Patterns of morphological variation in coiling forms of the planktic foraminifer Pulleniatina obliquiloculata across the Pleistocene L5 coiling event (Solomon Sea)

Abstract

The Plio-Pleistocene boundary, an interval marked by global changes in oceanic and climatic conditions, is thought to be influenced by shifts in the Pacific warm pool and East African monsoon around 2.1–1.7 million years ago (Ma). This interval is characterized by the globally recognized L5 event when specimens of the planktic foraminiferal genus Pulleniatina shifted the coiling of chambers from dominantly dextral to sinistral. The L5 event offers a unique opportunity to examine the morphological response of foraminifera to changing oceanographic and climatic conditions. This study utilizes a dataset of the species Pulleniatina obliquiloculata from the Solomon Sea (ODP Hole 1115B) across the L5 event by applying novel 2D Landmark geometric-morphometric analyses to examine morphological variation of coiling morphotypes prior to, during, and immediately after the L5 coiling event. Results suggest distinctive morphologies in dextral and sinistral forms beside coiling arrangement before the L5, with morphological disparity drastically decreasing during the L5. Subsequently, morphological variation and disparity increased again during and after the L5 event, leading to distinct Left and Right morphotypes compared to prior forms. Results suggest that near-cryptic populations may have existed within Pulleniatina obliquiloculata, and are potentially indicative of a regional faunal turnover event and a morphological bottleneck at L5 initiation.