Thursday , June 24 2021

Rare spiders retain 100-million-year-old luminous eyes

This is a carbon map showing where the molecules of carbon are located on the sample, explained to Selden of Gizmodo.
Photograph: Tae-Yoon S Park

A new discovery of fossil spiders involves a surprising discovery: remnants of reflective eye tissue.

Although common today, spiders do not appear much in fossil data because their soft bodies do not keep well, according to the publication published in the Journal of Systematic Palaeontology. This is the first time a family of spiders are spotted outside amber, and the first time that the reflecting tissue of the spider's eye is found in a fossil.

"This opens up a new world about how these things lived and how they would catch their loot," said Paul Selden, one of the newspaper's authors and director of the Paleontology Institute at Kansas University.

A Korean high school student and amateur fossil hunter Kye-Soo Nam first discovered fossils in a 112-year chalk called Chinju in South Korea. The formation gives tons of other fossils, including plants, molluscs, fish and dinosaurs, as well as unidentified species of fossil spiders.

The new study analyzes 10 specimens of spider in dark gray shale by viewing and measuring them under microscopes. Scientists have found that they represent seven different species. It's just surprising and shows that there are probably a lot more extinct species of spiders that have not yet been discovered.

The spider's copy
Photo: Paul Selden

Some of the fossils come from a family of Lagonomegopidae spiders, for the first time such fossils are found outside amber. But finding the spider, preserved in stone instead of amber, allowed the researchers to see structures they had not seen before, like the reflective eye tissue. This discovery allowed the researchers to infer the behavior of these spiders.

The specimens showed "remarkable preservation" of canoe-shaped pieces of reflective tissue in the eyes of the spiders, both apparently seen in the fossil itself, and emphasized when scientists analyze the chemical composition of the fossil. They interpret this reflective tissue as a tapetum that the eyes of some animals (but not humans) use to see in bright light. That's why pets and other mammals often have bright, laser eyes on photos taken with a flash.

You may wonder how the researchers found they were looking at the tapetum and not on anything else. According to the report, since the spider's tapetum is formed by crystals of the guanine molecule, it is more likely to be retained by other soft tissues. "Moreover, the shape of the structure – apparently in the shape of a canoe," confirms their suspicions, they write.

Every new fossil discovery adds more detail to the history of life on Earth – a story that may never be complete. But besides learning more about ancient spiders, it's pretty cool to see the glow of 112 million-year-old spider webs.

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