Evidence for increased animal pollination during the Paleocene-Eocene Thermal Maximum

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 due to rapid warming and drying. The hotter and
more seasonally dry climates not only facilitated the northward range
shift of plant taxa, but also their insect and/or vertebrate pollinators.
The dramatic floral changes during the PETM in the Bighorn Basin may also
have changed available resources for insect and/or vertebrate pollinators.