This colonial type of specimens is potentially interesting as a guide for both paleoenvironment and paleobiology! It’s also a specimen so nice they name it twice, though in this case on two separate occasions by two separate groups of researchers. Originally, specimens fitting this description were called Coniunctiophycus by Zhang et al. back in 1981, a reference to how all of the little cells were conjoined together within a translucent sheath or envelope. A different assemblage with fossils that fit a similar description were found by Golovenok and Belova in 1984, and they called it Eomicrocystis, or ‘dawn of Microcystis‘. In some ways, this description is both helpful and misleading. It helpfully relates to the morphology of a current organism, Microcystis, that many microbiologists have investigated as a colonial microbe that floats at the air-water interface in ponds and lagoons. But it’s also misleading; just because the organism resembles Microcystis does not make it a direct ancestor, nor does the similar morphology necessarily mean that Microcystis and its fossil counterpart lived under the same conditions. Ultimately, the arbiter of all things nomenclature provides guidance to resolve this name-calling dilemma: all things equal, Coniunctiophycus takes precedence in the case of this fossil because it was the first formal description of the type.

Let’s dig a little more closely into this fossil. Like Microcystis, the fossil has a thin rim of a sheath that extends around the entire colony. You can see this on the right of the specimen, where the walls of the little interior cells become less defined and more light passes through. And also like Microcystis, this colony has wrapped back around onto itself to form a reticulate shape. Finally, the size of the little cells is also comparable to Mictocystis. Overall, there is at least some morphological basis for comparing this particular fossil to the modern organism. Finally, the fine-grained mudstones of the Chamberlain Formation that contain this fossil have been interpreted by Zeig and Godlewski to be consistent with a very shallow body of water, perhaps an environment comparable to a restricted lagoon. Their interpretation was based only on the properties of the host rocks as a distinct source of information.

These are all features that are indeed consistent with the behavior and setting of Microcystis. Even though Coniunctiophycus/Eomicrocystis fossils have a spotty (i.e., discontinuous) record throughout Precambrian rocks, I have argued that the combination of inferred lithological and paleobiological characteristics are consistent with one another, further corroborating Zeig and Godlewski’s interpretation of the lower Chamberlain Formation as having been deposited in a very shallow body of water.

You can read more about this interpretation in my paper in GSA Special Volume 522- Paleoenvironmental Implications of an Expanded Microfossil Assemblage from the Chamberlain Formation, Belt Supergroup, Montana.




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