Ancient Spider Fossils Preserved in Rock Reveal Reflective Eyes

Two of the fossil specimens discovered in Korea had reflective eyes, a feature still apparent under light. (Image: Paul Selden)
Two of the fossil specimens discovered in Korea had reflective eyes, a feature still apparent under light. (Image: Paul Selden)

Usually, soft-bodied species like spiders aren’t fossilized in rock like animals with bones and teeth. More often, ancient spiders and insects are more likely to be discovered preserved in amber. Yet a new paper in the Journal of Systematic Palaeontology, co-written by a University of Kansas researcher, describes fossil spiders found in an area of Korean shale called the Lower Cretaceous Jinju Formation.

What’s most remarkable is that two of the fossils from the extinct spider family Lagonomegopidae feature reflective eyes that enabled their nighttime hunting. Paul Selden, Gulf-Hedberg Distinguished Professor of Geology and director of the Paleontological Institute at KU’s Biodiversity Institute and Natural History Museum, said:

Selden said that some contemporary spiders feature eyes with a tapetum, but the new paper is the first to describe the anatomical feature in a fossilized spider. The research team said the discovery provides evidence for lagonomegopid enlarged eyes being posterior medians. Selden added:

Selden’s collaborators were Tae-Yoon Park of the Korea Polar Research Institute and amateur fossil hunter Kye-Soo Nam of the Daejeon Science High School for the Gifted, who found the fossils preserved in the shale.

Flint rock preserved characteristics of the spider fossils differently than the more common amber-preserved spiders. (Credit: Paul Selden)

Flint rock preserved characteristics of the spider fossils differently than the more common amber-preserved spiders. (Credit: Paul Selden)

The description of the fossils boosts the number of known spiders from the Jinju Formation from 1 to 11. The KU researcher said the spiders, which lived between 110 and 113 million years ago, must somehow have been protected from deterioration to have become so well-preserved in the shale formation. Selden said:

Locality map of the study area. A, distribution of Cretaceous sedimentary basins around the Korean Peninsula; rectangular area is magnified in B. B, simplified geological map of the Gyeongsang Arc System; the sedimentary rocks represent the Gyeongsang Backarc Basin, while the volcanic rocks represent the Gyeongsang Volcanic Arc; rectangular area is magnified in C (modified from Chough & Sohn 2010; the displacement by the Yangsan Fault has been recovered). C, road map of the study area showing the two fossil localities (stars). (Credit: Paul Selden)

Locality map of the study area. A, distribution of Cretaceous sedimentary basins around the Korean Peninsula; rectangular area is magnified in B. B, simplified geological map of the Gyeongsang Arc System; the sedimentary rocks represent the Gyeongsang Backarc Basin, while the volcanic rocks represent the Gyeongsang Volcanic Arc; rectangular area is magnified in C (modified from Chough & Sohn 2010; the displacement by the Yangsan Fault has been recovered). C, road map of the study area showing the two fossil localities (stars). (Image: Paul Selden)

The discovery was made possible because of the unique geography of South Korea, where the shale containing the fossils was exposed during a construction project. Selden added:

According to Selden, the shale preserved the spider fossils in a manner that highlighted the reflectivity of the tapetum, a feature that may have been missed had the spiders been preserved in amber instead, as is more typical, saying:

Beyond the novelty of discovering the first fossilized-spider tapetum, Selden said the spiders informed the scientific understanding of Cretaceous biodiversity:

Provided by: University of Kansas [Note: Materials may be edited for content and length.]

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