Scott L. Wing

Richard Bambach was a leading figure in the “paleobiology revolution” of the late 1960s and 1970s, keeping the movement grounded with his keen geological and ecological insights. With interests ranging from the functional biology of individual organisms to the largest macroevolutionary trends in the history of life, he was especially adept at linking paleoecological and macroevolutionary patterns across spatiotemporal scales. He authored seminal publications during five different decades and was recognized with both the Moore Medal from the Society for Sedimentary Geology and the Paleontological Society Medal.

The Paleocene–Eocene thermal maximum (PETM) was the largest early Cenozoic hyperthermal event, one of a series of carbon cycle and climate perturbations marked by massive releases of carbon into the atmosphere and spikes in global temperature. Previous studies have documented major changes in the composition of terrestrial plant and animal communities during the PETM, as well as changes in arthropod herbivory. Here, we examine possible changes in pollination mode during the PETM in the Bighorn Basin, Wyoming, USA, as inferred from three lines of evidence: (1) the prevalence of fossil pollen preserved as clumps, (2) the pollination mode of nearest living relatives (NLR), and (3) angiosperm pollen morphological diversity. These suggest animal pollination became more common and wind pollination less common during the PETM. The decrease in wind pollination during the PETM reflects the basin-scale extirpation of wind-pollinated lineages and their replacement by dominantly animal-pollinated lineages concomitant with rapid warming and drying. The hotter and seasonally drier climates not only facilitated the northward range shift of plant taxa, but likely their insect and/or vertebrate pollinators as well. The dramatic floral changes during the PETM in the Bighorn Basin may also have changed available resources for insect and/or vertebrate pollinators.

A long-term record of global mean surface temperature (GMST) provides critical insight into the dynamical limits of Earth’s climate and the complex feedbacks between temperature and the broader Earth system. Here, we present PhanDA, a reconstruction of GMST over the past 485 million years, generated by statistically integrating proxy data with climate model simulations. PhanDA exhibits a large range of GMST, spanning 11° to 36°C. Partitioning the reconstruction into climate states indicates that more time was spent in warmer rather than colder climates and reveals consistent latitudinal temperature gradients within each state. There is a strong correlation between atmospheric carbon dioxide (CO ₂ ) concentrations and GMST, identifying CO ₂ as the dominant control on variations in Phanerozoic global climate and suggesting an apparent Earth system sensitivity of ~8°C.

Photorespiration can limit gross primary productivity in terrestrial plants. The rate of photorespiration relative to carbon fixation increases with temperature and decreases with atmospheric [CO ₂ ]. However, the extent to which this rate varies in the environment is unclear. Here, we introduce a proxy for relative photorespiration rate based on the clumped isotopic composition of methoxyl groups ( R –O–CH ₃ ) in wood. Most methoxyl C–H bonds are formed either during photorespiration or the Calvin cycle and thus their isotopic composition may be sensitive to the mixing ratio of these pathways. In water-replete growing conditions, we find that the abundance of the clumped isotopologue ¹³ CH ₂ D correlates with temperature (18–28 °C) and atmospheric [CO ₂ ] (280–1000 ppm), consistent with a common dependence on relative photorespiration rate. When applied to a global dataset of wood, we observe global trends of isotopic clumping with climate and water availability. Clumped isotopic compositions are similar across environments with temperatures below ~18 °C. Above ~18 °C, clumped isotopic compositions in water-limited and water-replete trees increasingly diverge. We propose that trees from hotter climates photorespire substantially more than trees from cooler climates. How increased photorespiration is managed depends on water availability: water-replete trees export more photorespiratory metabolites to lignin whereas water-limited trees either export fewer overall or direct more to other sinks that mitigate water stress. These disparate trends indicate contrasting responses of photorespiration rate (and thus gross primary productivity) to a future high-[CO ₂ ] world. This work enables reconstructing photorespiration rates in the geologic past using fossil wood.

The extensive array of mid‐20^th century stratigraphic event signals associated with the ‘Great Acceleration’ enables precise and unambiguous recognition of the Anthropocene as an epoch/series within the Geological Time Scale. A mid‐20^th century inception is consistent with Earth System science analysis in which the Anthropocene term and concept arose, and would reflect the reality that our planet has sharply exited the range of natural variability characterizing the Holocene Epoch/Series, which the Anthropocene would therefore terminate. An alternative, recently proposed ‘geological event’ approach to the Anthropocene is primarily an interdisciplinary concept, encompassing historical and socio‐cultural processes and their global environmental impacts over a diachronous timeframe that extends back at least many millennia. Resembling more closely a geological episode than an event, it would decouple the Anthropocene from its chronostratigraphic delineation and association with an abrupt planetary perturbation; but separately defined and differently named it might be usefully complementary. We recommend a clear separation of epochs, events and episodes. An epoch is a formal subdivision of the Geological Time Scale, and its correlation may be assisted by one or more events; an event is usually, and particularly in the Quaternary, a brief incident or perturbation with a sedimentary expression; and an episode is a longer, internally complex time interval that may include several events and even extend across several epochs.

Premise: Biodiversity results from origination and extinction, justifying interest in identifying traits that influence this balance. Traits implicated in the success or failure of lineages include dispersal, colonization ability, and geographic range size. We investigated the impact of dispersal and range size on contemporary diversity in the Rosales.Methods: We used the multiple‐state speciation and extinction (MuSSE) method to explore the effects on genus‐level diversification of two genus‐level traits (geographic range size and within‐genus proclivity to speciate) and two species traits (seed dispersal and growth habit) and the multiple hidden‐state speciation and extinction (MuHiSSE) method for species‐level associations. Finally, we conducted a PGLS (phylogenetic least‐squares) analysis to distinguish between speciation within genera versus origination of new genera.Results: At the species level, animal dispersal enhances diversification rate in both woody and herbaceous lineages, while woody lineages without animal dispersal have higher extinction rates than speciation rates. At the genus level, herbaceous taxa have positive diversification rates regardless of other character states. Diversification rate variation is also explained by two interactions: (1) a three‐way interaction between large geographic range, animal‐mediated dispersal, and high within‐genus species richness, whereby genera possessing all three traits have high diversification rates, and (2) a four‐way interaction by which the three‐way interaction is stronger in woody genera than in herbaceous genera.Conclusions: Colonization ability may underlie the relationship between dispersal type and range size and may influence past diversification rates by decreasing extinction rates during late Cenozoic climate volatility. Thus, colonization ability could be used to predict future extinction risk to aid conservation.

Premise: Understanding the evolutionary history of flowering plants has been enriched by the integration of molecular phylogenies and evidence from the fossil record. Fossil fruits and leaves from the late Paleocene and Eocene of Wyoming and Eocene of Kentucky and Tennessee are described as extinct genera in the tropical American Bowdichia clade of the legume subfamily Papilionoideae. Recent phylogenetic study and taxonomic revision of the Bowdichia clade have facilitated understanding of relationships of the fossil taxa and their evolutionary implications and paleoenvironmental significance.Methods: The fossils were studied using standard methods of specimen preparation and light microscopy and compared to fruits and leaves from extant legume taxa using herbarium collections. Phylogenetic relationships of the fossil taxa were assessed using morphology and DNA sequence data.Results: Two new fossil genera are described and their phylogenetic relationships are established. Paleobowdichia lamarensis is placed as sister to the extant genus Bowdichia and Tobya claibornensis is placed with the extant genera Guianodendron and Staminodianthus.Conclusions: These fossils demonstrate that the tropical American Bowdichia clade was present in North America during a period when tropical or subtropical conditions prevailed in the northern Rocky Mountains during the late Paleocene and the Mississippi Embayment during the middle Eocene. These fossils also document that the Bowdichia clade had diversified by the late Paleocene when the fossil record of the family is relatively sparse. This result suggests that future work on early fossil legumes should focus on tropical and subtropical climatic zones, wherever they may occur latitudinally.