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In palaeontological studies, groups with consistent ecological and morphological traits across a clade's history (functional groups) 1 afford different perspectives on biodiversity dynamics than do species and genera 2,3 , which are evolutionarily ephemeral. Here we analyse Triton, a global dataset of Cenozoic macroperforate planktonic foraminiferal occurrences 4 , to contextualize changes in latitudinal equitability gradients 1 , functional diversity, palaeolatitudinal specialization and community equitability. We identify: global morphological communities becoming less specialized preceding the richness increase after the Cretaceous-Palaeogene extinction; ecological specialization during the Early Eocene Climatic Optimum, suggesting inhibitive equatorial temperatures during the peak of the Cenozoic hothouse; increased specialization due to circulation changes across the Eocene-Oligocene transition, preceding the loss of morphological diversity; changes in morphological specialization and richness about 19 million years ago, coeval with pelagic shark extinctions 5 ; delayed onset of changing functional group richness and specialization between hemispheres during the mid-Miocene plankton diversification. The detailed nature of the Triton dataset permits a unique spatiotemporal view of Cenozoic pelagic macroevolution, in which global biogeographic responses of functional communities and richness are decoupled during Cenozoic climate events. The global response of functional groups to similar abiotic selection pressures may depend on the background climatic state (greenhouse or icehouse) to which a group is adapted., (© 2024. The Author(s), under exclusive licence to Springer Nature Limited.)

The geographic ranges of marine organisms, including planktonic foraminifera 1 , diatoms, dinoflagellates 2 , copepods 3 and fish 4 , are shifting polewards owing to anthropogenic climate change 5 . However, the extent to which species will move and whether these poleward range shifts represent precursor signals that lead to extinction is unclear 6 . Understanding the development of marine biodiversity patterns over geological time and the factors that influence them are key to contextualizing these current trends. The fossil record of the macroperforate planktonic foraminifera provides a rich and phylogenetically resolved dataset that provides unique opportunities for understanding marine biogeography dynamics and how species distributions have responded to ancient climate changes. Here we apply a bipartite network approach to quantify group diversity, latitudinal specialization and latitudinal equitability for planktonic foraminifera over the past eight million years using Triton, a recently developed high-resolution global dataset of planktonic foraminiferal occurrences 7 . The results depict a global, clade-wide shift towards the Equator in ecological and morphological community equitability over the past eight million years in response to temperature changes during the late Cenozoic bipolar ice sheet formation. Collectively, the Triton data indicate the presence of a latitudinal equitability gradient among planktonic foraminiferal functional groups which is coupled to the latitudinal biodiversity gradient only through the geologically recent past (the past two million years). Before this time, latitudinal equitability gradients indicate that higher latitudes promoted community equitability across ecological and morphological groups. Observed range shifts among marine planktonic microorganisms 1,2,8 in the recent and geological past suggest substantial poleward expansion of marine communities even under the most conservative future global warming scenarios., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)

The latitudinal diversity gradient (LDG) is a prevalent feature of modern ecosystems across diverse clades 1-4 . Recognized for well over a century, the causal mechanisms for LDGs remain disputed, in part because numerous putative drivers simultaneously covary with latitude 1,3,5 . The past provides the opportunity to disentangle LDG mechanisms because the relationships among biodiversity, latitude and possible causal factors have varied over time 6-9 . Here we quantify the emergence of the LDG in planktonic foraminifera at high spatiotemporal resolution over the past 40 million years, finding that a modern-style gradient arose only 15 million years ago. Spatial and temporal models suggest that LDGs for planktonic foraminifera may be controlled by the physical structure of the water column. Steepening of the latitudinal temperature gradient over 15 million years ago, associated with an increased vertical temperature gradient at low latitudes, may have enhanced niche partitioning and provided more opportunities for speciation at low latitudes. Supporting this hypothesis, we find that higher rates of low-latitude speciation steepened the diversity gradient, consistent with spatiotemporal patterns of depth partitioning by planktonic foraminifera. Extirpation of species from high latitudes also strengthened the LDG, but this effect tended to be weaker than speciation. Our results provide a step change in understanding the evolution of marine LDGs over long timescales., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)

Ocean dynamics in the equatorial Pacific drive tropical climate patterns that affect marine and terrestrial ecosystems worldwide. How this region will respond to global warming has profound implications for global climate, economic stability and ecosystem health. As a result, numerous studies have investigated equatorial Pacific dynamics during the Pliocene (5.3-2.6 million years ago) and late Miocene (around 6 million years ago) as an analogue for the future behaviour of the region under global warming 1-12 . Palaeoceanographic records from this time present an apparent paradox with proxy evidence of a reduced east-west sea surface temperature gradient along the equatorial Pacific 1,3,7,8 -indicative of reduced wind-driven upwelling-conflicting with evidence of enhanced biological productivity in the east Pacific 13-15 that typically results from stronger upwelling. Here we reconcile these observations by providing new evidence for a radically different-from-modern circulation regime in the early Pliocene/late Miocene 16 that results in older, more acidic and more nutrient-rich water reaching the equatorial Pacific. These results provide a mechanism for enhanced productivity in the early Pliocene/late Miocene east Pacific even in the presence of weaker wind-driven upwelling. Our findings shed new light on equatorial Pacific dynamics and help to constrain the potential changes they will undergo in the near future, given that the Earth is expected to reach Pliocene-like levels of warming in the next century., (© 2021. The Author(s), under exclusive licence to Springer Nature Limited.)

The ocean-the Earth's largest ecosystem-is increasingly affected by anthropogenic climate change 1,2 . Large and globally consistent shifts have been detected in species phenology, range extension and community composition in marine ecosystems 3-5 . However, despite evidence for ongoing change, it remains unknown whether marine ecosystems have entered an Anthropocene 6 state beyond the natural decadal to centennial variability. This is because most observational time series lack a long-term baseline, and the few time series that extend back into the pre-industrial era have limited spatial coverage 7,8 . Here we use the unique potential of the sedimentary record of planktonic foraminifera-ubiquitous marine zooplankton-to provide a global pre-industrial baseline for the composition of modern species communities. We use a global compilation of 3,774 seafloor-derived planktonic foraminifera communities of pre-industrial age 9 and compare these with communities from sediment-trap time series that have sampled plankton flux since AD 1978 (33 sites, 87 observation years). We find that the Anthropocene assemblages differ from their pre-industrial counterparts in proportion to the historical change in temperature. We observe community changes towards warmer or cooler compositions that are consistent with historical changes in temperature in 85% of the cases. These observations not only confirm the existing evidence for changes in marine zooplankton communities in historical times, but also demonstrate that Anthropocene communities of a globally distributed zooplankton group systematically differ from their unperturbed pre-industrial state.