I just kinda threw that out there was a one-line thing to see if it sparked any interest, but actually there’s a fair amount of debate about it. The thing I was referring to is called the Paleocene–Eocene Thermal Maximum (PETM). Global temperatures have usually been quite a bit hotter than what they are now, tending to hover around 21 deg C (we’re closer to 14 deg C right now), but during the PETM they went up by another 6 deg C or so, causing a rather significant extinction event.
Exactly how sustainable life was near the equator is a matter of debate, though it is clear that the temperature difference between the poles and the equator became a lot less than what it is today (otherwise there wouldn’t be any debate - all life near the equator would have clearly been completely fried). I don’t want to hijack this thread any further, but I will warn you that if you try to do a lot of reading about it, you’ll find that a lot of information is significantly biased as they tend to tie it into the current global warming debate. For that reason alone it’s probably best to spawn this topic off into another thread if you have further interest in it.