Knightoconus Temporal range: Dresbachian ~ | |
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Artistic reconstruction of Knightoconus antarcticus | |
Scientific classification ![]() | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Mollusca |
Class: | Monoplacophora |
Order: | † Archinacelloidea |
Genus: | † Knightoconus Yochelson et al., 1973 [2] |
Species: | †K. antarcticus |
Binomial name | |
†Knightoconus antarcticus Yochelson et al., 1973 [2] | |
Knightoconus antarcticus is an extinct species of fossil monoplacophoran from the Cambrian Minaret Formation of Antarctica. [2] It is thought to represent an ancestor to the cephalopods. It had a chambered conical shell, but lacked a siphuncle. [3]
The absence of a siphuncle in K. antarcticus has been taken as evidence against its being an ancestor of cephalopods, as factors that would allow a siphuncle to penetrate preexisting septal chambers remain 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. [4]
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. [5] Unlike monoplacophoran fossils, there is no evidence of muscle scarring in Knightoconus fossils. [5] Scars from the closely related Hypseloconus have been used to determine its orientation. [6] Knightoconus started life with an exogastric shell that became endogastric as the organism grew. [7]
An alternate taxonomy is: Tergomya: Kiringellida: Hypseloconidae. [1]