Biology:Palaeoscolecid

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Short description: Extinct class of worms

Palaeoscolecida
Temporal range: Upper Early Cambrian–Silurian[1]
Scathascolex 83939d.png
The Burgess Shale palaeoscolecid Scathascolex minor. Image from Smith (2015)[4][5]
Scientific classification e
Domain: Eukaryota
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[6] to the late Silurian;[7] they are mainly found as disarticulated sclerites, but are also preserved in many of the Cambrian lagerstätten.[8] They take their name from the typifying genus Palaeoscolex.[7] Other genera include Cricocosmia from the Lower Cambrian Chengjiang biota.[9] Their taxonomic affinities within Ecdysozoa have been the subject of debate.

Morphology

Palaeoscolecids bear an annulated trunk ornamented with circular patterns of phosphatic tesselating plates; a layered cuticle; and an armoured proboscis.[2] They are long and narrow, and can reach tens of centimetres in length. Their cuticle is annulated, typically in complete rings, but sometimes the rings split or only encircle part of the trunk. Each annulus is essentially identical to its neighbours; the only trunk differentiation is at the anterior and posterior.[2] The anterior is radially symmetrical, typically comprising an introvert, whereas the trunk is bilaterally symmetrical.[2] The posterior hosts the terminal anus and sometimes one or two hooks.[2] 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]

Growth

Palaeoscolecids can grow by the continuous addition of plates, or by the continued growth of individual plates.[10]

Taxonomic position

Palaeoscolecids are somewhat challenging to define, and probably represent a paraphyletic grouping. Their most current systematic diagnosis[11] references their annulated worm-like body form, the presence of rows (usually) of phosphatic plates, and a straight gut, with the anus at the end of the animal. The group contains a wide and continuous spectrum of morphological variety, making further division of the group difficult; moreover, non-palaeoscolecid taxa likely evolved from palaeoscolecid-like ancestors, and it is thus difficult to demarcate a single clade that corresponds to the palaeoscolecid concept.[11]

They are considered by some to belong to the Cycloneuralia,[12] although their position within this group is unresolved; they may lie with the priapulids or Nematomorpha.[13] They have also been described as a sister-group to the Ecdysozoa,[14] although as more characters are described a position closer to the priapulids becomes most probable.[2] This said, their pharynx has the sixfold symmetry that likely characterised the ancestral ecdysozoan, rather than the fivefold symmetry of priapulans.[15] 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.[3][1] Some authors choose to include paleoscolecids within Priapulida.[16]

Martin R. Smith and Alavya Dhungana suggested in a 2022 publication that palaeoscolecids are a grade including sister taxa to Panarthropoda, highlighting similarities between the dorsal plates of taxa such as cricocosmiids and those of lobopodians such as Microdictyon.[17] This proposal was made in response to a 2021 paper that found in a phylogenetic analysis that paleoscolecids were stem-group priapulids.[18]

Taxonomy

As palaeoscolecids may represent a grade rather than a clade, drawing up a formal taxonomy proves problematic.[2] What is more, two parallel taxonomies exist: a form taxonomy for sclerites, and a true taxonomy for articulated fossils. The most recent holistic study of priapulids by Harvey et al. (2010) defines a core of palaeoscolecids characterized by a cuticle that is made up of interlocking plates of multiple sizes, and a looser assemblage (palaeoscolecids sensu lato) including other unconfirmed and palaeoscolecid-like forms:

Palaeoscolecids sensu stricto

Articulated macrofossils

  • Palaeoscolex piscatorum (early Ordovician)
  • Palaeoscolex (=Mafangscolex) sinensis (early Cambrian, China)
  • Sanxiascolex papillogyrus (early Cambrian, China)[19]
  • Scathascolex minor (Burgess Shale, mid-Cambrian)[11]
  • Arrakiscolex aasei (Drumian, Cambrian; Marjum Formation, Utah)[20]
  • Sahascolex (early Cambrian of Siberia)
  • Gamascolex (early Ordovician, Czech Rep.)
  • Plasmuscolex (early Ordovician, Czech Rep.)
  • ?Guanduscolex minor (early Cambrian, China)
  • ? Family Chalazoscolecidae:
  • Wronascolex? johanssoni (mid-Cambrian, Scandinavia)[21]
  • Maotianshania? sp. (late early Cambrian, Scandinavia)[21]

Articulated microfossils

(from Orsten-type deposits, preserved in three dimensions)

Palaeoscolecidae From Australia
  • Austroscolex Muller & Hinz 1993[22]
  • Corallioscolex Muller & Hinz 1993[22]
  • Euryscolex Muller & Hinz 1993[22]*
  • Hadimopanella Gedik 1977[22][23]
  • Kaloskolex Muller & Hinz 1993[22]
  • Milaculum Muller 1973
  • Murrayscolex Muller & Hinz 1993[22]
  • Pantoioscolex Muller & Hinz 1993[22]
  • Rhomboscolex Muller & Hinz 1993[22]
  • Schistoscolex Muller & Hinz 1993[22]
  • Shergoldiscolex Muller & Hinz 1993[22]
  • Thoracoscolex Muller & Hinz 1993[22]
From China
  • Dispinoscolex [24]
  • Houscolex Zhang & Pratt[25] (Order and Family uncertain)
  • Hunanoscolex Duan & Dong[26] (= Ornatoscolex Duan & Dong[26])[27]

Palaeoscolecids sensu lato

Other long and narrow Palaeozoic worms that exhibit an invariant body width are commonly referred to the palaeoscolecids, even though they lack the cuticular structure that defines the group; this 'Palaeoscolecid sensu lato' group includes Louisella, Cricocosmia, Tabelliscolex, Tylotites and others.[2] Maotianshania and, by extension, the family Maotianshaniidae, was excluded from the "Palaeoscolecids sensu stricto" by Harvey et al. (2010), but it has been argued that members of this family do exhibit the requisite cuticular structure, if discreetly.[21]

Status impossible to determine from current material

It is possible that Markuelia represents an embryonic Palaeoscolecid.[28]

Linnean taxonomy

Order Uncertain
  • Family Chalazoscolecidae Conway Morris & Peel 2010
    Defined by the presence of smooth, folded and sclerite-bearing cuticular regions
    • Chalazoscolex pharkus
    • Xystoscolex boreogyrus
Order Cricocosmida Han et al. 2007[29]
Defined by the presence of an unarmoured neck between the proboscis and the trunk, and a single pair of posterior hooks.[29]
  • Family Cricocosmiidae
    • Tabelliscolex:
      • Tabelliscolex hexagonus
      • Tabelliscolex maanshanensis
      • Tabelliscolex chengjiangensis
    • Cricocosmia:
      • Cricocosmia jinningensis
    • Houscolex
  • Family Maotianshaniidae
    • Maotianshania cylindrica Sun and Huo, 1987
  • Family Palaeoscolecidae
    • Wronascolex
      Defined by presence of Hadimopanella sclerites with three to ten nodes.[30]
    • Palaeoscolex
      Defined by presence of Milaculum-type plates, i.e. rectangular with parallel rows of nodes[30]
    • Utahscolex Whitaker et al. 2020[31]
    • Ashetscolex Muir et al 2014[32]
    • Sanduscolex Muir et al 2014[32]
  • Family Tylotitidae
    • Tylotites petiolaris Luo and Hu, 1999
Other Palaeoscolecidae or unassigned
Microfossil material

Genus level taxonomy

Palaeoscolex

Palaeoscolex has been abused as a wastebasket taxon for palaeoscolecid macrofossils. The most recent proposal is that Palaeoscolex should only include taxa with Milaculum-type sclerites, as in the type species P. piscatorum.[30][37] As such, P. ratcliffei and P. huainanensis should not be included in Palaeoscolex.[30]

Wronascolex

Originally described from Siberia, Wronascolex should now be considered to include all taxa with Hadimopanella sclerites that have 3–10 nodes in a single circle, perhaps including Yunnanoscolex.[30]

Guanduscolex, Wudingscolex

Though these genera have sclerites that resemble Hadimopanella knappologicum, they remain valid genera.[30]

Mafangscolex

This genus[38] has simple sclerites with a single (small but prominent) node in the middle, so can be separated from Palaeoscolex[30](unless this simplicity is taphonomic). Its introvert has a six-fold symmetry, whereas its proboscis has quincuncially arranged teeth that resemble those of other Cambrian ecdysozoan worms.[15]

Utahscolex

Originally described from the Spence Shale of Utah, Utahscolex has four transverse rings of plates per annulus, arranged as two 'bands' of double rows of plates separated by a central naked zone. Occasionally, single row bifurcates into two rows (for up to 6 rows per annulus). The plates are circular, and unornamented. Platelets and microplates are absent.

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:10.1666/0094-8373(1998)024[0177:CARDTP2.3.CO;2]. 
  2. ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 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. ↑ 3.0 3.1 Ma, X.; Aldridge, R. J.; Siveter, D. J.; Siveter, D. J.; Hou, X.; Edgecombe, G. D. (March 2014). "A New Exceptionally Preserved Cambrian Priapulid from the Chengjiang Lagerstätte". Journal of Paleontology 88 (2): 371–384. doi:10.1666/13-082. Bibcode: 2014JPal...88..371M. 
  4. ↑ Smith, Martin R. (2015). "A palaeoscolecid worm from the Burgess Shale". Palaeontology 58 (6): 973–979. doi:10.1111/pala.12210. Bibcode: 2015Palgy..58..973S. 
  5. ↑ Smith, Martin R. (2015). "Lagerstatten". Data from: A palaeoscolecid worm from the Burgess Shale. Dryad Digital Repository. Dryad. doi:10.5061/dryad.cf493. 
  6. ↑ Andrey Y. Ivantsov; Ryszard Wrona (2004). "Articulated palaeoscolecid sclerite arrays from the Lower Cambrian of eastern Siberia". Acta Geologica Polonica 54 (1): 1–22. http://www.geo.uw.edu.pl/agp/table/pdf/54-1/wrona.pdf. Retrieved 2009-06-03. 
  7. ↑ 7.0 7.1 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. https://books.google.com/books?id=QOIFgqC4X_sC&q=palaeoscolecid&pg=PA60. 
  8. ↑ Zhu, M.; Babcock, L.; Steiner, M. (2 May 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 (1–2): 31–37. doi:10.1016/j.palaeo.2003.03.001. Bibcode: 2005PPP...220...31Z. 
  9. ↑ 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". Acta Palaeontologica Polonica 52 (2): 423–431. http://www.app.pan.pl/archive/published/app52/app52-423.pdf. 
  10. ↑ Xian, Xiao-Feng; Eriksson, Mats E.; Zhang, Hua-Qiao (2023). "Growth patterns of palaeoscolecid sclerites from the Furongian (Upper Cambrian) Wangcun section, western Hunan, South China". Palaeoworld. doi:10.1016/j.palwor.2023.03.005. 
  11. ↑ 11.0 11.1 11.2 Smith, Martin R. (2015). "A palaeoscolecid worm from the Burgess Shale". Palaeontology 58 (6): 973–979. doi:10.1111/pala.12210. Bibcode: 2015Palgy..58..973S. 
  12. ↑ 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. http://app.pan.pl/article/item/app20090058.html. 
  13. ↑ conference, http://gf.tmsoc.org/Documents/Mikro2009/GFSP15.pdf#page=82
  14. ↑ Peel, J. S. (March 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. Bibcode: 2010JPal...84..332P. 
  15. ↑ 15.0 15.1 Yang, Jie; Smith, Martin R.; Zhang, Xi-Guang; Yang, Xiao-yu (2020). "Introvert and pharynx of Mafangscolex, a Cambrian palaeoscolecid". Geological Magazine 157 (12): 2044–2050. doi:10.1017/S0016756820000308. Bibcode: 2020GeoM..157.2044Y. http://dro.dur.ac.uk/30652/1/30652.pdf. 
  16. ↑ Whitaker, Anna F.; Jamison, Paul G.; Schiffbauer, James D.; Kimmig, Julien (December 2020). "Re-description of the Spence Shale palaeoscolecids in light of new morphological features with comments on palaeoscolecid taxonomy and taphonomy" (in en). PalZ 94 (4): 661–674. doi:10.1007/s12542-020-00516-9. ISSN 0031-0220. Bibcode: 2020PalZ...94..661W. http://link.springer.com/10.1007/s12542-020-00516-9. 
  17. ↑ Smith, Martin Ross; Dhungana, Alavya (2022). "Discussion on 'Tabelliscolex (Cricocosmiidae: Palaeoscolecidomorpha) from the early Cambrian Chengjiang Biota and the evolution of seriation in Ecdysozoa' by Shi et al. 2021 (JGS, jgs2021-060)". Journal of the Geological Society 179 (3). doi:10.1144/jgs2021-111. Bibcode: 2022JGSoc.179..111S. 
  18. ↑ Shi, Xiaomei; Howard, Richard J.; Edgecombe, Gregory D.; Hou, Xianguang; Ma, Xiaoya (March 2022). "Tabelliscolex (Cricocosmiidae: Palaeoscolecidomorpha) from the early Cambrian Chengjiang Biota and the evolution of seriation in Ecdysozoa" (in en). Journal of the Geological Society 179 (2): jgs2021–060. doi:10.1144/jgs2021-060. ISSN 0016-7649. Bibcode: 2022JGSoc.179...60S. 
  19. ↑ Yuning, Yang; Xingliang, Zhang (2016). "Distinctive Scleritome with Marginal Tubercles of a New Palaeoscolecid Worm from the Shipai Fauna (Cambrian Epoch 2) at Three Gorges, South China". Acta Geologica Sinica - English Edition 90 (3): 807. doi:10.1111/1755-6724.12724. Bibcode: 2016AcGlS..90..807Y. 
  20. ↑ Leibach, Wade; Lerosey-Aubril, Rudy; Whitaker, Anna; Schiffbauer, James; Kimmig, Julien (2021). "First palaeoscolecid from the Cambrian (Miaolingian, Drumian) Marjum Formation of western Utah". Acta Palaeontologica Polonica 66. doi:10.4202/app.00875.2021. 
  21. ↑ 21.0 21.1 21.2 Streng, Michael; Ebbestad, Jan Ove R.; Berg-Madsen, Vivianne (2016). "Cambrian palaeoscolecids (Cycloneuralia) of southern Scandinavia". Papers in Palaeontology 3: 21–48. doi:10.1002/spp2.1067. 
  22. ↑ 22.00 22.01 22.02 22.03 22.04 22.05 22.06 22.07 22.08 22.09 22.10 Müller, K. J.; Hinz-Schallreuter, I. (1993). "Palaeoscolecid worms from the Middle Cambrian of Australia". Palaeontology 36: 549–592. http://www.palass-pubs.org/palaeontology/pdf/Vol36/Pages. 
  23. ↑ Topper, T. P.; Brock, G. A.; Skovsted, C. B.; Paterson, J. R. (2009). "Palaeoscolecid scleritome fragments with Hadimopanella plates from the early Cambrian of South Australia". Geological Magazine 147: 86–97. doi:10.1017/S0016756809990082. 
  24. ↑ Xian, Xiao-Feng; Eriksson, Mats E.; Zhang, Hua-Qiao (2023). "Growth patterns of palaeoscolecid sclerites from the Furongian (Upper Cambrian) Wangcun section, western Hunan, South China". Palaeoworld. doi:10.1016/j.palwor.2023.03.005. 
  25. ↑ Zhang, X.-G.; Pratt, B. R. (1996). "Early Cambrian palaeoscolecid cuticles from Skaanxi, China". Journal of Paleontology 70 (2): 275–279. doi:10.1017/s0022336000023350. Bibcode: 1996JPal...70..275Z. 
  26. ↑ 26.0 26.1 Duan B, Dong X. 2013. Furongian (Late Cambrian) palaeoscolecid cuticles from Hunan Province, South China: the growth impact on the worm cuticle. Acta Scientiarum Naturalium Universitatis Pekinensis 49: 591–602. https://www.researchgate.net/profile/Xi_Ping_Dong/publication/264275844_Furongian_%28_Late_Cambrian_%29_Palaeoscolecid_Cuticles_from_Hunan_Province__South_China_the_Growth_Impact_on_Worm_Cuticle/links/53d894d70cf2631430c3250c.pdf
  27. ↑ Xian, Xiao-Feng; Eriksson, Mats E.; Zhang, Hua-Qiao (2023). "Growth patterns of palaeoscolecid sclerites from the Furongian (Upper Cambrian) Wangcun section, western Hunan, South China". Palaeoworld. doi:10.1016/j.palwor.2023.03.005. 
  28. ↑ 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): 613–622. doi:10.1111/j.1475-4983.2012.01148.x. Bibcode: 2012Palgy..55..613D. https://www.dora.lib4ri.ch/psi/islandora/object/psi%3A11695. 
  29. ↑ 29.0 29.1 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". Acta Palaeontologica Polonica 52 (2): 423–431. https://www.app.pan.pl/archive/published/app52/app52-423.pdf. 
  30. ↑ 30.0 30.1 30.2 30.3 30.4 30.5 30.6 García-Bellido, D. C.; Paterson, J. R.; Edgecombe, G. D. (2013). "Cambrian palaeoscolecids (Cycloneuralia) from Gondwana and reappraisal of species assigned to Palaeoscolex". Gondwana Research 24 (2): 780–795. doi:10.1016/j.gr.2012.12.002. Bibcode: 2013GondR..24..780G. 
  31. ↑ Whitaker, Anna F.; Jamison, Paul G.; Schiffbauer, James D.; Kimmig, Julien K. (2020). "Re‑description of the Spence Shale palaeoscolecids in light of new morphological features with comments on palaeoscolecid taxonomy and taphonomy". PalZ 94 (4): 661–674. doi:10.1007/s12542-020-00516-9. Bibcode: 2020PalZ...94..661W. 
  32. ↑ 32.0 32.1 Muir, Lucy A.; Ng, Tin-Wai; Li, Xiang-Feng; Zhang, Yuan-Dong; Lin, Jih-Pai (2014). "Palaeoscolecidan worms and a possible nematode from the Early Ordovician of South China". Palaeoworld 23: 15–24. doi:10.1016/j.palwor.2013.06.003. 
  33. ↑ 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: 154–164. doi:10.1016/j.palaeo.2013.11.004. Bibcode: 2014PPP...398..154H. 
  34. ↑ 34.0 34.1 34.2 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: 93–106. doi:10.3140/bull.geosci.1238. 
  35. ↑ Goñi, Iban; Skovsted, Christian; Li, Luoyang; Li, Guoxiang; Betts, Marissa; Dorjnamjaa, Dorj; Altanshagai, Gundsambuu; Enkhbaatar, Batkhuyag et al. (2023). "New Palaeoscolecid plates from the Cambrian Stage 3 of northern Mongolia". Acta Palaeontologica Polonica 68. doi:10.4202/app.01030.2022. 
  36. ↑ Repetski, John E. (1981). "An Ordovician Occurrence of Utahphospha Müller & Miller". Journal of Paleontology 55 (2): 395–400. 
  37. ↑ Conway, Morris S. (1997). "The cuticular structure of the 495-Myr-old type species of the fossil worm ~Palaeoscolex~, ~P. piscatorum~ (?Priapulida)". Zoological Journal of the Linnean Society 119: 69–82. doi:10.1111/j.1096-3642.1997.tb00136.x. 
  38. ↑ Shixue Hu (October 2005). Taphonomy and palaeoecology of the early Cambrian Chengjiang Biota from eastern Yunnan, China. 7. Berliner Paläobiologische Abhandlungen. pp. 1–197. ISBN 3980853179. https://www.researchgate.net/publication/258246958. 

Wikidata ☰ Q7126500 entry



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