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While a fossilised spider is a rare enough find in itself, a recent discovery uncovered creatures whose eyes still glow in the dark.
The vast majority of ancient fossilised remains found scattered across the world are from creatures whose tough, rugged bones were able to survive as shadows etched into soil. By contrast, soft-bodied, fragile creatures such as a spider very rarely have the ability to survive as fossils and are mostly discovered encased within amber.
However, a team of scientists from the University of Kansas (KU) and Korea excitedly announced that it has uncovered the fossilised remains of 10 spiders from the extinct family known as Lagonomegopidae in the largely unexplored area of Korean shale called the Lower Cretaceous Jinju Formation.
Describing the find in the Journal of Systematic Palaeontology, the team said it was shocked to discover that two of the fossils’ eyes were preserved well enough to maintain their reflective properties.
“Because these spiders were preserved in strange slivery flecks on dark rock, what was immediately obvious was their rather large eyes brightly marked with crescentic features,” said Paul Selden, director of the Paleontological Institute at KU’s Biodiversity Institute and Natural History Museum.
“I realised this must have been the tapetum – that’s a reflective structure in an inverted eye where light comes in and is reverted back into retina cells. This is unlike a straightforward eye where light goes through and doesn’t have a reflective characteristic.”
While modern-day spiders are known to feature eyes with a tapetum, this latest discovery is the first to show the feature in a fossilised spider and now helps palaeontologists more accurately place its path in the spider family tree.
Two of the fossil specimens discovered in Korea had reflective eyes, a feature still apparent under light. Image: Paul Selden
A series of fortunate events
“In spiders, the ones you see with really big eyes are jumping spiders, but their eyes are regular eyes – whereas wolf spiders at night time, you see their eyes reflected in light like cats,” Selden said. “So, night-hunting predators tend to use this different kind of eye.”
The fact that these spiders would have lived between 110 and 113m years ago makes the fossils discovery all the more amazing. Selden said it must have taken a “very special situation” for the remains to have been fossilised, such as being washed into a body of water.
“Normally, they’d float. But here, they sunk, and that kept them away from decaying bacteria – it may have been a low-oxygen condition,” Selden added.
“These rocks also are covered in little crustaceans and fish, so there maybe was some catastrophic event like an algal bloom that trapped them in a mucus mat and sunk them – but that’s conjecture. We don’t really know what caused this, but something killed off a lot of animals around the lake at one time or on an annual basis.”
