World's largest spider fossil was of a different species after all

The world’s largest spider fossil just got a name change, and it’s all because of a boy.

A new, sensational discovery at the Daohugou fossil beds in Inner Mongolia has prompted scientists to change the taxonomic nomenclature of Nephila jurassica, an arachnid predator that crawled across the Jurassic landscape 165 million years ago.

Amazing similarities

First discovered two years ago in Inner Mongolia’s volcanic ash deposits, the fossilized female spider was initially believed to be related to golden orb-weavers (Nephila), the oldest known species of the largest web-weaving spiders on the planet still alive today.

Researcher Paul Selden recalled there was no reason to believe otherwise at the time. “It was so much like the modern golden orb weaver," said Selden, a paleontologist from the University of Kansas. "We couldn't find any reason not to put it in the same genus of the modern ones."

Spectacular revelations

However, an adult male spider to match the previously-found female was recently unearthed from Daohugou’s volcanic rock layer. According to the researchers’ findings, which were published on December 7 in the online journal Naturwissenschaften, the newly-discovered fossil suggests that these prehistoric arachnids may have actually spun out of a different spider family’s web.

Size was one factor. The male spider fossil’s body checks in at about 0.65 inches (1.65 centimeters) in length, with a 2.29-inch (5.82 cm) first leg. This made the male spider almost as large as the female, which had a body one inch (2.54 centimeters) in length and legs that stretch up to 2.5 inches (6.3 cm) long. Selden noted that this was an odd occurrence, as male orb-weavers are typically smaller than the females.

Additionally, the fossilized male had more feathery strands of hair running across its body than Nephila males, as evidenced by the microscopic imprints of the spider’s hair seen under an electron microscope. Selden observed that, instead of one or two scales along each bristle, the fossilized spider had “spirals of hairlets” on its body.

The male fossil also had more primitive-looking pedipalps than Nephila males. Pedipalps are the secondary appendages found near a spider’s jaws, used for transferring sperm to a female spider during reproduction.

A web of reclassification

In line with these findings, the researchers created a new genus and species name for the fossilized spiders. Now renamed Mongolarachne jurassica, the spiders are believed to be more closely related to the so-called ogre-faced spiders (Deinopoidea). These spiders possess more “woolly” webbing, but create orb-shaped webs just like the Nephila spiders.

Because of their soft bodies, spiders aren’t exactly superior candidates for fossilization. However, since volcanic ash has been known to preserve delicate specimens in the fossil record (such as 2.7 billion-year old raindrops in South Africa), the Daohugou fossil beds have proven to be a quite a friendly neighborhood for ancient arachnids, with paleontologists finding hundreds of them preserved in the Mongolian region’s volcanic deposits.

— TJD, GMA News

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