Antonino Briguglio

Growth oscillation in larger foraminifera.

Abstract This work shows the potential for applying three-dimensional biometry to studying cell growth in larger benthic foraminifera. The volume of each test chamber was measured from the three-dimensional model obtained by means of computed tomography. Analyses of cell growth based on the sequence of chamber volumes revealed constant and significant oscillations for all investigated specimens, characterized by periods of approximately 15, 30, 90, and 360 days. Possible explanations for these periods are connected to tides, lunar cycles, and seasonality. The potential to record environmental oscillations or fluctuations during the lifetime of larger foraminifera is pivotal for reconstructing short-term paleoenvironmental variations or for gaining insight into the influence of tides or tidal current on the shallow-water benthic fauna in both recent and fossil environments.

Fossilized bioelectric wire – the trace fossil Trichichnus

The trace fossil Trichichnus is proposed as an indicator of fossil bioelectric bacterial activity at the oxic–anoxic interface zone of marine sediments. This fulfils the idea that such processes, commonly found in the modern realm, should be also present in the geological past. Trichichnus is an exceptional trace fossil due to its very thin diameter (mostly less than 1 mm) and common pyritic filling. It is ubiquitous in some fine-grained sediments, where it has been interpreted as a burrow formed deeper than any other trace fossils, below the redox boundary. Trichichnus, formerly referred to as deeply burrowed invertebrates, has been found as remnant of a fossilized intrasediment bacterial mat that is pyritized. As visualized in 3-D by means of X-ray computed microtomography scanner, Trichichnus forms dense filamentous fabric, which reflects that it is produced by modern large, mat-forming, sulfide-oxidizing bacteria, belonging mostly to Thioploca-related taxa, which are able to house a complex bacterial consortium. Several stages of Trichichnus formation, including filamentous, bacterial mat and its pyritization, are proposed to explain an electron exchange between oxic and suboxic/anoxic layers in the sediment. Therefore, Trichichnus can be considered a fossilized “electric wire”.

New results on the hydrodynamic behaviour of fossil Nummulites tests from two nummulite banks from the Bartonian and Priabonian of northern Italy.

Settling velocities of 58 well-preserved tests of fossil Nummulites were experimentally determined using a settling tube. The tests were collected from the nummulite banks of Pederiva di Grancona (A forms of N. lyelli and N. striatus, Middle Eocene) and San Germano dei Berici (A and B forms of N. fabianii, Late Eocene), both in the Berici Mts. (Veneto, northern Italy). The data were compared with estimated settling velocities that the same specimens might have had in life conditions. This was done by reconstructing their densities simulating water-filled condition and, to simulate post-diagenetic effects, under calcite-filled condition. These simulations show that A and B forms, even if they greatly diverge in shape, volume and size, still possess comparable settling velocities, and that each nummulite bank is characterized by specific hydrodynamic parameters. The use of settling velocity as a parameter to quantify the hydrodynamic behaviour of particles in seawater enables estimation of palaeoenvironmental conditions such as depth, substrate and the energy scenario. Such information is useful in obtaining further insights into the genesis of nummulite banks, the autochthony or allochthony of which is still being debated. Our results point to an autochthonous interpretation.

Methods for Estimating Individual Growth of Foraminifera Based on Chamber Volumes

Based on chamber volumes, different methods for evaluating growth of individual foraminifera are shown using the generalized logistic growth function or the Gompertz function. Residuals to the theoretical functions were calculated to differentiate between instantaneous or oscillatory deviations. The chamber-building rate must be calculated allowing inferences of time-dependent influences by environmental factors.

TOWARDS A CALIBRATED LARGER FORAMINIFERA BIOSTRATIGRAPHIC ZONATION: CELEBRATING 18 YEARS OF THE APPLICATION OF SHALLOW BENTHIC ZONES

Abstract: The Shallow Benthic Zonation is one of the most important achievements of biostratigraphy in the last twenty years. Here we summarize the state of the art in the field of Larger Benthic Foraminifera (LBF) and sketch the main lines of research that are improving the precision and usefulness of this scale. The goal of updating the zonation requires a wealth of data coming not only from biostratigraphic investigations but also from paleoenvironmental analyses, biological knowledge, rigorous taxonomic determination, and understanding of paleobiogeography. The papers collected for this special issue are contributions to this broad research program.

Changing Investigation Perspectives: Methods and Applications of Computed Tomography on Larger Benthic Foraminifera

The use of computed tomography to investigate the structure of Larger Benthic Foraminifera is presented. Several steps are required to obtain sharp and usable images with MicroCT machines. These steps are explained in detail along with select insights on larger foraminifera. This technique, which delivers three dimensional models, gives the operator the possibility to measure nearly every possible morphometric parameter on either a two- and three-dimensional basis.

DEPTH-RELATED MORPHOCLINES OF MEGALOSPHERIC TESTS OF HETEROSTEGINA DEPRESSA D'ORBIGNY: BIOSTRATIGRAPHIC AND PALEOBIOLOGICAL IMPLICATIONS

Abstract: Morphometric characters of equatorial sections of larger benthic foraminifera have been widely applied to define species for both biostratigraphic and evolutionary studies. In order to test the hypothesis that some of the observed morphological differences may reflect environmental conditions rather than evolutionary changes, we applied morphometric analysis to equatorial sections of megalospheric Heterostegina depressa tests from the reef slope of Sesoko-Jima, NW-Okinawa. Only living specimens were analyzed, thereby eliminating any postmortem alteration of the distribution of H. depressa along the water depth gradient. The analyses clearly differentiated two morphogroups corresponding to two megalospheric generations: gamonts with significantly larger proloculi and schizonts with smaller proloculi. Due to their asexual reproduction strategy, schizonts dominate in high-energy shallower environments. After a transition zone between 35 to 55 m, where both generations are present, schizonts are replaced by gamonts deeper on the slope. Both generations retain the characters of their initial tests regardless of depth. Where both megalospheric generations co-occur, the change in proportion of generations with depth results in an environmental morphological trend that matches apparent fossil evolutionary trends. These results are important for understanding relationships among fossil Heterostegina species, where continuous changes in morphological characters of the initial test part are interpreted as evolutionary trends.

BIOSTRATIGRAPHY AND EVOLUTIONARY TENDENCIES OF EOCENE HETEROSTEGINES IN WESTERN AND CENTRAL CUBA BASED ON MORPHOMETRIC ANALYSES

Abstract: Megalospheric specimens of Heterostegina from four localities in Western and Central Cuba were morphometrically investigated using test characters, which are described by 15 growth-independent and growth-invariant attributes that enable complete test reconstruction in equatorial sections. The species Heterostegina cubana, H. ocalana, and Heterostegina sp. indet. were classified by nonmetric multidimensional scaling and cluster analysis. Discriminant analysis yielded significant separators between species such as the perimeter ratio of the first chamberlets, the decrease in chamberlet length from the previous spiral to the marginal side, the chamber height at the spiral side of the previous whorl, and the proloculus size. Based on a further discriminant analysis, specimens of H. ocalana from different localities, including specimens from Panama, are strongly separated by the number of operculinid chambers, the extension grade of the marginal spiral and the backward bend of chambers, documenting paleogeographic differences and apparent evolutionary trends such as the reduction of the number of operculinid chambers. In Cuba, Heterostegina is represented by H. cubana and Heterostegina sp. indet. in the Bartonian to lower Priabonian (calcareous nannofossil Zones NP 16-NP 17), while Heterostegina ocalana ranges from Priabonian (nannofossil Zones NP 17 to NP 19-20/CP 15) to probably lower Oligocene (Rupelian) in the lower and middle part of the planktic foraminiferal Zone O 1 (P 18) and in the middle part of the calcareous nannofossil Zone NP 21 (CP 16).

The Natural Laboratory of Algal Symbiont-Bearing Benthic Foraminifera: Studying Individual Growth and Population Dynamics in the Sublittoral

Reproduction period, longevity and the chamber-building rate of symbiont-bearing benthic foraminifera, which are important for population dynamic studies can be estimated from field data. Laboratory investigations changing the grade of ecological variables cannot substitute for the complexity of natural conditions. Therefore, methods are developed, especially for the deeper sublittoral species, to estimate reproduction, lifespan and the individual growth rate under natural conditions for demonstrating the influence of environmental parameters.

Morphological variations in Cycloclypeus carpenteri: Multiple embryos and multiple equatorial layers

In this work, 17 specimens of Cycloclypeus carpenteri have been analysed by means of microCT scanning. It has been observed that many specimens possess multiple embryos, multiple nepionts and some tests show more than one equatorial layer. The diameter of each proloculus has been measured, and it seems that they are very variable even within the same specimen, therefore questioning the long known theory that schizonts have smaller proloculi than gamonts and also questioning the fact that proloculi in the same species should all have comparable size. Whenever the nepionts are positioned on different planes, thus creating an angle between them, this angle has a significant correlation to the angle connecting different equatorial layers. T-shaped connections are located at the junction between two equatorial layers; these junctions are made by a chamberlet, which possesses an unusually higher number of apertures, resembling the chamberlet structure of the genus Spiroclypeus. Antonino Briguglio. Faculty of Science, Universiti Brunei Darussalam, Jalan Tungku Link, Gadong BE1410, Brunei Darussalam, antonino.briguglio@ubd.edu.bn; Shunichi Kinoshita. Department of Palaeontology, University of Vienna, Geocenter, Althanstrasse 14, A1090 Vienna, Austria. shunichi.kinoshita@univie.ac.at Johann Hohenegger. Department of Palaeontology, University of Vienna, Geocenter, Althanstrasse 14, A1090 Vienna, Austria. johann.hohenegger@univie.ac.at Erik Wolfgring. Department of Geodynamics and Sedimentology, University of Vienna, Geocenter, Althanstrasse 14, A-1090 Vienna, Austria. erik.wolfgring@univie.ac.at