Eocene–Oligocene extinction event

[13] A leading model of climate cooling at this time predicts a decrease in atmospheric carbon dioxide, which slowly declined over the course of the Middle to Late Eocene.

[17] This cooling reached some threshold approximately 34 million years ago,[18][19][4] precipitating the formation of a large ice sheet in East Antarctica in response to falling carbon dioxide levels.

[26] The deepening of the calcite compensation depth increased carbonate ion storage in the ocean shortly before the onset of the Antarctic glaciation, suggesting the events may have been coupled.

[31] In the Gulf of Mexico, marine turnover is associated with climatic change, though the ultimate cause according to the study was not the drop in average temperatures themselves but colder winters and increased seasonality.

[37][38] Imprints of sunspot cycles from the Bohai Bay Basin (BBB) show no evidence that any significant change in solar activity occurred across the EOT.

[39] In central North America, reptiles, amphibians, and gastropods underwent drastic faunal turnover likely spurred on by a precipitous drop in mean annual temperature (MAT) over approximately 400,000 years.

[40] The Grande Coupure, or 'great break' in French,[41] with a major European turnover in mammalian fauna about 33.5 Ma, marks the end of the last phase of Eocene assemblages, the Priabonian, and the arrival in Europe of Asian species.

[42] It was given its name in 1910 by the Swiss palaeontologist Hans Georg Stehlin, to characterise the dramatic turnover of European mammalian fauna, which he placed at the Eocene–Oligocene boundary.

Before the Grande Coupure, European faunas were dominated by anoplotheriid, xiphodontid, choeropotamid, cebochoerid, dichobunid, and amphimerycid artiodactyls, palaeotheriid perissodactyls, pseudosciurid rodents, adapid and omomyid primates, and nyctitheriids.

However, the 1999 discovery of a mouse-sized early Oligocene omomyid, reflecting the better survival chances of small mammals, undercut the Grande Coupure paradigm.

[44] Balkanatolia acted as a staging ground for Asian taxa that immigrated into Europe following the extinction of its own mammal fauna during the Grande Coupure.

[46] It has been suggested that this was caused by climate change associated with the earliest polar glaciations and a major fall in sea levels, or by competition with taxa dispersing from Asia.

[52] The EOT is often considered to be a critical turning point in the rise of diatoms to their present-day evolutionary prominence, though this paradigm has been criticised for being based on incomplete evidence.