Sunken Civ, please give these folks the likely answer provided by Firestone et al, and their book. I think you also posted some recent articles on the wider recognition their asteroid/comet crash theory has provided.
There was a statement that all the mammoths were the same as the ones in Siberia. I wonder if DNA testing has been done comparing similar remains in Alaska and Canada. I remember reports that some smaller remnants remained in north eastern Canada islands as recently as 8000 year ago, rather than the circa 13,000 year old age of the mass freeze/burial in several northern areas.
The Cycle of Cosmic Catastrophes:
Flood, Fire, and Famine
in the History of Civilization
by Richard Firestone,
Allen West, and
Simon Warwick-Smith