What happened during this time?
Earth's poles were cool and temperate
Early Paleocene cooler and dryer than the preceding Cretaceous Period
Temperatures rose sharply during the Paleocene–Eocene
The Paleocene-Eocene Thermal Maximum (PETM) occurred around 56 million years ago.
Global temperatures rose at least 5°C (9°F), and the PETM warmth lasted 200,000 years before the Earth system was able to remove the extra CO2 from the atmosphere.
There are five potential candidate causes of the PETM (PennState)
Gas hydrates in marine sedimentary rocks
Coals in terrestrial sedimentary rocks
Melting of permafrost
Volcanism in the North Atlantic ocean coincident with the opening of the sea between Norway and Greenland
The Paleocene was a time of recovery from the Chicxulub Impact. Evidence indicates that forests changed after the impact. Based on evidence from both pollen and leaves, there are three explanations for the change, all of which may be correct (Carvalho et al. 2021)
Dinosaurs kept pre-impact forests open by feeding and moving through the landscape.
Falling ash from the impact enriched soils throughout the tropics, giving an advantage to the faster-growing flowering plants.
Preferential extinction of conifer species created an opportunity for flowering plants to take over the tropics.
Subtropical vegetation growing in Greenland and Patagonia
Marked by the development of modern plant species
Cacti are thought to have originated as leafy shrubs in the Caribbean, or southern Mexico, similar to Leuenbergia and some species of Pereskia (e.g. P. lychnidiflora, P. aureiflora), which lacked the ability to perform stem photosynthesis (Edwards et al. 2005)
The evolution of cacti brought a delay in bark formation, the presence of stomata on the stem, and the start of stem photosynthesis, as seen in leafy forms like Rhodocactus. Stem photosynthesis is found in all other spiny cacti.
Thick tropical, sub-tropical, and deciduous forest cover around the globe
Flowering plants continued to develop and proliferate, and insects coevolve to feed on these plants and pollinate them
Today, legumes are a dominant family in tropical rainforests, and through associations with bacteria, take nitrogen from the air and turn it into fertilizer for the soil. The rise of legumes would have dramatically affected the nitrogen cycle.
Before the impact, different types of plants have different types of insect damage: feeding was host-specific. After the impact, the same kinds of damage is found on almost every plant, meaning that feeding was much more generalistic.(Carvalho et al. 2021)
Placental mammals radiate after the K-T boundary (O'Leary et al. 2013)
Early primates evolving in tropical palm forests of northern Wyoming
Evidence of insect recovery to pre-extinction levels occurred within approximately 4 Myr in Patagonia, and approximately 9 Myr in western interior of North America (Donovan et al. 2016)