC.
But, he continued, "We've not found fossils before that showed this, and so finding this now was a huge (but really fantastic) surprise."
An abstract of the study says the "new fossil most likely represents the earliest branch of the Araneae, and implies that there was a lineage of tailed spiders that presumably originated in the Palaeozoic and survived at least into the Cretaceous of Southeast Asia."
That would mean that the tailed spider lived for about 200 million years side-by-side with spiders, Garwood said.
Experts have not ruled out the possibility that some modern day version may still exist in the rain forests of Southeast Asia but they are so small and their habitat is so remote, there is no evidence that they continue to live there, in or near tree trunks, as their ancestors did.
What makes the fossils so unusual, according to the two teams the leading studies, is that they possess both a tail-like appendage similar to those of other ancient arachnids and multi-segment silk-spinning organs only seen in more modern spiders. And, though it was capable of using its spinnerets to produce silk, it was unlikely to have woven webs.
But that's as much as the two teams can agree on. Nature Ecology & Evolution writes:
"Gonzalo Giribet at Harvard University in Cambridge, Massachusetts, Diying Huang at the Chinese Academy of Sciences in Nanjing and their colleagues analysed two fossils of the animal dating to about 100 million years ago. On the basis of the creature's tail, they conclude that it belongs to the Uraraneida, a group of spider relatives that was thought to have gone extinct around 275 million years ago. But Bo Wang, also at the Chinese Academy of Sciences in Nanjing, and his colleagues examined two other fossils of the species and argue that its advanced silk-spinning apparatus shows it was part of a lineage of tailed spiders that survived until at least 100 million years ago.
"Silk-spinning spiders with and without tails co-existed for millennia, the authors agree."
Brian Brown, curator of entomology at the Natural History Museum of Los Angeles County, told NPR that discoveries like these are becoming more common because Burmese amber is more accessible now than ever before.
"In the last few years, this kind of amber has become much more available and because of its age — it's a hundred million years old or older — it lets us see really far back into the past," he said.
Brown says the opening up of the amber market has created a burgeoning new area of potential research. Which is why, he says, "Now, we are seeing evidence of lots of primitive forms of animals that are just starting to become the modern versions that we know today."
Brown said that's what researchers found with the Chimerarachne and it applies to many other species of animals.
But the commercialization of the amber trade also has a downside, Brown suspects. He fears potentially significant scientific artifacts could be falling into the hands of collectors, where they will likely remain outside of the scope of research.