Stenothecoida

Stenothecoida is a taxon of bivalved fossils from the Early to middle Cambrian period. They look a bit like brachiopods or bivalve molluscs.

Not to be confused with Stenothecidae.

Stenothecoida
Temporal range: Early–mid-Cambrian, 525–500 Ma[1][2]
Scientific classification
Kingdom: Animalia
Phylum: Mollusca (?)
Class: †Stenothecoida
Yochelson, 1968[3]
Genera
  • Stenothecoides Resser
  • Bagenovia Radugin
  • Cambridium Horny
  • Bagenoviella Aksarina
  • Sulcocarina Aksarina
  • Kaschkadakia Aksarina
  • Makarakia Aksarin
(given in JSTOR 1739764)

Affinity

Their affinity is uncertain. They were considered by E. L. Yochelson 1968 to belong to Mollusca, whereas Runnegar and Pojeta (1974) suggested that they might be 'bivalved monoplacophorans'. This said, the morphology of the shell does not resemble the shell of any other class of molluscs; they also look a little like brachiopods[1] It's not clear whether their two valves are each other's mirror images, as in bivalve molluscs, though they aren't identical to one another [?].[1] It's more likely that the valves each have a single plane of symmetry (as in brachiopods), suggesting a brachiopod affiliation.[1]

As with many other Cambrian taxa,[4][5] it has been suggested that they arise through reduction of a Halkieria-like ancestor.[1]

Mineralogy

Thought to be low-Mg calcite.[6]

Occurrence

The earliest occurrence dates to 525 Ma.[2]

These fossil shells have been found in Canada, China, Greenland, Kazakhstan, Kyrgyzstan, and the USA.

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References
  1. Kouchinsky, Artem V. (2000). "15. Mollusks, Hyoliths, Stenothecoids, and Coeloscleritophorans". Molluscs, hyoliths, stenothecoids, and coeloscleritiphorans. doi:10.7312/zhur10612-015. ISBN 9780231505161.
  2. Kouchinsky, A. V., Bengtson, S., Runnegar, B.N., Skovsted, C.B., Steiner, M., and Vendrasco, M.J. (2012). Chronology of early Cambrian biomineralization. Geol. Mag. 149, 221–251.
  3. Yochelson, Ellis L. (1969). "Stenothecoida, A Proposed New Class of Cambrian Mollusca". Lethaia. 2: 49–62. doi:10.1111/j.1502-3931.1969.tb01250.x.
  4. 1. Cohen, B.L., Holmer, L.E., and Lüter, C. (2003). The brachiopod fold: a neglected body plan hypothesis. Palaeontology 46, 59–65.
  5. Skovsted, C.B., Betts, M.J., Topper, T.P., and Brock, G.A. (2015). The early Cambrian tommotiid genus Dailyatia from South Australia. Mem. Assoc. Australas. Palaeontol. 48, 1–117.
  6. Kouchinsky, A. V. et al. Chronology of early Cambrian biomineralization. Geol. Mag. 149, 221–251 (2012).


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