A team of paleontologists have announced the discovery of spider fossils dating from the Cretaceous period. These ancient arachnids, which have glow in the dark eyes, probably lived at night. The details of the study were published in the Journal of Systematic Palaeontology.
An exceptional discovery
Finding spider fossils is very rare. Even rarer still as their body is soft. In fact they have no bones, no cartilage and no hard surface which is favourable for fossilization. This is why the majority of spiders are generally found trapped in amber. Although it is rare to find spider fossils it is not impossible. The recent discovery of fossilised spides in the Jinju Formation, in South Korea is proof. A dozen spider fossils were found. Each measured less than two centimetres and were alive at the time of the dinosaurs.
If you wandered around this region around 110 million years ago at night, you would have been able to see two pairs of shining eyes spying on you in the dark. This is the main characteristic of this ancient spider. “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,” explained Paul Selden, Gulf-Hedberg Distinguished Professor of Geology and director of the Paleontological Institute at KU’s Biodiversity Institute and Natural History Museum. “I realized this must have been the tapetum—that’s a reflective structure in an inverted eye where light comes in and is reverted back into retina cells.”
Trapped in sediment
Some spiders in modern day have eyes with a tapedum especially those that hunt at night. However such a characteristic has never been discovered in fossilised spiders. Researchers have proposed a possible scenario which has resulted in this exceptional preservation. As the researchers described “Normally, they’d float. But here, they sunk, and that kept them away from decaying bacteria—it may have been a low-oxygen condition.” They continued by highlighting the fact that the rocks are covered in crustaceans and fish. As a result they estimate that “there maybe was some catastrophic event like an algal bloom that trapped them in a mucus mat and sunk them—but that’s conjecture.”
During this period the landscape of South Korea would have been very different to what it is like today. The area was once lined with shallow pools where fish and bivalves flourished with some dinosaurs and pterosaurs around. The spider bodies were buried in the sediment of one of these lakes. The minerals then transformed their bodies, preserving them for tens of millions of years. Even the hairs that once covered their legs are still visible.
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