Fossil Of 305-Million-Year-Old 'Almost Spider' Indicate That It Is Missing Link In Arachnid Evolution

An interesting, new specimen of a 305-million-year-old "almost spider" has given an insight into the evolutionary gap between modern spiders and ancient arachnids.

Named Idmonarachne brasieri after the Greek mythological figure Idmon, who was also the father of the skilled weaver Arachne, the specimen was found preserved in iron carbonate from central France.

It was interesting that this one-centimeter-long arachnid showed legs, mouthparts and body that were all like spiders. However, this ancient arthropod did not have spinnerets that can turn silk into webs.

"When I first saw it, I was unsure what kind of arachnid it was," said  Russell Garwood, a paleontologist from the University of Manchester.

While only its abdomen was first visible in the fossil sample, later high-resolution CT scans showed some more attributes in the Carboniferous-age stone.

"The legs and entire front half of the body was buried in the rock," Garwood added.

Arachnid ancestors that lived in the late Carboniferous period also suggested that it was a unique species. But Idmonarachne did not possess  a tail-like appendage like the arachnids.

It had a single bulbous structure on the entire back half of its body, so Idomarachne had segments along its abdomen, just like other archaic forms of arachnids.

Idmonarachne is thus believed to be one of the spider relatives that became extinct, even while its other close cousins went on to develop into modern spiders.

"It's not quite a spider, but it's very close to being one," Garwood said. "Arachnids as a whole are an incredibly successful group. They're the most diverse group of living organisms after insects. They're really, really successful - but we have a very limited understanding of how they are related to each other."

Their findings were recently published in the journal Proceedings of the Royal Society B: Biological Sciences.