> What is key here is that the plants which formed the base of
> that ecosystem could not grow above the Arctic circle, even if
> it were warmer, because the land is in perpetual darkness 6
> months out of the year.
Only at the Poles is there perpetual darkness for 6 months of the year.
On the Arctic Circle, there is perpetual darkness for 1 day a year - this increases as one moves northwards.
Plants grow quite readily within the Arctic Circle today. Greenland once had quite extensive forests until the Vikings chopped all the trees down and their livestock prevented regrowth .....
There is no reason to suppose that species capable of living in very cold, arid, steppe environments today could not have done so 40,000 years ago.
Also worth remembering than the Ice Age was not a period of continuous cold - some interstadials were as warm as today.
However, were, for example, Siberia further south then we might well have serious problems in explaining the presence of cold, arid, steppe adapted megafauna
btw the megafauna died out in Siberia because it turned wetter - and those which retreated to refugiums, in which they might otherwise have survived, met a new deadly killer called homo sapien. Large species have slow reproductive rates and a combination of reduced population and increased predation led to the inevitable.
Extraordinary claims require at least some evidence.