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It is possible to make spiders creepier, ancient fossils in amber show

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These 100-million-year-old fossils look like spiders — but have tails.

An artist’s reconstruction of C. Yingi, which probably used its long, whip-like tail as a kind of antenna to sense its environment.
An artist’s reconstruction of C. Yingi, which probably used its long, whip-like tail as a kind of antenna to sense its environment.
Image by the University of Kansas | KU News Service

About 100 million years ago, when dinosaurs roamed the Earth, four, tiny spider-like creatures became trapped in amber. Today, scientists announced they belong to an entirely new species. But experts disagree about how these fossils relate to modern-day spiders, because there’s something strange about their crumpled corpses: all four of them have tails.

The fossils, described today in two different studies in the journal Nature Ecology & Evolution, look like spiders. But no living spiders have tails. That’s why one of today’s studies argues that this new species is a member of an extinct group of primitive spider relatives called uraraneids — which did have tails. The other claims that this new species may instead represent a very early branch of modern-day spiders.

The four fossils came from the amber mines of northern Myanmar — a treasure trove of fossils like a dinosaur tail trapped in amber, and ancient ticks that feasted on dino blood. This latest collection of finds ended up with two different research groups at the Nanjing Institute of Geology and Palaeontology. The two groups didn’t know they were working on such similar fossils until it came time to publish their findings, says Paul Selden, director of The Paleontological Institute at the University of Kansas and a co-author of one of today’s studies.

Other insects were found trapped in the amber as well, including adult and nymph millipedes, and a beetle.
Other insects were found trapped in the amber along with C. Yingi, including adult and nymph millipedes, and a beetle.
Photo by Bo Wang

The creatures are less than a quarter-inch long (5.5 millimeters) including their tails, which account for half that length. They’re also all male, which Selden says makes sense based on the behavior of modern spiders: adult male spiders are more likely to be wandering around somewhere they could become trapped in the flowing tree sap that hardened into amber.

The fossils resemble modern-day spiders: they have eight legs, silk-spinning organs called spinnerets, and eye-dropper-like appendages that male spiders use to stick sperm into their mates — just like today’s eight-legged crawlers. But they also have long, thin tails that these ancient arachnids probably used to sense their environments, a much more primitive feature seen only in fossilized proto-spiders known as uraraneids. The strange combination of features gave the new species its name: Chimerarachne yingi, for the hybrid creatures called chimeras in Greek mythology.

The specimens had spinnerets, or silk-spinning organs, jutting from the bottom of their abdomens — a feature they share with modern-day spiders.
The specimens had spinnerets, or silk-spinning organs, jutting from the bottom of their abdomens — a feature they share with modern-day spiders.
Photo by Bo Wang

Even though the two studies placed these new specimens in slightly different spots on the spider family tree, the differences are minor, Selden says. And discovering new fossils could settle the debate. For example, if they discover that these ancient creatures made venom, that could place them more firmly in the modern spider lineage. “They’re a classic missing link, really,” he says. “When you find a missing link, it opens two new gaps.”