Researchers have found prehistoric spider fossils trapped in a shale at a fossil site in South Korea. Two of the specimens are particularly interesting because their eyes still glow in the dark 110 million years after the now extinct spiders died.

Preserved In Rock

The spiders were unearthed in the Lower Cretaceous Jinju Formation, a geological area dating back from the Mesozoic era, between 252 and 66 million years ago. The spiders, which belonged to the family of spiders known as Lagonomegopidae, were found during a construction project.

Spiders are soft-bodied creatures so they are rarely found preserved in rocks. Scientists normally study specimens trapped in amber, so some of the features are overlooked.

The newly found fossils, however, were preserved in a dark rock allowing the scientists to easily see the creatures' reflective eyes that likely allowed them to hunt prey at night. The glow in the dark eyes could be seen when the arachnids were placed under light.


The researchers said the spiders appear to have what is known as a tapetum, a reflective layer behind the retina that bounces light around within the eye. This allows the eye to absorb what little light is available during night time producing the eerie glowing eyes similar to those of cats, owls, and other nocturnal animals that hunt for prey in the dark.

"The first non-amber Lagonomegopidae are described, with the first preservation of a spider eye tapetum in the fossil record," study researcher Paul Selden, from the University of Kansas, and colleagues wrote in a study published in the peer-reviewed Journal of Systematic Palaeontology on Jan. 28.

The researchers said the discovery sheds light on the evolution of spiders. The glowing eyes suggest the ancient spiders loosely resembled modern jumping spiders, which feature big eyes, albeit the two spiders do things differently.

"It's nice to have exceptionally well-preserved features of internal anatomy like eye structure. It's really not often you get something like that preserved in a fossil." Selden said in a statement.

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