Field of Science

Rugosofusulinids?

We return once again to the fusulinoids, large, complex Foraminifera of the late Palaeozoic. For this post, I'm taking a look at the Rugosofusulinidae, a group known from the last part of the Carboniferous and the earliest part of the Permian. Or to put it more technically, from the Gzhelian and Asselian epochs; their numbers collapsed at the end of the Asselian (Leven 2003).

Axial section of Rugosofusulina prisca, from Loeblich & Tappan (1964).


In an earlier post, I referred to a historical divide that has existed between American and Russian classifications of fusulinoids, with the Russian system recognising a more divided arrangement of taxa. The rugosofusulinids are one example of this: whereas Rauzer-Chernousova et al. (1996) recognise them as a distinct family in the order Schwagerinida, Loeblich & Tappan (1964) treated the entire group of 'schwagerinidans' as a subfamily Schwagerininae in the Fusulinidae (I believe more recent western authors might be inclined to at least treat Schwagerinidae as a separate family but would probably still not separate the rugosofusulinids). Whatever level you wish to place them at, the most distinctive feature of rugosofusulinids as a group is a distinct rugosity of the outer wall of the chambers. This may be due to undulations in the entire chamber wall or rugosity of the outer surface only. When first described, it was thought that this unevenness reflected ridges on the outer surface, but it was later observed that the rugosity looked much the same whatever angle the foram was cut at (remember, fusulinoids are most commonly studied in thin sections rather than as entire separated fossils) so probably represented more discrete ornaments. Skinner & Wilde (1966) suggested that "the outer surface [of Rugosofusulina] is scored by numerous sharp furrows which are directed both axially and sagittally, resulting in a surface which resembles a miniature cobblestone pavement".

The question of whether you wish to recognise rugosofusulinids as a distinct family is definitely not helped by a question hanging over recognition of the name Rugosofusulina. The problem is not really with Rugosofusulina itself but with another genus, Pseudofusulina, recognised in the Rauzer-Chernousova et al. (2007) system as type of another family of Schwagerinida, Pseudofusulinidae, and its type species P. huecoensis. Classically, this genus and family has been supposed to have a smooth rather than rugose outer tectum. However, the type specimen of P. huecoensis was re-examined by Skinner & Wilde (1966) who found that it did indeed have 'Rugosofusulina'-type external rugosities. They consequently synonymised the two genera with Pseudofusulina standing as the older name. The response of Russian authors to this challenge to their system, it seems, was generally to ignore it. Pseudofusulina and Rugosofusulina may still potentially be distinguishable as genera by degree of rugosity (Zhang et al. 2013) but this seems a weak basis for a full family distinction. Even if 'Rugosofusulina' is okay, 'Rugosofusulinidae' may not be.

REFERENcES

Leven, E. J. 2003. The Permian stratigraphy and fusulinids of the Tethys. Rivista Italiana di Paleontologia e Stratigrafia 109 (2): 267–280.

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".

Skinner, J. W., & G. L. Wilde. 1966. Type species of Pseudofusulina Dunbar & Skinner. University of Kansas Paleontological Contributions 13: 1–7.

Zhang, Y.-C., Y. Wang, Y.-J. Zhang & D.-X. Yuan. 2013. Artinskian (Early Permian) fusuline fauna from the Rongma area in northern Tibet: palaeoclimatic and palaeobiogeographic implications. Alcheringa 37 (4): 529–546.

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