100-Million-Year-Old "Chimera" Arachnids In Amber Shine A Light On The Construction Of Spiders

Spiders are an evolutionary extravagance, no matter whether you consider them to be misunderstood mischief-makers or malevolent monsters. Their history extends back tens of millions of years, and today, they can be found all over the world, occupying the shadows and nooks in the corners of our eyes.

Palaentologists are often fascinated by these eight-legged marvels, and two new studies published in Nature Ecology & Evolution highlight why. These utterly captivating specimens, members of a new species found trapped in Burmese amber, are 100 million years old – and the creature's mix of ancient and somewhat contemporary features are causing something of a schism.

In some ways, it resembles a modern specimen: it contains, for example, multi-segmented spinnerets, which are used to spin silk and create spectacular web patterns. At the same time, it’s a little alien: it’s adorned with tail-like ornaments named telsons that are far more common today in scorpions.

It’s fitting, then, that the species has been named Chimerarachne yingi, whose genus name roughly translates to “chimera spider.”

Both papers feature researchers from across the world, but both are led by the Chinese Academy of Sciences. The first paper concludes that this species represents one of the first true spiders, part of the extant order Araneae. The second study considers the species of encapsulated beastie to be part of an order of extinct spider relatives, the Uraraneida.

Regardless of which conclusion is ultimately proven to be correct by further research, both have powerful implications for how we understand spider evolution.

Ventral view. Bo Wang

If it’s the former interpretation that’s borne out by additional analysis, then we know that it represents one of, if not the earliest branches of the true order of spiders. If it’s the latter, then, as the authors of the paper explain “the new fossil extends the record of Uraraneida 170 million years towards the present, thus showing that Uraraneids and spiders co-existed for a large fraction of their evolutionary history.”

Defining a new species using fossilized or preserved remnants of a long-dead critter is far from easy. Apart from the fact that the concept of a species itself is somewhat nebulous, palaentologists have to generally rely on common and unique physical features to compare and contrast with other animals.

In this case, this chimeric spider’s features have caused a little trouble. There’s no doubt that it’s a new species, one that roamed what is now Myanmar at the same time as tank-sized dinosaurs wandered across what is now Maryland, but the teams can’t quite agree as to where it should fit on the evolutionary tree.

Talking to IFLScience about the “stunning” fossils, Dr Russell Garwood, a lecturer at the School of Earth and Environmental Sciences at the University of Manchester – and co-author of the Araneae-leaning paper – explains that the findings in the two papers are nevertheless pretty similar.

“Any apparent differences largely boil down to the semantics about how you define a spider. Should it be a thing that has spinnerets, or a thing that has lost a tail, say?”

“I don't think this is as interesting a question as the other implications of both studies – that building a spider, as it were, is a series of step-wise changes, and we're gradually working out which order these came in!”

The Araneae order goes back at least 305 million years, long before dinosaurs walked the Earth. The Uraraneids emerge a little later during the Permian Period, shortly before the greatest mass extinction in Earth’s history took place – something both lineages clearly withstood.

This discovery “means that there was a lineage of tailed spider-like things that survived for at least another 200 million years for us to find this specimen,” something that Garwood considers to be “really kinda cool, and totally unexpected.”

Whatever the order, that fact alone makes this chimera a stunning piece of biological machinery with a storied legacy.

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