NETWORK ANALYSIS OF THE MARINE MICROPALAEONTOLOGICAL RECORD (PART 1): GLOBAL MARINE MICROPLANKTON COMMUNITY STRUCTURE RESPONSES TO CENOZOIC CLIMATE DEVELOPMENT

Understanding the structure in latitudinal patterns of organismal functional diversity is an important problem in both modern and paleo-ecology. Determining the dynamics of these patterns over geological time and the factors that influence them are key in predicting the biogeographical impacts of human-driven climate change and environmental alteration. Exploring these relationships requires both a rich dataset spanning both global geography and deep time, and methods that can capture the complexity of species occurrence patterns. The fossil record of the macroperforate planktonic foraminifera, which possess a highly resolved phylogeny with species-specific morphological and ecological data, is one such dataset, and tools from network science provide relevant methods.

Here, we use Triton, a recently constructed high-resolution global dataset of planktonic foraminiferal occurrences through Cenozoic (last 66 Ma) to reconstruct the spatio-temporal dynamics of marine plankton. We focus on morpho- and ecogroup data from Triton and use bipartite network metrics and null models to quantify various aspects of functional group diversity, latitudinal specialization, and latitudinal equitability, and contextualize the patterns through the lens of environmental perturbations in Cenozoic.

Patterns in the network metrics indicate (1) morphospace reoccupation and endemism following the post Cretaceous-Palaeogene (~66 Ma) mass extinction event (2) climate refugia amongst ecological groups at cooler, higher latitudes during the peak of the Cenozoic Greenhouse (~50 Ma) (3) a northward migration of morphologically specialized populations from the southern latitudes following the Middle Eocene Climatic Optimum (~40 Ma) and into the Oligocene, and most interestingly (4) a global equatorward shift in distinct latitudinal zones which promoted clade-wide ecological habitability during late Cenozoic (<8 Ma) bipolar cryosphere formation.

Collectively, the usage of novel network methods on the high-resolution Triton data reveals quantifiable dynamic patterns in ecological and morphological functional communities during major evolutionary and paleoclimatic events through the Cenozoic, with substantial evidence for endemism and refugia across southern paleolatitudes throughout the Palaeogene.