Kirengellidae

Kirengellidae Temporal range: Late Cambrian–Mid Ordovician PreЄ Є O S D C P T J K Pg N
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca or Brachiopoda?

The Kirengellids are a group of problematic Cambrian fossil shells of marine organisms. The shells bear a number of paired muscle scars on the inner surface of the valve.

These fossils have conventionally been regarded as monoplacophoran molluscs, and possibly ancestral to gastropods or cephalopods.^[1] They were presumed to be exogastric on the presumption that their larger muscle scars were anterior,^[2][3] but it may be dangerous to compare these scars with molluscan musculature.^[4] In any case, they coiled in the opposite direction to Romaniella.^[4] However, their calcitic shells, the position of the muscle scars, and putative association with secondary shell elements, make a brachiopod affinity possible, by analogy with the mobergellans: a group of phosphatic shells from the same time period, with a similar set of muscle scars.^[4] There is also strong similarity to the contemporary brachiopod group, the Craniopsids. In the case of this diagnosis, a simple lophophore apparatus is postulated to sit between the muscle scars and the edges of the shell.^[4]

Included taxa

After ^{[4]:fig. 5}

• Kirengella Rozov, 1968 (Upper Cambrian)
  • Kirengella ayaktchica - type species
  • Kirengella expansus]
  • Kirengella oregonensis
  • Kirengella pyramidalis
  • Kirengella washingtonense
• Hypseloconus (Upper Cambrian)
• Lenaella (Tremadoc / Lower Ordovician)
• Nyuella (Tremadoc / Lower Ordovician)
• Romaniella (Arenig / late Lower Ordovician)
• Moyerokania (Arenig / late Lower Ordovician)
• Angarella (Arenig / late Lower Ordovician)
• Pygmaeoconus (Llanvirn / early Middle Ordovician)

References

1. e.g. 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. Yochelson, E.L. (1978). "An alternative approach to the interpretation of the phylogeny of ancient mollusks". Malacologia 17 (2): 165–191.
3. Yochelson, E.L; Webers, G.F. (2006). A restudy of the Late Cambrian Molluscan fauna of Berkey (1898) from Taylors Falls, Minnesota (PDF). Minnesota Geological Survey Report of Investigations 64. p. 60.
4. Dzik, Jerzy (2010). "BRACHIOPOD IDENTITY OF THE ALLEGED MONOPLACOPHORAN ANCESTORS OF CEPHALOPODS" (PDF). Malacologia 52 (1): 97-113.