From Wikipedia, the free encyclopedia
Jump to navigation Jump to search

Temporal range: Early Franconian
~501–488 Ma
Scientific classification edit
Kingdom: Animalia
Phylum: Mollusca
(unranked): Monoplacophora
Order: Archinacelloidea
Genus: Knightoconus
Yochelson et al., 1973[1]
Species: K. antarcticus
Binomial name
Knightoconus antarcticus
Yochelson et al., 1973[1]

Knightoconus antarcticus is a species of monoplacophoran from the Cambrian Minaret Formation of Antarctica.[1] It is thought to represent an ancestor to the cephalopods. It had a chambered conical shell, but lacked a siphuncle.[2] The absence of a siphuncle has been taken as evidence against cephalopod ancestry, as the factors that would influence the siphuncle to penetrate preexisting septal chambers remains unknown. The prevailing argument suggests that a strand of tissue remained attached to the previous septum as the mollusc moved forwards and deposited its next septum, stopping that new septum from closing completely and becoming mineralised itself.[3] Ten or more septa are found in mature individuals, occupying around a third of the shell - septa form very early and have been found in specimens as small as 2 mm in length.[4] Unlike monoplacophoran fossils, there is no evidence of muscle scarring in Knightoconus fossils.[4] Scars from the closely related Hypseloconus have been used to determine its orientation.[5] Knightoconus started life with an exogastric shell, that becomes endogastric as the organism grew.[6]

Alternate taxonomy is: Tergomya, Kiringellida, Hypseloconidae.[7]

See also[edit]


  1. ^ a b c d Yochelson, E. L.; Flower, R. H.; Webers, G. F. (1973), "The bearing of the new Late Cambrian monoplacophoran genus Knightoconus upon the origin of the Cephalopoda", Lethaia, 6 (3): 275–309, doi:10.1111/j.1502-3931.1973.tb01199.x
  2. ^ "Origin and Evolution". Cephalopods - ecology and fisheries. 2005. p. 36. doi:10.1002/9780470995310.ch3.
  3. ^ Holland, C. H. (1987). "The nautiloid cephalopods: a strange success: President's anniversary address 1986". Journal of the Geological Society. 144: 1–15. doi:10.1144/gsjgs.144.1.0001.
  4. ^ a b Webers, G. F.; Yochelson, E. L. (1989). "Late Cambrian molluscan faunas and the origin of the Cephalopoda". In Crame, J. A. Origins and Evolution of the Antarctic Biota. 47. Geological Society, London: Special Publications. p. 29. doi:10.1144/GSL.SP.1989.047.01.04.
  5. ^ 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. The Early Evolution of Metazoa and the Significance of Problematic Taxa. Cambridge University Press. pp. 157–177. ISBN 978-0-521-40242-2.
  6. ^ Webers, G. F.; Pojeta Jr, J.; Yochelson, E. L. (1992). "Cambrian Mollusca from the Minaret Formation, Ellsworth Mountains, West Antarctica". Geology and Paleontology of the Ellsworth Mountains, West Antarctica. pp. 181–248. ISBN 978-0-8137-1170-6.
  7. ^ The Paleobiology Database. Accessed 6 August 2009.