Thanks for the interesting information.
I will note that ~11,000 years ago is close to the Clovis extinction event when many/most of the large animals in North America disappeared. (as well as the clovis culture).
Something happened back then, eventually we will figure it out.
We're already far afield, so here's the book about the megafauna extinction you mention:
The Cycle of Cosmic Catastrophes:
Flood, Fire, and Famine
in the History of Civilization
by Richard Firestone,
Allen West, and
Simon Warwick-Smith