Chernyshinelloidea

Belongs within: Endothyroida.

Teardrops in the Palaeozoic
Published 29 July 2022

Among the early major radiations of foraminiferans in the Palaeozoic era was the assemblage known as the endothyroids, regarded by most researchers as the fore-runners of the iconic fusulinoids*. Like fusulinoids, endothyroids had test walls constructed of microgranular calcite, but generally had a simpler internal structure (Loeblich & Tappan 1964). The classification of endothyroids was reviewed in Rauzer-Chernousova et al. (1996) and among the various assemblages recognised therein was the superfamily Chernyshinelloidea.

*Though, as is all too common in summary depictions of palaeontology, describing them as ‘fore-runners’ is arguably somewhat misleading. It is true that fusulinoids probably derived from ancestors that would be classed as endothyroids, but endothyroid-type forams did not disappear as soon as the fusulinoids were on the scene. Indeed, they remained a diverse component of the fauna right to the end of the Palaeozoic, and may have even outlasted their more renowned scions.

Cross-sections and external views of Chernyshinella glomiformis, from Loeblich & Tappan (1987).

Chernyshinelloids formed part of the marine fauna from the late Devonian to the mid-Carboniferous, being diverse enough in this time that some species are significant biostratigraphic markers. The test began development as a flat or plectogyral spiral (a ‘plectogyral’ pattern is one in which the plane of the spiral changes between subsequent volutions). In at least some species, the mature test would then straighten out with ‘chambers’ in one or two rows. I’ve put ‘chambers’ in inverted commas because, though the test appears divided into sections, they are not always divided internally by properly developed septa. These pseudo-chambers are asymmetrically inflated towards one end so they appear teardrop-shaped in cross section.

These distinctively shaped chambers appear to have been the primary factor for Rauzer-Chernousova et al.(1996) in recognising Chernyshinelloidea. Their concept has not been universally accepted; Brenckle & Hance (2005), for instance, criticised their inclusion of taxa with different wall micro-structures in the superfamily. Once again, the question of chemistry vs morphology remains a critical one in foram classification.

References

Loeblich, A. R., Jr & H. Tappan. 1964. Treatise on Invertebrate Paleontology pt C. Protista 2. Sarcodina: chiefly “thecamoebians” and Foraminiferida vol. 1. The Geological Society of America, and The University of Kansas Press.

Rauzer-Chernousova, D. M., F. R. Bensh, M. V. Vdovenko, N. B. Gibshman, E. Y. Leven, O. A. Lipina, E. A. Reitlinger, M. N. Solovieva & I. O. Chedija. 1996. Spravočnik po Sistematike Foraminifer Paleozoâ (Èndotiroidy, Fuzulinoidy). Rossijskaâ Akademiâ Nauk, Geologičeskij Institut, Moskva “Nauka”.

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