Stenothecoida is a taxon of bivalved fossils from the Early to middle
Cambrian
The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ag ...
period. They look a bit like brachiopods or bivalve molluscs.
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
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*Morphology (archaeology), study of the shapes or forms of artifacts
*Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies, ...
of the
shell
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Architecture and design
* Shell (structure), a thin structure
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** Thin-shell structure
Science Biology
* Seashell, a hard o ...
does not resemble the shell of any other class of molluscs; they also look a little like brachiopods
[ 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 ][ It's more likely that the valves each have a single plane of symmetry (as in brachiopods), suggesting a brachiopod affiliation.][
As with many other Cambrian taxa, it has been suggested that they arise through reduction of a '']Halkieria
The halkieriids are a group of fossil organisms from the Lower to Middle Cambrian. Their eponymous genus is ''Halkieria'' , which has been found on almost every continent in Lower to Mid Cambrian deposits, forming a large component of the smal ...
''-like ancestor.[
]
Mineralogy
Thought to be low-Mg calcite.[Kouchinsky, A. V. et al. Chronology of early Cambrian biomineralization. Geol. Mag. 149, 221–251 (2012).]
Occurrence
The earliest occurrence dates to 525 Ma.Canada
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, China, Greenland
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, Kazakhstan
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, Kyrgyzstan
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, and the USA
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.
References
Start of article at Springer Reference
Paleobiology Database info on this class
Abstract of a Yochelson 2007 article on the proposed class
Prehistoric mollusc taxonomy
Mollusc classes
Prehistoric protostome classes
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