Evidence for increased animal pollination during the Paleocene-Eocene thermal maximum

Abstract

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.