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Conostichus

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Conostichus
Temporal range: Ordovician–Cretaceous[1]
Trace fossil classification Edit this classification
Ichnogenus: Conostichus
Lesquereux, 1876
Type ichnospecies
Conostichus omatus
Lesquereux, 1876
Ichnospecies[2]
  • Conostichus omatus Lesquereux, 1876
  • Conostichus broadheadi Lesquereux, 1880
  • Conostichus typicus (King, 1955)
  • Conostichus wycherlyi (King, 1955)
  • Conostichus stouti Branson, 1961

Conostichus is an ichnogenus of cnidarian trace fossil.[3][4] They are nowadays considered to represent a burrow structure serving as a holdfast for an anemone-like organism.[1]

Description

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Conostichus is a plug-shaped vertical trace fossil, with a diameter varying from half to double the height.[1] Transverse constrictions and longitudinal fluting may be present, while the burrow fills occasionally show concentric laminae. The apex bears a twelve-fold symmetry, with the apical disc varying from small in C. broadheadi to broad and flat in C. typicus.[5]

Preservation

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The fossils display a wide variety of preservation modes, with well-preserved specimens being found alongside poorly preserved ones. The former are believed to be the result of rapid infilling with fine-grained carbonate particles, while the latter would have been passively filled with coarser carbonate sediments.[6]

Classification

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Before being identified as a trace fossil, Conostichus was variously interpreted as a calcareous algae, or as a body fossil that decayed after being covered in sediment, and was later filled by another type of sediment.[7] Branson (1961) classified Conostichus as part of Scyphomedusae, interpreting the fossils as representing a basal disk and lappets corresponding to the strobilation stage of modern scyphozoans.[3] This hypothesis was later criticized, as it could not explain why the successive cones observed in Conostichus fossils did not share the same center and size, and were separated by layers of clay.[8]

They are now believed to be trace fossils made by relatives of Actinaria, possibly close to the Halcampoididae.[1]

See also

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References

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Bibliography

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  • Branson, Carl C. (May 1961). "New Records of the Scyphomedusan Conostichus" (PDF). Oklahoma Geology Survey. 21 (5).
  • Patel, Satish J.; Shitole, Apurva D.; Joseph, Jaquilin K. (1 January 2018). "Plug shaped burrows Conichnus - Conostichus from the Late Cretaceous of Bagh Group, Gujarat, western India". Journal of the Geological Society of India. 91 (1): 41–46. doi:10.1007/s12594-018-0818-9. ISSN 0974-6889.
  • Pfefferkorn, Hermann W. (1971). "Note on Conostichus broadheadi Lesquereux (Trace Fossil: Pennsylvanian)". Journal of Paleontology. 45 (5): 888–892. ISSN 0022-3360.
  • Thomka, James R.; Bantel, Thomas E.; Tomin, Marissa J. (August 2016). Melchin, Mike (ed.). "Unusual preservation of the trace fossil Conostichus in middle Silurian carbonate facies of Indiana, USA". Canadian Journal of Earth Sciences. 53 (8): 802–807. doi:10.1139/cjes-2015-0198. ISSN 0008-4077.
  • Pemberton, S. George; Frey, Robert W.; Bromley, Richard G. (1988). "The ichnotaxonomy of Conostichus and other plug-shaped ichnofossils". Canadian Journal of Earth Sciences. 25 (6): 866–892. doi:10.1139/e88-085.
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