Ancient fossil spider has glowing eyes after 110 million years

110 million year old spider fossil.

Paleontologists in South Korea have found fossils of ancient spiders with eyes that still glow after hundreds of millions of years, according toLive Science. Eleven spiders from the Cretaceous period were preserved in shale on the Korean Peninsula. The eyes of two of the spiders emitted a blue light.

Spider eyes glow because of a mirror structure in the eye called the tapetum, which reflects light from the back of the eye through the retina. Animals use this to improve their night vision, although they may see things a little blurry.

"In spiders, the ones that have really big eyes are jumping spiders, but their eyes are normal, whereas wolf spiders' eyes reflect light at night like a cat's eyes. So nocturnal predators often use this different type of eye. This is the first time the tapetum has been found in fossils," said study co-author Paul Selden, director of the Paleontology Institute at the University of Kansas Biodiversity Institute and Natural History Museum.

The canoe-like shape of the tapetum from 110 to 113 million years ago helps the team place the spider fossils on the evolutionary tree, Selden said. Spider fossils are rare, according to the study published on January 28 in the journal Systematic Paleontology. Their bodies are so soft that they usually decompose completely after death, leaving no trace unless they are trapped in amber.

"It must have been a very special situation. The spiders were swept into the water. Normally they float, but here they sank and were not exposed to the bacteria that cause decomposition. It was probably an anaerobic environment," Selden speculated. The rock layer where the spider fossils were found also contained the remains of small crustaceans and fish, suggesting that an algal bloom may have trapped them in the slimy mat, eventually sinking.