Insights into the meridional ornamentation of the planktonic foraminiferal genus Rugoglobigerina (Late Cretaceous) and implications for taxonomy

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doi: 10.1016/j.cretres.2013.11.001
Author(s): Falzoni, Francesca; Petrizzo, Maria Rose; Huber, Brian T.; MacLeod, Kenneth G.
Author Affiliation(s): Primary:
Universita degli Studi di Milano, Dipartimento di Scienze della Terra A. Desio, Milan, Italy
Smithsonian Institution, United States
University of Missouri-Columbia, United States
Volume Title: Cretaceous Research
Source: Cretaceous Research, Vol.47, p.87-104. Publisher: Elsevier, United Kingdom. ISSN: 0195-6671
Note: In English. 90 refs.; illus., incl. charts, strat. cols., 3 tables, sketch map
Summary: Wall texture and ornamentation in Cretaceous planktonic foraminifera, as with modern and Cenozoic taxa, are generally considered to be genetically controlled and thus taxonomically significant. For instance, the iterative development of meridional ornamentation is a diagnostic criterion used to discriminate between the Santonian-early Campanian genus Costellagerina, and the Campanian-Maastrichtian genus Rugoglobigerina. An alternative ecophenotypic explanation for differences based on observed poleward decreases in meridional ornamentation has not been widely accepted largely due to absence of evidence. Our study of Rugoglobigerina specimens recovered at three mid-low latitude localities (Exmouth Plateau, eastern Indian Ocean; Shatsky Rise, northwestern Pacific Ocean; Eratosthenes Seamount, eastern Mediterranean) confirms that meridional ornamentation is a primary character of their tests, but development of this feature is highly variable throughout the geographic and stratigraphic distribution of the genus. Within assemblages of Rugoglobigerina, there is a continuous morphological range from specimens with well-developed costellae arranged in a meridional pattern to specimens with relatively short ridges that are randomly oriented to meridionally aligned. Stable isotope (δ13C and δ18O) analyses indicate that specimens showing a more strongly developed meridional ornamentation consistently yield higher δ13C values than co-occurring less ornamented morphotypes at each examined locality, whereas patterns in the δ18O values are site-dependent. Interpretation of these patterns is not simple and might be related to different controlling factors acting together or separately. Potential explanations for the differential development of the ornamentation include: (1) adaptation to different ecological niches within a population, (2) species-level genetic differences, (3) variation in metabolic rate or activity within individuals, and (4) changes in the seawater carbonate ion saturation through space and time, including seasonality. In addition, we highlight the difficulty of discriminating between Rugoglobigerina and Costellagerina when they co-occur in lower Campanian deposits and among Rugoglobigerina, Costellagerina and Archaeoglobigerina at high latitude localities where species placed in all three genera show very similar shell morphology and ornamentation. Finally, our study challenges the general assumption that some external features of the wall are sufficiently reliable for taxonomic discrimination of Cretaceous planktonic foraminifera. This latter conclusion suggests that environmental conditions such as water temperature, water column stratification, nutrient concentration and carbonate ion saturation may have played a key role in triggering the external expression of genetically controlled wall ornamentation in the planktonic foraminifera. Abstract Copyright (2014) Elsevier, B.V.
Year of Publication: 2014
Research Program: ODP Ocean Drilling Program
Key Words: 10 Paleontology, Invertebrate; 12 Stratigraphy, Historical Geology and Paleoecology; Archaeoglobigerina; Biogeography; Biostratigraphy; C-13/C-12; Campanian; Carbon; Cathodoluminescence; Classification; Costellagerina; Cretaceous; Depositional environment; East Mediterranean; Electron microscopy data; Eratosthenes Seamount; Exmouth Plateau; Foraminifera; Indian Ocean; Invertebrata; Isotope ratios; Isotopes; Leg 122; Leg 160; Leg 198; Maestrichtian; Mediterranean Sea; Meridional ornamentation; Mesozoic; Microfossils; North Pacific; Northwest Pacific; O-18/O-16; ODP Site 1210; ODP Site 762; ODP Site 967; Ocean Drilling Program; Ornamentation; Oxygen; Pacific Ocean; Paleo-oceanography; Paleoenvironment; Paleogeography; Paleolatitude; Paleomagnetism; Photosymbiosis; Planktonic taxa; Protista; Rugoglobigerina; SEM data; Shatsky Rise; Solution; Stable isotopes; Taxonomy; Upper Cretaceous; West Pacific
Coordinates: S195315 S195314 E1121515 E1121514
N340411 N340411 E0324331 E0324331
N321300 N321300 E1581600 E1581600
Record ID: 2015056241
Copyright Information: GeoRef, Copyright 2017 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands