If the Eocene-Oligocene boundary wasn't a cooling but actually another thermal maximum, stronger than the Eocene? How would that affect evolution?
Well, a device the size of a large closet lands on Earth accidentally, the device belongs to a civilization that is so advanced that it travels through universes, and an object of theirs accidentally reaches Earth and can release from nowhere huge amounts of CO2, Methane, Silver Iodide, Sodium Chloride in mass. Well, huge amounts are released into the atmosphere. Silver Iodide is released in mass for 3 million years continuously. CO2 and Methane are released permanently and well controlled (the device knows how much to release and how much not to do to ensure the habitability of the Earth). Instead of the cooling at the end of the Eocene we have a thermal maximum that approaches even the Permian-Triassic peaks for a few million years but not catastrophic with volcanoes, then stabilizes between the Permian-Triassic and Cretaceous hothouse values. Well, it prevents any cooling. As it would be evolution? Mammals? Reptiles? Could it be mammals? Amphibians? Modern groups that had appeared in that very period? Multiberculates are disappearing, choristodera? Reptiles claim everything? Birds? Ecosystems from the poles to the equator?