Monday, 26 May 2014

A giant Spider from the Middle Jurassic Daohugou Biota.

In 2011 Paul Seldon of the College of Life Sciences at Capital Normal University in Beijing, the Paleontological Institute and Department of Geology at the University of Kansas and the Natural History Museum in London, along with ChungKun Shih and Dong Ren, also of the College of Life Sciences at Capital Normal University, described a large female Spider, from the Middle Jurassic Daohugou Biota of Inner Mongolia, as a member of the modern Golden Orb-weaver Spider genus Nephila, in a paper in the journal Biology Letters, naming it Nephila jurassica (the Jurassic Golden Orb-weaver Spider).

Finding a modern example of a terrestrial Arthropod species from the Middle Jurassic is, to say the least, somewhat surprising, and in 2013 a team of Scientists led by Matjaž Kuntner of the Institute of Biology of the Scientific Research Centre of the Slovenian Academy of Sciences and Arts, the Department of Entomology at the National Museum of Natural History and the College of Life Sciences at Hubei University published a molecular phylogeny of Orb-weaving Spiders as a whole, in a paper in the journal Molecular Phylogenetics and Evolution which concluded that all living members of the group had a most recent common ancestor more recent than the Middle Jurassic, making the placement of the Daohugou Biota specimen in any modern genus inappropriate.

In a paper published in the journal Naturwissenschaften on 7 December 2013, Seldon, Shih and Ren describe a second giant Spider from the Daohugou Biota, this time a male, which they assign to the same species as the first. They accept Kuntner et al.’s conclusions about the origin of Orb Weaving Spiders, and assign the two specimens to a new genus, Mongolorachne, meaning ‘Mongolian Arachnid’ as Mongolorachne jurassica

Mongolorachne jurassica: (a) male  (♂) and female (♀) specimens compared; (b) male part; for explanation see (c). (c) male part, explanatory drawing of (b). Abbreviations: 1, 2, 3, 4, leg numbers; ca, calamistrum; ch, chelicera; cr, cribellar area; cx, coxa; f, fovea; fe, femur; lb, labium; mt, metatarsus; mx, maxilla; op, opisthosoma; pa, patella; Pd, pedipalp; st, sternum; ta, tarsus; ti, tibia; tr, trochanter. Photographs (a) dry, (b) under polarized light with specimen under 70% ethanol; scale bars are 5 mm. Seldon et al. (2013).

Mongolorachne jurassica is placed in a new family, Mongolarachnidae, which are thought to be a stem-group Orb-weaver Spiders, i.e. a members of the lineage which lived before the most recent common ancestor of all modern Orb-weavers, and which may or may not be ancestral to it.

See also…

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