a geologically brief time interval characterized by a 5–8 °C (9–14 °F)global average temperature rise and massive input of carbon into the ocean and atmosphere

[…]

The PETM arguably represents our best past analogue by which to understand how global warming and the carbon cycle operate in a greenhouse world.

[…]

What has become clear over the last few decades is that stratigraphicsections across the PETM reveal numerous changes beyond warming and carbon emission.[2] Consistent with an Epoch boundary, fossilrecords of many organisms show major turnovers. In the marine realm, a mass extinction of benthicforaminifera, a global expansion of subtropical dinoflagellates, and an appearance of excursion taxa, including within planktic foraminiferaand calcareous nannofossils, all occurred during the beginning stages of the PETM. On land, many modern mammal orders (including primates) suddenly appear in Europe and in North America.[10]