Helcionellid

Helcionellid
Temporal range: Fortunian–Early Ordovician[1]
Latouchella costata restored as a gastropod
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Mollusca
Class: †Helcionelloida
Subclass: †Archaeobranchia
Order: †Helcionelliformes
Geyer, 1994[2]
Subgroups

See text.

Synonyms

Helcionelliformes Golikov & Starobogatov, 1975

Helcionellid or Helcionelliformes is an order of small fossil shells that are universally interpreted as molluscs,[3] though no sources spell out why this taxonomic interpretation is preferred.[4] These animals are first found about 540 to 530 million years ago[3] in the late Nemakit-Daldynian age, which is the earliest part of the Cambrian period. A single species persisted to the Early Ordovician.[5][6][7][8] These fossils are component of the small shelly fossils (SSF) assemblages.[5]

These are thought to be early molluscs with rather snail-like shells, although they lack any compelling molluscan synapomorphies and thus may not belong to the group.[9]

They have been alleged to represent ancestors of the modern conchiferans, a group that includes all the well-known modern classes – gastropods, cephalopods and bivalves.[10][11] They have also been considered to represent direct ancestors to the cephalopods.[12]

Parkhaev (2006, 2007) considers these animals to be crown-group gastropods. Previous to the 2006 classification by Parkhaev, helcionellids were classified within the separate class Helcionelloida or as "Uncertain position (Gastropoda or Monoplacophora)" within "Paleozoic molluscs of uncertain systematic position" according to the taxonomy of the Gastropoda by Bouchet & Rocroi, 2005.[13]

  1. ^ Kouchinsky A. V., Bengtson S., Runnegar B. N., Skovsted C. B., Steiner M., Vendrasco M. J. (2012). "Chronology of early Cambrian biomineralization". Geological Magazine. 149 (2): 221–251. Bibcode:2012GeoM..149..221K. doi:10.1017/s0016756811000720.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  2. ^ Christian B. Skovsted; John S. Peel (2007). "Small shelly fossils from the argillaceous facies of the Lower Cambrian Forteau Formation of western Newfoundland". Acta Palaeontologica Polonica. 52 (4): 729–748.
  3. ^ a b Nelson R Cabej (2019). Epigenetic Mechanisms of the Cambrian Explosion. Elsevier Science. p. 152. ISBN 9780128143124.
  4. ^ Zhao Fangchen, Smith Martin R., Yin Zongjun, Zeng Han, Li Guoxiang, Zhu Maoyan (2017). "Orthrozanclus elongata n. sp. and the significance of sclerite-covered taxa for early trochozoan evolution". Scientific Reports. 7 (1): 16232. Bibcode:2017NatSR...716232Z. doi:10.1038/s41598-017-16304-6. PMC 5701144. PMID 29176685.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  5. ^ a b Budd, Graham E (2003). "The Cambrian Fossil Record and the Origin of the Phyla" (Free full text). Integrative and Comparative Biology. 43 (1): 157–165. doi:10.1093/icb/43.1.157. PMID 21680420.
  6. ^ Michael Steiner; Guoxiang Li; Yi Qian; Maoyan Zhu; Bernd-Dietrich Erdtmann (2007). "Neoproterozoic to early Cambrian small shelly fossil assemblages and a revised biostratigraphic correlation of the Yangtze Platform (China)". Palaeogeography, Palaeoclimatology, Palaeoecology. 254 (1–2): 67–99. Bibcode:2007PPP...254...67S. doi:10.1016/j.palaeo.2007.03.046.
  7. ^ Gubanov, Alexander P.; Peel, John S. (2003). "Latest Helcionelloid Molluscs from the Lower Ordovician of Kazakhstan". Palaeontology. 44 (4): 681–694. doi:10.1111/1475-4983.00198.
  8. ^ Peel, John S.; Radvan J. Horný (2004). "A new problematic Early Ordovician univalve mollusc from France". Palaeontology. 47 (6): 1629–1639. Bibcode:2004Palgy..47.1629P. doi:10.1111/j.0031-0239.2004.00414.x.
  9. ^ Zhao Fangchen, Smith Martin R., Yin Zongjun, Zeng Han, Li Guoxiang, Zhu Maoyan (2017). "Orthrozanclus elongata n. sp. and the significance of sclerite-covered taxa for early trochozoan evolution". Scientific Reports. 7 (1): 16232. Bibcode:2017NatSR...716232Z. doi:10.1038/s41598-017-16304-6. PMC 5701144. PMID 29176685.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  10. ^ Peel, J.S. (1991). "Functional morphology of the Class Helcionelloida nov. and the early evolution of the Mollusca". In Simonetta, A.M.; Conway Morris, S. (eds.). The Early Evolution of Metazoa (The Significance of Problematic Taxa). Cambridge University Press. pp. 157–177. ISBN 978-0-521-40242-2.
  11. ^ Gubanov, A.P.; Peel, J.S. (November 2003). "The early Cambrian helcionelloid mollusc Anabarella Vostokova". Palaeontology. 46 (5): 1073–1087. Bibcode:2003Palgy..46.1073G. doi:10.1111/1475-4983.00334. S2CID 84893338.
  12. ^ Cite error: The named reference Weber1989 was invoked but never defined (see the help page).
  13. ^ Bouchet P. & Rocroi J.-P. (Ed.); Frýda J., Hausdorf B., Ponder W., Valdes A. & Warén A. 2005. Classification and nomenclator of gastropod families. Malacologia: International Journal of Malacology, 47(1-2). ConchBooks: Hackenheim, Germany. ISBN 3-925919-72-4. ISSN 0076-2997. 397 pp. http://www.vliz.be/Vmdcdata/imis2/ref.php?refid=78278