Preserved in the rock formation was a spider specimen with eerily glowing eyes, that a team of researchers now believe dates back as far as 113 million years ago.
Their findings are published in a paper in the Journal of Systematic Palaeontology and have been hailed as the first time the tapetum, an anatomical feature that enables spiders to have reflective eyes, has been found in a fossil.
It’s also said to be the first time researchers have discovered this family of spiders, called the lagonomegopids, outside of amber.
Paul Selden, director of the Paleontological Institute at the University of Kansas, Tae-Yoon Park of the Korea Polar Research Institute and amateur fossil hunter and Korean high school student Kye-Soo Nam discovered the spiders in exposed shale uncovered during a construction project.
Spiders and other insects are often found in amber, not fossilized in rock, because their soft bodies don’t preserve well over time.
They were astonished to find the lagonomegopids preserved in 112-million-year-old Cretaceous-period rock, located near the city of Jinju in South Korea.
‘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,’ Selden explained.
The fossils allowed scientists to understand in remarkable detail how this family of spiders were able to survive between 110 million and 113 million years ago.
Scientists believe the reflective tapetum in the spiders’ eyes helped them hunt at night.
‘It’s opening up a whole new world about how these things lived and how they would have caught their prey,’ Selden told Gizmodo.
The tapetum is a reflective structure located behind the eye where light comes in and is reverted back onto the retina, Selden noted.
Lagonomegopids aren’t the only family of spiders with reflective eyes – wolf spiders have them too, in addition to other types.
Other animals, such as cats, have tapetums, which is why their eyes appear similar to lasers in certain light or when captured by a camera flash.
The lagonomegopids had tapetums that were ‘canoe-shaped,’ helping the researchers distinguish them from the other 10 spider specimens found in the shale.
‘This is an extinct family of spiders that were clearly very common in the Cretaceous and were occupying niches now occupied by jumping spiders that didn’t evolve until later,’ Selden explained.
‘But these spiders were doing things differently. Their eye structure is different from jumping spiders.
‘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,’ he added.