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Old spider fossils are silvery, shimmering eyes

This fossilized spider has teensy mirrors in her eyes.
(Paul Seldon)

Paleontologists working in South Korea found in the old spider fossils with still glistening eyes.

Spider fossils are rare, the researchers wrote in an article online Jan. 28 in the Journal of Systematic Paleontology. Their bodies are so soft that they typically decay completely soon after death, leaving no trace unless they happen to be eventually trapped in amber. But 11 spiders from the Cretaceous period are preserved in shale on the Korean Peninsula. And two of the fossils included the still shiny traces of sparkling eyes.

That glittering pieces of mirror structures in the eye called tapetums that bounce the light from the back of the eye back through the retina. Animals use their night vision, usually to the detriment of a total vagueness. [See 15 Beautiful Animal Eyes — Rectangular Pupils to Wild Colors]

“ln spiders, you see, are really with big eyes jumping spiders, but their eyes are not ordinary eyes — where the wolf spiders at night, then you can see their eyes reflected in the light, like cats,” study co-author Paul Selden, director of the Paleontological Institute of The University of Kansas Biodiversity Institute and Natural History Museum, said in a statement. “So, night-hunting predators tend to use a different form of the eye. This was the first time that a tapetum had found in a fossil.”

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Selden said the canoe-like shape of the 110 – to 113-million-year-old tapetums will help researchers the place of the rare spider fossils on the evolutionary tree.

This particular piece of South Korean rock turned out to be a gift from heaven for paleontologists.

“This is so rare because [spiders] are very soft, they do not have hard shells so they are very easy to decay,” Selden said. “It has a very special situation in which they were washed in a body of water. Normally she would float. But here, they sunk, and that kept them away from decaying bacteria — however, it may be a hypoxic condition [where bacteria that cause decay cannot survive].”

He added that the rocks where the spider fossils were found were also covered with the remains of small crustaceans and fish, which suggests that there may be a bloom trapped in a slime mat, causing them to sink. “But that is a presumption,” Selden said. “We don’t really know what the cause of this, but something killed off a lot of animals around the lake at one time or on an annual basis.”

What killed them, it did paleontologists of the future a great favor. And left a small, glittering structures intact to survive through the centuries.

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Originally published on Live Science.

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