Helcionellid or Helcionelliformes is an order of small fossilshells 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-Daldynianage, 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]
This speculative restoration of the tiny Helcionellid fossil Yochelcionella shows water flowing in under the shell, over the gills and out through the "exhaust pipe".[16]
Helcionellids have a single shell, in which the peak forms a distinctive curve.[17] Some have horizontal "inhalent siphons"[12] ("exhaust pipes"[verification needed]) on the concave edges of their shells, and there is debate about whether these pointed forwards or backwards.[16] Most helcionellid fossils that have been collected are only a few millimeters long (1⁄8 inch) and rather snail-like. However specimens a few centimeters long (1–2 inches) have also been found, mainly limpet-like in shape, although some were laterally compressed and others were tall. The smallest specimens may have been juvenile or larval forms of the larger specimens.[17]
Inside the shell are a series of longitudinal ridges stretching to the apex. Some people reckon that they are to do with controlling water currents in a mantle cavity; others think that they are to do with support or muscle attachment.[18]
Shell muscles attach near the concave side of the shell.[19]
Fossil recordedit
The earliest helcionellid, in Siberian sections, is Oelandiella.[20][1]
They first appear in the late Nemakit-Daldynian (lower Early Cambrian),[5] and are a constituent of the small shelly fauna (SSF). Larger individuals, reaching centimeters in diameter, have also been found.[17]
Helcionellids have been interpreted as juvenile stages of larger limpet-like molluscs.[21]
Referencesedit
^ abKouchinsky 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)
^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.
^ abNelson R Cabej (2019). Epigenetic Mechanisms of the Cambrian Explosion. Elsevier Science. p. 152. ISBN9780128143124.
^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. PMC5701144. PMID 29176685.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^ abcBudd, 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.
^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.
^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.
^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.
^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. PMC5701144. PMID 29176685.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^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. ISBN978-0-521-40242-2.
^ abWebers, G.F.; Yochelson, E.L. (1989). "Late Cambrian molluscan faunas and the origin of the Cephalopoda". In Crame, J.A. (ed.). Origins and Evolution of the Antarctic Biota. Vol. 47. Geological Society, London: Special Publications. p. 29. Bibcode:1989GSLSP..47...29W. doi:10.1144/GSL.SP.1989.047.01.04. S2CID 128682549. {{cite book}}: |journal= ignored (help)
^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. ISBN3-925919-72-4. ISSN 0076-2997. 397 pp. http://www.vliz.be/Vmdcdata/imis2/ref.php?refid=78278
^P. Yu. Parkhaev (2006). (PDF). In S.V. Rozhnov (ed.). Evolution of the biosphere and biodiversity. Towards the 70th anniversary of A. Y. Rozanov. Moscow. pp. 282–296. Archived from the original (PDF) on 2015-06-10. Retrieved 2009-11-03.{{cite book}}: CS1 maint: location missing publisher (link)
^P. Yu. Parkhaev (2007). The Cambrian 'basement' of gastropod evolution. Vol. 286. Geological Society. pp. 415–421. Bibcode:2007GSLSP.286..415P. doi:10.1144/SP286.31. ISBN978-1-86239-233-5. S2CID 130979274. {{cite book}}: |journal= ignored (help)
^ abcMus, M.M.; Palacios, T.; Jensen, S. (2008). "Size of the earliest mollusks: Did small helcionellids grow to become large adults?". Geology. 36 (2): 175. Bibcode:2008Geo....36..175M. doi:10.1130/G24218A.1.
^The Functional Morphology of the Cambrian Univalved Mollusks—Helcionellids. 1
^P. Yu. Parkhaev (2004). "New Data on the Morphology of Shell Muscles in Cambrian Helcionelloid Mollusks". Paleontological Journal. 38 (3): 254–256.
^Gubanov A. P., Peel J. S. (1999). "Oelandiella, the earliest Cambrian helcionelloid mollusc from Siberia". Palaeontology. 42 (2): 211–222. Bibcode:1999Palgy..42..211G. doi:10.1111/1475-4983.00070. S2CID 129393470.
^Mus, M.M.; Palacios, T.; Jensen, S. (2008). "Size of the earliest mollusks: Did small helcionellids grow to become large adults?". Geology. 36 (2): 175. Bibcode:2008Geo....36..175M. doi:10.1130/G24218A.1. Retrieved 2008-10-01.
External linksedit
December 15, 2023
helcionellid, helcionelliformes, order, small, fossil, shells, that, universally, interpreted, molluscs, though, sources, spell, this, taxonomic, interpretation, preferred, these, animals, first, found, about, million, years, late, nemakit, daldynian, which, e. 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 HelcionellidTemporal range Fortunian Early Ordovician 1 PreꞒ Ꞓ O S D C P T J K Pg NLatouchella costata restored as a gastropodScientific classificationDomain EukaryotaKingdom AnimaliaPhylum MolluscaClass HelcionelloidaSubclass ArchaeobranchiaOrder HelcionelliformesGeyer 1994 2 SubgroupsSee text SynonymsHelcionelliformes Golikov amp Starobogatov 1975These 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 amp Rocroi 2005 13 Contents 1 2006 2007 taxonomy 2 Morphology 3 Fossil record 4 References 5 External links2006 2007 taxonomy editAccording to P Yu Parkhaev 14 15 the order Helcionelliformes is within the subclass Archaeobranchia Parkhaev 2001 in the class Gastropoda Order Helcionelliformes Golikov amp Starobogatov 1975 Superfamily Helcionelloidea Wenz 1938 Family Helcionellidae Wenz 1938 Family Carinopeltidae Parkhaev 2013 syn Igarkiellidae Parkhaev 2001 Family Coreospiridae Knight 1947 Superfamily Yochelcionelloidea Runnegar amp Jell 1976 Family Trenellidae Parkhaev 2001 Family Yochelcionellidae Runnegar amp Jell 1976 Family Stenothecidae Runnegar amp Jell 1980 Subfamily Stenothecinae Runnegar amp Jell 1980 Subfamily Watsonellinae Parkhaev 2001Morphology edit nbsp This speculative restoration of the tiny Helcionellid fossil Yochelcionella shows water flowing in under the shell over the gills and out through the exhaust pipe 16 Helcionellids have a single shell in which the peak forms a distinctive curve 17 Some have horizontal inhalent siphons 12 exhaust pipes verification needed on the concave edges of their shells and there is debate about whether these pointed forwards or backwards 16 Most helcionellid fossils that have been collected are only a few millimeters long 1 8 inch and rather snail like However specimens a few centimeters long 1 2 inches have also been found mainly limpet like in shape although some were laterally compressed and others were tall The smallest specimens may have been juvenile or larval forms of the larger specimens 17 Inside the shell are a series of longitudinal ridges stretching to the apex Some people reckon that they are to do with controlling water currents in a mantle cavity others think that they are to do with support or muscle attachment 18 Shell muscles attach near the concave side of the shell 19 Fossil record editThe earliest helcionellid in Siberian sections is Oelandiella 20 1 They first appear in the late Nemakit Daldynian lower Early Cambrian 5 and are a constituent of the small shelly fauna SSF Larger individuals reaching centimeters in diameter have also been found 17 Helcionellids have been interpreted as juvenile stages of larger limpet like molluscs 21 References edit a b 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 a href Template Cite journal html title Template Cite journal cite journal a CS1 maint multiple names authors list link 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 a b Nelson R Cabej 2019 Epigenetic Mechanisms of the Cambrian Explosion Elsevier Science p 152 ISBN 9780128143124 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 a href Template Cite journal html title Template Cite journal cite journal a CS1 maint multiple names authors list link a b c 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 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 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 Peel John S Radvan J Horny 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 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 a href Template Cite journal html title Template Cite journal cite journal a CS1 maint multiple names authors list link 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 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 a b Webers G F Yochelson E L 1989 Late Cambrian molluscan faunas and the origin of the Cephalopoda In Crame J A ed Origins and Evolution of the Antarctic Biota Vol 47 Geological Society London Special Publications p 29 Bibcode 1989GSLSP 47 29W doi 10 1144 GSL SP 1989 047 01 04 S2CID 128682549 a href Template Cite book html title Template Cite book cite book a journal ignored help Bouchet P amp Rocroi J P Ed Fryda J Hausdorf B Ponder W Valdes A amp Waren 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 P Yu Parkhaev 2006 Adaptive radiation of the Cambrian helcionelloid mollusks Gastropoda Archaeobranchia PDF In S V Rozhnov ed Evolution of the biosphere and biodiversity Towards the 70th anniversary of A Y Rozanov Moscow pp 282 296 Archived from the original PDF on 2015 06 10 Retrieved 2009 11 03 a href Template Cite book html title Template Cite book cite book a CS1 maint location missing publisher link P Yu Parkhaev 2007 The Cambrian basement of gastropod evolution Vol 286 Geological Society pp 415 421 Bibcode 2007GSLSP 286 415P doi 10 1144 SP286 31 ISBN 978 1 86239 233 5 S2CID 130979274 a href Template Cite book html title Template Cite book cite book a journal ignored help a b Runnegar B Pojeta Jr J Oct 1974 Molluscan Phylogeny the Paleontological Viewpoint Science 186 4161 311 317 Bibcode 1974Sci 186 311R doi 10 1126 science 186 4161 311 JSTOR 1739764 PMID 17839855 S2CID 46429653 a b c Mus M M Palacios T Jensen S 2008 Size of the earliest mollusks Did small helcionellids grow to become large adults Geology 36 2 175 Bibcode 2008Geo 36 175M doi 10 1130 G24218A 1 The Functional Morphology of the Cambrian Univalved Mollusks Helcionellids 1 P Yu Parkhaev 2004 New Data on the Morphology of Shell Muscles in Cambrian Helcionelloid Mollusks Paleontological Journal 38 3 254 256 Gubanov A P Peel J S 1999 Oelandiella the earliest Cambrian helcionelloid mollusc from Siberia Palaeontology 42 2 211 222 Bibcode 1999Palgy 42 211G doi 10 1111 1475 4983 00070 S2CID 129393470 Mus M M Palacios T Jensen S 2008 Size of the earliest mollusks Did small helcionellids grow to become large adults Geology 36 2 175 Bibcode 2008Geo 36 175M doi 10 1130 G24218A 1 Retrieved 2008 10 01 External links edithttps web archive org web 20080930105735 http www palaeos com Invertebrates Molluscs BasalMollusca Conchifera Helcionelloida html Retrieved from https en wikipedia org w index php title Helcionellid amp oldid 1182575730, wikipedia, wiki, book, books, library,
