April 20, 2011

Scientists Name Fossil Spider from the Middle Jurassic of China

With a leg span of more than five inches, a recently named Jurassic period spider from China is the largest fossil specimen discovered, and one that has modern relatives in tropical climates today.

A research team of KU and Capital Normal University (Beijing) researchers said the spider belongs to the living genus Nephila, or golden orb-weavers. An extremely long range for any animal genus, the nephilids are example of living fossils. Nephilids are the largest web-weaving spiders alive today (body length up to 5 cm, leg span 15 cm) and are common to the tropical and subtropical regions today. This suggests that the paleoclimate of Daohugou, China, where the specimen was found, was probably similarly warm and humid during the Jurassic.

Nephila females weave some of the largest orb webs known (up to 1.5 m in diameter) with distinctive gold-colored silk to catch a wide variety of medium-sized to large insects, but occasionally bats and birds as by-catch. Typically, an orb-weaver spider first weaves a non-sticky spiral with space for sticky spirals in between. Unlike most other orb-weaving spiders, Nephila do not remove the non-sticky spirals after weaving the sticky spirals. This results in a ‘manuscript paper’ effect when the orb is seen in the sunlight, because the sticky spirals reflect the light while the non-sticky spirals do not, thus resembling musical staves.

This fossil finding provides evidence that golden orb-webs were being woven and capturing medium to large insects in Jurassic times, and predation by these spiders would have played an important role in the natural selection of contemporaneous insects. 

The research was published in the online edition of Biology Letters as “A golden orb-weaver spider (Araneae: Nephilidae: Nephila) from the Middle Jurassic of China.” Paul A. Selden, Gulf-Hedberg Distinguished Professor at KU and director of the Paleontological Institute, as well as ChungKun Shih and Dong Ren, professors from Capital Normal University, Beijing, China, authored the research.

In the image above, the figure on the left is of a fossil female golden orb-weaver spider (Nephila jurassica) from the Middle Jurassic of China. The body length about 1 inch, front legs about 2.5 inches (= leg span more than 5 inches). Next to it is an image of a living female golden orb-weaver spider (Nephila pilipes), in Queensland, Australia, on her golden orb web. It is about the same size as the fossil specimen.