Uraraneida

Uraraneida
Temporal range: Middle Devonian–Permian
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Chelicerata
Class: Arachnida
Clade: Tetrapulmonata
Order: †Uraraneida
Selden & Shear, 2008

Uraraneida is an extinct order of arachnids, known from fossils of Middle Devonian and Permian age, suggesting the order persisted from at least 393 to 252 million years ago. As of March 2016, two genera of fossils were placed in this order: Attercopus and Permarachne. They were initially identified as spiders, but now constitute the Uraraneida, a separate but closely related group.[1]

Characteristics

The first fossil now placed in the order was found in Gilboa, New York. In 1987, it was initially tentatively placed in the extinct order Trigonotarbida and named Gelasinotarbus? fimbriunguis.[2] Later, partly on the basis of a supposed spinneret, it was identified as a spider and named Attercopus fimbriunguis.[3] Further specimens of this species were found, and when examined in detail, along with those assigned to the genus Permarachne, features inconsistent with their placement as spiders were revealed. Silk producing spigots are present, but are borne along the rear edges of ventral plates, not on appendage-like spinnerets, as in spiders. The specimens also have a long, jointed "tail" or flagellum at the end of the abdomen, after the anus, a feature lacking in spiders but present in some other arachnids, such as uropygids.[1]

Phylogeny and classification

A 2014 study placed the Uraraneida in the Tetrapulmonata, a clade of arachnids defined by the apomorphy (derived feature) of two pairs of book lungs. The Tetrapulmonata divide into two main clades, one of which, Serikodiastida (Greek for "silk workers"), unites Uraraneida and Araneae (spiders), groups that share the ability to produce and use silk.[4]

An alternative classification suggested by Wunderlich in 2015, based on the same phylogeny, makes Uraraneida a suborder of Araneae, with "true spiders" treated as suborder Araneida.[5]

Selden et al. Wunderlich
clade Serikodiastida
  • order Uraraneida
  • order Araneae
 order Araneae
  • suborder Uraraneida
  • suborder Araneida

In 2016, a fossil arachnid from the Late Carboniferous (Pennsylvanian) age was described under the name Idmonarachne brasieri. It resembles uraraneids in lacking spinnerets, but unlike them resembles spiders in lacking a flagellum. The Late Carboniferous appears to be a time when there was a greater diversity of tetrapulmonate arachnids, of which the uraraneids were just one group.[6]

Genera and species

Dunlop et al. (2015) accepted two species:[7]

References

  1. 1 2 Selden, P.A.; Shear, W.A. & Sutton, M.D. (2008), "Fossil evidence for the origin of spider spinnerets, and a proposed arachnid order", Proceedings of the National Academy of Sciences 105 (52): 20781–20785, doi:10.1073/pnas.0809174106
  2. ↑ Shear, William A.; Selden, Paul A.; Rolfe, W.D.I.; Bonamo, Patricia M. & Grierson, James D. (1987), "New terrestrial arachnids from the Devonian of Gilboa, New York", American Museum Novitates 2901: 1–74
  3. ↑ Selden, Paul A.; Shear, William A. & Bonamo, Patricia M. (1991), "A spider and other arachnids from the Devonian of New York, and reinterpretations of Devonian Araneae", Palaeontology 34: 241–281
  4. ↑ Garwood, Russell J. & Dunlop, Jason (2014), "Three-dimensional reconstruction and the phylogeny of extinct chelicerate orders", PeerJ 2: e641, doi:10.7717/peerj.641
  5. ↑ Wunderlich, J. (2015), "On the evolution and the classification of spiders, the Mesozoic spider faunas, and descriptions of new Cretaceous taxa mainly in amber from Burmese (Burma) (Arachnida: Araneae)", in Wunderlich, J., Beiträge zur Araneologie 9, p. 21, cited in Dunlop, Penney & Jekel (2015, p. 127)
  6. ↑ Garwood, Russell J.; Dunlop, Jason A.; Selden, Paul A.; Spencer, Alan R.T.; Atwood, Robert C.; Vo, Nghia T. & Drakopoulos, Michael (2016). "Almost a spider: a 305-million-year-old fossil arachnid and spider origins". Proceedings of the Royal Society B 283 (1827): 20160125. doi:10.1098/rspb.2016.0125.
  7. ↑ Dunlop, J.A.; Penney, D.; Jekel, D. (2015), "A summary list of fossil spiders and their relatives" (PDF), World Spider Catalog (Natural History Museum Bern), retrieved 2016-03-20
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