Abstract: New fossil spiders (Arachnida: Araneae) from Middle Jurassic (ca. 165 Ma) strata of Daohugou, Inner Mongolia, China are described as Eoplectreurys gertschi gen. et sp. nov. and referred to the modern haplogyne family Plectreuridae. This small family is restricted to southwestern USA, Mexico, and the adjacent Caribbean area today and hitherto has only a sparse Cenozoic fossil record. The morphology of Eoplectreurys is remarkably similar to modern forms and thus demonstrates great evolutionary conservatism. This new discovery not only extends the fossil record of the family by at least 120 Ma to the Middle Jurassic but also supports the hypothesis of a different distribution of the family in the past than today and subsequent extinction over much of its former range.
Via Wired Science:
Scientists have unearthed an almost perfectly preserved spider fossil in China dating back to the middle Jurassic era, 165 million years ago. The fossilized spiders, Eoplectreurys gertschi, are older than the only two other specimens known by around 120 million years.
The level of detail preserved in the fossils is amazing, said paleontologist Paul Selden of the University of Kansas and lead author of the study appearing Feb. 6 in Naturwissenschaften. “You go in with a microscope, and bingo! It’s fantastic.”
The fossils were found at a site called Daohugou in Northern China that is filled with fossilized salamanders, small primitive mammals, insects and water crustaceans. During the Jurassic era, the fossil bed was part of a lake in a volcanic region, Selden said.
Spider fossils from this period are rare, because the arachnids’ soft bodies don’t preserve well. The pristine fossil pictured in these photos was probably created when the spider was trapped in volcanic ash. The ultrafine clay particles squashed the spider without breaking up the animals’ delicate cuticle as more coarse sediment would, Selden said.
E. gertschi shows all the features of the modern members of the family, found in North America, suggesting it has evolved very little since the Jurassic period, Selden said. “The scimitar-shaped structure you notice out of the male is so distinctive,” he said. “Looking at modern ones, you think, well, it’s just a dead ringer.”
The findings also suggest this family of spiders, the Plectreuridae, was once much more widespread than it is today. Currently, the family has only been found living in California, Arizona, Mexico and Cuba. Yet 165 million years ago, they lived on a small continent called the North China Block.
“At some point something caused their range to contract to this part of southern North America,” Selden said. He speculates that changes in vegetation during an ice age or other climactic event wiped them out in other areas, “but they were still happy in these arid areas of the Southwest.”
Images © Paul Selden
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