Review of 'GLOBAL EVOLUTION AND PALEOGEOGRAPHIC DISTRIBUTION OF MID - CRETACEOUS ORBITOLINIDS'

Each time a micropaleontologist analyzes a sample, be it a thin section or a washed residue, he or she formulates a scientific hypothesis. It starts from observation, previous knowledge and models, and the classification of microfossils, in order to produce different kinds of hypotheses: systematical, biostratigraphical, paleoenvironmental, paleoecological, paleo-oceanographical, paleogeographical, etc. Scientific hypotheses are possible explanations for something that has been observed and are valid for a certain set of conditions; thus, they vary in broadness. They may be tested, expanded, falsified, or corroborated by other evidence; they may also entail corollaries and predictions.

Following this dynamic approach, in the present paper M.K. BouDagher-Fadel and G.D. Price have erected at least three broader hypotheses basing on an important group of larger foraminifera, the Cretaceous orbitolinids. I list them here without any particular order.

The first is a paleobiogeographical hypothesis. In previous papers (e.g., BouDagher-Fadel & Price 2014, 2017), along with other authors they argued that in the Paleocene several larger foraminiferal lineages migrated following a W-E route, from the Caribbean area to the Western Neo-Tethys and beyond, reaching SE Asia and the Western Pacific (I will refer to this as the W-E hypothesis). Here, basing in part on new data on orbitolinids from Tibet and SE Asia, they hypothesize that in the late late Barremian-earliest Aptian a first migration from the Tethyan area towards the Americas took place. I will refer to this as the E-W hypothesis. The E-W hypothesis hinges in part on independent planktic foraminiferal data, useful for dating the orbitolinid species. However, it also hinges in part on the interpretation of the stratigraphic ranges of orbitolinid taxa, which in the past has been a debated issue, leading to different biostratigraphic orbitolinid zonal schemes.

As stated above, scientific hypotheses can be tested. Namely, the W-E hypothesis has been long demonstrated for the Eocene-Miocene (see e.g. Benedetti et al. 2018). For the Paleocene, although likely, it is still lacking more precise stratigraphic data (Ozcan et al., 2019). This poses the question which additional taxa among larger benthic foraminifera could be used for testing the mid-Cretaceous E-W hypothesis, and opens the field for analytical testing.

The second broad scientific hypothesis posed by the manuscript is that orbitolinids are meso- to oligotrophic taxa. I shall refer to this as the trophic hypothesis. As far as I know, this hypothesis goes back to Vilas et al. (1995) and Pittet et al. (2001), who suggested a relationship between terrigenous influx, orbitolinid abundance and their functional morphology; terrigenous run-off leads to increased nutrient supply and thus meso- to eutrophic conditions. This hypothesis posits orbitolinids as an exception to the prevailing paradigm that extant and fossil larger foraminifera in general are linked to oligotrophic conditions. It is clearly interesting considering the major Cretaceous OAEs and their expression in carbonate settings, such as the “Orbitolina levels” in Southern Italy (Cherchi et al., 1978). This hypothesis is not discussed in great detail in the manuscript; one wonders whether this is intentionally so and this issue may become the topic of a future work. I find this hypothesis particularly interesting. Fig. 12 of the manuscript is linked to this hypothesis, and shows an oligotrophic pelagic domain and an oligotrophic-mesotrophic neritic domain; it is not easy to understand and could benefit from redrafting.

The third broad hypothesis posed in the manuscript is a classification of the Lower to mid Cretaceous orbitolinids into groups. This is a complex issue, that requires a careful analysis of characters, lineages, etc. Also hypothesis may fuel further analysis and is likely to be debated by orbitolinid specialists. A fundamental question that arises from this classification is whether the recognized groups are natural, i.e., monophyletic, or at least paraphyletic, since the post-Cenomanian orbitolinids are not discussed in this paper.

Other issues:

(1) Orthogenesis. -- The concept of ‘orthogenesis’ (p. 16 of the pdf) should be better avoided, since it is fraught with controversy. Here, only homoplasy (non-evolutionary morphological convergence) is implied.

(2) Nomenclature. -- Incidentally, the manuscript shows one of the weaknesses of the ICZN (1999). The manuscript as well as several previous authors, e.g., Clavel et al. (2010) and Schroeder et al. (2010), wrongly used Palorbitolinoides orbiculata Zhang, 1986, as if the genus Palorbitolinoides were of feminine gender. The issue is the gender of a genus ending in -oides, in this case Palorbitolinoides Cherchi & Schroeder, 1980. Its type species is Palorbitolinoides hedini Cherchi & Schroeder, 1980; according to its authors, the gender was considered as monospecific when it was established. The specific name of the type species and only species referred by its authors to their new genus is in the genitive, and does not provide any indication whether this genus was originally construed to be masculine or feminine. According to the ICZN (1999: Art. 30.1.4.4), a compound genus-group name ending in the suffix -ites, -oides, -ides, -odes, or -istes is to be treated as masculine unless its author, when establishing the name, stated that it had another gender or treated it as such by combining it with an adjectival species-group name in another gender form. The examples cited in the ICZN (1999) are: "Hoplitoides and Harpides are masculine, but Aleptinoides (meaning "like Aleptina") is treated as feminine because that was the gender adopted by its original authors." Since Cherchi & Schroeder (1980) did not treat Palorbitolinoides as feminine, it is to be treated as masculine. Thus Palorbitolinoides orbiculata is incorrect according to the ICZN (1999); the correct form is P. orbiculatus.

By this article the ICZN (1999), suppressing a former scientific Latin practice, begets needless confusion in respect to the previous ICZN (1985: Art. 30b), that stated that all compound genus-group names ending in -ides, -istes, -ites, -odes, or -oides (e.g. among foraminiferans genera such as Cibicides, Nummulites, Orbitoides) are substantivated adjectives and are masculine.

Conclusions

As many a thin-section micropaleontologist has experienced, determining orbitolinids in thin section is often frustrating, because of the lack of oriented sections passing through the embryonal apparatus. Clavel et al. (2014) have shown how complex and time-consuming obtaining thin sections is for studying orbitolinid assemblages. So, any study on orbitolinids is complex. This manuscript proposes novel data and hypotheses for orbitolinid systematics, paleobiogeography and paleoecology. I definitely endorse its publication.

Note

I have annotated on the PDF of the manuscript a number of minor suggestions. Not being familiar with the ScienceOpen platform, I do not know whether I can upload the annotated PDF. In case, I'll e-mail it to the authors.

References

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BouDagher-Fadel M.K. & Price G.D. 2014. The phylogenetic and palaeogeographic evolution of the nummulitoid larger benthic foraminifera. Micropaleontology, 60, 483-508.

BouDagher-Fadel M.K. & Price G.D. 2017. The paleogeographic evolution of the orthophragminids of the Paleogene. Journal of Foraminiferal Research, 47, 337-357.

Cherchi A. & Schroeder R. 1980. Palorbitolinoides hedini n. gen. n. sp., grand Foraminifère du Crétacé inférieur du Tibet méridional. Comptes rendus hebdomadaires des séances de l'Académie des sciences, (Série D, Sciences naturelles), 291, 385-389.

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