Fossil discoveries in Inner Mongolia have unveiled two rare specimens of an extinct genus of giant spiders, shedding light on the fascinating evolutionary pathways of arachnids during the Jurassic period. Named Mongolarachne jurassica, these spiders once lived some 165 million years ago, preserved in time by volcanic ashfalls that formed finely layered sedimentary rocks.
The newly identified genus rewrites earlier assumptions about ancient spiders and raises intriguing questions about the diversity of prehistoric ecosystems.
Fossils Preserved In Ash Tell A Different Story
According to Heritage Daily, the initial discovery came in 2005 when farmers in the Wuhua Township uncovered a remarkably well-preserved female fossil from the Jiulongshan Formation. This specimen, measuring approximately 24.6 millimeters in body length with front legs stretching to 56.5 millimeters, was first classified as Nephila jurassica, believed to belong to the same genus as modern-day golden orb weavers—famed for their ability to spin 1.5-meter-wide webs of strong, golden silk.
But in 2013, scientists reevaluated the fossil following the discovery of a second specimen, a male found near the same location. With a body length of 16.54 millimeters and a front leg measuring 58.2 millimeters, the male fossil showed distinct anatomical features that challenged its original classification. Researchers identified “stem-orbicularian traits” and observed characteristics typical of cribellate spiders, leading to a reclassification into a new genus: Mongolarachne.
“It was so much like the modern golden orb weaver. We couldn’t find any reason not to put it in the same genus of the modern ones,” explained Paul Selden, a paleontologist with the University of Kansas.
New Genus Hints At Evolutionary Secrets
This taxonomic shift marked the creation of a monogeneric family, Mongolarachnidae, distinct from the previously assumed lineage of orb weavers. Unlike modern Nephila males, which exhibit clear sexual dimorphism and unique sex appendages, the Mongolarachne specimens demonstrate little difference between sexes. Their preserved anatomy lacks the specialized features found in today’s orb-weaving spiders, suggesting a unique evolutionary branch.
Comparative analysis with both Juraraneidae and modern spider families revealed that Mongolarachnidae might share lineage with Deinopidea, also known as net-casting spiders. These arachnids are famed for their orb-shaped, Velcro-like silk webs rather than gluey traps. The study also identified links to possible relatives in the Nicodamidae and Austrochilidae families, broadening the potential phylogenetic web.
Largest Spider Fossils Ever Found
Among all known fossilized spiders, the Mongolarachne jurassica specimens are the largest ever discovered. Their size, web-building traits, and anatomical features provide a unique window into the behavioral ecology of ancient arachnids. While only two fossils have been unearthed so far, their exceptional preservation offers rare insight into spider evolution during the Mesozoic era.
According to paleontologists, the fossils were preserved as compression fossils in a pale laminated sedimentary tuff, a geological formation caused by ancient volcanic eruptions. This type of preservation allows for detailed observations of morphological structures, critical for reinterpreting lineage placement.
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These spiders would be dwarfed by many of today’s spiders. “Terrorized” by them in fact.
Did anyone else’s mind go to the “giant Spider” that terrorized the crew on Gilligan’s Island?
If you want it to look big put it in millimeters .if you want it to seem smaller put it in centimeters and if you want it to be real put it in inches