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    A novel insight on systematics, paleobiogeography and paleoecology of orbitolinids
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    Members of the Larger Benthic Foraminiferal (LBF) family Orbitolinidae occured from the Cretaceous to the Paleogene, however, they were most diverse during the mid-Cretaceous, and dominated the agglutinated LBF assemblages described from limestones of that period. Various orbitolinid species have been used to zone and date lithologies formed in the shallow, warm waters of the Aptian to the Early Cenomanian, and many, sometimes inaccurate, generic and sub-generic nomenclatures have been proposed to differentiate the often subtle morphological changes that orbitolinids exhibit over time. Until now, it has not been possible to develop an effective global overview of their evolution and environmental development because descriptions of specimens from Asia have been relatively rare. Following our recent study of over 1800 orbitolinid-rich thin sections of material from 13 outcrops of the Langshan Limestone, from the Southern Tibetan Plateau, and from the Barito Basin, South Kalimantan, Indonesia, it has been possible to compare the stratigraphic ranges of these orbitolinids with previously described Tethyan and American forms, based on the use of a planktonic zonal (PZ) scheme, itself tied to the most recent chronostratigraphic scale. This has allowed the reconstruction of the phylogenetic and paleogeographic evolution of the orbitolinids from their Valanginian origin in the Tethys. Although Tethys remained the paleogeographic focus for the orbitolinids, it is inferred here for the first time that a bi-directional paleogeographic migration of some orbitolinid genera occurred from Tethys to the Americas and also to the Western Pacific region. Our observations and dating confirm that global marine regressions in the Aptian were coincident with, and may well have facilitated, these orbitolinid transoceanic migrations. However, migration stopped after rising sea-level in the Early Albian appears to have again isolated these provinces from each other. Tectonic forces associated with the subduction of the Farallon Plate and further sea-level raises led to the opening of the Western Interior Seaway in the North America, which correlates with, and may have been the cause of, the Middle Albian (top of PZ Albian 2) extinction of the American orbitolinids. The extinction of the orbitolinids revealed that the Western Pacific province was split into two sub-provinces, with extinction occurring at the end of the Early Albian (top of PZ Albian 1) in the Northwest Pacific sub-province, and at the end of the Albian (top of PZ Albian 4) in the sub-province that is today South East Asia (on the margins and west of the Wallace Line). The final virtual extinction of the orbitolinids occurred at the end of the Cenomanian in the Tethyan province, which coincides with, and may have been caused by, global anoxic oceanic events that correlate with a near-peak Mesozoic eustatic sea-level high-stand that led to the overall global collapse of the paleotropical reef ecosystem at that time.

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      This work has been published open access under Creative Commons Attribution License CC BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Conditions, terms of use and publishing policy can be found at www.scienceopen.com.

      Earth & Environmental sciences
      Ecology,Foraminifera,palaeogeographic distribution,,Global anoxic events,biostratigraphy,,Sea-level changes,The Environment,Climate,phylogeny,,Extinctions,mid-Cretaceous,,Orbitolinids,

      Review text

      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., 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.



      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.



      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.



      Benedetti A., Less G., Parente M., Pignatti J., Cahuzac B., Torres-Silva A.I. & Buhl D. (2018). Heterostegina matteuccii sp. nov. (Foraminiferida: Nummulitidae) from the lower Oligocene of Sicily and Aquitaine: a possible transatlantic immigrant. Journal of Systematic Palaeontology, 16 (2), 87-110.

      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.

      Cherchi A., De Castro P. & Schroeder R. 1978. Sull’età dei livelli a Orbitolinidi della Campania e delle Murge Baresi (Italia meridionale). Bollettino della Società dei Naturalisti in Napoli, 87, 363-385.

      Clavel B., Charollais J., Busnardo R., Granier B., Conrad M., Desjacques P. & Metzger J. 2014. La plate-forme carbonatée urgonienne (Hauterivien supérieur-Aptien inférieur) dans le Sud-Est de la France et en Suisse: synthèse. Archives des sciences, 67, 1-100.

      Clavel B., Decrouez D., Charollais J. & Busnardo R. 2010. «Paracoskinolina» praereicheli n. sp., un orbitolinidé (Foraminifère) nouveau de l’Hauterivien supérieur et du Barrémien inférieur (Crétacé) à faciès urgonien (SE France, Jura franco-suisse, Préalpes suisses). Archives des Sciences, 62[2009], 1-10.

      Özcan E., Mitchell S.F., Less G., Robinson E., Bryan J.R., Pignatti J. & Yücel A.O. 2019. A revised suprageneric classification of American orthophragminids with emphasis on late Paleocene representatives from Jamaica and Alabama. Journal of Systematic Palaeontology Published online: 24 Jan 2019. DOI: 10.1080/14772019.2018.1539778

      Pittet B., Van Buchem F.S.P., Hillgärtner H., Razin P., Grötsch J. & Droste H. 2002. Ecological succession, palaeoenvironmental change, and depositional sequences of Barremian-Aptian shallow-water carbonates in northern Oman. Sedimentology, 49 (3), 555-581.

      Schroeder R., Van Buchem F.S.P., Cherchi A., Baghbani D., Vincent B., Immenhauser A. & Granier B. 2010. Revised orbitolinid biostratigraphic zonation for the Barremian – Aptian of the eastern Arabian Plate and implications for regional stratigraphic correlations. GeoArabia Special Publication, 4(1), 49-96.

      Vilas L., Masse J.P. & Arias, C. 1995. Orbitolina episodes in carbonate platform evolution: the early Aptian model from SE Spain. Palaeogeography, Palaeoclimatology, Palaeoecology, 119, 35-45.


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