Im not entirely sure about the grizzly/polar bear thing, I just really don't think that could happen :S
I worked at NZA in Canberra, we had tigons. They only recently died in the past few years after I left, they were soooo old, even for captive cats. They were taken in from a circus, where they were a total accident, concieved through a chain link fence. At least that's the story we were told, seems the circus may have been a bit dodgy, who knows what the case may be.
The tigons were adorable. Sometimes they would like water like the tigers and other times hate it like the lions. And their noises were a mix of the two depending how they felt. I miss them <3
And all this about the earth not being cold enough for mammoths...haven't any of you seen 10,000BC? Mammoths helped build the pyramids of egypt. HAHAHAHAHA worst movie ever.