Fixed.
Good point. I forgot about the aliens that built the pyramids.
Fixed.
We don't know, there might have been some super-advanced race that was so intelligent that they lived in such perfect harmony with nature that they went extinct without any feature of their existence remaining.
frack baby frack
While there were mass extinctions there were also mass evolution generating many modern day mammals during the period you cite.
Plus, I wonder if the most intelligent life to ever live on Earth would somehow find a way to survive.
Lastly, I found this interesting.
https://www.express.co.uk/features/view/280948/Is-global-warming-over-