The Frozen Planet

The climate of the Pleistocene was highly variable. With long periods of glaciation and over a dozen interglacial periods (which were even warmer than the Earth's climate today), the Pleistocene can be seen as somewhat "Ecologically Challenged".

Hippopotomus has been found as far North as present day Britain, and arctic hare has been found as far south as Mexico.
Here's a map of North America at the height of the last glaciation, some 18 000 years ago:

As can bee seen in the map, North America's climate was vastly different than it is at the present day. What isn't well represented is the wide extent of the coastal plains which bordered the continent, which extended out in places hundereds of kilometers.