Biometrical studies of miliolid foraminifera using high resolution micro-CT reconstructions

Abstract

Growth patterns of foraminifers are indicative of environmental and ecological conditions. The novel method of high-resolution X-ray micro-computed tomography (micro-CT) allows three-dimensional, high-resolution analysis of microscopic tests. It provides detailed information on external and internal morphological features and biometrical measurements and quantitative data on growth and test volume. Using stacked 2D-images we successfully created three-dimensional models of a range of different morphotypes of benthic foraminifers to quantitatively analyze chamber volume and solid shell material. Our biometric studies show that the mode of growth in individual taxa correlates with their chamber arrangement. We quantify the volume accretion of the chamber lumina during ontogeny and compile growth curves of miliolid morphotype foraminifers. The volume increase of all taxa shows a strong exponential chamber expansion and is probably related to rapidly changing environmental conditions.

Full text

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Biometrical studies of modern miliolid
foraminifera using high resolution
micro-CT reconstructions
Steinmann Institut für Geologie,
Mineralogie und Paläontologie
Universität Bonn, Germany
janine.koenen@uni-bonn.de
Growth patterns like volume increase in benthic foraminifera reflect conditions and
processes of specific oceanic environments. High-resolution
X-ray micro-computed tomography (micro-CT) allows 3D reconstructions by
stacking groups of 2D slice images of microscopic organisms.
We have applied micro-CT to a variety of miliolid foraminifera from different
localities. Volume rendering, biometric measurements and detailed external and
internal morphological features can be visualized and quantified with this
technique. We measure rates of volume increase and establish growth rates to
compare different environmental settings.
Scanning
Reconstruction
250 µm
2000 µm
Looking at the volumetric data, all analyzed smaller non symbiont-
bearing foraminifera with miliolid coiling exhibit a significant
exponential increase in volume. The total number of chambers ranges
between 11 –19. The volume increase in smaller miliolids with few
chambers is rapid when compared to other morphotypes with more
chambers. A characteristic feature of these taxa is that the last three
chambers make up the largest portion of the total chamber volume
(Quinqueloculina sp.: 81.2 % –Pseudotriloculina sp.: 90.9 % ).
The final chamber contains nearly
half of the total test volume
(Quinqueloculina sp.: 44.7 % -
Pseudotriloculina sp.: 55.8 %).
Spiroloculina sp. 1 Spiroloculina sp. 2
Quinqueloculina? sp. 1
Lachlanella corrugata
JANINE KÖNEN, MARTIN R. LANGER
Pseudotriloculina sp. 1
Measuring
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
0.040
0.045
0246810 12
Chamber lumina volume [mm3]
Chamber number
0.000
0.010
0.020
0.030
0.040
0.050
0.060
0.070
0246810 12 14
Chamber lumina volume [mm3]
Chamber number
500 µm
0.000
0.025
0.050
0.075
0.100
0.125
0 2 4 6 8 10 12 14
Chamber lumina volume [mm3]
Chamber number
500 µm
0.000
0.025
0.050
0.075
0.100
0.125
0.150
0.175
0.200
0 2 4 6 8 10 12
Chamber lumina volume [mm3]
Chamber number
500 µm
0.000
0.005
0.010
0.015
0.020
0 5 10 15 20
Chamber lumina volume [mm3]
Chamber number
500 µm
Lachlanella corrugata
The symbiont-bearing
miliolid Peneroplis planatus with
a planispiral morphology differs from
the other miliolid taxa. All peneroplid specimens
generally have more chambers (22 –26). None of
the chambers contains more than 20 %
(Peneroplis sp. 3) of the total test volume.
The volume increase shows a more linear growth
curve. This may potentially be related to the slower
growth rate in peneroplids than in individuals with
abi-, tri-or quinqueloculine chamber
arrangement.
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
0.040
0 5 10 15 20 25
Chamber lumina volume [mm3]
Chamber number
Peneroplis sp. 1
Peneroplis sp. 2
Peneroplis sp. 3
500 µm
Peneroplid foraminifers
CONCLUSION:
Micro-CT reconstructions is a novel method for high-resolution morphometric
analysis in microfossils. Different morphotypes in miliolid foraminifera reveal different
rates of volume increase: Exponential and linear rates of volume increase.
1.) Exponential growth appears in eutrophic environmental settings as an adaptation to
permanently changing conditions.
2.) Linear growth is observed in symbiont-bearing larger benthic foraminifera in stable,
oligotrophic environmental settings.
3.) Growth curves and volumetric data in miliolid foraminifera highlight their potential for
paleoenvironmental reconstructions
Growths rates
0
10
20
30
40
50
60
70
0 5 10 15 20 25 30
Relative chamber lumina volume [%]
Chamber number
Lachlanella corrugata
Quinqueloculina sp. 1
Spiroloculina sp. 1
Spiroloculina sp. 2
Pseudotriloculina sp. 1
Peneroplis sp. 1
Peneroplis sp. 2
Peneroplis sp. 3