Conostichus

Conostichus Temporal range: Ordovician–Cretaceous [1] PreꞒ Ꞓ O S D C P T J K Pg N
Trace fossil classification
Ichnogenus:	† Conostichus Lesquereux, 1876
Type ichnospecies
Conostichus omatus Lesquereux, 1876
Ichnospecies [2]
Conostichus omatusLesquereux, 1876 Conostichus broadheadiLesquereux, 1880 Conostichus typicus(King, 1955) Conostichus wycherlyi(King, 1955) Conostichus stoutiBranson, 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

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

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

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 Actiniaria, possibly close to the Halcampoididae. ^[1]

See also

• Conichnus , a similar trace fossil

References

1. Patel, Shitole & Joseph 2018, p. 45.
2. Pemberton, Frey & Bromley 1988, p. 872.
3. Branson 1961, p. 134.
4. Patel, Shitole & Joseph 2018, p. 42.
5. Patel, Shitole & Joseph 2018, p. 42–43.
6. Thomka, Bantel & Tomin 2016, p. 802.
7. Pfefferkorn 1971, p. 889.
8. Pfefferkorn 1971, p. 889–890.

Bibliography

• 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.

External links

• Chuck D. Howell's Ichnogenera Photos