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Making the link between evolutionary processes and development in extinct organisms is usually hampered by the lack of preservation of ontogenetic stages in the fossil record. Planktic foraminifers, which grow by adding chambers, are an ideal target organism for such studies as their test incorporates all prior developmental stages. Previously, studies of development in these organisms were limited by the small size of their early chambers. Here, we describe the application of synchrotron radiation X-ray tomographic microscopy (SRXTM) to document the ontogenetic history of the foraminifers Globigerinoides sacculifer and Globorotalia menardii. Our SRXTM scans permit resolution at submicrometre scale, thereby displaying additional internal structures such as pores, dissolution patterns and complexity of the wall growth. Our methods provide a powerful tool to pick apart the developmental history of these microfossils and subsequently assist in inferring phylogenetic relationships and evolutionary processes. [ABSTRACT FROM AUTHOR]

Abstract: Body size is a central feature of any organism, reflecting its physiology, ecology and evolutionary history. Marine microplankton are major contributors to the particulate inorganic carbonate (foraminifers and coccolithophorids) and opal flux (radiolaria and diatoms) in the ocean and, hence, size changes in these organisms can influence global biogeochemical cycles. This paper is discussing abiotic influences on micro- and macroecological size changes among major marine plankton groups, linking these to evolutionary size changes during the Neogene. We review the patterns and outline the causes of size changes geographically and through time in coccolithophorids, foraminifers and radiolarians. The main feature of the Neogene size record is a dramatic size increase in foraminifers, a similarly dramatic reduction in the size range of coccolithophorids and highly variable size patterns in radiolarians. We argue that the observed pattern is too complex to be explained by a simple common forcing and propose that speculations on the response of oceanic biomineralisation to global warming have to consider the scales at which marine plankton evolve. [Copyright &y& Elsevier]

The iterative evolutionary radiation of planktic foraminifers is a well-documented macroevolutionary process. Here we document the accompanying size changes in entire planktic foraminiferal assemblages for the past 70 My and their relationship to paleoenvironmental changes. After the size decrease at the Cretaceous/Paleogene (K/P) boundary, high latitude assemblages remained consistently small. Size evolution in low latitudes can be divided into three major phases: the first is characterized by dwarfs (65–42 Ma), the second shows moderate size fluctuations (42–14 Ma), and in the third phase, planktic foraminifers have grown to the unprecedented sizes observed today.Our analyses of size variability with paleoproxy records indicate that periods of size increase coincided with phases of global cooling (Eocene and Neogene). These periods were characterized by enhanced latitudinal and vertical temperature gradients in the oceans and high diversity (polytaxy). In the Paleocene and during the Oligocene, the observed (minor) size changes of the largely low-diversity (oligotaxic) assemblages seem to correlate with productivity changes. However, polytaxy per se was not responsible for larger test sizes. [Copyright &y& Elsevier]

Morphological variability of the planktic foraminifer Globorotalia truncatulinoides, estimated by size, shape, and coiling direction of the test, has been studied throughout the last 140 kyr in three cores in the South Atlantic. The biogeographic component of the morphological variation has been identified as difference between the three cores, located in the subantarctic frontal system, the equatorial upwelling zone, and the northern margin of the subtropical gyre. Temporal variability of morphology has been quantified and compared to biogeographic morphological variations, and paleoenvironmental proxies. The most important morphological differentiation is related to biogeography. Size and shape vary according to a temperature gradient across the different cores. This pattern is likely the result of differences between the four cryptic genetic species that have been previously identified within the taxon, and that are associated with different ecological preferences. Temporal variations can be recognized within each of the three cores, even in the most stable situation of the subtropical gyre. Significant correlations emerge between morphology and paleoenvironmental proxies, suggesting that the morphological variations are a response to environmental change. The same shape–temperature relationship emerges from both, biogeographic differences and local temporal variations. This suggests that the complex of species G. truncatulinoides mainly reacted to the glacial–interglacial climatic fluctuations of the last 140 kyr by a process of habitat tracking, i.e. the different species shifted their geographic distribution without major modifications of their ecological preferences. Yet, evolution may be involved as a response to environmental changes on a longer time scale. [Copyright &y& Elsevier]