Palaeoscolecid

Palaeoscolecid
Temporal range: Upper Early Cambrian–Silurian[1]
Scientific classification
Kingdom: Animalia
Clade: Cycloneuralia
Class: †Palaeoscolecida
Conway Morris & Robinson, 1986
Families, genera and species
(sensu Harvey et al. 2010[2])[3]

See text

The palaeoscolecids are a group of extinct ecdysozoan worms resembling armoured priapulids. They are known from the Lower Cambrian[4] to the late Silurian;[5] they are mainly found as disarticulated sclerites, but are also preserved in many of the Cambrian lagerstätten.[6] They take their name from the typifying genus Palaeoscolex.[5]

Morphology

Palaeoscolecids bear an annulated trunk ornamented with circular patterns of phosphatic tesselating plates; a layered cuticle; and an armoured proboscis.[2] They are usually a few centimetres in length. There is no one character that unites the palaeoscolecids as a clade (indeed they are likely paraphyletic), and few individual specimens contain all characteristic palaeosolecid traits.[2]

Taxonomic position

They are considered to belong to the cycloneuralia,[7] although their position within this group is unresolved; they may lie with the priapulids or nematomorpha.[8] They have also been described as a sister-group to the ecdysozoa,[9] although as more characters are described a position closer to the priapulids becomes most probable.[2] A nematomorph affinity appears to be an artefact that results from under-sampling of the priapulid stem group.[2] Their relationship with Archaeopriapulida is unclear, and either group may be paraphyletic to the other.[10]

Other genera include Cricocosmia from the Lower Cambrian Chengjiang biota.[11] Their relationship with the archaeopriapulida is also unclear; it could be that both groups are a paraphyletic assemblage containing the priapulids.[1]

Taxonomy

In addition to the genera listed in the taxobox, other worms are commonly referred to the palaeoscolecids, even though they lack the cuticular structure that defines the group.[2] These include Louisella, Maotianshania, Cricocosmia, Tabelliscolex, Tylotites and others.[2] It's also possible that Markuelia represents an embryonic Palaeoscolecid.[12]


References

  1. ↑ 1.0 1.1 Wills, M. A. (1 April 1998). "Cambrian and Recent Disparity: the Picture from Priapulids". Paleobiology 24 (2): 155–286. doi:10.2307/2401237 (inactive 2015-03-21). JSTOR 2401237.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Harvey, T. H.; Dong, X.; Donoghue, P. C. (2010). "Are palaeoscolecids ancestral ecdysozoans?". Evolution & Development 12 (2): 177–200. doi:10.1111/j.1525-142X.2010.00403.x. PMID 20433458.
  3. ↑ Ma, X.; Aldridge, R. J.; Siveter, D. J.; Siveter, D. J.; Hou, X.; Edgecombe, G. D. (2014). "A New Exceptionally Preserved Cambrian Priapulid from the Chengjiang Lagerstätte". Journal of Paleontology 88 (2): 371. doi:10.1666/13-082.
  4. ↑ Andrey Y. Ivantsov & Ryszard Wrona (2004). "Articulated palaeoscolecid sclerite arrays from the Lower Cambrian of eastern Siberia" (PDF). Acta Geologica Polonica 54 (1): 1–22.
  5. ↑ 5.0 5.1 Xianguang Hou, Richard Aldridge, Jan Bergström, David Siveter, Derek Siveter (2004). The Cambrian fossils of Chengjiang, China: the flowering of early animal life. Wiley-Blackwell. p. 233. ISBN 978-1-4051-0673-3.
  6. ↑ Zhu, M.; Babcock, L.; Steiner, M. (2005). "Fossilization modes in the Chengjiang Lagerstätte (Cambrian of China): testing the roles of organic preservation and diagenetic alteration in exceptional preservation". Palaeogeography Palaeoclimatology Palaeoecology 220: 31–37. doi:10.1016/j.palaeo.2003.03.001.
  7. ↑ Conway Morris, S.; Peel, J. S. (2010). "New palaeoscolecidan worms from the Lower Cambrian: Sirius Passet, Latham Shale, and Kinzers Shale". Acta Palaeontologica Polonica 55 (1): 141–156. doi:10.4202/app.2009.0058.
  8. ↑ conference, http://gf.tmsoc.org/Documents/Mikro2009/GFSP15.pdf#page=82
  9. ↑ Peel, J. S. (2010). "A Corset-Like Fossil from the Cambrian Sirius Passet Lagerstätte of North Greenland and Its Implications for Cycloneuralian Evolution". Journal of Paleontology 84 (2): 332–340. doi:10.1666/09-102R.1.
  10. ↑ Ma, X.; Aldridge, R. J.; Siveter, D. J.; Siveter, D. J.; Hou, X.; Edgecombe, G. D. (2014). "A New Exceptionally Preserved Cambrian Priapulid from the Chengjiang Lagerstätte". Journal of Paleontology 88 (2): 371. doi:10.1666/13-082.
  11. ↑ Jian Han, Jianni Liu, Zhifei Zhang, Xinglian Zhang & Degan Shu (2007). "Trunk ornament on the palaeoscolecid worms Cricocosmia and Tabelliscolex from the Early Cambrian Chengjiang deposits of China" (PDF). Acta Palaeontologica Polonica 52 (2): 423–431.
  12. ↑ Duan, B.; Dong, X. -P.; Donoghue, P. C. J. (2012). "New palaeoscolecid worms from the Furongian (upper Cambrian) of Hunan, South China: Is Markuelia an embryonic palaeoscolecid?". Palaeontology 55 (3): 613. doi:10.1111/j.1475-4983.2012.01148.x.
  13. ↑ Han, J., Liu, J., Zhang, Z., Zhang, X., and Shu, D. (2007). "Trunk ornament on the palaeoscolecid worms Cricocosmia and Tabelliscolex from the Early Cambrian Chengjiang deposits of China" (PDF). Acta Palaeontologica Polonica 52 (2): 423–431.
  14. ↑ Huang, D.; Chen, J.; Zhu, M.; Zhao, F. (2014). "The burrow dwelling behavior and locomotion of palaeoscolecidian worms: New fossil evidence from the Cambrian Chengjiang fauna". Palaeogeography, Palaeoclimatology, Palaeoecology 398: 154. doi:10.1016/j.palaeo.2013.11.004.
  15. ↑ 15.0 15.1 15.2 Hu, S.; Steiner, M.; Zhu, M.; Luo, H.; Forchielli, A.; Keupp, H.; Zhao, F.; Liu, Q. (2012). "A new priapulid assemblage from the early Cambrian Guanshan fossil Lagerstätte of SW China". Bulletin of Geosciences: 93. doi:10.3140/bull.geosci.1238.