Cenozoic dynamics of shallow-marine biodiversity in the Western Pacific

Abstract

Cenozoic dynamics of large-scale species diversity patterns remain poorly understood, especially for the Western Pacific, in part because of the paucity of well-dated fossil records from the tropics. Here we show the spatiotemporal dynamics of species diversity in the Western Pacific through the Cenozoic, focusing on the tropical Indo-Australian Archipelago (IAA) biodiversity hotspot. We analyzed well-preserved fossil ostracodes from the tropical Western Pacific and combined their diversity data with other published data from the region to reconstruct Cenozoic dynamics of species diversity in the tropical- and northwestern Pacific Ocean. We fit generalized additive models to test for differences in richness over time and across geographic regions while accounting for sample size variation among samples. Low-, mid- and high-latitude regions all show a similar diversity trajectory: diversity is low in the Eocene and Oligocene, increases from the Early Miocene to the Plio-Pleistocene but then declines to the present day. Latitudinal diversity patterns are relatively flat and rarely show the typical decline from tropics to high-latitude. Modern-level high biodiversity in the tropical IAA and the northwestern Pacific Ocean was established during the Pliocene. The modest diversity decline from the Plio-Pleistocene to the present day may be attributable to large amplitude glacial-interglacial climate and sea-level changes. The weak and irregular (i.e., inverse, mid-latitude-peaked, or mid-latitude-depressed) latitudinal species diversity gradients are unexpected, because the northwestern Atlantic Ocean displays a standard tropical-high and temperate-low diversity pattern throughout the Cenozoic. In addition, ostracodes are known to show standard latitudinal diversity gradients in the North Atlantic. These differences suggest an important role for regional factors (e.g., plate tectonics and temporal geomorphological dynamics), in shaping the biodiversity of the Western Paci