Thursday, January 23, 2014

[Paleontology • 2013] Mongolarachne jurassica • A Giant Spider from the Jurassic of China reveals Greater Diversity of the orbicularian Stem Group

Mongolarachne jurassica
(Selden, Shih & Ren, 2011)

A large female spider, Nephila jurassica, was described from Middle Jurassic strata of north-east China and placed in the modern genus Nephila (family Nephilidae) on the basis of many morphological similarities, but, as with many ancient fossils, the single specimen lacked synapomorphies of the family (Selden et al. 2011). In order to test the placement within the nephilid phylogenetic tree, Kuntner et al. (2013) calibrated the molecular phylogeny using N. jurassica in three different scenarios based on inferred mitochondrial substitution rates. They concluded that N. jurassica fitted better as a stem orbicularian than a nephilid. Now, a giant male spider has been discovered at the same locality that yielded N. jurassica. The two sexes are considered conspecific based on their similar morphological features, size, and provenance. The male cannot be accommodated in Nephilidae because of its pedipalp morphology, so the new genus Mongolarachne and family Mongolarachnidae are erected for the species. Comparison with possibly related families show that Mongolarachnidae is most likely on the orbicularian stem, close to other cribellate orbicularians (e.g., Deinopoidea), which suggests a greater diversity of cribellate orbicularians during the Middle Jurassic.

Keywords: Araneae, Chelicerata, Deinopoidea, Hypochiloidea, Mesozoic, Orbiculariae

The largest known fossil spiders (left: male, right: female) belong to a newly described species of extinct arachnids, Mongolarachne jurassica.
photo: Paul Selden

male Mongolarachne jurassica

Systematic palaeontology

Order Araneae Clerck, 1757
Suborder Opisthothelae Pocock, 1892
Infraorder Araneomorphae Smith, 1902

Family Mongolarachnidae fam. nov.
Etymology from the genus Mongolarachne gen. nov.

Mongolarachne gen. nov.
Etymology from the Inner Mongolia Autonomous Region, where the fossils were discovered, and the Greek άράχνη (L. arachne), a spider.

Mongolarachne jurassica (Selden, Shih and Ren, 2011) comb. nov.

Selden, P. A.; Shih, C.K.; Ren, D. 2013. A Giant Spider from the Jurassic of China reveals Greater Diversity of the orbicularian Stem Group. Naturwissenschaften. 100 (12): 1171–1181.
doi: 10.1007/s00114-013-1121-7.
Selden, P. A.; Shih, C.K.; Ren, D. 2011. A golden orb-weaver spider (Araneae: Nephilidae: Nephila) from the Middle Jurassic of China. Biology Letters. 7 (5): 775–8. doi: 10.1098/rsbl.2011.0228
 Kuntner, M; Arnedo, M. A.; Trontelj, P.; Lokovše, T; Agnarsson, I. 2013. A molecular phylogeny of nephilid spiders: Evolutionary history of a model lineage. Molecular Phylogenetics and Evolution. 69 (3): 961–979. doi: 10.1016/j.ympev.2013.06.008

Biggest Spider Fossil Now Has a Mate — But It's Complicated