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Conulariida

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Conulariida are an extinct group of medusozoan cnidarians known from fossils spanning from the latest Ediacaran up until the Late Triassic.[1][2][3] They are almost exclusively known from their hard external structures (alternatively referred to as a theca, periderm or test), which were pyramidal in shape and made up of numerous lamellae.

Conulariida
Temporal range: Late Ediacaran-late Triassic, 545–205 Ma
Conulariid from the Mississippian (c. 360 to 325 mya) of Indiana; scale in mm.
Two Conularia gratiosa specimens from the Salem Limestone aged to the Middle Mississippian.
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Cnidaria
Order: †Conulatae
Clade: †Conulariida
Miller and Gurley, 1896
Genera

See text.

Structure

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The conulariids are fossils preserved as shell-like structures made up of rows of calcium phosphate rods, resembling an ice-cream cone with fourfold symmetry, usually four prominently-grooved corners.[4] New rods were added as the organism grew in length; the rod-based growth falsely gives the fossils a segmented appearance. Exceptional soft-part preservation has revealed that soft tentacles protruded from the wider end of the cone, and a holdfast from the pointed end attached the organisms to hard substrate. The prevailing reconstruction of the organism has it look superficially like a sea anemone sitting inside an angular, hard cone held perpendicular to the substrate. Conulariid shell is composed of francolite with carbonate ion concentration 8.1 wt%. The lattice parameters of conulariid apatite are a = 9.315(7) Å, c = 6.888(3) Å.[5] The fine structure of their shell comprises multiple lamellae of alternately organic-rich and organic-poor layers.[6]

Fossil record

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Close-up of a conulariid from the Mississippian of Indiana; scale in mm.
 
Conularia milwaukeensis from the Middle Devonian of Wisconsin.
 
A pair of Conularia niagarensis specimens from the Lower Silurian Waukesha Biota site in Wisconsin.

With the inclusion of the possible Ediacaran conulariid Vendoconularia, which may or may not be a conulariid at all,[7] and the definite late Ediacaran conulariid Paraconularia ediacara,[2] the Conulata fossil record begins with undeniable specimens in the Upper Ediacaran and extends without significant break through numerous major mass extinctions. The Conulariids finally disappear from the fossil record during the Late Triassic, by which time they were very rare, with only 8 documented occurrences across the entire Triassic. Their extinction may have been due to the rise of durophagous organisms as part of the Mesozoic marine revolution.[8]

In North America, conulariids are generally more common in rocks of Ordovician and Carboniferous age.

Lifestyle

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Life restoration of a conulariid, showing the soft-bodied anatomy

Conulariids were benthic animals that were sessile and attached to a substrate at the base of the theca, older individuals may have become recumbent (tipped over).[9] They are generally proposed to have been predators, using tentacles to ensnare prey.[10]

Phylogeny

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About 20 genera and 150 species are known,[11] but except for local occurrences, Conulariids are relatively uncommon.

The conulariids were originally thought to be anthozoan cnidarians. However, the lack of septa or other features diagnostic of anthozoans led researchers to abandon this hypothesis. Ivantsov and Fedonkin (2002) posit that the conulariids were ancestrally tri-radially symmetrical, as typified with Vendoconularia, typical of the structure seen in Vendozooans.[12] Conulariids are, however, technically a part of the Ediacaran biota as their fossil record starts at latest parts of that period.[2]

It is now also thought that the conulate trilobozoans derived their fourfold symmetry from a sixfold symmetry, as seen in Vendoconularia. This in turn, is thought to be originally derived from an ancestral disk-like trilobozoan three-fold symmetry.[citation needed]

Conulariids have generally been thought to be of Cnidarian affinity, occupying a position near the base of the Cnidarian family tree. However, since the 2010s, authors consider conulariids to be members of the subclade Medusozoa, though their exact placement within the clade is uncertain.[3]

Pearls

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Conulariids produced pearls within their shells, similar to the way molluscs such as oysters, other pelecypods, and some gastropods do today. These pearls give a clue as to the internal anatomy of the conulariid animal. But due to their calcium phosphate composition, their crystal structure, and their extreme age, these pearls tend to be rather unattractive for use in or as decorative objects.[13]

List of genera

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References

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  1. ^ Ben M. Waggoner; David Smith (1994). "Study of conulariid and related phosphatic conical exoskeletons from the Prague Basin (Czech Republic)". In G. L. Albanesi; M. S. Beresi; S. H. Peralta (eds.). Ordovician from the Andes. Serie Correlación Geológica Nº 17. INSTITUTO SUPERIOR DE CORRELACIÓN GEOLÓGICA.
  2. ^ a b c Leme, J. M.; Van Iten, H.; Simões, M. G. (2022). "A New Conulariid (Cnidaria, Scyphozoa) From the Terminal Ediacaran of Brazil". Frontiers in Earth Science. 10: Article 777746. Bibcode:2022FrEaS..10.7746L. doi:10.3389/feart.2022.777746.
  3. ^ a b Van Iten, Heyo; Hughes, Nigel C.; John, Douglas L.; Gaines, Robert R.; Colbert, Matthew W. (2023-04-27). "Conulariid soft parts replicated in silica from the Scotch Grove Formation (lower Middle Silurian) of east-central Iowa". Journal of Paleontology: 1–10. doi:10.1017/jpa.2023.6. ISSN 0022-3360. S2CID 258389436.
  4. ^ Waggoner, B.M. & D. Smith (1994): The Conulariida, Mystery fossils. University of California Museum of Paleontology web page [1]
  5. ^ Vinn, O.; Kirsimäe, K. (2015). "Alleged cnidarian Sphenothallus in the Late Ordovician of Baltica, its mineral composition and microstructure". Acta Palaeontologica Polonica. 60: 1001–1008. doi:10.4202/app.00049.2013.
  6. ^ Ford, Robert C.; Van Iten, Heyo; Clark, George R. (2016). "Microstructure and composition of the periderm of conulariids". Journal of Paleontology. 90 (3): 389. doi:10.1017/jpa.2016.63. S2CID 133541791.
  7. ^ Van Iten, H.; De Moraes Leme, J.; Coelho Rodrigues, S.; Guimaraes Simoes, M. (2005). "Reinterpretation of a Conulariid-Like Fossil from the Vendian of Russia". Palaeontology. 48 (3): 619–622. doi:10.1111/j.1475-4983.2005.00471.x. hdl:11449/31655. S2CID 247733826.
  8. ^ Lucas, Spencer G. (2012-03-22). "The Extinction of the Conulariids". Geosciences. 2 (1): 1–10. doi:10.3390/geosciences2010001. ISSN 2076-3263.
  9. ^ Iten, Heyo Van; Vyhlasová, Zdenka (2004-12-31), Webby, Barry D.; Paris, Florentin; Droser, Mary L.; Percival, Ian G. (eds.), "14. Conulariids", The Great Ordovician Biodiversification Event, Columbia University Press, pp. 119–123, doi:10.7312/webb12678-015, ISBN 978-0-231-12678-6, retrieved 2023-06-25
  10. ^ Leme, Juliana M.; Van Iten, Heyo; Simões, Marcello G. (2022-06-08). "A New Conulariid (Cnidaria, Scyphozoa) From the Terminal Ediacaran of Brazil". Frontiers in Earth Science. 10. Bibcode:2022FrEaS..10.7746L. doi:10.3389/feart.2022.777746. ISSN 2296-6463.
  11. ^ "ZooBank: The World Register of Animal Names". www.zoobank.org. Archived from the original on 27 September 2007. Retrieved 14 January 2022.
  12. ^ Ivantsov, A. Y.; Fedonkin, M. A. (2002). "Conulariid-like fossil from the Vendian of Russia: a metazoan clade across the Proterozoic/Palaeozoic boundary". Palaeontology. 45 (6): 1119–1129. doi:10.1111/1475-4983.00283.
  13. ^ Boucot, A.J. (2013). Evolutionary Paleobiology of Behavior and Coevolution. Elsevier. pp. 750 (page 69). ISBN 9781483290812.

Bibliography

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