Paleontology provides insights into the history of the planet, from the origins of life billions of years ago to the biotic changes of the Recent. The scope of paleontological research is as vast as it is varied, and the field is constantly evolving. In an effort to identify “Big Questions” in paleontology, experts from around the world came together to build a list of priority questions the field can address in the years ahead. The 89 questions presented herein (grouped within 11 themes) represent contributions from nearly 200 international scientists. These questions touch on common themes including biodiversity drivers and patterns, integrating data types across spatiotemporal scales, applying paleontological data to contemporary biodiversity and climate issues, and effectively utilizing innovative methods and technology for new paleontological insights. In addition to these theoretical questions, discussions touch upon structural concerns within the field, advocating for an increased valuation of specimen-based research, protection of natural heritage sites, and the importance of collections infrastructure, along with a stronger emphasis on human diversity, equity, and inclusion. These questions offer a starting point—an initial nucleus of consensus that paleontologists can expand on—for engaging in discussions, securing funding, advocating for museums, and fostering continued growth in shared research directions.

Modern grasslands on the Indian subcontinent, North and South America, and East Africa expanded widely during the late Miocene – earliest Pleistocene, likely in response to increasing aridity. Grasses utilizing the C4 photosynthetic pathway are more tolerant of high temperatures and dry conditions, and because they induce less C isotope fractionation than plants using the C3 pathway, the expansion of C4 grasslands can be traced through the δ13C of organic matter in soils and terrigenous marine sediments. We present a high-resolution record of the elemental and isotopic composition of bulk organic matter in the Nicobar Fan sediments from IODP Site U1480, off western Sumatra, to elucidate the timing and pace of the C3–C4 plant transition within the ∼1.5 × 106 km2 catchments of the Ganges/Brahmaputra river system, which continue to supply voluminous Himalaya-derived sediments to the Bay of Bengal. Using a multi-proxy approach to correct for the effects of marine organic matter and account for major sources of uncertainty, we recognize two phases of C4 expansion starting at ∼7.1 Ma, and at ∼3.5 Ma, with a stepwise transition at ∼2.5 Ma. These intervals appear to coincide with periods of Indian Ocean and East Asian monsoon intensification, as well as the expansion of Northern Hemisphere glaciation starting at ∼2.7 Ma. Our data from the deep sea for a multi-phased C4 expansion on the Indian subcontinent are in agreement with terrestrial data from the Indian Siwaliks.

The diffusive exchange of dissolved material between fluid flowing in a fracture and the enclosing wallrocks (rock matrix diffusion) has been proposed as a mechanism by which radionuclides derived from a radioactive waste repository may be removed from groundwater and incorporated into the geosphere. To test the effectiveness of diffusive exchange in igneous and metamorphic rocks, we have carried out an investigation of veins formed at low temperatures (<100°C), comparing the oxygen isotopic composition of vein calcite with that of secondary calcite in the wallrocks. Two examples of veins from the Borrowdale Volcanic Group, Cumbria, and one from the Mountsorrel Granodiorite, Leicestershire, UK, have remarkably similar vein calcite compositions, ca. +20‰(SMOW) or greater, substantially heavier than the probable compositions of the host rocks, and these vein calcite compositions are inferred to reflect the infiltrating fluid and the temperature of vein formation. Calcites from the wallrocks are similar to those in veins, with little evidence for exchange with the wallrocks. The results support existing models for this type of vein which suggest low-temperature growth from formation brines originally linked to Permian or Triassic evaporites. The results are consistent with flow through fractures being attenuated through a damage zone adjacent to the fracture and provide no evidence of diffusional exchange with pore waters from wallrocks.

Seeman, Morris, and Summers misrepresent or misunderstand the arguments we have made, as well as their own previous work. Here, we correct these inaccuracies. We also reiterate our support for hypothesis-driven and evidence-based research.

The protected Tel-Dor coastal embayment in the eastern Mediterranean preserves an unusually complete stratigraphic record that reveals human–environmental interactions throughout the Holocene. Interpretation of new seismic profiles collected from shallow marine geophysical transects across the bay show five seismic units were correlated with stratigraphy and age dates obtained from coastal and shallow-marine sediment cores. This stratigraphic framework permits a detailed reconstruction of the coastal system over the last ca. 77 ka as well as an assessment of environmental factors that influenced some dimensions of past coastal societies. The base of the boreholes records lowstand aeolian deposits overlain by wetland sediments that were subsequently flooded by the mid-Holocene transgression. The earliest human settlements are submerged Pottery Neolithic (8.25–7 ka) structures and tools, found immediately above the wetland deposits landward of a submerged aeolianite ridge at the mouth of the bay. The wetland deposits and Pottery Neolithic settlement remains are buried by coastal sand that records a middle Holocene sea-level rise ca. 7.6–6.5 ka. Stratigraphic and geographic relationships suggest that these coastal communities were displaced by sea-level transgression. These findings demonstrate how robust integration of different data sets can be used to reconstruct the geomorphic evolution of coastal settings as well as provide an important addition to the nature of human–landscape interaction and cultural development.

ABSTRACT IMPACT: These findings identify a new way in which the COVID-19 pandemic exacerbates racial/ethnic health disparities, and will thus direct future research to explore potentially avoidable hospitalizations, as well as direct health policy to improve the value of this specific aspect of care without further widening the disparity. OBJECTIVES/GOALS: Racial and ethnic disparities in potentially avoidable hospitalizations predate COVID-19. In order to identify and address healthcare disparities exacerbated by the pandemic, we examined whether and to what extent the pandemic affected numbers of potentially avoidable hospitalizations by race and ethnicity. METHODS/STUDY POPULATION: This single-center pre-post study of 904 patients at UCLA included all patients admitted to an internal medicine service for an ambulatory care sensitive condition (ACSC) between March-August of 2020 (post) and March-August of 2019 (pre). We measured the change in number of potentially avoidable hospitalizations (defined per the Agency for Healthcare Research and Quality guidelines) stratified by race and ethnicity. We calculated 95% CIs for the number of potentially avoidable hospitalizations using a cluster bootstrap procedure, clustering at the level of patients. We inverted the bootstrap CIs to calculate p-values for overall changes within racial/ethnic groups as well as differential changes between groups. Patients with missing or unspecified racial/ethnic data were excluded (n=1,003; 7.8%). RESULTS/ANTICIPATED RESULTS: Between March 1 and August 31, 2020, 347 out of 4,838 hospitalizations (7.2%) were potentially avoidable, compared to 557 out of 6,248 (8.9%) during the same 6-months of 2019. Reductions in potentially avoidable hospitalizations among Non-Hispanic White (-50.3%; 95% CI, -60.9 - -41.2; p<0.001) and Latinx (-32.3%; 95% CI, -59.8 - -12.2%, p<0.001) patients were statistically significant, whereas reductions among African American (-8.0%; 95% CI, -39.9 - +16.2) and Asian (-16.1%; 95% CI, -75.7 - +20.4) patients were not statistically different from 0%. The relative differences in magnitudes of reduction were only statistically significant between African American and non-Hispanic White patients (-50.3% v. -8.0%; 95% CI as above; p=0.015). DISCUSSION/SIGNIFICANCE OF FINDINGS: Racial disparities in potentially avoidable hospitalizations increased during the COVID-19 pandemic at this large urban health system. Healthcare leaders, researchers, and policy makers should focus on efforts to prevent a post-pandemic resurgence of low-value hospitalizations in ways that do not further widen disparities.

Under stress, corals and foraminifera may eject or consume their algal symbionts (“bleach”), which can increase mortality. How bleaching relates to species viability over warming events is of great interest given current global warming. We use size-specific isotope analyses and abundance counts to examine photosymbiosis and population dynamics of planktonic foraminifera across the Paleocene–Eocene thermal maximum (PETM, ~56 Ma), the most severe Cenozoic global warming event. We find variable responses of photosymbiotic associations across localities and species. In the NE Atlantic (DSDP Site 401) PETM, photosymbiotic clades (acarininids and morozovellids) exhibit collapsed size-δ13C gradients indicative of reduced photosymbiosis, as also observed in Central Pacific (ODP Site 1209) and Southern Ocean (ODP Site 690) acarininids. In contrast, we find no significant loss of size-δ13C gradients on the New Jersey shelf (Millville) or in Central Pacific morozovellids. Unlike modern bleaching-induced mass mortality, populations of photosymbiont-bearing planktonic foraminifera increased in relative abundance during the PETM. Multigenerational adaptive responses, including flexibility in photosymbiont associations and excursion taxon evolution, may have allowed some photosymbiotic foraminifera to thrive. We conclude that deconvolving the effects of biology on isotope composition on a site-by-site basis is vital for environmental reconstructions.

Pelagic (open-ocean) species have enormous population sizes and broad, even global, distributions. These characteristics should damp rates of speciation in allopatric and vicariant evolutionary models since dispersal should swamp diverging populations and prevent divergence. Yet the fossil record suggests that rates of evolutionary turnover in pelagic organisms are often quite rapid, comparable to rates observed in much more highly fragmented terrestrial and shallow-marine environments. Furthermore, genetic and ecological studies increasingly suggest that species diversity is considerably higher in the pelagic realm than inferred from many morphological taxonomies.

Zoogeographic evidence suggests that ranges of many pelagic groups are much more limited by their ability to maintain viable populations than by any inability to disperse past tectonic and hydrographic barriers to population exchange. Freely dispersing pelagic taxa resemble airborne spores or wind-dispersed seeds that can drift almost anywhere but complete the entire life cycle only in favorable habitats. It seems likely that vicariant and allopatric models for speciation are far less important in pelagic evolution than sympatric or parapatric speciation in which dispersal is not limiting. Nevertheless, speciation can be quite rapid and involve cladogenesis even in cases where morphological data suggest gradual species transitions. Indeed, recent paleoecological and molecular studies increasingly suggest that classic examples of “phyletic gradualism” involve multiple, cryptic speciation events.

Paleoceanographic and climatic change seem to influence rates of turnover by modifying surface water masses and environmental gradients between them to create new habitats rather than by preventing dispersal. Changes in the vertical structure and seasonality of water masses may be particularly important since these can lead to changes in the depth and timing of reproduction. Long-distance dispersal may actually promote evolution by regularly carrying variants of a species across major oceanic fronts and exposing them to very different selection pressures than occur in their home range. High dispersal in pelagic taxa also implies that extinction should be difficult to achieve except though global perturbations that prevent populations from reestablishing themselves following local extinction. High rates of extinction in some pelagic groups suggests either that global perturbations are common, or that the species are much more narrowly adapted than we would infer from current taxonomies.

Imaging bundles provide a convenient way to translate a spatially coherent image, yet conventional imaging bundles made from silica fibre optics typically remain expensive with large losses due to poor filling factors (~40%). We present the characterisation of a novel polymer imaging bundle made from poly(methyl methacrylate) (PMMA) that is considerably cheaper and a better alternative to silica imaging bundles over short distances (~1 m; from the middle to the edge of a telescope’s focal plane). The large increase in filling factor (92% for the polymer imaging bundle) outweighs the large increase in optical attenuation from using PMMA (1 dB/m) instead of silica (10−3 dB/m). We present and discuss current and possible future multi-object applications of the polymer imaging bundle in the context of astronomical instrumentation including: field acquisition, guiding, wavefront sensing, narrow-band imaging, aperture masking, and speckle imaging. The use of PMMA limits its use in low-light applications (e.g., imaging of galaxies); however, it is possible to fabricate polymer imaging bundles from a range of polymers that are better suited to the desired science.

Analysis of the evolution of the Globorotalia (Fohsella) lineage of planktic foraminifera suggests that reproductive ecology and shell shape have evolved independently in this group. The silhouette of fohsellid shells displays a nearly unbroken anagenetic trend, yet isotopic data show that the fohsellids changed their depth of reproduction during the anagenetic evolution of their skeletons. Remarkably, there are no correlations between anagenesis in skeletal shape and the establishment of reproductive isolation. Apparently, anagenesis masks at least one speciation event that is apparent only in the isotopic evidence for a change in reproductive ecology. Although anagenetic trends have been widely cited as evidence for gradual speciation in planktic foraminifera and other microfossil groups, our data suggest that they should not always be considered to record either the tempo or mode of speciation.

Speciation was apparently uncoupled from morphological evolution in fohsellids because these evolutionary phenomena occurred in different phases of ontogeny. Gradual morphological changes were associated with the main phase of shell growth of both the ancestor and descendant species in the near-surface ocean. Reproductive isolation occurred when ancestral and descendant populations became established at different depths near the end of the life cycle. Morphological evolution may also be uncoupled from reproductive isolation in other organisms that experience very different selection pressures over the duration of their ontogenies, such as parasites with many hosts, species with multiple phases of metamorphosis, and organisms that broadcast their gametes.

Symbioses are often regarded as an important means for the creation of evolutionary novelty as well as a trigger for the abrupt appearance of higher taxa. The fossil record of foraminifer-algal symbiosis suggests that the appearance of this ecological association contributed to the radiation of Paleogene planktic foraminifera. Isotopic evidence shows that photosymbiosis evolved in synchrony with a major diversification of trochospiral planktic foraminifera about 3.5 m.y. after the end-Cretaceous extinction. In modern planktic foraminifera, photosymbiotic species tend to have more cosmopolitan distributions than asymbiotic foraminifera and a greater ability to withstand periods of nutrient stress. The simultaneous taxonomic radiation and acquisition of photosymbiosis are evidence that the ecological strategy permitted Paleocene foraminifera to expand their niche in pelagic environments by diversifying into low-nutrient surface waters.

A comparison of the species longevities of Neogene and Paleogene symbiotic clades suggests that photosymbiosis does not regulate the characteristic rate of taxonomic turnover in clades after they appear. Species longevities are much shorter in Paleocene and Eocene photosymbiotic morphospecies than they are among photosymbiotic Neogene clades; apparently photosymbiosis does not exert a significant control over long-term evolutionary rates. In addition, the absence of a characteristic morphology associated with photosymbiosis in Cenozoic planktic foraminifera suggests that morphology, as with rate of evolutionary turnover, is linked to symbiosis only because of common inheritance instead of a functional relationship. Although the coincidence between the acquisition of photosymbiosis and generic diversification does suggest a linkage between this ecology and the appearance of foraminiferal higher taxa, there is little indication at the present that symbioses control long-term morphological or ecological patterns within these groups after their appearance. Photosymbiosis, and other evolutionary innovations, may be more a catalyst for the differentiation of major groups than a predictable governor on evolutionary rates.

Radiations are commonly believed to be linked to the evolutionary appearance of a novel morphology or ecology. Previous studies have demonstrated a close relationship between the evolutionary appearance of algal photosymbiosis in planktonic foraminifera and evolutionary diversification of Paleogene photosymbiotic clades. For example, the evolution of photosymbiosis was synchronous with the abrupt evolution of four major groups of Paleogene planktonic foraminifera including two clades within the genus Morozovella, as well as the genera Acarinina and Igorina. Our new isotopic and biogeographic data suggest that the acarininids evolved from a photosymbiotic ancestor (which we identify as Praemurica inconstans or early representatives of Praemurica uncinata), but also demonstrate that photosymbiosis did not trigger an immediate species-level radiation in this group. Instead, the acarininids remained a low-diversity taxon restricted to high latitudes for nearly 1.8 million years before radiating ecologically and taxonomically. The eventual radiation of the acarininids is tied to an expansion of their geographic range into the mid and low latitudes. Biogeographic analyses of modern plankton suggest that high-latitude environments may be less conducive to establishing radiations simply because there are fewer niches available to be filled than there are in the tropics. Accordingly, the acarininids may have initially failed to diversify because they started off in environments that presented few opportunities to sustain a large radiation. The high-latitude origin of the acarininids continued to retard their overall diversification until they were able to develop strategies that allowed them to expand into tropical environments and fully exploit their photosymbiotic ecology.

The directionality of long-term trends can be strongly biased by forces intrinsic to a clade. Trends in body size and skeletal shape may be dictated more by variations in survivorship that reflect differences in ecology than by long-term directional changes in the environment. Hence, mass extinctions can help drive evolutionary trends by selectively eliminating some morphologies and permitting the survivors to found the next radiation.

Examples include repeated trends toward larger maximum body size and the evolution of keeled species from those with globose tests in planktonic foraminifera. Both the trends in size and shape develop because small species with globose tests are significantly more resistant to extinction than species that are large or have peripheral keels. Hence, the survivors of both the Cretaceous-Tertiary and Eocene-Oligocene extinction episodes are small, unkeeled taxa. Large species and species with keels evolved convergently after both mass extinctions as the founders radiated anew.

Comparison of three radiations of planktonic foraminifera suggest that the convergent evolution of similar test shapes and sizes is not due to synchronous changes in oceanography that track evolutionary trends. Instead, the reestablishment of habitat heterogeneity is needed to permit the ensuing radiation to unfold rather than to closely guide its progress. Similar evolutionary trends will develop in each radiation as long as the founders have similar morphology and the evolution of variants present in the previous radiation is not precluded by the environment.

Populations of planktic foraminifera display “proportionate” coiling (approximately 50% sinistral and dextral individuals given the data at hand) or may have “biased“ coiling, in which populations are dominated by either sinistral or dextral individuals. The major radiations of planktic foraminifera in the Late Cretaceous, the Paleocene to early Eocene, the middle Eocene, and the Neogene were each initiated by clades with proportionate coiling but subsequently accumulated sinistral and dextral species over time. Upper Maastrichtian foraminifera were predominantly dextral, but only the small number of species with proportionate coiling actually survived the Cretaceous/Paleogene mass extinction. The first Paleocene species with biased coiling appeared about four million years after the extinction and gradually came to represent as much as 50–60% of the tropical species diversity by the latest Paleocene. Tropical taxa with biased coiling suffered a second extinction in the late early Eocene and renewed a trend toward an increased abundance of species with biased coiling in the middle Eocene.

Our results for the Paleogene reflect a recurring theme in foraminifer evolution. In each radiation, once the founding species of a clade developed a biased-coiling mode, the descendants tended to maintain biased coiling until the extinction of the clade. The iterative evolution of biased coiling appears to represent an example in which a fundamental feature of development becomes fixed in a clade and inhibits reversion to an ancestral state. Apparently, coiling patterns are heritable in contrast with previous interpretations that coiling is environmentally controlled. On evolutionary timescales, species with proportionate coiling are less susceptible to extinction than species dominated by sinistral or dextral forms. Differential survivorship ensures that each radiation is initiated from founders with proportionate coiling following mass extinction. Hence, coiling preferences represent a case where the establishment of an evolutionary trend is caused by drift away from a “limiting boundary,” much like the evolution of large body size from ubiquitous small ancestors.