Planktonic foraminifera are heterotrophic, single-celled protists with calcite shells of generally a fraction of a millimeter in diameter that live between the surface and the seasonal thermocline of the open ocean. They are one of the most widely used of all microfossil groups for biostratigraphy, biochronology, paleoceanography and paleoenvironmental reconstructions since the Cretaceous (ca. 143 Ma), thanks to their rapid evolution, widespread distribution, high preservation potential, abundance in pelagic and hemipelagic sediments, and extensive fossil record.

Planktonic foraminifera first appeared in the Early Jurassic in the Tethyan Bioprovince and progressively diversified from the Early Cretaceous onwards. Faunal provinces similar to the modern can be traced into the Cretaceous with some variations related to the progressive changes in land-sea distributions and the latitudinal positions of paleoclimatic belts. Correlation across latitudinal belts is discussed being a major challenge which requires improved understanding of the paleogeographic distributions of key species, diachroneity of species occurrences, endemism, provincialism, and serves to interpret the paleoenvironmental changes across latitudes over geological time.

The paleoecology that characterizes Cretaceous and Cenozoic species abundance, diversity and their paleobiogeographic distributions are illustrated through examples from low and high latitudes sedimentary records. This information is particularly important for reconstructing past environments characterized by extreme warming events (e.g., Paleocene Eocene Thermal Maximum, Cenomanian-Turonian Thermal Maximum) and by perturbations of the global carbon cycle (e.g., Cretaceous Oceanic Anoxic Events).

Examples of key features in planktonic foraminiferal taxonomy and species identification in evolutionary trends are examined because highly relevant to paleoclimatic and paleoceanographic reconstructions, and to the practice and application of biostratigraphy and biochronology. The crucial role of planktonic foraminifera in the development of geological timescales is demonstrated by the identification of primary and secondary boundary events in the Global Stratotypes Sections and Points (GSSP). The significance of planktonic foraminifera for chronostratigraphic correlations and integration with other stratigraphic tools (e.g., magnetostratigraphy, chemostratigraphy, orbital tuning) is highlighted in terms of precision and accuracy of the data, and calibration difficulties are discussed in detail through case-studies.

Planktonic foraminiferal changes in species composition over time is used to reveal patterns of evolution and extinction that enhances our understanding of how organisms have adapted to changing environments throughout Earth's history and informs current models of biological resilience and vulnerability.