[M-IS14] Paleoclimatology and paleoceanography

[MIS14-22] Morphological Variation, Speciation, and Cryptic Populations in the L5 Left Coiling Event of the Foraminifera Pulleniatina, Pleistocene 2.1-1.7 Ma Interval, Solomon Sea

*Robert Edward Swisher¹, Li Lo¹, Wei-Lun Chen¹, Jyh-Jaan Huang¹, Jia-Cih Kang¹, Katsunori Kimoto², Li-Wei Kuo³, Yen-Fang Song⁴, Gung-Chian Yin⁴ (1.Department of Geosciences, National Taiwan University, Taipei, Taiwan, 2.Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan, 3.Department of Earth Sciences, National Central University, Taoyuan, Taiwan, 4.National Synchrotron Radiation Research Center, Hsinchu, Taiwan)

Keywords:Planktonic foraminifera, Pleistocene, Geometric Morphometric Analysis, Cryptic Species Populations

Studying the impact of shifting long-term environmental conditions on marine organisms has become a problem of increasing concern given the modern climate crisis and on-going Holocene extinction event. Observing and assessing the consequences of these climatic shifts on organisms presents complex challenges that require multidisciplinary approaches and fossil datasets that extend beyond the limitations of extant analyses. The Plio-Pleistocene boundary presents an ideal opportunity to examine such questions, globally recording shifting oceanic and climatic conditions hypothesized to be influenced by shifts in the Pacific warm pool and East African monsoon approximately 2.1-1.7 million years ago. Particularly, this interval provides a unique chance to examine the morphological response of foraminifera, protists with biomineralized skeletons, to changing environmental conditions.

This analysis examines a Pulleniatina obliquiloculata dataset collected from the ODP 1115B core, Solomon Sea's. Importantly, Pulleniatina globally records two distinctive shifts in coiling direction over the 2.2-1.7 million year interval, transitioning dominantly from right to left. This study examines the L5 left coiling event. The drivers of "left coiling" events are poorly understood and it has been proposed that these shifts may represent the evolution and replacement of cryptic species or morphotype populations. This study applies a novel morphometric analyses as well as a preliminary 3D CT-scan data towards our analysis. Results indicate distinctive left and right coiling forms existed prior to the L5 coiling event, with morphological disparity drastically decreasing at its onset, suggestive of a faunal turnover event at the boundary and a morphological bottleneck within genus regionally. Throughout the L5 morphological variation and disparity increased, leading to disparate left and right morphotypes, distinctive from the forms present prior to the L5 event. This trend continues after the L5 event with right and left coiling forms maintaining distinction. Results support the presence of cryptic populations and morphotypes within Pulleniatina driving the observed L5 faunal patterns. This analysis highlights the importance of applying detailed quantitative methodologies towards the analysis of complex evolutionary and biostratigraphic problems, particularly towards understanding subtle morphological variations and cryptic specie complexes.