The Grand Coupure

The end of the Eocene in both timelines is marked by a decrease in global temperatures. Even with a prolonged hothouse earth this is still true in this timeline, seeing a considerably more sudden drop (if not quite as low as in our timeline). By this point, enough carbon had been sequestered from the atmosphere, and Antarctica’s isolation lead to the formation of cold circumpolar currents (though the continent would remain habittable for longer in this timeline), so this event was inevitable.

Additionally, this is when Europe and Balkanatolia connected to Asia. In our world the process might have actually began much earlier than previously expected, but higher sea levels due to higher global temperatures ensured a period of prolonged isolation in this timeline. Once again, this effect was made thrice as intense here, the inhabittants of both landmasses even less prepared for the changing climates and arrivals of new competitors than in ours.

The end result, the Grand/Great Coupure, was the greatest extinction event since the demise of the non-avian dinosaurs, made considerably more devastating here. In our world, it caused aproximately 35% of all life to go extinction; here, this number grows to 45%.

The northern continents were the subjects of a great faunal turnover. Europe and Balkanatolia were naturally the most severely affected landmasses, with the former’s native land mammal fauna composed of taeniolabidids, boffiids, ferugliotheriids, ptilodontoideans, galulatheriids, symmetrodonts and local microcosmodontids and eucosmodontids and the latter’s composed of kogaionids, meniscoessids, symmetrodonts and galulatheriids was violently displaced by an Asian fauna of microcosmodontids, lambdopsalids, eucosmodontids, sudamericids and adalatheriids. Only the flying pteroectypodids and insulonycteriids survived, both cosmopolitan clades by that point. While competitive exclusion likely played a role, drastic biotic changes from tropical and subtropical forests to steppe and temperate forests likely played a major role, clearing out the locals before the Asian species came to replace them.

Taeniolabidids and ptilodontoideans (barring the volant pteroectypodids) also vanish from the northern continents, allowing sudamericid and adalatheriid gondwanatheres to make it to North America and for microcosmodontids to become the apex predators across Laurasia. Whatever relictual therians and non-snake squamates endured perish for good, and so do terrestrial crocodylomorphs and several bird lineages like the megafaunal gastornithids or the perching zygodactylids. Most of the flying djadochtatheroideans went extinct, but one lineage, the nascent acamapichtliids, not only would survive but vastly surpass them.

The impact in the southern continents is less obvious due to a scarcer fossil reccord; however, sudamericids, ferugliotheriids, notoptilodontoideans and mesungulatids are all severely affected, while greniodontids and the newly arrived African afroptilodontoideans, galulatheriids and boffiids have caused local faunal turnovers. In the seas, however, most of the marine reptiles die out, with only choristoderes, “true sea turtles”, seabirds (among these, penguins suffered especially heavy casualties), gharials and a few pleurodires surviving. A large percentage of mid-to large sized ray finned fish also died out, which will have interesting consequences for the future oceans.

Still, after the sudden climatic shifts and faunal interchanges the world’s ecosystems were quick to recover, in less than a million years. The survivors made it to the Oligocene.