The key point is how fast the temperature changes. Over several thousands of years that change can be tolerated by the ecosystem (animals and plants evolve over several hundreds of generations and can survive). We already increased the temperature of 1. something degrees Celsius in perhaps a 100 of years and the trend in accelerating. That's way too fast for natural selection to make a difference.

So, yeah, Eocene was super warm, but the flora and fauna was well adapted to survive in those conditions.

Also, if you don't believe me, look better in the article you linked: https://en.wikipedia.org/wiki/Geologic_temperature_record#/m... (pay attention to the non uniform time axis...)