Test flattening in the larger foraminifer Heterostegina depressa: predicting bathymetry from axial sections

Previous attempts to quantify the test-flattening trend in Heterostegina depressa with water depth have been rather unsuccessful. Due to its broad depth distribution, H. depressa is a perfect model species to calibrate test flattening as a bathymetric signal for fossil assemblages. This might enable...

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Bibliographic Details
Published in:Paleobiology 2018-02, Vol.44 (1), p.76-88
Main Authors: Eder, Wolfgang, Hohenegger, Johann, Briguglio, Antonino
Format: Article
Language:English
Subjects:
Allochthonous deposits
Asia
Bathymetry
biometry
computed tomography data
Diatoms
Far East
Flattening
Foraminifera
Fossil assemblages
Fossils
Heterostegina
Heterostegina depressa
Irradiation
Japan
Light
Light intensity
Light levels
Light penetration
living taxa
Luminous intensity
microfossils
Model testing
modern analogs
Morphology
North Pacific
Northwest Pacific
Nummulitidae
Okinawa
Ontogeny
Pacific Ocean
paleobathymetry
Paleoenvironments
Radiation
regression analysis
Rotaliacea
Rotaliina
Ryukyu Islands
Sesoko Island
statistical analysis
Stratigraphy
tests
three-dimensional models
Tomography
Water depth
West Pacific
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Summary:Previous attempts to quantify the test-flattening trend in Heterostegina depressa with water depth have been rather unsuccessful. Due to its broad depth distribution, H. depressa is a perfect model species to calibrate test flattening as a bathymetric signal for fossil assemblages. This might enable us to better reconstruct paleoenvironments of fossil communities of larger foraminifera or even provide clues to the degree of transport in allochthonous deposits. In this study, we used growth-independent functions to describe the change of test thickness throughout ontogeny. Four growth-invariant characters, deriving from these functions, clearly quantify a transition of individuals with thicker to thinner central parts along the water-depth gradient. This transition is probably controlled by light intensity, because the photosymbionts of H. depressa (diatoms) are most effective at low irradiation levels. Thus, specimens at shallower depths grow thicker to reduce light penetration, whereas specimens living deeper than the light optimum increase their surface by flattening to obtain better exposure to light.
ISSN:0094-8373
1938-5331
DOI:10.1017/pab.2017.24